WO2000003060A1

WO2000003060A1 - Chemical vapor deposition apparatus employing linear injectors for delivering gaseous chemicals and method

Info

Publication number: WO2000003060A1
Application number: PCT/US1999/008702
Authority: WO
Inventors: Daniel M. Dobkin; Walter Strifler; Anthony Mcgrogan
Original assignee: Silicon Valley Group Thermal Systems, Llc
Priority date: 1998-07-10
Filing date: 1999-04-21
Publication date: 2000-01-20
Also published as: TW467960B; AU3965499A

Abstract

There is provided a chemical vapor deposition apparatus for depositing substantially uniform films or layers onto a substrate or wafer. The apparatus includes a chamber (11) with an injector assembly (12) including spaced linear injectors (16) and a chemical vapor delivery system for delivering chemicals to said injectors (16) to form spaced adjacent deposition regions. Translation means (44) reciprocally move said substrate or wafer a predetermined distance in a direction perpendicular to the long axis of the linear injectors (16) while maintaining the substrate surface parallel and adjacent to the chemical delivery surface of the linear injector assembly (12) whereby the deposition regions of adjacent injectors merge to form a film or layer of substantially uniform thickness.

Description

CHEMICAL VAPOR DEPOSITION APPARATUS EMPLOYING LINEAR INJECTORS FOR DELIVERING GASEOUS CHEMICALS AND METHOD

BRTFF DESCRIPTION OF THR TNVRNTTON

This invention relates generally to a chemical vapor deposition apparatus which employs a plurality of linear injectors for delivering gaseous chemicals to substantially rectangular deposition regions on a substrate which is reciprocally moved past the linear ejectors to merge the deposition regions on the substrate, and a method of depositing uniform films on a substrate employing linear injectors.

BACKGROUND OF THE INVENTION Linear gaseous injectors provide a means for depositing regions of film which are substantially linear — that is, the thickness of the deposited film is a function of distance from a center line and only weakly dependent on position along the center line. For example, U.S. Patent Nos. 5,136,975 and 5,683,516 describe a linear injector which can be used in chemical vapor deposition of various films, the resulting instantaneous deposition region being roughly rectangular in shape. In the prior art, for example U.S. Patent No. 4,834,020, a wafer or substrate has been moved at a constant rate, passing completely under said injectors using e.g. a flexible metal transport belt, in order to convert the narrow rectangular deposition region into a uniform film over the complete substrate surface.

Rather than having the injectors spread out, the injectors can be placed near one another to deposit consecutive linear "stripes" in close proximity to one another. This would permit the fabrication of more compact apparatus for the same amount of deposition. For example, U.S. Patent application Serial No. filed simultaneously herewith and incorporated herein by reference describes a modified version of the aforesaid injector technology in which multiple applicators or injectors are placed closely adjacent to one another, typically as a single block of metal, in order to effect reductions in the cost and size of the resulting deposition system. With a multiplicity of injectors to form deposition regions next to one another, the width of the region under which a wafer must pass using the prior art translation method extends from the leading edge of the first injector to the trailing edge of the last injector. It is easily demonstrated that the required translation distance increases as the number or spacing of injectors increases, and also increases as the size of the wafer or substrate increases. In fact, since the wafer must completely pass under the injectors, each increase of one centimeter in wafer size gives rise to a 2 centimeter increase in chamber size. This size requirement represents an obstacle to incorporation of such an injector within a single- wafer chamber design, since the chamber size must accommodate motion of the wafer under all of the injectors.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the present invention to provide chemical vapor deposition apparatus employing spaced linear gaseous chemical injectors in which the wafers or substrate onto which a film is to be deposited is linearly reciprocated adjacent the injectors.

It is another object of the present invention to provide a chemical vapor deposition apparatus in which the size of the chambers is comparable to the size of the multiple injector assembly.

It is another object of this invention to minimize the required distance of wafer motion by employing a reciprocating linear translation of the wafer by a distance comparable to the separation between successive injectors.

In accordance with the present invention, there is provided a chemical vapor deposition apparatus for depositing substantially uniform films or layers onto a substrate or wafer. The apparatus includes a chamber with an injector assembly including spaced linear injectors and a chemical vapor delivery system for delivering chemicals to said injectors to form spaced adjacent deposition regions. Translation means move said substrate or wafer in a direction perpendicular to the long axis of the linear injectors while maintaining the substrate surface parallel and adjacent to the chemical delivery surface of the injector assembly whereby the deposition regions of adjacent injectors merge to form a film or layer of substantially uniform thickness. BRTEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects of the invention will be more clearly understood from the following description when taken in conjunction with the accompanying drawings of which: Figure 1 is a cross-sectional view of a chemical deposition apparatus in accordance with the invention.

Figure 1 A is an enlarged view of the injectors of Figure 1. Figure 2 is a perspective view of the wafer support and translation means of Figure 1. Figure 3 is a perspective view showing the linear drive system.

Figure 4 is a perspective view of the linear translation system. Figure 5 is a flow diagram showing the flow of chemicals into the chemical vapor deposition apparatus of Figure 1.

Figure 6 is a schematic diagram showing a stationary substrate beneath a pair of linear inj ectors.

Figure 7 is a schematic depiction of a typical deposition thickness profile resulting from the injectors of Figure 5.

Figure 8 is a top plan view showing the linear rectangular deposition region under the injectors of Figure 5. Figures 9A-9C show the time history of deposition for a point PI outside the deposition region of injector number 1.

Figures 10 A- 10C are schematic representations of a moving wafer considering a point P2 which starts at the center line of the first injector in time t=0. Figures 11A-1 IC depicts the region of a wafer or substrate in which a film or layer is uniformly deposited.

Figures 12A-12B schematically show the velocity profile and position versus time for a single reciprocating motion.

Figure 13 shows the allowable left-most position of travel for a wafer or substrate. Figure 14 shows the effect of variations in travel length for Linj - 63.9 mm.

Figure 15 shows deposition for two single sweeps of varying pitch (61 and 63.5 mm), and average of the two (projected equivalent of 62.3 mm sweep). Figure 16 shows thickness vs. position in direction of travel; fixed translate velocity, three different distances of translation.

Figure 17 is a comparison of thickness (relative to average, scaled by standard deviation) for identical motion pitch but different translation velocities.

DESCRIPTION OF PREFERRED EMBODIMENT The chemical vapor deposition apparatus of the present invention includes a chamber 11, Figure 1, which may be at atmospheric pressure for APCVD deposition or may be evacuated for CVD deposition. The chamber supports an injector assembly 12 for injecting gaseous chemicals into deposition zones 13a, 13b and 13b defined by the injector assembly and the wafer or substrate surface as will be presently described. As will become apparent from the following description, the injector assembly may comprise any number of individual injectors assemblies; three are shown in Figure 1 for illustrative purposes. A detailed description of the operation of an injector such as injector 12 can be found in co-pending application

Serial No. filed simultaneously herewith. Briefly, however, the injector assembly 12, shown more clearly in the enlarged view of Figure 1 A, comprises a plurality of injectors 16 and a plurality of members 17 spaced on each side of the injectors 16 to form a plurality of exhaust channels 18 to exhaust gases from the deposition zones 13. An exhaust manifold 19 is associated with each exhaust channel. Each injector of the injector assembly includes front, back, top and end surfaces and a bottom gas delivery surface for delivery of gases to the respective deposition zones 13. Preferably, each deposition zone is defined by two rounded side regions 22, a center recessed region 23, and noses 24 of members 17. At least one first elongated passage 26 formed in each injector extends between the end surfaces to receive a gas. Additionally formed within each injector member is at least one distribution slot 27 which extends between the elongated passage 26 and the center recess 23. Additional elongated passages 28 and 29 communicate with slots 31 and 32 and deliver gases to the associated zone 13. The member 17 includes front, back, top and end surface and a bottom surface. The bottom surface generally includes a planar region 33 and at least one contoured nose 24. The nose is placed adjacent to and spaced from the rounded side regions 22 such that a rounded exhaust channel is formed. The members 17 may also include elongated passages 34 which communicate with the end surface via a slot 36. Etchant gases may be applied through the slots 34 to etch away any deposits which may be formed on the planar region or surface 33. The injectors or applicators 16, members 17, passages 26, 28, 29 and 34, slots 27, 31, 32 and 36, exhaust channels 18, and noses

24 are formed in a single block of material. A second block of material includes exhaust channels 18 and exhaust manifolds 19. The two blocks are joined to one another by screws extending into wells 37.

The substrate or wafer onto which the film or layer is to be deposited is supported on a chuck 41, Figures 1 and 2, and retained on the chuck by applying a vacuum through openings 50 (circles and cross) in the chuck to the underside of the wafer or substrate to hold the substrate or wafer. The chuck support assembly is preferably water cooled as illustrated by the conduits 42 and 43. The water cooling protects the ancillary components which hold the hot chuck in position, move lift pins, etc. The chuck is supported on a platform 44 mounted on drive assembly 45 supported in the chamber 11, Figures 3 and 4. The platform is guided for linear movement by rails 46 and 47. The platform is moved by a lead screw 48 driven by motor 49 by a train 51 which extends through a vacuum seal 52. A flexible coupling 54 couples the drive train 51 to the lead screw 48. Proximity switches 53, 54, Figure 4, are mounted on guide rails and provide for switching the motor drive to provide forward and reverse limits of travel of the carriage plate. Thus, the carriage plate is reciprocally driven whereby the chuck mounted thereon moves back and forth under the injector assembly 12. The chuck 41 and drive assembly 45 are supported on leveling screws 56 which extend through the lower wall of the chamber 11 and engage bearings 59. The screws 56 are driven by motors 58 to raise, lower and level the chuck 41.

With the chuck in its lower position, a wafer or substrate mounted on a support is moved into the chamber 11 by a robotic arm 61. The chuck is equipped with three lift pins (not shown) which extend through access holes, Figure 2. When the robot arm has placed the support above the chuck, the robotic arm lowers the support and the lift pins rise up from the chuck surface to capture the support. The robot arm is removed from the chamber. After a preheat of the wafer in this position, the lift pins are lowered into the chuck and the chuck vacuum turned on as the wafer settles onto the chuck surface. The preheat time is empirically determined to prevent the wafer from warping when it touches the chuck surface, and allow the vacuum hold-down to capture it. The chuck may then be moved into its exact deposition position with the wafers closely adjacent to the lower surface of the injector assembly to thereby define the deposition regions 13 beneath each of the injectors. The wafer or substrate is then reciprocally translated a pre-determined distance in a direction perpendicular to the long axis of the linear injectors while maintaining the substrate surface parallel and in cooperative relationship with the deposition zones.

As an example of the use of the apparatus, the flow of gaseous chemicals for the deposition of silicon dioxide is described. It is of course apparent that the apparatus can be used for other chemical vapor deposition processes, such as the deposition of doped oxides such as boron phosphorous silicate glass. Figure 5 shows the flow for ozone, TEOS and nitrogen into the chemical vapor deposition apparatus. When there is no deposition, the ozone and the TEOS are switched by fast acting pneumatic valves 62, arranged in opposed pairs to direct the ozone and TEOS directly to the vent line 63 connected to a vacuum pump. A similar or identical flow of nitrogen runs to the deposition zones 13 via the passages 26, 28 and 29. When deposition is to be started, the fast acting valves are switched to cause the ozone and TEOS to flow into the passages 26, 28 and 29 and to the deposition zones 13, and the nitrogen to flow to the vent line. In this fashion the composition of the gas stream switches very rapidly (the transition is roughly as fast as the valves can activate) so that deposition starts and ends quickly. Since the mass flow controllers for these gases do not change their settings, the total gas flow remains constant, and there are no long transients associated with starting or stopping the deposition.

In accordance with the present invention, the wafer is reciprocally moved a predetermined distance underneath the injectors to provide a uniform film or layer on the substrate or wafer. In order to obtain a substantially uniform layer or film, the wafer or substrate is reciprocated a travel distance which is determined by the distance between adjacent injectors. The actual travel distance and injector pitch or spacing is controlled to provide a uniform film with minimum travel to provide a compact chemical vapor deposition apparatus.

For a better understanding of the present invention we consider two adjacent spaced injectors as shown in Figure 1 and the schematic representations of Figures 6 to 13. It will be apparent that the principles of the present invention extend to any injection means which creates closely spaced, linear, rectangular deposition regions.

Figure 6 shows two spaced injectors in cooperative relationship with a stationary wafer or substrate 71. Figure 7 shows the thickness of the deposition region 72 on the substrate, and Figure 8 shows the liner rectangular shape of the deposition region 72. Since the deposition is typically localized beneath the injector or applicator regions, the resulting film thickness on a stationary wafer or substrate varies greatly from one location to another in the transverse direction (presuming that the size of the substrate is greater than the width of a single deposition region). Such a film is useful for diagnostic purposes but of limited practical applicability; in most cases it is desired that the film thickness be as uniform as possible at all locations on the wafer or substrate.

Consider that the wafer or substrate is moving at a fixed velocity "v" prior to and during the deposition process. The requirement that the film thickness be uniform at all points on the wafer or substrate is equivalent to the requirement that any point P on the substrate or wafer have the same cumulative deposition thickness resulting from the deposition process. Consider therefore the point PI (Figure 9 A), chosen so that at the initial time t=0 of the transverse travel of the wafer or substrate it lies beyond the deposition region of injector 1. As the substrate or wafer moves relative to the injectors (in this example to the right), the point PI will pass completely under injector 1 for any distance of motion L>(L1 + W), where W is the injector deposition region half- width. In particular, if L=Linj is the injector separation, then the point PI will, at the end of travel, be in exactly the same position relative to injector 2 that it was relative to injector 1 at the start of travel. The deposition thickness after this time will be the time integral of the deposition rate profile shown schematically in Figure 9B. The deposition rate as a function of time for a velocity "v" is shown in Figure 9C.

Similarly, we may consider any other location on the substrate, and in particular location which at t=0 are within the deposition region, such as P2 of Figure 10A. In this case it is clear that in order for the deposition history of P2 to be identical to that of PI, independent of the exact starting position of P2, the travel distance must be equal to Linj, and the deposition profile (rate vs. position) of injector 1 must be the same as that of injector 2. This is illustrated in Figure IOC.

By extending this argument, it is clear that every location Pj on the substrate which is located between (Linj/2) to the left of the centerline of injector 1, and (Linj/2) to the left of the centerline of injector 2, (shown as the "uniformity region" in Figure 1 IB) will have exactly the same thickness if the two injectors have identical deposition profiles and the distance of travel is L=Linj, irrespective of the shape of the deposition profiles. In particular, the cumulative deposition will be uniform even if the deposition extends to the line of symmetry between the injectors, and thus to the starting point PI, as long as the deposition to the left of the symmetry line is due to injector 1 and that to the right is due to injector 2. (If this condition were to fail, the deposition to the right of injector 2 might be different from that between the injectors, due to the absence of an additional "injector 3", and similarly to the left of injector 1.) If the deposition were initiated instantaneously at t=0 and terminated instantaneously at t=Linj/v, this region of the substrate, of length Linj, would be covered with a uniform film. Thus, in order to design a system to coat a substrate of length Lsub uniformly, using two injectors, the distance Linj is chosen at least as large as the length Lsub. (Lsub may be less than the total length of the substrate, if e.g. non- uniformity is permitted in a region near the substrate edges.) In the general case of n injectors, the distance Linj between each injector would be chosen to be

Linj = (Lsub)/(n-l) (1)

For many designs, such as the injector discussed in the said co-pending application, the deposition region will be of limited and well-controlled extent, e.g 2W as depicted schematically in Figures 6-11. In this case, there exists an "extended uniformity region", of length 2(Linj-W) in which each point will receive the same deposition thickness, as shown in Figure 13.

In order to achieve uniform coatings on a portion of the substrate whose length is Lsub, we choose the injector pitch from Lsub=2(Linj-W) or Linj=^:(Lsub+2W)/2. In the general case of n injectors, the distance between injectors is then:

Linj = (Lsub +2W)ln (2)

Note that IFmay vary depending on process conditions; thus in a practical implementation, it would be prudent to choose an injector spacing Linj somewhat larger than this minimum spacing in order to ensure that a uniform deposition can be achieved, at the cost of some reduction in average deposition rate.

The total film thickness for the single pass described above will vary inversely as the velocity of transit, "v". Adjustments of thickness may be made simply by changing the velocity. However, variations in film properties from one lateral location to another within the deposition regions will be converted into variations of the film properties with depth, and the variation will be different for different locations on the wafer, due to the different starting points. Therefore it may be desirable to arrange for the substrate to pass beneath the deposition region a multiplicity of times. The substrate velocity vs. time in this ideal case is shown in Figure 12 A. If the reversal is carried out in a time very short compared to the process time, and the motion of the substrate has a negligible effect on the deposition process, then the net result will be to create a mirror image of the deposition rate vs. time profile for each point; when the substrate returns to its initial position x=0 each point on the "uniformity region" or the "extended uniformity region" will again have experienced the same deposition history (assuming again symmetry as above) and have the same cumulative film thickness.

The substrate position, being the integral of the velocity with time, will in this case execute a "sawtooth" reciprocating motion from the initial position to the final position, Figure 12B, with the total amount of travel again being adjusted to be equal to Linj. Clearly, this cycle may be repeated as many times as desired to accumulate an arbitrary total film thickness (subject to any constraints imposed by the deposition chemistry or film properties).

It is clear from e.g. Figure 13 that the leftmost position of the left edge of the substrate (or of that region of the substrate for which uniform deposition is required) when deposition is on should be no more than (Linj-W) to the left of the centerline of the leftmost injector, since the rightmost substrate position is Linj to the right, and must result in the point PI passing completely under injector 1. On the other hand, the leftmost position of the right edge can be no less than Wto the left of the centerline of the rightmost injector, to ensure that the point P3 passes completely under the rightmost injector. Therefore, the leftmost position of the left edge when deposition is on, measured with respect to the centerline of the leftmost injector, can range from

xleftl = -(Linj -W) to xleft2 = (n -\ )Linj - Lsub - W (3)

as shown in Figure 13. Note that if Linj is quite large, xleft2 may be >0; that is, the leftmost extent of deposition may be to the right of injector 1 , and still result in uniform deposition on Lsub. Naturally, such a condition results in an inefficient system (half or more of injector 1 is never used to deposit film on the wafer) and should be avoided for practical reasons. On the other hand, if the injector distance Linj is chosen to be exactly (Lsub + 2W)/n as described above, xleftl = xleft2. In this case not only must the distance of motion be exactly set at Linj, but the position of leftmost travel is fixed at a single location if the substrate Lsub is to be uniformly coated.

If multiple passes of reciprocating motion are employed as discussed in the above, the paragraph above constrains the position of the leftmost edge of the substrate at the leftmost excursion of each cycle of motion. However, deposition may be initiated at any location xstart within this length of travel, so long as it terminates at the same position xstart moving in the same direction, or equivalently so long as the total path length is an integral multiple of Linj, and the distance from the leftmost to the rightmost position is equal to Linj. The discussion above has implicitly assumed that the deposition profile of each injector is symmetric about the centerline of the injector, for simplicity of discussion. However, it is easy to establish that the formulae given above apply equally well to any arbitrary deposition profile, even one which is not symmetric about the center line, with the appropriate changes in notation. It is most convenient to simply redefine the center line for each injector to be that location midway between the leftmost and rightmost extent of the region of deposition; this location may no longer correspond to the physical centerline of the injector, but again as long as the deposition from each injector is identical, the half- width W is then well defined, and all the formulae given above will be applicable in this asymmetric case. Several practical requirement must be met for successful deposition of a film with thickness uniformity in the direction of motion of a few percent:

a) Control of Time Dependence of Deposition

The deposition must be initiated and terminated on a time scale rapid compared to the total process time. For typical semiconductor deposition times of 1 to 5 minutes, this requires deposition to initiate and terminate within 0.5 to 2 seconds. Such a requirement is most easily met by employing valves 71 to switch a constant flow of reactive gases to or away from the injector, while at least partially compensating with a "balance" flow of an inert gas (nitrogen), so as to avoid transient fluctuations encountered during the turn-on and turn-off of mass flow controller units, or slow turn-off of deposition due to stagnant gases. This configuration is often known as a "run/vent" arrangement in the art. As noted above, depending on the design of the injector it may also be necessary to ensure precise control of the absolute position of the wafer at the time deposition starts; in such a case, it is necessary to control precisely when the gases actually turn on, correcting for any fixed delays in the control system or gas handling system.

The deposition rate profile must be held constant to high precision during the time the deposition is on; this requires accurate metering of gases and liquids, maintenance of constant wafer temperature, and for some designs, also careful control of substrate-to-injector spacing, during the deposition (the exact requirements in each case being dependent on the deposition process and conditions). The quantitative limits on variability for each parameter can be established in the normal fashion by empirically or theoretically determining the dependence of film thickness on variations in that parameter, and then requiring the total variation in thickness due to that parameter to be within the specification for overall variation, with statistical provisions well known in the art for combining random variations in multiple parameters.

The metering of vapors of liquids requires special care. Bubblers are often used in the art to deliver vapors from a liquid, but typically suffer from long stabilization transients. Thus, in this application it would be necessary to operate the bubbler continuously, even when the resulting vapor is directed towards the vent during e.g. substrate loading operations, which is wasteful.

Liquids may be metered directly by the use of displacement pumps coupled to a vaporizer; examples of this apparatus may be purchased from MKS Instruments. Typically such pumps consist of two cylinders so that liquid delivery may continue from one cylinder while the other is refilled. The inventors have found that such pumps may be suitable, but that it is very important to ensure that liquid delivery of the two cylinders is precisely matched and that there are no transients during the change from one cylinder to the other. The liquid pressure between the pumping elements and the vaporizer may be used as a diagnostic tool to ensure such uniformity. The use of liquid mass flow controllers coupled with vaporizers, such as those available from STEC Instruments, is an acceptable means for delivery of vapors in this process.

b) Translation of the Wafer or Substrate

The motion of the wafer or substrate must proceed at a velocity uniform to within the requirements on film uniformity, as discussed in a) above, since variations in velocity will cause variations in thickness along the wafer. The velocity must change sign at the inflection points; this requires a high acceleration to avoid anomalously thick regions when direction changes, if deposition operates during the reversal. Thus, the translation system should have low backlash and minimal vibration, and this motion must be accurately and smoothly transmitted to the wafer support apparatus (wafer chuck). The translation system must support specification of smooth motion trajectories. The spacing and planarity between the substrate and the gas injection must be maintained to within better than 0.1 mm at all times during the substrate motion.

The drive system must have a high dynamic range, allowing for rapid acceleration and deceleration such that direction changes are nearly instantaneous relative to the deposition times. This allows the deposition gases to remain turned on continuously during multiple reciprocal cycles. (If this capability is not available, the invention can still be practiced by turning deposition gases off just prior to reversal of direction and then on again at the same position, which however increases control complexity and decreases deposition efficiency.) A nominal acceleration on the order of 400-500 cm/sec² are sufficient for typical transit speeds v=l to 2 mm/sec.

The position measuring system must establish the linear position of the substrate to an accuracy sufficient to ensure that the length of travel is precisely equal to the injector pitch; the inventors have found this requirement to be on the order of 0.1 mm for a deposition half- width W of about 15 mm and pitch around 60 mm. In such an embodiment, a change of 1% in average velocity "v" or deposition width IT has little effect on film uniformity, merely shifting the average film thickness by a similar 1% variation; however, a change of 1% in the length of travel (i.e. around 0.6 mm) gives rise to a 6% change in film thickness in the "seam" region between the injectors, severely impacting film uniformity.

c. Tnjector Matching

Achievement of uniform film deposition using the method described herein relies on the deposition regions of each injector being identical to every other injector. Variations in average deposition rate, position of deposition with respect to the injector centerline, or any other parameter from one injector to the next will give rise to corresponding non-uniformities in the resulting film. A well-controlled method of fabricating the gas injector, such as that described in the co-pending application, is required to employ the method.

d. Compensating Velocity Adjustment and Reduced Pitch

Real motion systems will provide finite acceleration and deceleration, leading to a "rounding off of the sawtooth motion profile shown in Figure 12B. Using the high accelerations discussed above such effects are negligible; however, if these high accelerations are not achievable, it is apparent that one will encounter an increased dwell time at the position where velocity is reversed, and therefore anomalously thick deposition on those locations of the substrate where the deposition rate is high at this time. There are two means of correcting this situation:

i. the gases may be turned off prior to velocity reversal and turned on again after it has been accomplished. In this case, no deposition takes place during acceleration and deceleration, at the cost of added complexity in specification of machine operation, and increased sensitivity to any delays or non-idealities occurring during the turn-on and turn-off of deposition gases.

ii. the pitch of motion may be reduced

A modest decrease in the distance of travel will compensate for increased deposition during the deceleration/acceleration period. The desired lateral uniformity of film properties will be maintained as long as the adjustment required is small compared to the width IF of the individual injection deposition regions. For small adjustments it may be shown that the amount of adjustment dL is approximately:

dL = 2v²/A (4)

where v is the velocity of travel (e.g. cm/second) and A the deceleration/acceleration (cm/sec²), but the actual adjustment required may be easily determined by experiment.

Example 1:

A chemical vapor deposition apparatus as shown in Figure 1 having three independent deposition regions with a spacing of approximately 63 mm was tested. The wafer motion system employed the components as described above. The width of the individual deposition regions was approximately 2W=30mm. TEOS and ozone were used to deposit silicon dioxide on the substrates in a fashion well-known in the art, at total pressure of about 500 Torr and a temperature of 400 C. The substrates were 200 mm diameter silicon wafers. Initially a sequence was employed in which the substrate started moving at x=-(L/2), deposition was turned on at x=0; the substrate proceeded to the right to x=(L/2), reversed direction and traveled to x=- (L/2), then reversed again and returned to the original position; at x=0 deposition was turned off, and travel stopped at x=(L/2). Thus a cumulative total of two complete passes of length L were performed. Figure 14 shows that the three isolated uniform regions formed for L «Linj merge into one long region of uniformity when L is roughly equal to Linj; forJ >Linj, regions of excess deposition form.

The uniformity of Figure 14 is obviously optimal for L near Linj, but was affected by random variations in the supply of precursor with time. This difficulty was resolved in the data of Figure 15, in which a simple motion profile with deposition on at x— (L/2) and off at x=(L/2) was employed, and the wafer was manually rotated 180 degrees and the deposition repeated to average out any variations between the left and right deposition regions, with runs using L=61 and 63.5 mm. A residual difference in deposition between the center and the outer injectors remains. However, it is apparent that the merging of neighboring deposition regions is very sensitive to the exact distance of travel; nearly ideal merging of the deposition regions is projected for a sweep distance of 62.5 mm. Note that the physical pitch Linj between injectors is 63.9 mm; the optimal pitch is reduced slightly from the actual pitch, possibly due to uncontrolled delays in turning gases on and off.

A change of J by 2 mm changes the thickness in the "seam" regions by 20%, showing that accurate control of the distance of travel is essential for achieving good uniformity. We can also verify that the length of the "extended uniformity region" is about 160 mm, in good agreement with the expected value of 3(63.9) - (30) = 162 mm.

Example 2: An embodiment of the invention having four independent deposition regions, with a spacing of approximately 66.55 mm, was tested. The wafer motion system employed the components as described above. The width of the individual deposition regions was approximately 2W=30 mm. TEOS, ozone, and phosphorus and boron sources were used to deposit doped silicon dioxide (BPSG) on the substrates in a fashion well known in the art, at total pressure of about 200 Torr and a temperature of 500 C. The substrates were 200 mm diameter silicon wafers. Six experimental depositions were performed. In each case, the motion sequence was as follows, using the convention that the wafer position at time t=0 is x=0:

motion was started with velocity -V at t=0, x=0 at x=-10 mm deposition was initiated at x—L/2 motion was reversed (-V goes to V) at x=+L/2 motion was reversed (V goes to -V) at x=- 10 mm deposition was terminated

Thus, a cumulative total of two complete passes of length L were performed. The six runs consisted of three using V=1.35 mm/second, and three using V=2.3 mm/second. For each set, one run was performed at L=66.7 mm ("standard"), and one each at L=68.7 mm ("standard + 2mm") and at L=64.7 mm ("standard - 2mm").

Figure 16 shows the thickness of the resulting deposition versus position on the wafer, measured in the direction of travel, with the center of the wafer at x=0, for a velocity of 1.35 mm/second and varying distances. Note that in this figure the thickness for the "std" sample has been increased by 165 A (3%) at all points in order to match thickness in the "flat" regions; the offset of this sample from the other two is presumed due to a small variation in average deposition rate unrelated to the substrate motion.

It is apparent from Figure 16 that uniform deposition can be obtained using the correct motion pitch L, which is quantitatively in good agreement with the physical separation between injectors Linj. One again observes the importance of accurate control of position; a variation of 4 mm (6%) in the distance of travel corresponds to a change of about 1240 A (25%) in film thickness. The "standard" motion profile achieves a standard deviation along the direction of motion of 1.7% of the average value, despite the presence of disturbances related to the wafer edges, clearly demonstrating that it is possible to accurately merge deposition from neighboring injectors as discussed above.

In Figure 17, we show similar data for two different velocities V=1.35 and 2.3 mm/second, and using the same motion pitch L=68.7 mm (the longer pitch being used to emphasize the overlap regions). As noted above, the nominal acceleration in this motion system is about 400-500 cm²/second. Here we depict the scaled value T(scaled) = (thickness - <average>)/(standard deviation) so that the two different runs can be plotted on the same axes.

It is apparent that the results are essentially identical for these two velocities, demonstrating that the high accelerations employed in this embodiment provide effectively instantaneous reversal of motion at these velocities, so that any excess deposition during the reversal is negligible.

Thus there has been provided a chemical vapor deposition apparatus employing linear injectors for delivering the gaseous chemicals which is compact and achieves high average deposition rates and good film thickness uniformity, using close-spaced multiple linear injectors and reciprocating linear motion.

Claims

CLAIMSWhat is claimed is:

1. A chemical vapor deposition apparatus of the type including a chemical vapor deposition chamber having a plurality of spaced linear injectors for introducing chemical vapors into said chamber to form substantially rectangular deposition regions characterized in that said apparatus includes means for supporting a substrate to be coated adjacent said linear injector assembly and means for linearly reciprocating said substrate support means in a direction perpendicular to the long axis of said deposition regions so that neighboring deposition regions merge.

2. A chemical vapor deposition apparatus as in claim 1 in which the supporting means is reciprocated over a distance which is equal to the distance between the center lines of the rectangular deposition regions.

3. A chemical vapor deposition apparatus as in claim 1 in which the introduction of chemical vapors for a deposition of a film of predetermined uniform thickness is initiated and terminated at the same point in the reciprocating cycle.

4. A chemical vapor deposition apparatus as in claim 3 in which the deposition is initiated and terminated on a time scale which is rapid with respect to the rate of travel of the substrate support means.

5. A chemical vapor deposition apparatus as in claim 3 in which the flow of gases and velocity of the wafer is maintained substantially constant during the deposition of the film of uniform thickness.

6. A chemical vapor deposition apparatus for depositing substantially uniform films or layers on a substrate or wafer including a chamber with spaced linear injectors and a system for delivering chemicals to said linear injectors whereby to form adjacent deposition regions, and means for linearly moving said substrate or wafer past said deposition region in a direction perpendicular to the long axis of said linear injectors, characterized in that said means for linearly moving said substrate is configured to reciprocally move the substrate a pre-determined distance substantially equal to the distance between the centerline of the injectors whereby the deposition regions of adjacent injectors merge to form a film or layer of substantially uniform thickness.

7. A chemical vapor deposition apparatus as in claim 6 in which the desired length in the direction of travel of the uniform film is Lsub, the width of the deposition regions is W, and the distance between injectors is at least Linj=(Lsub+2W)/n, where n is the number of inj ectors.

8. A chemical vapor deposition apparatus as in claim 6 in which the delivery of chemicals for deposition of a film of predetermined thickness is initiated and terminated at the same point in the reciprocating cycle.

9. A chemical vapor deposition apparatus as in claim 7 in which the delivery of chemicals for deposition of a film of predetermined thickness is initiated and terminated at the same point in the reciprocating cycle.

10. A chemical vapor deposition apparatus as in claims 8 or 9 in which the deposition is initiated and terminated on a time scale which is rapid with respect to the rate of travel of the substrate support means.

11. A chemical vapor deposition apparatus as in claims 8 or 9 in which the flow of gases and velocity of the wafer is maintained substantially constant during the deposition of the film of uniform thickness.

12. A chemical vapor deposition apparatus as in claims 6 or 7 in which the linear injectors are configured to provide substantially identical deposition regions.

13. A chemical vapor deposition apparatus as in claims 1, 6 or 7 in which the effects of acceleration and deceleration of the substrate support on the film thickness is compensated by terminating the flow of gases just prior to reversal of direction of travel, and resumed just after reversal of travel.

14. A chemical vapor deposition apparatus as in claims 1, 2, 6 or 7 in which the effects of acceleration and deceleration of the substrate support on film thickness is compensated by controlling the distance of travel.

15. A chemical vapor deposition apparatus as in claim 14 in which the adjustment in distance of travel dL is equal to 2v╧äA where "v" is the velocity of travel and "A" the deceleration/acceleration in cm/sec² the distance of travel the substrate supports.

16. A chemical vapor deposition apparatus for depositing substantially uniform films or layers on a substrate or wafer including a deposition chamber, a plurality of linear gaseous chemical injectors positioned to deliver gaseous chemicals to a plurality of spaced rectangular deposition regions in said chamber, a chuck for supporting a substrate in cooperative relationship with said gaseous chemical injectors whereby spaced rectangular film regions are deposited on said substrate, means for reciprocally linearly moving said chuck in a direction perpendicular to the long axis of the linear injectors a predetermined distance whereby the spaced rectangular film regions merge to form a film of substantially uniform thickness.

17. A chemical vapor deposition apparatus as in claims 16 including means for introducing a wafer into said chamber opposite said chuck and pin means in said chuck for receiving said wafer and lowering it onto the surface of the chuck and means for lifting the chuck to bring the wafer into cooperative relationship with said injectors.

18. A chemical vapor deposition apparatus as in claim 17 in which the desired length in the direction of travel of the uniform film is Lsub, the width of the deposition regions is W, and the distance between injectors is at least Linj=(Lsub+2W)/n, where n is the number of injectors.

19. A chemical vapor deposition apparatus as in claim 18 in which the delivery of chemicals for deposition of a film of predetermined thickness is initiated and terminated at the same point in the reciprocating cycle.

20. A chemical vapor deposition apparatus as in claim 19 in which the deposition is initiated and terminated on a time scale which is rapid with respect to the rate of travel of the substrate support means.

21. A chemical vapor deposition apparatus as in claim 19 in which the flow of gases and velocity of the wafer is maintained substantially constant during the deposition of the film of uniform thickness.

22. A chemical vapor deposition apparatus as in claim 16 in which the linear injectors are configured to provide substantially identical deposition regions.

23. A chemical vapor deposition apparatus as in claim 16 in which the effects of acceleration and deceleration of the chuck on the film thickness is compensated by terminating the flow of gases just prior to reversal of direction of travel, and resumed just after reversal of travel.

24. A chemical vapor deposition apparatus as in claim 16 in which the effects of acceleration and deceleration of the substrate support on film thickness is compensated by controlling the distance of travel.

25. A chemical vapor deposition apparatus as in claim 24 in which the adjustment in distance of travel dL is equal to Iv^/A where "v" is the velocity of travel and "A" the deceleration/acceleration in cm/sec² the distance of travel the substrate supports.