US20020113027A1

US20020113027A1 - Retainer for use in heat treatment of substrate, substrate heat treatment equipment, and method of manufacturing the retainer

Info

Publication number: US20020113027A1
Application number: US10/067,769
Authority: US
Inventors: Masashi Minami; Ikuo Katsurada
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2001-02-20
Filing date: 2002-02-08
Publication date: 2002-08-22
Also published as: JP2002324830A; KR20020068267A; TW561503B

Abstract

There is provided a retainer for use in heat treatment of a substrate which enables an increase in the accuracy of flatness of support sections for supporting a substrate. The retainer includes silicon wafer support sections for supporting a plurality of substrates by means of surface contact, and spacers for defining intervals of the silicon wafer support sections with respect to a vertical direction. Since the support sections and the spacers can be manufactured separately from each other, the accuracy of flatness of the support sections and intervals between the support sections with respect to the vertical direction are determined by the accuracy of individual support sections and spacers. So long as initial accuracy of support sections and that of spacers are maintained, a high-precision retainer can be obtained.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a retainer for use in heat treatment of a substrate, substrate heat treatment equipment, and a method of manufacturing the retainer. More particularly, the present invention relates to a retainer for use in heat treatment of a substrate which is to be loaded into heat treatment equipment while having substrates such as semiconductor substrates mounted thereon.

2. Background Art

A semiconductor device, such as an MOS LSI or a bipolar LSI, is manufactured by way of a plurality of heat treatment processes, such as an oxidation process, a CVD process, and a diffusion process. When a vertical heat treatment system, such as a vertical low-pressure CVD furnace, is employed in a heat treatment process, silicon (Si) wafers, serving as material of semiconductor devices, are loaded into a reaction tube of the vertical heat treatment system while being placed on a boat constructed of SiC for use in vertical heat treatment.

The boat is generally constructed of a circular top plate, a base plate serving as a pedestal, and three supports for interconnecting the top and base plates. A plurality of silicon wafer support sections are formed in the three supports at an interval greater than the thickness of a silicon wafer. Each of the silicon wafer support sections is formed in the shape of a plate or rod, or is embodied by grooves cut directly in the supports.

The boat having silicon wafers provided thereon is loaded into the vertical heat treatment system. The vertical heat treatment system is loaded into a furnace and is subjected to heat treatment at a temperature of, e.g., 1000° C. Particularly in this case, considerable thought has been put into a temperature control method so as to prevent occurrence of thermal stress dislocations (i.e., slip), which would otherwise arise in heat treatment performed at a temperature of 1000° C. or more.

A boat for use in vertical heat treatment performed at a temperature of 1000° C. to 1050° C. or less differs from a boat for use in vertical heat treatment performed at a temperature of 1050° C. or more (such a boat will hereinafter be called a “high-temperature boat”)in terms of material and shape. In many case, a high-temperature boat is constructed of ceramic, such as SiC. In connection with the geometry of a silicon wafer support section, several types of support sections are used; namely, a support section of one type which supports, by way of three or more points or minute surfaces, positions located about two-thirds the radius of a silicon wafer from the center to the outer periphery; a support section of another type which supports a silicon wafer through use of the entirety of a plate-shaped surface extending from the periphery of the silicon wafer to a position located about two-thirds the radius of the silicon wafer from the center; and another support section which supports the periphery of a silicon wafer in an annular pattern. Here, an annular silicon wafer support section, which is expensive to manufacture and yields low productivity, is of little practical use as a boat for vertical heat treatment and is used for only research purposes.

As described in, e.g., Japanese Patent Application Laid-Open Nos. 205140/1997 and 189708/1998, heat treatment to be effected at a temperature in excess of 1100° C. is indispensable for recovering defects in connection with formation of an STI (Shallow Trench Isolation), one of several element isolation techniques which are the keys to miniaturization. Japanese Patent Application Laid-Open No. 133607/2000 describes a method of effecting oxidation at a temperature of 1100° C. and annealing at a temperature of 1150° C. even in an element isolation process of an SOI device.

Japanese Patent Application Laid-Open No. 205140/1997 describes a technique of annealing an insulating substance to be embedded into a semiconductor wafer, such as silicon, and into a trench during the course of formation of a shallow trench isolation (STI) structure at a temperature of 1100° C. through 1350° C. For heat treatment to be effected at a temperature of 1100° C., a retainer for use in heat treatment of a substrate (often called a “boat”) is formed from silicon carbide. Particularly, in relation to a retainer for use with a disk-shaped wafer having a diameter of 300 mm; for example, a wafer support member having a partially-cut ring-shaped geometry as described in Japanese Patent Application Laid-Open No. 260438/1994, a plurality of circular-arch wafer support members as described in Japanese Patent Application Laid-Open No. 168903/1994, and a ring-shaped wafer support member as described in Japanese Patent Application Laid-Open No. 163440/1994, have been known and used for preventing occurrence of crystal imperfections, dubbed slip, which would otherwise be caused by self-weight stress. However, a ring-shaped wafer support member is used for only research purposes and is not employed in a factory for manufacturing a semiconductor device.

The size of a silicon wafer has increased in association with advancement of semiconductor manufacturing technology. Dominating wafers have shifted from wafers measuring 200 mm across to wafers measuring 300 mm across. Prototype silicon wafers measuring 450 mm across, which are called super silicon, have been produced.

In the case of a boat designed for supporting silicon wafers having a diameter of 300 mm, thermal stress dislocations (i.e., slip) arise in a comparatively low temperature range in which no slip arises in a silicon wafer having a diameter of 200 mm, for reasons of an increase in the weight of the silicon wafers. A high-temperature boat has been used for preventing occurrence of slip. However, a temperature difference is likely to arise in the plane of a large-diameter silicon wafer. Since a silicon wafer is made of a single crystal, the silicon wafer is susceptible to deformation during heat treatment if a temperature difference arises in the surface of the silicon wafer, thereby inducing slip.

Even when wafers 300 mm in diameter are subjected to heat treatment at a temperature of 1000° C. for one hour through use of a high-temperature boat which supports wafers at three points, no slip arises. However, spot-like defects arise in areas on the surface of a wafer at which support sections are in contact with the wafer surface. In order to prevent occurrence of such spot-like defects, load must be dispersed by means of supporting a wafer through use of a plate-like plane. However, as mentioned above, a silicon wafer becomes deformed for reasons of a temperature difference, and hence occurrence of spot-like defects cannot be prevented.

A system capable of more uniformly heating a silicon wafer is on its way to becoming employed as vertical heat treatment system for use with a silicon wafer measuring 300 mm in diameter. For example, a commercially-available vertical diffusion furnace (model VF-570, manufactured by KOYO Thermo Systems Co., Ltd.) can maintain a uniform temperature distribution within a surface of a silicon wafer even when the temperature of a furnace is increased and lowered at comparatively high speed; namely, when the temperature is increased at a heating rate of 50° C./min. or more and lowered at a cooling rate of 15° C./min. or more. Further, the temperature of a furnace can be increased and lowered in the range from 200° C. to 1100° C. The present inventors have produced, from quartz, a boat of vertical heat treatment type which supports silicon wafers over the entirety of a plate-like plane, through use of the system. Further, the boat has been subjected to heat treatment. However, attempts to prevent occurrence of slip have ended in failure.

For example, as described in Japanese Patent Application Laid-Open No. 54447/1999, there has already been proposed a retainer for use in heat treatment of a wafer which is formed from quartz and has a structure resistant to slip, quartz being easier to machine and less costly than SiC. By reference to this patent application, the present inventors have prototyped a retainer for use with wafers measuring 300 mm in diameter. A test of the prototyped retainer shows that no slip arises up to a temperature of 1000° C. Annealing operation to be effected during a semiconductor device manufacturing process employing wafers 300 mm in diameter requires that no slip arise at a minimum temperature of 1100° C.

FIG. 43 shows a heat treatment tool prototyped by the present inventors on the basis of the invention described in Japanese Patent Application Laid-Open No. 54447/1999. When a heat treatment tool is produced as shown in the original drawings, there arises a problem of wafers moving after having been loaded in the heat treatment tool. A

positioning support

105 for securing wafers is provided in the heat treatment tool. Since the retainer is formed from quartz, if the retainer has been used for a long period of time at a temperature of 1100° C., the retainer will be deformed to assume a barrel-like shape. In order to prevent occurrence of deformation, reinforcing sections 106 are provided in the retainer. The reason why the uppermost reinforcing sections 106 are provided horizontally in a staggered configuration is to prevent bending of the boat supports 103 in a single direction. As mentioned above, this structure has failed to prevent occurrence of slip at high temperatures.

Quartz cannot be used at temperatures as high as those at which SiC is used. According to a viscosity characteristic graph appearing on a screen “Quartz Glass Data pertaining to Thermal Characteristics” in the home page of Toso Quartz Co., Ltd. (http://www.tqgj.co.jp/th.html) reproduced in FIG. 42, quartz which is produced by electrodissolution and is dubbed HR product in Toso Quartz Co., Ltd, has a viscosity of 10 ¹⁴poise at a temperature of 1150° C. It is seen that a temperature—at which a viscosity achieves a point of distortion (4×10¹⁴poise) and which is a guideline for the limit of practical heat-resisting temperature—ranges from 1120° C. to 1130° C. As mentioned above, it can be experimentally and theoretically ascertained that quartz can sufficiently withstand usage at a temperature of 1100° C. In relation to a point of distortion, a statement “a temperature at which viscous flow does not arise is a temperature below which distortion cannot be eliminated and at which viscosity assumes an index of 13.5 Pa·s” is provided in the section appearing immediately under 4. “Characteristic Temperature” on page 87, “Amorphous Silica Materials Handbook” (Hiroshi KAWAFUKU et. al by Realize Ltd.).

When ceramic, such as SiC, is used as material of the boat, SiC is processed before being fired. At this point in time, the accuracy of the boat is comparatively good. However, firing induces shrinkage in the boat, thus deteriorating the accuracy of the boat. Thus, a boat made of SiC involves more difficulty in ensuring accuracy than does a boat made of quartz glass. For this reason, when a boat for use in vertical heat treatment is manufactured from SiC, silicon wafer support sections, which particularly require accuracy, are produced in greater than a required number. Silicon wafer support sections that comply with specifications must be selected from the thus-produced support sections. If manufacturing yield of silicon wafer support section is not good, costs rise. Ceramic, such as SiC, can bear high temperatures for a long period of time. However, ceramic incurs costs several times those incurred by quartz. Moreover, in association with miniaturization of a design rule, among processes of manufacturing a semiconductor, the number of processes requiring a maximum temperature of about 1100° C. is increasing. As shown in FIG. 42, since some types of quartz possess distortion points (temperatures at which a viscosity index of 4.0×10 ¹³PaS is achieved) of 1100° C. or more, use of SiC in such semiconductor device manufacturing processes is highly uneconomical.

In association with a progressive increase in packing density of a semiconductor device, a circuit width tends to become smaller. In contrast, as mentioned above, silicon wafers have become larger in diameter, the industry having attained the stage of putting into practical use a wafer measuring 300 mm in diameter.

When an attempt is made to construct a factory compatible with 300 mm wafers, a high-temperature heat treatment system compatible with 300 mm wafers is not available. In other words, there is a necessity of developing a high-temperature heat treatment system simultaneous with construction of a factory. Accordingly, a retainer for use in heat treatment of a wafer for use in high-temperature heat treatment system has been constructed while the highest priority is assigned to prevention of crystal imperfections, dubbed slip, in a wafer, which would otherwise be caused by high-temperature heat treatment, without sufficient review of structure or material. Hence, the resultant retainer has become extremely costly.

Increasing the size of a wafer is originally intended for reducing costs for manufacturing devices and improving cost competitiveness internationally. A 300 mm wafer has 2.25 times the area of a 200 mm wafer. In short, provided that the number of manufacturing systems and material costs are held constant, the number of chips produced from a single 300 mm wafer becomes double or more the number of chips produced from a single 200 mm wafer, through unconditional computation. Hence, chip costs will be reduced by one-half or more. An increase in costs of manufacturing systems, in those of materials, and in those of components, which are compatible with wafers 300 mm in diameter, and elimination of a difference in chip manufacturing costs between manufacture of semiconductor devices from a wafer 200 mm in diameter and manufacture of semiconductor devices from a wafer 300 mm in diameter are not allowed. In view of these demands, a reduction in costs for manufacturing a wafer heat treatment retainer is of the highest priority.

More specifically, the following are conceivable reasons why the related-art substrate heat treatment retainer is expensive. SiC employed as material is expensive. For example, a retainer for use in heat treatment of a substrate compatible with heat treatment at a temperature of 1100° C. or more, which is shown in FIG. 44 and described in 260438/1994, has a structure which requires usage of a greater volume of SiC than is used in retainer for use in heat treatment of a substrates which had been known before the publication. In some cases, silicon is employed in place of SiC for a portion of the retainer. In such a case, material expenditures increase further. Moreover, silicon or polysilicon is vulnerable to oxidation, and silicon oxide increases in volume more than silicon does. Hence, when in use, silicon oxide presents a problem of greater distortion. For these reasons, consumption of silicon oxide is intensive, which in turn results in an increase in running costs. SiC is ceramic which becomes very difficult to process when sintered. Hence, processing of SiC is performed before firing. When SiC is sintered after having been processed, SiC is shrunken. When a high degree of processing precision is required, manufacturing costs increase greatly.

An attempt has been made to compute costs of a heat treatment retainer which is shown in FIG. 44, which is described in Japanese Patent Application Laid-Open No. 260438/1994, and which has been arranged so as to become compatible with a wafer measuring 300 mm in diameter. The costs have become triple or quadruple those of the related-art retainer for use in heat treatment of a wafer shown in FIG. 10. In relation to the heat-treatment retainer described in Japanese Patent Application Laid-Open No. 260438/1994, trenches for holding the

support member

5 horizontally are formed in four supports 16, as shown in FIG. 44. Trenches formed in the four supports 16 in the same tier must be formed accurately so as to constitute a single plane. Highly-accurate intervals are required between the trenches, and hence the time required for forming the trenches becomes longer. Stationary shaft holes for fastening support members must be opened in the respective support members with high accuracy. Requests for precision add to costs. Moreover, it is assumed that complexity in assembly of a retainer will also account for an increase in costs. A retainer for use in heat treatment of a wafer which has an analogous structure and is described in Japanese Patent Application Laid-Open NO. 150401/2000 is also costly.

The present inventors have reviewed an assembling method in connection with a method of preparing a retainer for use in heat treatment of a wafer shown in FIG. 44. The result of review is provided as follows: As shown in FIG. 44, grooves for holding

wafer support members

101 are formed in boat supports 103. Then, the boat supports 103 are welded to a bottom plate 102. There is a necessity of preventing occurrence of a difference in the extent to which the boat supports 103 sink, which would otherwise be caused by dissolution of quartz. For these reasons, the time required for fixing the boat supports 103 and the amount of flame of a burner must be held constant. In order to assemble the retainer highly accurately, a very high degree of experience is required. After fastening of the board supports 103, the retainer is annealed at a temperature of 1130° C. for removing internal distortion caused during welding. A required number of wafer support members 101 that have been prepared beforehand are provided on the retainer. Stationary shafts 107 are aligned with holes into which the stationary shafts 107 are passed. An indent is formed in the bottom plate 102 for fixing the stationary shafts 107. In consideration of workability, one or two of the boat supports 103 are temporarily fixed to the wafer support members 101 by means of welding. The retainer is turned upside down, and welding is performed while the top plate 104 is placed bottom. Here, there is no necessity of concerning sinking of the boat supports 103 due to welding. The retainer is annealed again at a temperature of 1130° C. for removing internal distortion caused by welding. If the appearance of the wafer heat treatment retainer is not obtrusive, there is no necessity of removing temporary weld. The foregoing operations are very complex when compared with operations for setting up supports on a bottom plate, turning upside down the retainer assembly, attaching a top plate to the assembly, and completing the assembly through annealing. Since SiC cannot machined through welding, SiC is assembled through use of a screw structure.

As described in, e.g., Japanese Patent Application Laid-Open No. 8203/1999, a boat for use in heat treatment is formed from quartz SiC silicon. In order to curtail costs, supports and support sections are prepared separately. Subsequently, the support sections are fitted into predetermined locations on the supports. Particularly, in the case of a high-temperature boat, plate-like support sections are made to a length such that they reach positions about one-third the radius of a wafer from the outer periphery thereof. Because of production errors in the thickness of fitting sections and production errors in support plates, the flatness of a plurality of plate-like support sections cannot be ensured. Further, since support sections are to be fitted into supports, the support sections must be made slightly thinner than grooves into which the support sections are to be fitted. When heavy substrates, such as wafers measuring 300 mm in diameter, are provided on the boat, the support sections are slightly tilted. As a result, the support sections rattle, thereby deteriorating the flatness of the silicon wafers. If this method is adopted, slip arises even at a temperature of 900° C. when wafers having a diameter of 300 mm are subjected to heat treatment.

When the structure of support sections is determined so as to prevent occurrence of slip, support sections must be actually manufactured in order to ascertain effects of various ideas. However, if all ideas pertaining to support sections are embodied, costs are enormous, and a test time also becomes longer. There is no guarantee that satisfactory results are obtained as a result of ascertainment of effects. Thus, ascertaining effects of ideas involves a risk.

During the course of having studied preparation of various retainer for use in heat treatment of a substrates for cost reduction, the present inventors have realized that the retainer shown in FIG. 44 involves structural defects. A wafer is loaded onto a retainer for use in heat treatment of a substrate by means of an automatic transporter. At this time, the wafer is transported into the retainer for use in heat treatment of a substrate while being placed on a carrier arm of the transporter. Operations required this time will now be described. First, the wafer is taken out from the carrier arm and is moved closed to the retainer for use in heat treatment of a substrate. Next, the carrier arm having the wafer provided thereon passes through the

wafer support members

101 arranged in the vertical direction and continues moving until the wafer is located at the center of the retainer for use in heat treatment of a substrate. The carrier arm moves downward. As a result, the wafer is automatically placed on the wafer support member 101. Subsequently, the carrier arm is pulled out horizontally. Wafers are loaded in the retainer through repetition of these procedures.

FIGS. 45, 46, and 47 show a series of descriptions relating to a case where the above-described procedures are applied to a wafer heat-treatment retainer having a wafer support member of structure shown in FIG. 44. As shown in FIG. 45, a wafer W is placed on a carrier arm 26, and the carrier arm 26 is moved to the retainer for use in heat treatment of a substrate. As shown in FIG. 46, the carrier arm 26 is moved to the wafer support members 101. As shown in FIG. 47, when the carrier arm 46 is moved downward, an extremity 26 a of the carrier arm 26 interferes with the wafer support member 101. Therefore, there has arisen a problem of difficulty in transporting a wafer W through the procedures set forth. As described in Japanese Patent Application Laid-Open NO. 260438/1994, there may be employed the idea of introducing a tossing machine. However, the tossing machine is bulky, and there is a necessity of newly ensuring a location for installing the machine. After wafers have been loaded on the retainer for use in heat treatment of a wafer, there is newly required a system for transporting the retainer for use in heat treatment of a wafer having the wafers provided thereon to a system. The retainer for use in heat treatment of a wafer must be moved over a considerable distance both in the vertical and horizontal directions. Immediate realization of the retainer for use in heat treatment of a wafer cannot be considered to be feasible for reasons of a hike in costs and system stability.

FIG. 48 shows silicon

wafer support members

101A and 101B, which are formed so as to become substantially identical with the outer edge of a wafer and split in two. Manufacturing the

silicon wafer members

101A and 101B with a high degree of plane accuracy is much harder than slicing a ring-shaped and partially-cut support member from a single plate. In the case of quartz, it is possible to actually place a wafer on a support member, and to visually check occurrence of a clearance between a wafer and a support member or to ascertain the height of the support members with use of a height gauge, thereby producing a retainer for use in heat treatment of a wafer while adjusting the silicon wafer support members through heat treatment. However, such a way to produce a retainer for use in heat treatment of a wafer is not practical. Realization of high precision through use of SiC which becomes shrunk after having sintered is nearly impossible. SiC contains impurities in larger volume than quartz does. Hence, a retainer for use in heat treatment of a wafer is used for a heat treatment system after having been coated with SiC through CVD. In this case, if a retainer for use in heat treatment of awafer is coated with nominal projections or foreign articles, the projections or foreign articles are enlarged, thereby deteriorating the flatness of the retainer to a much greater extent.

Japanese Patent Application Laid-Open No. 15041/2000 describes a method of rendering a retainer for use in heat treatment of a wafer knocked down for reducing costs and enabling replacement of components. In this case, when ceramic, such as SiC, which involves sintering and firing, is selected as material, the ceramic becomes shrunk after having been sintered. Hence, ceramic material cannot be used for a retainer for use in heat treatment of a wafer which requires stacking accuracy. Accordingly, a method of producing a large amount of component and selecting components satisfying specifications adds to costs.

SUMMARY OF THE INVENTION

The present invention has been conceived to solve the drawbacks set forth and is aimed at providing a retainer for use in heat treatment of a substrate which enables an increase in the accuracy of flatness of support sections for supporting a substrate.

The present invention is aimed at providing a retainer for use in heat treatment of a substrate which enables reliable holding of support sections and spacers, thus enabling assembly of a retainer with ease.

The present invention is aimed at providing a retainer for use in heat treatment of a substrate which enables assembly of a retainer while ascertaining errors in the phase of stacking operation and enables detection of defects at an early time.

The present invention is aimed at providing a retainer for use in heat treatment of a substrate which enables ascertainment of flatness of support sections while the substrate actually placed on support sections and enables detection of defects in the phase of manufacture of the retainer and addressing of the thus-found defects.

The present invention is aimed at providing a retainer for use in heat treatment of a substrate which enables manufacture of a substrate without involvement of thermal deformation or stress.

The present invention is aimed at curtailing costs by forming a retainer from primarily quartz glass.

The present invention is also aimed at providing a retainer for use in heat treatment of a substrate suitable for loading and unloading of substrates into or from the retainer through use of an automatic transporter.

The present invention is aimed at determining, in a short period of time and in a cost-saving manner, the structure of a retainer for use in heat treatment of a substrate which prevents occurrence of slip in the substrate, which would otherwise be caused during heat treatment of the substrate.

The present invention is aimed at manufacturing substrate support sections while an unnecessary portion of a plate which is to serve as raw material is minimized.

The present invention is aimed at inexpensively producing a retainer for use in heat treatment of a substrate having a structure for preventing occurrence of slip, which would otherwise be caused when wafers of large diameters loaded on the retainer are subjected to heat treatment, as well as at providing a vertical heat treatment system using the retainer for use in heat treatment of a substrate.

According to one aspect of the present invention, a for use in heat treatment of a substrate is provided. The retainer supports a plurality of substrates in a horizontal position while the substrates are spaced away from each other with respect to a vertical direction. The retainer comprises a plurality of support sections for supporting the respective substrates by way of surface contact, and spacers for defining intervals between the support sections with respect to the vertical direction.

According to the present invention, since the support section and the spacer can be manufactured separately, the plane accuracy of the support section and a vertical interval between the support sections are determined by the accuracy of a single support section and the accuracy of a single spacer. Hence, there can be provided a highly-accurate retainer for use in heat treatment of a substrate, by means of maintaining the initial accuracy of the support section and that of the spacer. Further, support sections and spacers can be selected in a manufacturing phase. Hence, there can be provided a highly-accurate retainer for use in heat treatment of a substrate. Moreover, a support section and a spacer are separated from each other. Hence, support sections and spacers can be mass-produced, thereby enabling a reduction in manufacturing costs.

According to another aspect of the present invention, a substrate heat treatment system comprises the retainer described above.

According to the present invention, as a result of a retainer being used in a substrate heat treatment system which features superior control of in-plane temperature of a substrate, there can be prevented occurrence of slip in a substrate, which would otherwise arise during high-temperature treatment. Hence, there can be provided a high-temperature substrate heat treatment system while enabling a reduction in manufacturing costs.

According to another aspect of the present invention, a method of manufacturing a retainer for use in heat treatment of a substrate is provided. The retainer supports a plurality of substrates in a horizontal position while spacing the substrates away from each other with respect to a vertical direction. The method comprises the following steps. Firstly a plurality of supports are fixedly placed upright on a pedestal. Secondly support sections for supporting the plurality of the substrates and spacers for defining intervals between the support sections in a vertical direction alternately fitting to each of the supports. Thirdly the support sections and the spacers are fixed while they remain in close contact with each other.

According to the present invention, since the support sections and the spacers are fastened to each other, while remaining in close contact with each other and being disposed between a nut secured to an upper end of the support and a pedestal, a retainer for use in heat treatment of a substrate is obtained without involvement of thermal deformation or stress.

Other and further objects, features and advantages of the invention will appear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a vertical heat treatment boat according to the embodiment. [0047]
FIG. 2 is a perspective view showing a boat support fastened to a bottom plate. [0048]
FIG. 3 shows the method of manufacturing the boat shown in FIG. 1. [0049]
FIG. 4 is a schematic diagram showing the positional relationship between the [0050] hole 1 a and the center of gravity of the silicon wafer support section.
FIG. 5 is a schematic diagram showing the positional relationship between the [0051] hole 1 a and the center of gravity of the silicon wafer support section.
FIG. 6 is a perspective view showing a boat support. [0052]
FIG. 7 shows the method of manufacturing the boat shown in FIG. 1. [0053]
FIG. 8 shows procedures for manufacturing a retainer for use in heat treatment of a substrate according to a second embodiment of the present invention. [0054]
FIG. 9 is a schematic perspective view showing a related-art vertical heat treatment boat employed in the tests as a comparative example. [0055]
FIG. 10 is a schematic perspective view showing an another related-art vertical heat treatment boat used in the test as a comparative example. [0056]
FIG. 11 shows results of observation of a wafer after subjecting to heat treatment at a temperature of 1000° C. through use of the related-art boat shown in FIG. 9. [0057]
FIG. 12 shows results of observation of a wafer after subjecting to heat treatment at a temperature of 1050° C. through use of the related-art boat shown in FIG. 9. [0058]
FIG. 13 shows results of observation of a wafer after subjecting to heat treatment at a temperature of 1050° C. through use of the related-art boat shown in FIG. 10. [0059]
FIG. 14 shows results of observation of a wafer after subjecting to heat treatment at a temperature of 1050° C. through use of the boat according to the first embodiment shown in FIG. 1. [0060]
FIG. 15 is a schematic diagram showing the positional relationship of support sections according to the first embodiment. [0061]
FIG. 16 is a schematic diagram showing the positional relationship of silicon wafer support sections spaced equally apart from each other along the periphery of a silicon wafer. [0062]
FIG. 17 is a schematic diagram showing the positional relationship of silicon wafer support sections extended the interval. [0063]
FIG. 18 is a schematic diagram showing the geometry and positional relationship of support sections according to the third embodiment. [0064]
FIG. 19 shows the silicon wafer support sections capable of preventing occurrence of slip in the same manner as the silicon wafer support sections shown in FIG. 18. [0065]
FIG. 20 shows the silicon wafer support sections capable of preventing occurrence of slip in the same manner as the silicon wafer support sections shown in FIG. 18. [0066]
FIG. 21 shows the silicon wafer support sections capable of preventing occurrence of slip in the same manner as the silicon wafer support sections shown in FIG. 18. [0067]
FIG. 22 is a perspective view showing a status in which a silicon wafer support, a spacer, and a boat support, all belonging to a retainer f or use in heat treatment of a substrate according to the fourth embodiment [0068]
FIG. 23 is a top view showing the silicon wafer support section, the spacer, and the boat support. [0069]
FIG. 24 is a plan view showing a silicon [0070] wafer support section 20 to be used in a retainer for use in heat treatment of a substrate according to a fifth embodiment.
FIG. 25 is a perspective view showing a spacer to be used in the retainer for use in heat treatment of a substrate according to the fifth embodiment. [0071]
FIG. 26A is a perspective view of a C-shaped [0072] spacer 27. FIG. 26B is a top view of the same.
FIGS. 27A and 27B are perspective views of the [0073] lowermost spacer 22 used for the lowermost portion of the retainer for use in heat treatment of a substrate according to the fifth embodiment.
FIG. 28 is a plan view showing a positional relationship between the carrier arm and the silicon wafer support section during transport of a wafer. [0074]
FIG. 29 is a perspective view showing the thus-completed retainer for use in heat treatment of a substrate. [0075]
FIG. 30 is a plan view showing the silicon wafer support section to be used in a retainer for use in heat treatment of a substrate according to a sixth embodiment of the present invention. [0076]
FIG. 31 is a plan view of the silicon wafer support section to be used in a retainer for use in heat treatment of a substrate according to a seventh embodiment. [0077]
FIG. 32 is a plan view showing the silicon wafer support section and the spacer, which are to be used in a retainer for use in heat treatment of a substrate according to an eighth embodiment. [0078]
FIG. 33 is a perspective view showing a retainer for use in heat treatment of a substrate using the silicon wafer support sections according to the eighth embodiment. [0079]
FIG. 34 is a plan view showing a silicon wafer support section to be employed in a retainer for use in heat treatment of a substrate according to a ninth embodiment of the present invention. [0080]
FIG. 35 shows one example of a spacer to be used with the silicon wafer support section described in connection with the ninth embodiment. [0081]
FIG. 36 is a plan view showing a silicon wafer support section to be used in a retainer for use in heat treatment of a substrate according to a tenth embodiment of the present invention. [0082]
FIG. 37 is a plan view showing a silicon wafer support section to be used in a retainer for use in heat treatment of a substrate according to an eleventh embodiment of the present invention. [0083]
FIG. 38 is a perspective view showing a boat support fastened to a bottom plate according to each embodiment of the present invention. [0084]
FIG. 39 is a plan view showing a single plate material from which the silicon wafer support section has been hollowed. [0085]
FIG. 40 is a plan view showing a quartz plate glass from which the silicon wafer support section has been hollowed according to an twelfth embodiment of the present invention. [0086]
FIG. 41 is a perspective view showing a boat support having a recess. [0087]
FIG. 42 is a viscosity characteristic graph. [0088]
FIG. 43 shows a heat treatment tool prototyped by the present inventors on the basis of the invention described in Japanese Patent Application Laid-Open No. 54447/1999. [0089]
FIG. 44 is a perspective view showing a boat support having a recess. the related-art substrate heat treatment retainer described in Japanese Patent Application Laid-Open No. 260438/1994. [0090]
FIG. 45 shows a series of descriptions relating to a case where the above-described procedures are applied to a wafer heat-treatment retainer having a wafer support member of structure shown in FIG. 44. [0091]
FIG. 46 shows a series of descriptions relating to a case where the above-described procedures are applied to a wafer heat-treatment retainer having a wafer support member of structure shown in FIG. 44. [0092]
FIG. 47 shows a series of descriptions relating to a case where the above-described procedures are applied to a wafer heat-treatment retainer having a wafer support member of structure shown in FIG. 44. [0093]
FIG. 48 shows silicon wafer support members, which are formed so as to become substantially identical with the outer edge of a wafer and split in two.[0094]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the invention will be described hereinbelow by reference to the accompanying drawings. [0095]
First Embodiment [0096]
The present inventors have conducted various tests upon conceiving the idea of the present invention. Tests were conducted with an emphasis on comparison between a vertical heat treatment boat according to the present invention and a related-art vertical heat treatment boat. First, the tests will be described, and then the vertical heat treatment boat according to the invention will be described. [0097]
As shown in FIG. 9, [0098] reference numeral 3 designates a boat support; 5 designates a top plate; 6 designates a bottom plate; 7 designates a boat positioning notch; 13 designates a'silicon wafer support rod; and 14 designates a silicon wafer contact section provided at the tip end of the silicon wafer support rod 13.
FIG. 10 is a schematic perspective view showing an another related-art vertical heat treatment boat used in the test as a comparative example. As shown in FIG. 10, [0099] reference numeral 3 designates a boat support; 5 designates a top plate; 6 designates a bottom plate; 7 designates a boat positioning notch; and 15 designates a silicon wafer support section formed integrally with the boat support 3.
FIG. 1 is a perspective view showing a vertical heat treatment boat according to the embodiment. As shown in FIG. 1, [0100] reference numeral 1 designates a silicon wafer support section; 2 designates a spacer; 3 designates a boat support; 5 designates a top plate; 6 designates a bottom plate(pedestal); and 7 designates a boat positioning notch. The boat shown in FIG. 1 is formed from components made of primarily quartz.
Tests were conducted on the vertical heat treatment boats shown in FIGS. 1, 9, and [0101] 10. While emphasis was placed on the silicon wafer support sections 1 and 15 and the silicon wafer support rods 13 belonging to each of the boats, the manner in which slip arises in wafers was examined in terms of differences in boat structure and different methods of forming boats. The tests used a vertical heat treatment system capable of effecting heat treatment while suppressing occurrence of a temperature difference in the entire surface of a wafer.
Processing conditions were as follows: [0102]
Diffusion furnace manufactured by KOYO Thermo Systems Co., Ltd.; High-speed furnace of temperature up/down type—model VF-5700; and Sample silicon wafer manufactured by Mitsubishi Material Co., Ltd., 300 mm diameter, type P, and having a crystallographic axis <100>, a specific resistance of 10 to 15 Ω cm, and an oxygen content of 1.1±0.1×10[0103] ¹⁸/cm³.
Heat treatment conditions: temperature of 1000° C. for two hours, and temperature of 1050° C. for one hour [0104]
Atmosphere: N[0105] ₂atmosphere
Observation of slip: X-ray toposystem manufactured by RIGAKU corporation. [0106]
Silicon wafers were subjected to heat treatment at a temperature of 1000° C. for two hours through use of the boat shown in FIG. 9, and occurrence of slip in the silicon wafers was observed. FIG. 11 shows results of observation of slip. As shown in FIG. 11, no slip arises under the above conditions. Spot-like defects that the present inventors call boat marks are seen to have arisen in areas on the silicon wafer remaining in contact with the silicon [0107] wafer contact sections 14 provided at the tip ends of the respective silicon wafer support rods 13. Since the wafer having a diameter of 300 mm has a heavy weight, boat marks arise in point contacts between the silicon wafer contact sections 14 and the silicon wafer.
Next, silicon wafers were subjected to heat treatment at a temperature of 1050° C. for one hours through use of the boat shown in FIG. 9, and occurrence of slip in the silicon wafers with changes in heat treatment conditions was observed. FIG. 12 shows the result of observation. As shown in FIG. 12, slip having a length in the neighborhood of 5 mm has arisen around the respective boat marks. As in the case of the boat marks shown in FIG. 11, concentration of load on the silicon [0108] wafer contact sections 14 primarily accounts for occurrence of defects. It is assumed that, in addition to concentration of load, deformation of silicon wafers arising at high temperatures induces slip.
Next, silicon wafers were subjected to heat treatment at a temperature of 1050° C. for one hour through use of the boat shown in FIG. 10, and occurrence of slip in the silicon wafers was observed. FIG. 13 shows the results of observation. Slip which has arisen in areas on a silicon wafer remaining in contact with the two silicon [0109] wafer support sections 15 and extends 20 mm or more from the periphery of the silicon wafer can be identified clearly without magnification. Spot-shaped defects called boat marks are not observed in the silicon wafer in this case. For these reasons, it can be estimated that no deformation has arisen in the silicon wafer. When the silicon wafer was again placed on the silicon wafer support sections 15 after observation and was again observed visually, it turned out that the silicon wafer did not remain in close contact with the silicon wafer support sections 15. In other words, it turned out that accuracy of flatness of the silicon wafer support sections 15 located at three positions was not attained. Therefore, it is understood that, although silicon wafers were received by the silicon wafer support sections 15 of the boat shown in FIG. 10 with surface contact, the silicon wafers were actually supported by edges of the support sections 15 with linear or point contact, for reasons of insufficient plane flatness of the silicon wafer sections 15. Consequently, such contact induces occurrence of slip.
Next, silicon wafers were subjected to heat treatment at a temperature of 1050° C. for one hour through use of the boat according to the present embodiment shown in FIG. 1, and the surface of the silicon wafer was observed. FIG. 14 shows results of observation. As shown in FIG. 14, when the boat according to the present embodiment was used in heat treatment, neither boat marks nor slip were observed. [0110]
On the basis of the results of the tests set forth, causes for deterioration in the flatness of the silicon [0111] wafer support sections 15 of the related-art boat shown in FIG. 10 were examined. It turned out that the accuracy of flatness of the silicon wafer support sections 15 cannot be improved by the manufacturing technique of the related art. It also turned out that, particularly when a boat is formed from primarily quartz, the required accuracy of flatness cannot be attained, for reasons of manufacturing processes.
The outline of processes for manufacturing the boat shown in FIG. 10 is as follows: [0112]
1. The silicon [0113] wafer support sections 15 are formed from the boat supports 3 by means of chipping, and the thus-formed silicon wafer support sections 15 are abraded. Here, the silicon wafer support sections 15 are chipped by automatic machine. In this phase, the boat support 3 having the high-accuracy silicon wafer support sections 15 can be produced in volume.
2. Three or more boat supports [0114] 3 are set up on the bottom plate 6. At this time, the boat supports 3 and the bottom plate 6 are welded through use of an oxyhydrogen burner. At this time, welding is effected at a temperature at which quartz becomes melt, and hence the boat supports 3 sink below the surface of the bottom plate 6. At the time of welding operation, setting up the boat supports 3 upright is inevitable. The depth to which the boat support 3 sinks is determined in accordance with a time required for setup.
3. The [0115] top plate 5 is welded to the tops of the boat supports 3, and the silicon wafer support sections 15 are polished by means of a burner. Such heat treatment may induce deformation in the silicon wafer support sections 15.
4. The boat is then annealed in a furnace for obviating warpage of the boat. Since annealing is effected at a temperature exceeding 1100° C., which exceed the point of distortion of quartz, deformation arises in the silicon [0116] wafer support sections 15.
As mentioned above, the processes for manufacturing the boat shown in FIG. 10 involve at least three heat treatment processes during which errors are bound to arise. These heat treatment processes account for deterioration in flatness of the silicon [0117] wafer support sections 15. In the present embodiment, which employs quartz as material of a boat, the accuracy of flatness of the silicon wafer support sections 15 can be improved by means of minimizing heat treatment.
Through the above-described tests and observations, the present inventors have conceived the present invention, which will be described by reference of embodiments provided below. The embodiments are now described in detail by reference to the drawings. [0118]
A specific example of a boat for use in heat treatment of a substrate according to the present embodiment shown in FIG. 1 relates to a quartz boat for use in vertical heat treatment and which is to be loaded into a vertical heat treatment furnace while holding semiconductor substrates (silicon wafers). [0119]
As shown in FIG. 1, the [0120] top plate 5 and the bottom plate 6 of the boat according to the present embodiment are connected together by way of the three boat supports 3. To the three boat supports 3, silicon wafer support sections 1 and spacers 2 are fitted alternately. The thicknesses of the silicon wafer support sections 1 and the spacers 2 are specified strictly. Hence, the flatness of upper surfaces of three silicon wafer support sections 1 fitted around the respective support supports 3, which support sections 1 are n^thfrom the bottom (where “n” represents an integer), is maintained with a very high degree of accuracy.
By reference to FIGS. 2, 3, and [0121] 7, the method of manufacturing the boat shown in FIG. 1 will be described. First, a required number of silicon wafer support sections 1 and spacers 2 are prepared. As shown in FIG. 2, three boat supports 3 are set upright on the bottom plate 6, and the boat supports 3 and the bottom plate 6 are welded together. Subsequently, the assembly is annealed for eliminating warpage which has arisen during welding operation. As shown in FIG. 3, the spacers 2 are fitted around each of the boat supports 3. A hole 2 a which the boat support 3 is to penetrate is formed in each of the spacers 2. An interior edge (not shown) of the hole 2 a formed in the lower surface of the spacer 2 is chamfered such that a welded portion between the boat support 3 and the bottom plate 6 does not cause interference. Next, the silicon wafer support sections 1 are fitted around each of the boat supports 3. A hole 1 a which the boat support 3 is to penetrate is formed in the silicon wafer support section 1. In this way, a required number of spacers 2 and silicon wafer support sections 1 are alternately fitted around each of the boat supports 3. After the last spacer 2 has been fitted around the boat support 3, a nut 4 is fastened to each of the boat supports 3, as shown in FIG. 7.
A [0122] male thread 16 around which the nut 4 is to be fastened is formed around an upper portion of each of the boat support 3. As shown in FIG. 7, the tip ends of the boat supports 3 are fitted into support holes 8 formed in the top plate 5 for fastening the top plate. The boat supports 3 and the top plate 5 are fastened together, thereby completing the boat. The only requirement is that the male thread 16 be formed in only an upper portion of the boat support 3. Play between the silicon wafer support sections 1 and the spacers 2 can be obviated by means of fastening the nuts 4.
Since no heat treatment follows assembly of the silicon [0123] wafer support sections 1 and the spacers 2, the flatness of each of the three silicon wafer support sections 15 for supporting a single wafer is determined by the accuracy of flatness of the individual silicon wafer support sections 1 and that of the individual spacers 2. The silicon wafer support sections 1 and the spacers 2 can be accurately produced in volume by means of an existing machine. Further, non-defective parts can be selected, thereby improving the accuracy of flatness of the silicon wafer support sections 15 to a much greater extent. If a defective silicon wafer support section 1 or spacer 2 is found, only the thus-found support section 1 or spacer 2 can be replaced with a non-defective support section 1 or spacer 2. Thus, effective use of resources can be implemented. Moreover, by means of the construction of the boat and the manufacturing method set forth, quartz can be used as principal material of a retainer for use in heat treatment of a substrate. Hence, manufacturing costs can be curtailed to a faction of those incurred for manufacturing a boat from ceramic such as SiC.
Next will be described a method of improving the flatness of the [0124] silicon support sections 1 by means of defining the positional relationship between a center of gravity 11 and the hole 1 a of the silicon wafer support section 1. FIGS. 4 and 5 are schematic diagrams showing the positional relationship between the hole 1 a and the center of gravity 11 of the silicon wafer support section 1.
As shown in FIG. 4, if the center of the [0125] hole 1 a of the silicon wafer support section 1 matches the center of gravity 11, the silicon wafer support sections 1 are maintained horizontal at all times during the course of being stacked. Hence, a boat can be manufactured while there is ascertained the accuracy of flatness of each of three silicon wafer support sections which support a single wafer.
Alternatively, as shown in FIG. 5, the center of the [0126] hole 1 a is offset from the center of gravity 11 toward the portion of the silicon wafer support section 1 which supports a silicon wafer. As a result, while the accuracy of flatness of the silicon wafer support sections 1 is ascertained with silicon wafers actually being placed on the boat, the silicon wafer support sections 1 and the spacers 2 can be stacked sequentially. Accordingly, if the support sections 1 for supporting a single wafer have insufficient flatness, these support sections 1 can be replaced with non-defective support sections during the course of being stacked.
The [0127] hole 1 a of the silicon wafer support section 1 is matched in shape with the boat support 3. If the boat support 3 has a columnar shape, a protuberance 9 for fixing purpose is provided in the hole 1 a for preventing displacement of angular position of the silicon wafer support section 1, as shown in FIGS. 4 and 5. As shown in FIG. 6, a mating slit 10 is formed in a corresponding position on the boat support 3. As a result, rotation of the silicon wafer support section 1 about the boat support 3 can be prevented.
Second Embodiment [0128]
Through repetition of the tests, the present inventors have become aware of a phenomenon that the silicon [0129] wafer support section 1 and the spacer 2 come to adhere to each other. Next, a second embodiment which actively utilizes the phenomenon will be described.
FIG. 8 shows procedures for manufacturing a retainer for use in heat treatment of a substrate according to a second embodiment of the present invention. The second embodiment is identical with the first embodiment in terms of basic structure and manufacturing processes. The second embodiment differs from the first embodiment in that both sides of each of the silicon [0130] wafer support sections 1 and both sides of each of the spacers 2 are mirror finished and the support sections 1 and the spacers 2 are bonded together by means of thermocompression bonding.
As shown in FIG. 8, in a phase in which the [0131] spacers 2 and the silicon wafer support sections 1 are alternately fitted around the boat support 3, both sides of each of the silicon wafer support sections 1 and both sides of each of the spacers 2 are mirror finished. Hence, the silicon wafer support section 1 and the spacer 2 adhere to each other. If insufficient adhesion is found in this phase, the support section 1 or the spacer 2 is deemed to be a mirror finishing failure and is replaced with a non-defective one. In the second embodiment, the only requirement is that the top plate 5 be placed on the boat supports 3 without use of the nuts 4. Therefore, there is no necessity of forming the male thread 16 on an upper portion of the boat support 3. After the top plate 5 has been placed on the boat supports 3, the boat is annealed at a temperature at which no deformation arises in quartz, whereby the silicon wafer support sections 1 and the spacers 2 completely adhere to each other by means of thermal compression bonding.
Even the method described in connection with the second embodiment enables formation of a boat capable of sufficiently bearing practical use. Even when the [0132] top plate 5 and the boat supports 3 are bonded together by means of welding the boat supports by way of the top plate 5 and the boat is then annealed, no visibly-recognizable dislocations arise in the boat.
Third Embodiment [0133]
Slip is observed in detail through use of an X-ray toposystem shown in FIG. 13. Slip has arisen in the areas on a silicon wafer corresponding to a silicon [0134] wafer support section 15B and a silicon wafer support section 15C shown in the transverse cross-sectional view of a quartz boat shown in FIG. 10. No slip has arisen in the area on the silicon wafer corresponding to a silicon wafer support section 15A. It can be estimated that the silicon wafer support sections 15B and 15C of the boat shown in FIG. 10 are arranged in parallel with each other, as shown in FIG. 15. If silicon wafer support sections 1A, 1B, and 1C are spaced equally apart from each other along the periphery of a silicon wafer so as to extend radially from the center of the silicon wafer as shown in FIG. 16, the interval between the boat supports 3 supporting the support sections 1B and 1C becomes narrow. At the time of loading of a silicon wafer, a silicon wafer 17 comes into collision with the boat supports 3. For this reason, this structure cannot be adopted.
If the silicon [0135] wafer support sections 1A, 1B, and 1C are elongated, as shown in FIG. 17, in order to extend the interval between the boat supports 3 such that loading and unloading of the silicon wafer 17 can be effected, the silicon wafer support sections 1A, 1B, and 1C interfere with a reaction tube 18 provided in a vertical heat treatment system. Therefore, this structure is also unadoptable. If the reaction tube 18 is spread so as to avoid interference, clearance between the silicon wafer 17 and the reaction tube 18 becomes excessively large, thereby hindering formation of a uniform film. Alternatively, if the silicon wafer support sections 1A, 1B, and 1C located within a single plane are interconnected, mechanical loading and unloading of the silicon wafer becomes impossible. Therefore, such a structure cannot be used in a mass-production site.
As shown in FIG. 18, according to the third embodiment, a silicon [0136] wafer support section 1D and a silicon wafer support section 1E have the shape of the letter L. As a result, the silicon wafer support sections 1D and 1E can be aligned with two of three lines 19 which originate from the center of the silicon wafer 17 and divide the silicon wafer 17 into three equal sectors.
FIGS. 19 through 21 show the silicon [0137] wafer support sections 1 capable of preventing occurrence of slip in the same manner as the silicon wafer support sections shown in FIG. 18. There are many conceivable examples of the geometry of the silicon wafer support section 1 which enables dispersion of load without posing a problem in flatness. However, determination through tests of a specific geometry which is superior to others in economy and slip prevention performance is not easy. In the third embodiment, if silicon wafer support sections 1 of various shapes and a single quartz boat for holding the silicon wafer support sections 1 are available, a test can be conducted while the plurality of silicon wafer support sections 1 are simultaneously attached to the quartz boat. Hence, an optimum structure can be determined with a lower number of tests.
Fourth Embodiment [0138]
There will now be described a fourth embodiment of the present invention in which clearance between a quartz tube provided in a vertical heat treatment system and silicon wafer support sections is reduced. FIG. 22 is a perspective view showing a status in which a [0139] silicon wafer support 1, a spacer 2, and a boat support 3, all belonging to a retainer for use in heat treatment of a substrate according to the fourth embodiment, are fitted together. FIG. 23 is a top view showing the silicon wafer support section 1, the spacer 2, and the boat support 3. As shown in FIG. 23, in the fourth embodiment, a semi-circular portion of the boat support 3 which is not to come into contact with the silicon wafer support section 1 is cut into a flat section 3 a. The silicon support section 1 and the spacer 2, which are to fit on the boat support 3, are also cut.
In order to ensure fitting of the silicon [0140] wafer support section 1 and the spacer 2 on the boat support 3, the flat section 3 a is located at a position outside the center of boat support 3, the position being diametrically opposite a position where the silicon wafer support section 1 is to come into contact with a silicon wafer. A cut of the silicon wafer support section 1 and that of the spacer 2 are located outside the center of the boat support 3 so as to be aligned with a flat section 3 a.
Thus, the [0141] flat section 3 a is formed in the boat support 3, and a cut is formed in the silicon wafer support section 1 and in the spacer 2, thereby enabling an decrease in the maximum diameter of a retainer. The reaction tube 18 of the vertical heat treatment system can be positioned closer to the back of the silicon wafer support section 1 toward a silicon wafer. As a result, the retainer according to the fourth embodiment yields the same advantage as that yielded in the first embodiment and a further increase in the efficiency of heat treatment effected when a silicon wafer is loaded into the vertical heat treatment system.
Although three [0142] supports 3 are used in each of the embodiments, four or more supports may also be used.
In the event that breakage of silicon wafer support sections, which would not arise often, arises for reasons of carelessness or failures of a system, only broken support sections can be replaced with new support sections. Hence, costs of repair can be curtailed. Further, when several silicon wafer support sections are considered to have been broken by themselves, the silicon wafer support sections are determined to have reached their endurance limits. At this time, replacement of all the silicon wafer support sections is desirable. [0143]
Constituent elements of the retainers described in connection with the embodiments; that is, the [0144] top plate 5, the bottom plate 6, the boat supports 3, the silicon wafer support sections 1, and the spacers 2, are formed as components, and these components can be produced by an NC machine. In contrast with a case where a related-art retainer for use in heat treatment of a substrate, such as that shown in FIG. 9 or 10, is manufactured, manufacturing costs, including labor costs, can be curtailed significantly. Use of quartz glass as principal material results in a reduction in manufacturing costs. As a result of constituent elements being formed as components, manufacturing costs can also be curtailed. Even when a retainer is formed from, e.g., SiC, manufacturing costs can be reduced as compared with a case in which a retainer of related-art structure is manufactured. In a case where SiC is used as material, the silicon wafer support sections 1 are susceptible to thermal deformation at high temperatures. Hence, so long as the top plate 5, the bottom plate 6, the boat supports 3, and the spacers 2 are formed from quartz glass and the silicon wafer support sections 1 are formed from SiC, deformation of the silicon wafer support sections 1 can be minimized, thus improving accuracy. Even when SiC is used, costs can be curtailed.
Fifth Embodiment [0145]
FIG. 24 is a plan view showing a silicon [0146] wafer support section 20 to be used in a retainer for use in heat treatment of a substrate according to a fifth embodiment. FIG. 25 is a perspective view showing a spacer 21 to be used in the retainer for use in heat treatment of a substrate according to the fifth embodiment. FIG. 27A and 27B are perspective views of the lowermost spacer 22 used for the lowermost portion of the retainer for use in heat treatment of a substrate according to the fifth embodiment (where FIG. 27A is a perspective view, and FIG. 27B is a cross-sectional view). FIG. 27B shows a cross section taken along line alternate long and short dash lines II-II′ shown in FIG. 27A. As shown in FIGS. 27A and 27B, a tapered surface 22 b is formed in a lower portion of the lowermost spacer 22.
A [0147] hole 21 a for enabling passage of a boat support 23 is formed in a spacer 21, and a hole 22 a is formed in the lowermost spacer 22. Similarly, a hole 20 a for enabling passage of the boat support 23 is formed in a silicon wafer support section 20. According to this method, a required number of lowermost spacers 22, spacers 21, and silicon wafer support sections 20 are prepared. As shown in FIG. 38, boat supports 23 are set up on the bottom plate 24 of the retainer for use in heat treatment of a substrate. In contrast, the lowermost spacer 22 is passed to the boat supports 23 while the side of the spacer 22 facing the tapered surface 22 b is held downward. The tapered surface 22 b is for preventing occurrence of interference between the lowermost spacer 22 and a prominence formed during welding of the bottom plate 24 and the boat support 23. Next, the silicon wafer support section 20 is passed to the boat supports 23, and the spacer 21 is passed to the same. Hereinafter, the silicon wafer support sections 20 and the spacers 21 are alternately passed to the boat supports 23. After all the silicon wafer support sections 20 and the spacers 21 have been passed to the boat supports 23, the top plate 25 is attached to the top of the boat supports 23, thereby completing a retainer for use in heat treatment of a substrate. FIG. 29 is a perspective view showing the thus-completed retainer for use in heat treatment of a substrate.
In the fifth embodiment, one silicon [0148] wafer support section 20 supports one wafer W. The silicon wafer support section 20 is formed into the shape of a ring so as to become substantially identical in size with the outer side of the wafer W. A notch is formed in a portion of the silicon wafer support section 20 so as to enable passage of the carrier arm 26.
As shown in FIG. 24, a silicon [0149] wafer contact section 20 b is formed so as to horizontally cut away a surface of the silicon support section 20 which comes into contact with a wafer W, in order to prevent movement of a wafer W after the wafer W has been loaded on a silicon wafer support section 20 (see a cross section taken along line I-I′ shown in FIG. 24). An arm recess 20 c is formed in a portion of the internal center area of the silicon wafer support section 20. As a result, an extremity 26 a of the carrier arm 26 described in connection with FIGS. 45 through 47 can be prevented from interfering with the silicon wafer support section 20. FIG. 28 is a plan view showing a positional relationship between the carrier arm 26 and the silicon wafer support section 20 during transport of a wafer W. By means of the arm recess section 20 c, loading and unloading of a wafer W into and from the retainer for use in heat treatment of a substrate can be effected by use of an automatic wafer transporter.
The [0150] space 21 is not limited to a ring shape shown in FIG. 25 and may assume a C-shaped geometry shown in FIGS. 26A and 26B. FIG. 26A is a perspective view of a C-shaped spacer 27. FIG. 26B is a top view of the same. No holes for enabling passage of the boat supports 23 are formed in the C-shaped spacer 27. A recess 27 a plays the role of a hole. The recess 27 a is oriented toward the outside of the retainer for use in heat treatment of a substrate through use of the C-shaped spacer 27, thereby preventing the spacer from extending off the retainer for use in heat treatment of a substrate. As a result, a clearance between the retainer for use in heat treatment of a substrate and a reaction tube can be reduced. Further, the recess 27 a is oriented toward the inside of the retainer for use in heat treatment of a substrate, thereby preventing occurrence of interference between the wafer W and the spacer.
A protruding [0151] section 27 b is formed in the C-shaped spacer 27 so as not to become dislodged from the boat supports 23. As shown in FIG. 41, a recess 23 a is formed in each of the boat supports 23 so as to fittingly receive the protrusion 27 b. When a protrusion is formed in each of the boat supports 23, a recess which fittingly matches the protrusion is formed in the spacer 27. In order to ensure coupling between the boat support 23 and the C-shaped spacer 27, a plurality of projections 27 b may be formed on one spacer 27, and a plurality of recesses 23 a may be formed in one boat support 23. As a result, dislodgment of the C-shaped spacer 27 from the boat support 23 can be prevented.
As in the case of the preceding embodiments, the thicknesses of the [0152] spacers 21, 22, and 27 are strictly defined. Since the silicon wafer support section 20 is cut out of a single plate, the thickness of the silicon wafer support section 20 is also strictly defined. Further, the plane accuracy of the silicon wafer support section 20 has already bee determined in a phase in which a plate is formed from material. Accordingly, the position and plane accuracy of an upper surface of the n^th(“n” is an integer) silicon wafer support section 20 attached to the boat supports 23 are remained highly accurately. Hence, no slips arises in a wafer during heat treatment. A retainer for use in heat treatment of a substrate compatible with high-temperature heat treatment to be effected at a temperature of 1100° C. or more must be formed from SiC. SiC-made spacers cause greater dimensional variations than quartz-made spacers do. When demand exists for precision because of use with an automatic transporter, spacers 21, 22, and 27 formed from quartz can be used up to a temperature of, e.g., 1150° C. Hence, use of a retainer for use in heat treatment of a substrate in which only the spacers 21, 22, and 27 are formed from quartz, is preferable. In this case, the plane accuracy of the SiC-made silicon wafer support section 20 is slightly inferior to that of a quartz-made silicon wafer support section 20.
The method of manufacturing a retainer for use in heat treatment of a substrate according to the fifth embodiment requires proficiency in only bonding the boat supports [0153] 23 to the bottom plate 24 and bonding the top plate 25 to the top of the boat supports 23. The remaining process involves a mere operation for stacking the silicon wafer support sections 20 and the spaces 21, 22, and 27 alternately. Thereby enabling a reduction in manufacturing costs. The spacers 21, 22, and 27 and the silicon wafer support sections 20 can be mass-produced. As the number of processes increases, a price scale becomes lower. Accordingly, there can be provided a retainer for use in high-temperature treatment of a substrate which satisfies both high dimensional precision and low costs.
Sixth Embodiment [0154]
FIG. 30 is a plan view showing the silicon [0155] wafer support section 20 to be used in a retainer for use in heat treatment of a substrate according to a sixth embodiment of the present invention. The silicon wafer support section according to the sixth embodiment is essentially identical with that described in connection with the fifth embodiment in terms of construction and processing steps. Triangular cuts are formed in a silicon wafer contact section 20 b of the silicon wafer support section 20 according to the sixth embodiment, thereby diminishing a contact area between the silicon wafer contact section 20 b and the wafer W. FIG. 30 shows sharp triangular cuts. U-shaped, semi-circular, or rectangular cuts may also be employed. In short, easy-to-process geometries can be adopted. This structure is effective for blocking heat escaping to surroundings of a wafer when the silicon wafer support section 20 is formed from quartz glass having particularly high specific heat (0.3 cal/g·° C. at 1100° C.).
Seventh Embodiment [0156]
FIG. 31 is a plan view of the silicon [0157] wafer support section 20 to be used in a retainer for use in heat treatment of a substrate according to a seventh embodiment. The silicon wafer support section according to the seventh embodiment is essentially identical with that described in connection with the fifth embodiment in terms of construction and processing steps. Holes 20 a for enabling passage of the boat supports 23 are not formed in the silicon wafer support section 20. Instead, external portions of the silicon wafer support section 20 which interfere with the boat supports 23 are cut away, thereby forming support engagement sections 20 d. This method is adopted in a case where the holes 20 a through which the boat supports 23 are to pass cannot be formed in the silicon wafer support section 20. In this case, the four engagement sections 20 d are matched in shape with the outer shapes of the spaces 21, 22, and 27. As a result, the silicon wafer support sections 20 can be retained in appropriate positions.
Eighth Embodiment [0158]
FIG. 32 is a plan view showing the silicon [0159] wafer support section 20 and the spacer 21, which are to be used in a retainer for use in heat treatment of a substrate according to an eighth embodiment, when the silicon wafer support section 20 and the spacer 21 overlap each other. The silicon wafer support section according to the eighth embodiment is essentially identical with that described in connection with the fifth embodiment in terms of construction and processing steps. The silicon wafer contact sections 20 b are not provided in the silicon wafer support section according to the eighth embodiment. Outer regions of four spacers 21 are utilized for securing a wafer W. Outer peripheries of the spacers 5 are arranged so as to prohibit movement of the wafer W, thereby enabling positioning of the wafer W. Such a structure enables a reduction in the number of processes of forming the silicon wafer support sections 20. FIG. 33 is a perspective view showing a retainer for use in heat treatment of a substrate using the silicon wafer support sections 20 according to the eighth embodiment. In the eighth embodiment, the occupation area of the silicon wafer support sections 20 can be diminished, thereby enabling a reduction in costs of components.
Ninth Embodiment [0160]
FIG. 34 is a plan view showing a silicon [0161] wafer support section 20 to be employed in a retainer for use in heat treatment of a substrate according to a ninth embodiment of the present invention. Quartz glass sufficiently withstands, as material for a retainer for use in heat treatment of a substrate, heat treatment effected at a temperature of 1100° C. or thereabouts. However, the present inventors have often experienced that he silicon wafer support sections is deformed to assume a barrel-like shape during the course of being used for a long period of time. A prismatic boat support 23 can bear such deformation greater than a columnar boat support 23. When the boat support 23 is formed so as to assume a prismatic geometry, the support engagement section 20 d assumes a rectangular and keen angle shape, as shown in FIG. 34. FIG. 35 shows one example of a spacer 28 to be used with the silicon wafer support section 20 described in connection with the ninth embodiment. The geometry of a hole 28 a through which a rectangular boat support 23 passes assumes a rectangular shape corresponding to the cross-sectional geometry of the support 23. Conceivable appearances of a spacer include the shape of a ellipse, the shape of a bottom-less box, and the shape of Ω. When a spacer assumes the shape of a letter U, the projections 28 b are provided, as in the case of the C-shaped spacer 27.
Tenth Embodiment [0162]
FIG. 36 is a plan view showing a silicon [0163] wafer support section 20 to be used in a retainer for use in heat treatment of a substrate according to a tenth embodiment of the present invention. When the silicon wafer support section 20 is formed from quartz, the tips of each of the silicon wafer support sections 20 may be deformed under self weight. With a view toward reducing the weight of the edges, holes 20 e are formed in addition to the holes 20 e through which the boat supports 23 are to pass. As a result, there can be prevented deformation of the tips of the silicon wafer support section 20 e, which would otherwise be caused when the silicon wafer support sections have been used for a long period of time.
Eleventh Embodiment [0164]
FIG. 37 is a plan view showing a silicon [0165] wafer support section 20 to be used in a retainer for use in heat treatment of a substrate according to an eleventh embodiment of the present invention. In the eleventh embodiment, a plurality of holes 20 e are formed in the entire surface of the silicon wafer support section 20, thereby reducing the entire weight of the retainer. Even when wafers W are loaded on the retainer, load is exerted on the entirety of the silicon wafer support section 20. Hence, loading of the wafers W does not induce deformation of specific portions of the silicon wafer support section 20.
Twelfth Embodiment [0166]
As can be seen from use of a quartz glass plate as a mask or a liquid-crystal display device, the quartz glass plate possesses considerably high plane accuracy. Hence, when quartz glass is employed as material, the silicon [0167] wafer support section 20 is hollowed from a single plate, thereby maintaining plane accuracy. FIG. 39 is a plan view showing a single plate material 30 from which the silicon wafer support section 20 has been hollowed. An ordinary quartz manufacturer purchases quartz glass for processing purposes from a quartz member manufacturer. The geometry of members to be purchased is limited to essential geometries, such as angular shapes, columnar shapes, plate-like shapes, and tube-like shapes. When processing is performed through use of such a quartz member, the silicon wafer support section 20 is hollowed from a very large single plate. As shown in FIG. 39, a very large unnecessary portion arises under this method.
As shown in FIG. 40, in the twelfth embodiment, a quartz plate glass is processed into small [0168] rectangular plate members 29. The plate members 29 are arranged so as to constitute a circular area and securely welded together so that the silicon wafer support section 20 can be hollowed from the plate members 29. The plate members 29 are abraded after having been welded together, thereby improving plane accuracy to the same level as that of a single plate. It is understood that, when compared with the example shown in FIG. 39, an unnecessary area can be significantly diminished. Although welded portions induce vein-like bulges, the bulges can be smoothed through abrasion.
As mentioned above, in the twelfth embodiment, undesired quartz glass chippings arising during the course of manufacture of the silicon [0169] wafer support section 20 can be diminished. The silicon wafer support section 20 can be manufactured from material recycled from quartz glass chippings.
The previous embodiments have described examples in which a silicon wafer is employed as a substrate. However, the present invention is not limited to these embodiments. The present invention can be applied to all types of substrates requiring heat treatment. [0170]
The previous embodiments have described only examples of implementation of the present invention. Therefore, the technical scope of the present invention should not be construed limitedly by the embodiments. In other words, the present invention can be implemented in various forms within the scope and principal features of the invention. [0171]
Since the present invention is embodied in the manner described above, the following advantages are yielded. [0172]
Since the support section and the spacer can be manufactured separately, the plane accuracy of the support section and a vertical interval between the support sections are determined by the accuracy of a single support section and the accuracy of a single spacer. Hence, there can be provided a highly-accurate retainer for use in heat treatment of a substrate, by means of maintaining the initial accuracy of the support section and that of the spacer. Further, support sections and spacers can be selected in a manufacturing phase. Hence, there can be provided a highly-accurate retainer for use in heat treatment of a substrate. Moreover, a support section and a spacer are separated from each other. Hence, support sections and spacers can be mass-produced, thereby enabling a reduction in manufacturing costs. [0173]
Since support sections and spacers are fitted around a support, the support sections and the spacers can be retained without fail, thereby improving the ease of assembly of a retainer. [0174]
Engagement sections of a support section or spacer are formed into holes. As a result, supports are passed into the holes, thereby enabling reliable engagement between a support section or spacer and the support. [0175]
Engagement sections of the support section are formed into cuts, thereby preventing extension of a support section to the outside of the retainer. [0176]
Since the spacer is C-shaped geometry, and the recess is oriented toward the outside of the retainer, thereby preventing the spacer from extending off the retainer for use in heat treatment of a substrate. [0177]
In connection with an engagement section between a spacer and a support, a protrusion is formed in either the spacer or the support, and a recess is formed in the remaining. Hence, the protrusion and the recess can be engaged with each other, thereby preventing dislodgment of the spacer having cuts formed therein from the spacer. [0178]
Since the position of a hole formed in a support section is substantially in agreement with the position of center of gravity of the support section within a horizontal plane, inclination of the support section during assembly can be suppressed. Accordingly, the support sections can be stacked while ascertaining the horizontal state of the support section. Since the retainer can be assembled while failures in a stacking phase are ascertained, failures can be detected and addressed at an early time. [0179]
Since the center of gravity of the support section is diametrically opposite a contact section with respect to the center of a hole of the support section within a horizontal plane, the support section can be maintained horizontal while actually supporting a substrate. The accuracy of flatness of the support section can be ascertained while a substrate is placed on the support section, and hence failures can be detected and addressed in a production phase. [0180]
Since the support sections and the spacers are fastened to each other, while remaining in close contact with each other and being disposed between a nut secured to an upper end of the support and a pedestal, a retainer for use in heat treatment of a substrate is obtained without involvement of thermal deformation or stress. [0181]
As a result of support sections and spacers being fastened to each other by means of thermocompression bonding, ease of assembly of a retainer can be improved. Both upper and lower surfaces of each of support sections and upper and lower surfaces of each of spacers are mirror finished, thereby facilitating thermocompression bonding. [0182]
The support section is formed into a ring-shape, and a cut is formed in a position on a support section where transport arm for transporting a substrate is to be loaded. As a result, loading and unloading of transport arm become possible without reducing a contact area between the support section and the substrate. [0183]
An inner portion of the support section facing a cut is expanded to the outside rather than the remaining region, thereby preventing occurrence of interference between the transport arm and the support section. [0184]
A step is formed in a substrate-side of the support section along a contact section, thereby prohibiting movement of a substrate. [0185]
A plurality of cuts are formed in the contact section, thereby preventing spread of heat to surroundings of the substrate. [0186]
Spacers are arranged such that the outer edges of a plurality of spacers arranged at the same level become close to the outer edge of the substrate, thereby prohibiting movement of a substrate on the support section. [0187]
Holes are formed in an area on the support section other than engagement sections where the support section engages with the support, thereby preventing deformation of the support section, which would otherwise be caused by self weight. [0188]
Since quartz glass is adopted as principal material, manufacturing costs can be curtailed. [0189]
As a result of a retainer according to the present invention being used in a substrate heat treatment system which features superior control of in-plane temperature of a substrate, there can be prevented occurrence of slip in a substrate, which would otherwise arise during high-temperature treatment. Hence, there can be provided a high-temperature substrate heat treatment system while enabling a reduction in manufacturing costs. [0190]
Since only a pedestal and supports, for which accuracy is not required, are welded together, there can be prevented deterioration of accuracy of the support sections, which would otherwise be caused by welding. Further, there can be prevented influence on accuracy of the retainer, which would otherwise be imposed as a result of annealing for obviating warpage of a retainer. [0191]
Further, a quartz glass plate is split into required shapes. The thus-split plates are welded into a single piece, thereby diminishing the amount of undesired quartz glass chippings which arise during manufacturing processes. [0192]
The structure of a boat which suppresses occurrence of slip in a substrate, which would otherwise arise during heat treatment, can be determined at low cost and in a short period of time. [0193]
Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may by practiced otherwise than as specifically described. [0194]
The entire disclosure of a Japanese Patent Application No. 2001-44066, filed on Feb. 20, 2001 and No. 2001-145387, filed on May 15, 2001 including specification, claims, drawings and summary, on which the Convention priority of the present application is based, are incorporated herein by reference in its entirety. [0195]

Claims

1. A retainer for use in heat treatment of a substrate which supports a plurality of substrates in a horizontal position while said substrates are spaced away from each other with respect to a vertical direction, said retainer comprising:

a plurality of support sections for supporting said respective substrates by way of surface contact; and

spacers for defining intervals between said support sections with respect to the vertical direction.

2. The retainer according to claim 1, further comprising a plurality of supports set upright on a pedestal for holding said support sections and the spacers, and wherein each of said support sections has a contact section for supporting said substrate bay way of surface contact as well as an engagement section engaging to said support; each of said spacers having an engagement section engaging to said support; and said support sections and said spacers being alternately fitted with said support.

3. The retainer according to claim 2, wherein the engagement section of said support section is a hole formed so as to penetrate through said support section.

4. The retainer according to claim 2, wherein said engagement section of said support section assumes the shapes of cut formed in said support section, and at least one portion of said cut are identical with the cross-sectional shape of said support.

5. The retainer according to claim 2, wherein said engagement section of said spacer is a hole formed so as to penetrate through said spacer.

6. The retainer according to claim 2, wherein said engagement section of said spacer assumes the shapes of cut formed in said spacer, and at least one portion of said cut are identical with the cross-sectional shape of said support.

7. The retainer according to claim 6, wherein, in connection with the engagement portion between the spacer and the support, a protrusion is formed in either said spacer or said support, and a recess is formed in the remaining, and said protrusion and said recess are engaged with each other.

8. The retainer according to claim 2, wherein said support sections and said spacers are fixed and sandwiched between a nut fastened to an upper end of each of said supports and said pedestal while remaining in close contact with each other with respect to a vertical direction.

9. The retainer according to claim 2, wherein said support sections and said spacers are fixed together by means of thermocompression bonding.

10. The retainer according to claim 9, wherein upper and lower surfaces of each of said support sections and upper and lower surfaces of each of said spacers are mirror finished.

11. The retainer according to claim 2, wherein said support section is formed into the shape of a ring, and a cut is formed in a position on said support section where transport arm for transporting said substrate is to be loaded.

12. The retainer according to claim 11, wherein an interior of said support section located opposite said cut is expanded outside from the remaining portion of said support section.

13. The retainer according to claim 11, wherein a step is formed in a substrate-side of said support section along said contact section.

14. The retainer according to claim 11, wherein said spacers are arranged such that the outer edges of a plurality of spacers arranged at the same level in height become close to the outer edge of said substrate.

15. The retainer according to claim 2, wherein quartz glass is used as a principal material.

16. A substrate heat treatment system comprising the retainer defined in any one of claims 1 through 15.

17. A method of manufacturing a retainer for use in heat treatment of a substrate, which retainer supports a plurality of substrates in a horizontal position while spacing said substrates away from each other with respect to a vertical direction, the method comprising the steps of:

fixedly placing a plurality of supports upright on a pedestal;

alternately fitting, to each of said supports, support sections for supporting the plurality of said substrates and spacers for defining intervals between said support sections in a vertical direction; and

fixing said support sections and said spacers while they remain in close contact with each other.

18. The method of manufacturing a retainer according to claim 17, wherein said support sections and said spacers are fixed while remaining in a close contact with each other, by means of fastening a nut to an upper end of each of said supports.

19. The method of manufacturing a retainer according to claim 17, further comprising a step of mirror finishing upper and lower surfaces of each of said support sections and upper and lower surfaces of each of said spacers; and wherein said support sections and said spacers are fixed to each other by thermocompression bonding.

20. The method of manufacturing a retainer according to claim 17, further comprising:

a step of connecting a plurality of quartz glass plates by welding before said support section is fitted to said supports;

a step of abrading a surface of the connected quartz glass plate; and

a step of forming said support section by hollowing the connected quartz glass plate.