WO2006067730A2

WO2006067730A2 - Device and method for holding a substrate

Info

Publication number: WO2006067730A2
Application number: PCT/IB2005/054315
Authority: WO
Inventors: Dirk M. Knotter; Abbas Rastegar
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-12-22
Filing date: 2005-12-19
Publication date: 2006-06-29
Also published as: TW200626447A; WO2006067730A3

Abstract

Device (1) for holding a substrate, comprising a box (2) and a substrate holder (4). The box (2) is arranged for holding the substrate holder (4), and the substrate holder (4) is arranged for holding the substrate (3). The box (2) comprises a gettering device (5) for gettering an impurity possibly being present within the box (2).

Description

Device and method for holding or transporting a substrate

The present invention relates to a device for holding a substrate in accordance with the preamble of claim 1. Also, the present invention relates to a method of holding a substrate. Furthermore, the present invention is related to the storage and transport of a substrate.

Masks as used in lithographic processing must be kept clean to avoid any deterioration of a pattern as present on the mask substrate. Such deterioration may affect the pattern transfer from the mask to an exposed substrate, e.g. a semiconductor wafer, during lithographic processing.

Contamination by particles drifting in the ambient may attach to the mask and interact with the pattern of the mask. When present on the mask, such particles may deteriorate the pattern transfer quality of the mask.

However, not only particles affect the quality of a pattern mask. Also molecules within the gaseous ambient such as hydrocarbon-compounds may contaminate the surface of a mask substrate. Such molecules may impinge on the substrate and adhere to it.

Due to the continuous effort in the micro-electronic industry to reduce feature sizes of micro-electronic devices (e.g., logic, memory, etc.), the exposure of a semiconductor wafer during lithographic processing is usually performed with relatively short wavelength typically at 192 nm wavelength or less. The exposure with such short wavelength radiation may thus affect the quality of the pattern on the mask since the relatively high energy of the short wavelength radiation may decompose molecular (organic) compounds that may have adsorbed on the mask substrate. By the decomposition of the molecular compounds residues may form on the mask, which may adversely affect the pattern on the mask. A device for holding a mask substrate, such as a storage box or transport box, is known from US 6,492,067. US 6,492,067 discloses a box for holding a mask substrate, which utilizes a pellicle and two deployments of thermophoretic protection to keep particles off the mask. It is an object of the present invention, to improve the protection of mask substrates against contamination during storage and transport.

This object is achieved by a device for holding a substrate, comprising a box and a substrate holder, the box being arranged for holding the substrate holder, the substrate holder being arranged for holding the substrate, characterized in that the box comprises a gettering device for gettering an impurity possibly being present within the box.

The gettering device within the device for holding a substrate getters molecular impurities from the gaseous ambient in the box and functions as a sink for such impurities. The gettering process basically binds molecular compounds, impinging from the ambient, to the surface of the gettering device. Advantageously, the amount of molecular impurities in the ambient within the box is reduced.

Moreover, the present invention relates to a device for holding a substrate as described above, wherein the gettering device comprises a material having an affinity with the impurity to getter the impurity. Advantageously, the material provides a surface, which is active for gettering molecular compounds. The activity of the surface may relate to an increased surface-free energy, which may be caused by an appropriate surface treatment, for example a roughened surface, or an oxidized surface which has enhanced gettering properties. The material of the gettering device may comprise a metal. In a preferred embodiment, a gettering device comprises Aluminum as gettering material. In particular, the native oxide of Aluminum may have an advantageous effect for gettering molecular compounds.

It is considered that other metals may provide similar gettering properties. These metals which may form a native oxide surface layer are for example titanium, vanadium, magnesium, and chromium.

Also, the present invention relates to a device for holding a substrate as described above, wherein the substrate holder is arranged for heating a substrate relative to other parts of the box for providing a thermal gradient between the substrate and the other parts of the box. Advantageously, the local increase of the temperature of the substrate enhances the thermophoretic protection of the substrate.

Thermophoresis can be defined as the process, which transports particles within a gaseous ambient from a relatively hot location to a relatively colder location. By arranging the temperature of the substrate to be relatively higher than the surrounding parts of the storage box, particles are driven away from the mask substrate. Moreover, the present invention relates to a device for holding a substrate as described above, wherein the device further comprises a cooling element, the cooling element being arranged for cooling the other parts of the box relative to the substrate, for providing a thermal gradient between the substrate and the other parts of the box. In this way the thermophoretic protection may be enhanced.

Additionally, the present invention relates to the device as described above, wherein the gettering device comprises the cooling element. In this way, the gettering device has a reduced temperature relative to other parts of the device.

Cooling of the gettering device lowers a desorption of gettered molecular compounds from the gettering device's surface. At the same time, the thermophoretic protection of the mask substrate with respect to particles is maintained.

In addition, the present invention relates to a device for holding a substrate as described above, wherein the device for holding a substrate comprises a Peltier element, the Peltier element having a cold contact-side, when in use, connected to the cooling element for cooling the cooling element and a hot contact-side, when in use, connected to the substrate holder for relatively heating the substrate.

Advantageously, the application of a Peltier element allows a compact design of the heating and cooling system(s), and also reduces the burden of providing a warm medium to a relatively hot section of the device or, conversely, a coolant to a cold section of the device.

Furthermore, the present invention relates to a method of holding a substrate in a box, characterized by providing a gettering action for gettering an impurity possibly being present within the box, the gettering action being performed by a gettering device.

The invention will be explained in more detail below with reference to a few drawings in which illustrative embodiments thereof are shown. They are intended exclusively for illustrative purposes and not to restrict the inventive concept, which is defined by the claims. Fig. 1 shows a cross-sectional view of the device for holding a substrate according to a first embodiment of the present invention;

Fig. 2 shows a cross-sectional view of the device for holding a substrate according to a second embodiment of the present invention; Fig. 3 shows a cross-sectional view of the device for holding a substrate according to a third embodiment of the present invention.

Figure 1 shows a cross-sectional view of the device for holding a substrate according to a first embodiment of the present invention.

The device for holding a substrate 1 comprises a box-shaped container or box 2. The box 2 can be sealably closed in a way that the interior of the box 2 is isolated from the ambient outside the box 2. Note that within the possibilities for its use as a container, the box 2 may have any shape, either regular or irregular, suitable as a container for a substrate-like object.

Within the box 2, the device for holding a substrate 1 comprises a substrate holder 4 on which a substrate 3 can be arranged.

The substrate 3 which can be arranged on the substrate holder 4 may be a mask substrate on which a pattern (not shown) is located. The substrate 3 may be arranged as a mask for pattern transfer to a further substrate (not shown) by means of lithographic processing in a lithographic apparatus. Such a further substrate may be a semiconductor wafer on which micro-electronic devices are to be manufactured.

Further, a gettering device 5 is located in the vicinity of the substrate 3, preferably located at a location facing the substrate 3 on the substrate holder 4.

Within the box 2, molecular compounds, for example hydrocarbons, may be present within the gaseous ambient. Such molecular compounds may typically impinge on a surface. Depending on the properties of the surface, the molecular compounds may stick and adsorb there. Such a surface may be the surface 3' of the mask substrate 3. In the present invention, a gettering device 5 is arranged for gettering molecular compounds from the gaseous ambient within the box 2, in order to reduce the amount of molecular compounds in the ambient within the box 2. Consequently, the amount of molecular compounds that may reach the surface 3' of the substrate 3 and adsorb on that surface 3' is reduced also. The gettering device 5 comprises a material, which has a physical, chemical or physicochemical affinity with the impurity (that is the molecular compound) to getter the impurity. This affinity with the impurity is such that the impurity is substantially bound to the surface and not released from the surface without a further treatment of the material. Optional treatments will be discussed later. Materials suitable as gettering agents comprise metals such as aluminum, titanium, vanadium, magnesium, and chromium, and their alloys.

The gettering property of aluminum is considered to arise from an interaction of the native aluminum oxide (on the surface of the aluminum metal matrix) with molecular compounds such as hydrocarbons. Other metals such as vanadium, chromium, titanium, and magnesium, which form a native oxide, may have similar properties. Other metals may be possible as well, the range of metals is limited only by their inability to getter.

Also, materials may be applicable of which the gettering properties may depend on a chemical or physical reaction, and/or chemico- and physico-sorption. Furthermore, the gettering device 5 may be shaped as a solid plate as shown in

Figure 1.

It is also conceivable that the gettering device 5 consists of sponge-like material such as a metal-sponge. In this way the active surface of the gettering device 5 can be enlarged to allow a larger area where gettering can take place. Also, the gettering device 5 may comprise a plurality of pellets of a gettering material or metal as described above. Again, the active surface for gettering is effectively enlarged. When using pellets the gettering device 5 may be enclosed in some shell (not shown), which holds the pellets at a substantially fixed position within the box 2.

In a further development, the substrate holder 4 is arranged to have a relatively high temperature in comparison with its surroundings, i.e. other parts of the box 2, for example the walls of the box. To obtain a relatively high temperature at the substrate holder 4 a heat flow, indicated by arrow 6, is supplied to the substrate holder 4. By such an arrangement, an additional thermophoretic protection of the substrate 3 may be achieved. Advantageously, a flow caused by the thermophoresis process of the substrate holder 4 directed to the gettering device 5 located may enhance the gettering action at the gettering device.

Additionally, the gettering device 5 can be cooled by a cooling flow (indicated by a second arrow) 7 to enhance the adsorption of a molecular compound on the surface (by reducing its energy state). The cooling flow can be established by means of a separate cooling element arranged adjacent to the gettering device 5. In Figure 1 the cooling element is shown as part of the gettering device 5.

Advantageously, cooling of the gettering device 5 enhances the thermophoresis process. Figure 2 shows a cross-sectional view of the device for holding a substrate according to a second embodiment of the present invention.

In Figure 2 entities with the same reference number refer to identical entities as shown in Figure 1. In the second embodiment, the gettering device 5 comprises a thin layer of the gettering material as discussed above, which is deposited on one or more of the inner walls of the box 2. In Figure 2, arrow 5' indicates the presence of a deposited thin layer on the top inner wall of the box 2.

It is noted that various thin layer deposition techniques may be available to deposit a thin layer on the inner wall(s). For metals, for example, evaporation, sputter- deposition, and plasma spraying may be used. Other techniques may be used as will be appreciated by the person skilled in the art.

If cooling (by cooling flow 7) of the thin layer gettering device 5' is required, the cooling element may be arranged as a cooling chamber 7' on box 2. The cooling chamber 7' has preferably one wall adjacent to and in contact with the wall of the box comprising the thin layer gettering device 5'. The cooling chamber 7' may be integrally formed with the box 2.

Figure 3 shows a cross-sectional view of the device for holding a substrate according to a third embodiment of the present invention. In Figure 3 entities with the same reference number refer to identical entities as shown in the preceding Figures.

In a further development of the embodiments shown in Figures 1 and 2, the device 1 for holding a substrate comprises a Peltier element which is connected at one cold, when in use, contact side to the cooling flow 7 and/or cooling chamber 7' (cooling element), and at another hot, when in use, contact side to the heat flow 6 to the substrate holder 4.

Advantageously, the application of a Peltier element allows a compact design of the heating and cooling system(s).

Moreover, due to the generation of a temperature difference between hot and cold contact-sides by means of simply applying electrical power 9 to the Peltier element, also reduces the burden of providing a warm medium to the relatively hot substrate holder 4 of the device 1 and a coolant to cold gettering device section 5, 5' of the device 1.

In view of the above, the present invention also relates to a method of holding a substrate in a box or container. The method provides a gettering action for gettering impurity possibly present within the box. If preferred, the method may be enhanced by thermophoretic protection by maintaining a thermal gradient between the substrate 3 and the box 2 by heating the substrate 3 to a relatively higher temperature than the box 2. Also, the thermophoretic protection may be enhanced by cooling the gettering device, either directly or indirectly. Moreover, such cooling may enhance the gettering action of the gettering device.

The thermophoresis process acts on particles in any field where there is a relatively hot and relatively cold region. The larger the temperature difference between the hot and cold regions, the higher the thermal force on the particle is. So any suitable temperature difference may be used. However, some temperature value ranges may be preferred. For example, the temperature of the gettering device should not be lower than the dew point, which in a normal clean room of a wafer plant or fabrication facility is in the range of 10 to 20⁰C. Alternatively, if the atmosphere of the box is filled with dry air or nitrogen, the temperature of the getter plate can be set lower.

The maximum temperature of the substrate plate cannot be too high, because it may have an impact on the lithographic processing carried out with the substrate (mask). A usable temperature may be about 1-2 degrees above operating temperature of the lithographic apparatus, unless the mask is actively cooled before use.

For long-term storage or transport where the mask box remains closed for a longer time, the low and high temperature of the cold and hot region, respectively, can be more extreme.

When the gettering device 5 becomes saturated with molecular compounds from the ambient within the box, the effectiveness of the gettering action is reduced.

In the present invention, treatment of the gettering device can be provided to regenerate the ability of the device for gettering impurities such as molecular compounds. Such treatment relates to a treatment of a surface of the gettering device, which substantially cleans the surface from gettered molecular compounds.

This treatment of the surface may comprise a heat treatment of the gettering device in a furnace.

A cleaning treatment of the gettering device can for example be carried out as follows. The gettering device 5 is taken out of the storage box 2 and positioned in a furnace. Next, the gettering device 5 is heated to a temperature of about 400⁰C (depending on the actual material of the gettering device and also still below the melting point of the gettering device's material) in air or oxidizing ambient (containing an oxidizing compound e.g. oxygen O₂, ozone O₃, nitrogen oxides NO_x , or any other gaseous oxidizing agent). Alternatively, a cleaning treatment of the surface may comprise an exposure of the surface to an ambient containing oxygen or ozone, which reacts with the molecular compounds on the surface. In addition, the exposure to an ambient containing ozone may be carried out under application of ultraviolet (UV) radiation. For example, after removal from the storage box 2 the gettering device may be located in the vicinity of an UV lamp (or a radiation source with comparable radiation energy) with the gettering surface to be cleaned facing the lamp. Thus, a gap between the UV lamp and the surface to be cleaned is defined. The UV lamp may have a radiation spectrum comprising spectral components at 193nm and/or 254nm wavelengths (spectral components at other UV wavelengths which may also be effective may be present as well). A gaseous oxidizing agent like oxygen O₂, ozone O₃, nitrogen oxides NO_x is brought into the gap between the gettering surface and the UV lamp to react with the gettered molecular compounds on the gettering surface.

The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

CLAIMS:

1. Device (1) for holding a substrate, comprising a box (2) and a substrate holder (4), the box (2) being arranged for holding the substrate holder (4), the substrate holder (4) being arranged for holding the substrate (3), characterized in that the box (2) comprises a gettering device (5; 5') for gettering an impurity possibly being present within the box (2).

2. Device (1) for holding a substrate according to claim 1, wherein the gettering device (5; 5') comprises a material having an affinity with the impurity to getter the impurity.

3. Device (1) for holding a substrate according to claim 1 or 2, wherein the gettering device (5; 5') comprises a gettering plate.

4. Device (1) for holding a substrate according to claim 1 or 2, wherein the gettering device (5; 5') comprises a gettering layer deposited on at least one inner wall of the box (2).

5. Device (1) for holding a substrate according to claim 1 or 2, wherein the gettering device (5) comprises a gettering sponge.

6. Device (1) for holding a substrate according to claim 1 or 2, wherein the gettering device (5) comprises gettering pellets.

7. Device (1) for holding a substrate according to any one of the preceding claims, wherein the material of the gettering device (5; 5') comprises a metal.

8. Device (1) for holding a substrate according to claim 7, wherein the metal comprises at least one of aluminum, titanium, vanadium, magnesium, and chromium.

9. Device (1) for holding a substrate according to any one of the preceding claims, wherein the substrate holder (4) is arranged for heating the substrate (3) relative to other parts of the box (2) to provide a thermal gradient between the substrate (3) and the other parts of the box (2).

10. Device (1) for holding a substrate according to claim 8 or 9, wherein the device (1) further comprises a cooling element (7; 7'), the cooling element (7; 7') being arranged for cooling the other parts of the box (2) relative to the substrate (3), to provide a thermal gradient between the substrate (3) and the other parts of the box (2).

11. Device (1) for holding a substrate according to claim 10, wherein the gettering device (5) comprises the cooling element.

12. Device (1) for holding a substrate according to claim 10 or 11, wherein the device (1) comprises a Peltier element (8), the Peltier element (8) having a cold, when in use, contact-side connected to the cooling element (7; 7') for relatively cooling the cooling element and a hot, when in use, contact-side connected to the substrate holder (4) for relatively heating the substrate (3).

13. Method of holding a substrate (3) in a box (2), characterized by providing a gettering action for gettering an impurity possibly being present within the box (2), the gettering action being performed by a gettering device (5; 5').

14. Method of holding a substrate (3) in a box (2) according to claim 13, wherein the method further comprises: providing a thermal gradient between the substrate (3) and the box (2) allowing the substrate (3) to be at a relatively higher temperature than the box (2).

15. Method of holding a substrate (3) in a box (2) according to claim 13 or 14, wherein the method comprises: regenerating the gettering device (5; 5') by treatment of a surface of the gettering device.

16. Method f holding a substrate (3) in a box (2) according to claim 15, wherein the treatment of the surface of the gettering device (5) comprises a heat treatment of the gettering device in a furnace.

17. Method of holding a substrate (3) in a box (2) according to claim 15, wherein the treatment of the surface of the gettering device (5; 5') comprises an exposure of the surface to an ambient containing a gaseous oxidizing agent.

18. Method of holding a substrate (3) in a box (2) according to claim 17, wherein the gaseous oxidizing agent is at least one of oxygen, ozone, or a nitrogen oxide.

19. Method of holding a substrate in a box according to claim 17 or 18, wherein the exposure of the surface to the ambient containing the gaseous oxidizing agent is carried out under application of UV radiation to the surface.