WO2013090123A1

WO2013090123A1 - Thermal plate for environment and temperature control of motors used to move stages in lithography tools

Info

Publication number: WO2013090123A1
Application number: PCT/US2012/068294
Authority: WO
Inventors: Michael B. Binnard; Michel Pharand; Shigeru Morimoto; Alex Ka Tim Poon; Derek Coon; Leonard Wai Fung Kho; Gaurav Keswani
Original assignee: Nikon Corporation
Priority date: 2011-12-12
Filing date: 2012-12-06
Publication date: 2013-06-20

Abstract

A lithography tool having a stage for supporting and positioning a substrate, an array configured to move the stage, and a cover plate positioned between the stage and the array. In various embodiments, the array may be either a magnet or coil array. The cover plate acts as a thermal insulator that helps even out temperature variations across the array. Consequently, thermal disturbances to the array or other parts of the lithography tool are reduced, resulting in a minimization of positioning errors. In addition, the cover plate also protects the array and provides a smooth surface in the event of a "crash" of the substrate stage.

Description

THERMAL PLATE FOR ENVIRONMENT AND TEMPERATURE CONTROL OF MOTORS USED TO MOVE STAGES IN LITHOGRAPHY

TOOLS BACKGROUND

Field of the Invention.

[0001] This invention relates to lithography, and more particularly, to a thermal plate used for environmental and temperature control of the motors used to move stages in lithography tools.

Description of Related Art

[0002] Lithography systems are commonly used to transfer images from a reticle onto a substrate, such as a semiconductor wafer or flat panel display. A typical lithography system includes an optical assembly, a reticle stage for holding a reticle, a substrate stage assembly that positions the substrate, and a measurement system that precisely monitors the position of the reticle and the substrate.

[0003] During operation, an image defined by the reticle is projected by the optical assembly onto the substrate. In a scanning type lithography tool, the reticle and the substrate move synchronously with respect to one another during exposure so that a portion of the substrate is imaged. After a scan is performed, the substrate stage moves the substrate relative to the reticle before the next scan begins. Alternatively, in a step-and-repeat type lithography tool, exposure of a first portion of a substrate is performed while the substrate and reticle are stationary. After exposure, the substrate stage "steps" the substrate to a new position so that a next portion of the substrate can be exposed. With either the scanning or step-and-repeat type tools, the two above- described sequences are repeatedly performed until all of the desired portions of the substrate are patterned. The substrate is then removed, a new substrate is exchanged in its place, and the above scanning or step-and-repeat process is repeated on the new substrate.

[0004] The size of the features patterned onto substrates by lithography tools is extremely small. The current state of the art is capable of patterning features of less than 40 nanometers. In the future, these feature sizes are likely to decrease even further with each new generation of lithography tools. [0005] The substrate stage assembly typically includes a base, a coarse stage positioned above the base, and a fine stage positioned above the coarse stage. The coarse stage is responsible for long- stroke movements of the fine stage, while the fine stage is responsible for precise positioning of the substrate. One or more actuators, such as linear or planar motors, are used for moving and positioning both the coarse and fine stages.

[0006] The ability of the substrate stage to move and position a substrate must be highly accurate. If the position of the substrate varies only slightly from its intended position during exposure, overlay and other exposure issues may result. The ability for actuators to precisely position either the coarse or fine stage, however, is often complicated by temperature variations in the environment surrounding the actuators. With a linear motor for example, the temperature may vary across magnet arrays or coil arrays. These temperature variations will typically change the temperature and index of refraction of the ambient environment around the lithography machine, which in turn, may affect optical measurements of the substrate stage position. As a consequence, the linear force generated by the actuators may vary, resulting in unintended positioning errors.

[0007] One known approach for controlling the operational environment of an actuator used for substrate stage positioning is a closed-loop air shower. With this approach, cooled air is continuously circulated through the substrate stage, including the coil and magnet arrays of the actuators, using a vacuum pump and an air cooler. See for example U.S. Patent Numbers 7,679,720 and 7,359,032. The problem with this approach, however, is that the air shower cannot reach every part of the chamber surrounding the substrate stage. As a result, the temperature across the actuator surface may vary, potentially causing unintended positioning errors due to changes in the temperature and index of refraction of the air surrounding the substrate stage.

SUMMARY OF THE INVENTION

[0008] The aforementioned problems are solved by a lithography tool having a stage for supporting and positioning a substrate, an array configured to move the stage, and a cover plate positioned between the stage and the array. In various embodiments, the array may be either a magnet or coil array. The cover plate acts as a thermal insulator that helps reduce temperature variations across the array. Consequently, variations in the lithography environment are reduced, resulting in a minimization of positioning errors. In addition, the cover plate also protects the array and provides a smooth surface in the event of a "crash" of the substrate stage.

[0009] In various embodiments, the cover plate is made of a low thermal conductivity material, such as carbon fiber or a polymer sheet. The use of a material with low thermal conductivity helps insulate the array environment from temperature variations. In addition, the cover plate can also be a metal sheet. The cover plate may also be either perforated or non-perforated. One or more channels may also be provided under the cover plate surface adjacent the array. During operation, a vacuum source pulls air through the optional perforations in the cover plate and through the one or more optional channels, reducing the incidence of the formation of hot and/or cold air pockets within the vicinity of the array. As a result, a stable temperature environment surrounding the array is maintained. The vacuum also helps hold the cover plate in place, eliminating the need to use fasteners or adhesives.

[0010] In yet another embodiment, an intermediate plate is provided between the cover plate and the array. The intermediate plate effectively doubles the number of insulating boundary layers between the array and the cover plate created by the vacuum. With the effective increase in the number of boundary layers, heat transferred from the array to the cover plate is reduced, improving overall system performance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The invention may best be understood by reference to the following description taken in conjunction with the accompanying drawings, which illustrate specific embodiments of the invention.

[0012] Figure 1 is a diagram of a lithography tool in accordance with a non-exclusive embodiment of the invention.

[0013] Figure 2A is a diagram of a non-exclusive embodiment of a substrate stage and cover plate in accordance with the principles of the present invention.

[0014] Figure 2B is an exploded diagram of the cover plate and housing of Figure 2A.

[0015] Figures 2C is a cross section illustrating the coil array, housing and cover plate of Figure 2B. [0016] Figures 3A and 3B illustrate another non-exclusive embodiment of the cover plate used in cooperation with a linear motor in accordance with the principles of the present invention.

[0017] Figure 4 is a diagram of an intermediate plate between the cover plate and array in accordance with another non-exclusive embodiment of the invention.

[0018] Figures 5A and 5B illustrate two additional non-exclusive embodiments in accordance with the principles of the present invention

[0019] Figures 6 A and 6B are flow charts that outline a process for designing and making a substrate device.

[0020] It should be noted that like reference numbers refer to like elements in the figures.

[0021] The above-listed figures are illustrative and are provided as merely examples of embodiments for implementing the various principles and features of the present invention. It should be understood that the features and principles of the present invention may be implemented in a variety of other embodiments and the specific embodiments as illustrated in the Figures should in no way be construed as limiting the scope of the invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0022] The invention will now be described in detail with reference to various embodiments thereof as illustrated in the accompanying drawings. In the following description, specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art, that the invention may be practiced without using some of the implementation details set forth herein. It should also be understood that well known operations have not been described in detail in order to not unnecessarily obscure the invention.

[0023] Referring to Figure 1, a schematic illustrating a lithography tool 10 in accordance with the principles of the present invention is shown. The tool 10 includes a frame 12, an illumination system 14 including a light source 16 and an illumination element 18, a reticle stage 20 for supporting a reticle 22, and an optical assembly 24. The tool 10 also includes a substrate stage 26 for supporting and positioning a substrate 28 under the optical assembly 24. The substrate stage 26, which is positioned on a base 30, includes a housing 32 for containing an array (not visible) of a motor stator 34 used for moving and positioning the substrate 28, a counter-mass 36, and one or more trim motors 38 for correcting the position of the counter-mass 36. The substrate stage 26 and base 30 are provided within an environmentally controlled chamber 40.

[0024] In various embodiments, the tool 10 may be either an immersion or conventional dry lithography tool. In addition, the tool may be either a scanning type or step-and-repeat type lithography tool. The substrate 28 may be either, for example, a semiconductor wafer, an LCD flat panel display, or any other type of work piece that needs to be patterned. The substrate stage 26 may include just a fine stage or a combination of both a fine stage and a coarse stage. In further embodiments, the light source 16 may be, for example, a g-line source (436nm), an i-line source (365 nm), a KrF excimer laser (248 nm), an ArF excimer laser (193 nm), an X-ray light source, an EUV light source, or any other light source that has currently or may be used in the future. In addition, the tool 10 does not necessarily use a reticle 22 for defining a pattern, but rather, may be used with a mask-less system.

[0025] In yet other embodiments, the motor stator 34 may be either a planar motor or a linear motor. The array contained in housing 32 may be either a magnet array or a coil array. For illustrative purposes, examples of planar and linear motors with coil and magnet arrays are described below in Figures 2A-2C and 3A-3B respectively.

[0026] Referring to Figure 2A, a non-exclusive embodiment of the substrate stage 26 and housing 32 in accordance with the principles of the present invention are shown. As evident in the figure, a cover plate 42 is positioned adjacent to and between the substrate stage 26 and the housing 32. In the embodiment shown, the cover plate 42 is perforated and includes a plurality of perforations 44. In an optional embodiment, one or more fasteners 46, such as screws, bolts, rivets, or an adhesive, is provided to secure the perimeter of the cover plate 42 to the housing 32. Although not illustrated, the cover plate 42 may also be retained by fasteners or an adhesive in the central area of the cover plate 42. In an alternative embodiment (not illustrated), the cover plate 42 provides a solid surface without any perforations 44. In either case, the cover plate 42 provides (i) a thermal insulation between the array (not visible) contained within the housing 32 and the substrate stage 26 and (ii) a smooth surface that protects the underlying array in the event of a "crash" of the substrate stage 26. [0027] In one non-exclusive embodiment, the cover plate 42 is made of a carbon fiber material. Carbon fiber provides the attributes of a relatively high thermal conductivity along the plane defined by the underlying array, with a relatively low thermal conductivity in the direction orthogonal to the plane (i.e., in the direction between the array and the substrate stage 26). In other embodiments, materials such as a thin sheet of metal, ceramic, or a polymer may be used.

[0028] Referring to Figure 2B, an exploded diagram of the housing 32 and the cover plate 42 is shown without the substrate stage 26. In this view, the cover plate 42 has been separated from the housing 32, revealing the array of coils 48 contained in the housing 32. In various embodiments, the array of coils can all be orientated in the same direction. As a result, the motor stator 34 generates forces in either the X or Y direction. Alternatively, some of the coils of the array 48 can be orientated in one direction, while other coils are oriented in an orthogonal direction. With this arrangement, the motor stator 34 generates forces in both the X and Y directions.

[0029] Referring to Figure 2C, a cross section illustrating the housing 32, cover plate 42 and coils 48 of the array is illustrated. In addition, a plurality of posts 50 is provided between the coils 48 of the array and the cover plate 42. The posts 50 support the cover plate 42 above the array of coils 48. In one non-exclusive embodiment, the posts 50 are as small as possible and made of a low thermal conductivity material so that a minimal amount of heat is conducted from the array of coils 48 to the cover plate 42. In addition, the posts 50 define one or more channels in the X and/or Y directions between the array of coils 48 and the cover plate 42. In a variation of this embodiment, the posts 50 may be in the shape of ribs (not illustrated).

[0030] A vacuum source 52 is provided in fluidic communication 53 with the gap between the coils 48 of the array and the cover plate 42. In a non-exclusive embodiment, the vacuum source 52 is provided to create an air flow from the chamber 40 containing the substrate stage 26, through the perforations 44 in the cover plate 42, along the one or more channels in the X and/or Y directions defined by the posts 50, to the periphery edge around the array of coils 48. The combination of the cover plate 42, along with the air flow created by the vacuum source 52, facilitates a reduction of hot and/or cold pockets of air on the surface of the cover plate 42. As a result, the cover plate 42 not only provides thermal insulation between the array of coils 48 and the housing 32, but also reduces temperature variations within the air inside the chamber 40. Both of these attributes help improve the accuracy of the lithography machine, resulting in a minimization of overlay errors. In addition, the negative or reduced air pressure created by the vacuum source 52 helps hold the cover plate 42 in place over the housing 32. As a consequence, the number of fasteners 46 and/or adhesive can be reduced or possibly eliminated altogether.

[0031] Referring to Figures 3A and 3B, another non-exclusive embodiment of the cover plate 42 used in the stator of a linear motor is shown. As evident in Figure 3A, the cover plate 42 is provided over the array of coils 48 contained in housing 32. Permanent magnets are provided in the linear mover 54. In alternative embodiments, coils 48, housing 32, and cover plate 42 may be contained in the linear mover, and permanent magnets can be used in the stator. In addition, the perforations 44 and fasteners 46 may optionally be used. In Figure 3B, the cover plate 42 and linear mover 54 have been removed for illustrative purposes to show the arrangement of the array of coils 48 within the housing 32. Although not visible in either figure, posts or ribs 50 may also optionally be provided to both support the cover plate 42 and to create the X and/or Y channels, which facilitate air flow to the periphery of the array 48 from the air in the chamber 40.

[0032] Referring to Figure 4, a diagram of an intermediate plate 56 between the cover plate 42 and the array 48 (of either coils or magnets) in accordance with another nonexclusive embodiment of the invention is shown. With this embodiment, the intermediate plate 56 effectively doubles the number of boundary layers between the array 48 and the cover plate 42. In a phenomena known as "Poiseuille Flow", the air movement created by the vacuum source 52 moves relatively fast (as represented by the long arrows 58), compared to the air moving adjacent the surfaces defined by the cover plate 42, array of coils 48 and intermediate plate 56 (as represented by the short arrows 60). The slow moving air adjacent these surfaces creates additional boundary layers, which act as insulating layers. As a result, the thermal transfer between the array of coils 48 and the cover plate 42 is reduced, further improving the precision and performance of the motor stator 34. [0033] Referring to Figure 5A, another non-exclusive embodiment in accordance with the principles of the present invention is shown. In this embodiment, a thermal insulating layer 70 is provided between the coils 48 of the array and the cover plate 42. The insulating layer 70 provides thermal insulation between the coils 48 of the array and the cover plate 42, which tends to reduce temperature variations across the surface of the cover plate 42. The insulating layer 70 also creates or defines a micro- channel cooling layer 72 adjacent the coils 48. In various embodiments, the insulating layer 70 is a vacuum insulation panel or any other material that provides heat insulation and low thermal conductivity.

[0034] Referring to Figure 5B, yet another non-exclusive embodiment in accordance with the principles of the present invention is shown. In this embodiment, a thermal conduction layer 74 is provided between the micro-channel 72 above the coils 48 of the array and the insulating layer 70 below the cover plate 42. The thermal conductive layer 74 provides thermal diffusion toward the areas where the coils 48 of the array tend to generate less heat. In addition, the thermal insulating layer 70 and the thermal conduction layer 74 together tend to reduce temperature variations across the surface of the cover plate 42. In various embodiments, the thermal conductive layer 74 is made of any highly thermally conductive material, such as, but not limited to, a planar graphite sheet.

[0035] With regard to Figures 5A and 5B, it should be noted that only partial cross- section diagrams are illustrated for simplicity. It should be understood that the use of the insulating layer 70 and/or the thermal conductive layer 74 may cover all or a portion of the coils 48 of the array. In various alternative embodiments, the insulating layer 70 may be place above the thermally conductive layer 74 as shown in Figure 5B, or vice- versa.

[0036] Substrates, such as semiconductor die on a wafer or LCD panels, are fabricated by the process shown generally in Figure 6A. In step 80 the function, performance characteristics, and geometry of the device are designed. In the next step 82, one or more reticles, each defining a pattern, are developed according with the previous step. In a related step 84 a "blank" substrate, such as a semiconductor wafer, is made and prepared for processing. The substrate is then processed in step 86 at least partially using the photolithography tool 10 as described herein. In step 88, the substrate is diced and assembled and then inspected in step 90.

[0037] Figure 6B illustrates a detailed flowchart example of the above-mentioned step 86 in the case of fabricating semiconductor substrates. In step 102 (ion implantation step), ions are implanted in the substrates. In step 104 (oxidation step), the substrate surface is oxidized. In step 106 (CVD step), an insulation film is formed on the substrate surface. In step 108 (electrode formation step), electrodes are formed on the substrate by vapor deposition. The above-mentioned steps 102 - 108 form the preprocessing steps for substrates during processing, and selection is made at each step according to processing requirements.

[0038] At each stage of substrate processing, when the above-mentioned preprocessing steps have been completed, the following post-processing steps are implemented. During post-processing, first, in step 110 (photoresist formation step), photoresist is applied to a substrate. Next, in step 112 (exposure step), the lithography tool 10 as described herein is used to transfer the pattern of the reticle 22 to the substrate. Then in step 114 (developing step), the exposed substrate is developed, and in step 116 (etching step), parts other than residual photoresist (exposed material surface) are removed by etching. In step 118 (photoresist removal step), unnecessary photoresist remaining after etching is removed. Multiple circuit patterns are formed by repetition of these preprocessing and post-processing steps. Although not described herein, the fabrication of LCD panels from glass substrates is performed in a similar manner.

Although many of the components and processes are described above in the singular for convenience, it will be appreciated by one of skill in the art that multiple components and repeated processes can also be used to practice the techniques of the system and method described herein. Further, while the invention has been particularly shown and described with reference to specific embodiments thereof, it will be understood by those skilled in the art that changes in the form and details of the disclosed embodiments may be made without departing from the spirit or scope of the invention. For example, embodiments of the invention may be employed with a variety of components and should not be restricted to the ones mentioned above. It is therefore intended that the invention be interpreted to include all variations and equivalents that fall within the true spirit and scope of the invention.

Claims

What is claimed is: 1. A lithography tool, comprising:

a stage for supporting and positioning a substrate;

an array configured to move the stage; and

a cover plate positioned adjacent the array and the stage.

2. The tool of claim 1, wherein the cover plate is positioned between the array and the stage.

3. The tool of claim 1, further comprising a motor stator including the array.

4 The tool of claim 3, further comprising a base including the motor stator.

5. The tool of claim 3, further comprising a counter-mass including the motor stator.

6. The tool of claim 1, wherein the array and cover plate are provided on the stage.

7 The tool of claim 1, wherein the cover plate provides thermal insulation between the array and the stage.

8. The tool of claim 1, wherein the cover plate reduces temperature variations across the array.

9. The tool of claim 1, wherein the cover plate provides a higher thermal conductivity along a plane defined by the array and a relatively lower thermal conductivity in a direction which is orthogonal to the plane defined by the array.

10. The tool of claim 1, wherein the cover plate provides a relatively flat surface between the stage and the array.

11. The tool of claim 1, wherein the cover plate is made of carbon fiber.

12 The tool of claim 1, wherein the cover plate is made of a polymer.

13. The tool of claim 1, wherein the cover plate is made of metal.

14. The tool of claim 1, wherein the cover plate is perforated.

15. The tool of claim 1, wherein the cover plate is non-perforated.

16. The tool of claim 1, further comprising a vacuum source to reduce the air pressure between the cover plate and the array.

17. The tool of claim 1, further comprising a vacuum source to create air flow from a chamber containing the stage toward the array.

18. The tool of claim 1, further comprising a vacuum source to create air flow from a chamber containing the stage through the array.

19. The tool of claim 1, further comprising a vacuum source to create air flow from a chamber containing the stage toward at least one outer periphery edge of the array.

20. The tool of claim 1, further comprising providing a vacuum source for at least partially holding the cover plate in place between the array and the stage.

21. The tool of claim 1, wherein the cover plate further includes a plurality of posts or ribs provided between the array and the cover plate.

22. The tool of claim 1, further comprising one or more channels provided between the array and the cover plate.

23. The tool of claim 22, further comprising a vacuum source for removing air between the stage and the array through the one or more channels.

The tool of claim 1, wherein the array is a coil array.

25. The tool of claim 1, wherein the array is a magnet array.

26. The tool of claim 1, further comprising a planar motor including the array.

27. The tool of claim 1, further comprising a linear motor including the array.

28. The tool of claim 1, further comprising an intermediate plate provided between the array and the cover plate.

29. The tool of claim 28, wherein the intermediate plate creates one or more insulating boundary layers between the array and the cover plate.

30. The tool of claim 1, further comprising a thermal insulating layer provided between the array and the cover plate.

31. The tool of claim 30, wherein the thermal insulating layer is a vacuum insulation panel.

32. The tool of claim 30, wherein the thermal insulating layer includes the attributes of high heat insulation and low thermal conductivity.

33. The tool of claim 30, wherein the thermal insulating layer defines a micro- channel cooling layer adjacent the array.

34. The tool of claim 30, wherein the thermal insulating layer acts to reduce temperature variations across the cover plate.

35. The tool of claim 30, further comprising a thermal conduction layer provided between the array and the cover plate.

36. The tool of claim 35, wherein the thermal conductive layer is made of a graphite sheet.

37. The tool of claim 35, wherein the thermal conductive layer defines a micro- channel cooling layer adjacent the array.

38. The tool of claim 35, wherein the thermal conduction layer and the thermal insulating layer cooperate together to reduce temperature variations across the cover plate.

39. The tool of claim 35, wherein the thermal conduction layer acts to create thermal diffusion toward areas where the array tends to generate less heat