Semiconductor processor high-accuracy XY positioning system

Abstract

To provide a semiconductor processor high-accuracy XY positioning system for precisely positioning a loading object of a semiconductor processor.SOLUTION: The present system comprises a fixed base part, two stationary linear guides that are fixed to the base part and extend along an X-direction in an orthogonal coordinate system, an X-stage and an X-linear motor, and a Y-stage and a Y-linear motor. The X-stage extending along a Y direction in the orthogonal coordinate system comprises cross-beams slidably engaged with the stationary linear guides, respectively. The Y-stage comprises a carriage, and at least one air bearing part including a pad face facing a guide face of the cross-beams, that is connected to the carriage. The latter comprises a frame made from a first material. The guide face comprises a ceramic coating, and a layer made from a second material between the ceramic coating and a frame of the cross-beams. The second material has a heat expansion coefficient smaller than that of the first material, and has a heat expansion coefficient larger than that of the ceramic coating.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to the field of positioning systems for the semiconductor industry, and more particularly to high precision XY positioning systems for accurately positioning payloads, particularly silicon wafer handling stages, in semiconductor processing equipment. [Background technology]

[0002]

[0002] Multi-axis positioning systems typically include mechanical bearings arranged to slide along rails to position a stage in an XY coordinate system associated with the system. Mechanical bearings have several limitations that prevent positioning systems from meeting the ever-tougher demands of the semiconductor industry. These limitations include, among others: - Parasitic movements or vibrations at the micron level due to irregularities in the rail surface of the positioning machine along which the mechanical bearing is intended to slide. - Friction occurs between the rolling elements of the mechanical bearing and the rail, which causes a hysteresis effect on the slide when stopping, making it impossible to position the stage with an accuracy of finer than 100 nm in the XY coordinate system. - Abrasion generates particles that can become airborne and contaminate surfaces. - The use of lubricants such as oil or grease to reduce friction, which also generates volatile particles that can contaminate sensitive parts.

[0003]

[0003] Various solutions have been proposed to overcome these limitations. For example, U.S. Patent Nos. 5,040,431 and 4,916,340 disclose XY positioning systems with air bearings slidably mounted on ceramic beams such as silicon carbide or alumina. Such structures have the advantage of being able to provide both tight flatness tolerances down to the micron level and small roughness down to 0.2 microns.

[0004] However, due to their hardness, ceramic beams have the disadvantage of requiring complex and heavy equipment to machine the beams, thereby increasing the manufacturing costs of these systems. In addition, ceramics, especially alumina, have low thermal conductivity. Therefore, ceramic beams do not adequately dissipate the heat generated by the motor, which adversely affects the accuracy of the system. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent No. 5,040,431 [Patent Document 2] U.S. Patent No. 4,916,340 [Non-patent literature]

[0006] [Non-Patent Document 1] New Way, “Air Bearing Application and Design Guide”, Rev.E, January 2006, https: / / www.newwayairbearings.com / sites / default / files / new_way_application_and_design_guide_%20Rev_E_2006-01-18.pdf Summary of the Invention [Problem to be solved by the invention]

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a high precision XY positioning system for positioning a payload in semiconductor processing equipment that overcomes the above-mentioned limitations. [Means for solving the problem]

[0008] This object is at least partially achieved by an XY positioning system for precisely positioning a semiconductor processing equipment load, the XY positioning system including a fixed base, two stationary linear guides fixed to the base and extending along the X direction of a Cartesian coordinate system, an X stage, an X linear motor configured to move the X stage along the X direction, and a Y stage, and a Y linear motor configured to move the Y stage along the Y direction. The X stage includes a cross beam extending along the Y direction of the Cartesian coordinate system between the two stationary linear guides, and two carriages connected to each end of the cross beam and slidably engaged with the respective stationary linear guides. The cross beam includes a frame of a first material and a guide surface. The Y stage includes a carriage configured to fixedly receive the semiconductor processing equipment load, and at least one air bearing connected to the carriage. The air bearing includes a pad surface facing the guide surface of the cross beam. The air bearing includes one or more ducts for venting pressurized air from the pad surface to create an air film of a predetermined thickness between the guide surface of the cross beam and the pad surface.

[0009]

[0007] The guideway comprises a ceramic coating and a layer of a second material between the ceramic coating and the cross beam frame, the second material having a thermal expansion coefficient less than that of the first material of the cross beam frame and greater than that of the ceramic coating.

[0010] In one embodiment, the Y linear motor comprises a magnetic track connected to the cross beam and a coil unit fitted inside the magnetic track, the latter being arranged to extend between two longitudinal sides of the cross beam along the Y direction.

[0011] In one embodiment, the flatness of the ceramic coating over the area defined by the length and width of the guideway is in the range of 1 to 2 micrometers. In one embodiment, the thickness of the air film is comprised between 3 micrometers and 6 micrometers while the positioning system is in operation.

[0012] In one embodiment, the ceramic coating is made of alumina (Al2O3). In one embodiment, the second material is nickel or a nickel alloy.

[0013] In one embodiment, the thickness of the ceramic coating is selected within the range of 200 micrometers to 1 millimeter.

[0013]

[0014] In one embodiment, the thickness of the second material is selected in the range of 30 micrometers to 200 micrometers, preferably between 40 micrometers and 60 micrometers.

[0014]

[0015] In one embodiment, the ceramic coating is impregnated with a resin, such as a phenolic resin.

[0016] In one embodiment, the cross beam frame is aluminum.

[0015]

[0017] In one embodiment, the second material and the ceramic coating are applied to the cross beam frame and the second material, respectively, by an Atmospheric Plasma Spraying (APS) process.

[0016]

[0018] The invention will be better understood with the help of the description of an embodiment given by way of example and illustrated by the figures. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a perspective view of a high precision XY positioning system for positioning a payload of semiconductor processing equipment, according to one embodiment. [Figure 2] 2 is an enlarged view of the Y stage of the positioning system of FIG. 1, cut out from the detail circle of FIG. 1; [Figure 3] 3 is a cross-sectional view of the Y stage of FIG. 2 taken along a plane perpendicular to the Y axis. [Figure 4] Figure 4 is an enlargement of Figure 3 at the interface between the guide surface of the cross beam and the air bearing. Figure 4a is an enlargement of the air bearing relative to the guide surface of Figure 4 at the level of the air bearing. Figure 4b is an enlargement of a portion of the guide surface of the cross beam of Figure 4. [Figure 5] FIG. 2 is a perspective view of a cross beam of the X stage of the positioning system of FIG. 1; DETAILED DESCRIPTION OF THE INVENTION

[0018]

[0019] 1, a high-precision XY positioning system 10 includes a conventional granite base 12 having a flat, smooth top surface 13. Two stationary linear guides 14a, 14b are fixed to the top surface 13 of the granite base 12 near its ends. The two linear guides 14a, 14b are arranged parallel to each other along the X direction of a Cartesian XY coordinate system and drive an X stage 20 in both directions along this direction.

[0019]

[0020] X stage 20 includes a cross beam 21 extending along the Y direction of a Cartesian coordinate system. Two X carriages 30a, 30b are connected to each end of cross beam 21 and slidably engaged with respective stationary linear guides 14a, 14b. More specifically, each X carriage 30a, 30b includes a mechanical bearing (not shown) attached to a rail 15 fixed along the side of each stationary linear guide 14a, 14b.

[0020]

[0021] The XY positioning system 10 further includes two X linear motors 16, each including a magnetic track 17 extending along each linear guide 14a, 14b and a glider 18 with a set of coils fitted in the magnetic track and connected to each carriage 30a, 30b. Thus, the cross beam 21 is moved in the X direction when the coils of the gliders 18 of the motors 16 are energized. The XY positioning system 10 also includes two linear encoders for positioning the X stage 20 along the X direction. Each linear encoder includes an encoder scale 32 disposed above the respective linear guide 14a, 14b and an optical reader 34 attached to the respective carriage 30a, 30b facing the respective encoder scale 32.

[0021]

[0022] In an embodiment not shown, the precision XY positioning system may comprise only one X linear motor for driving one end of the cross beam along the X direction, while the other end of the cross beam is simply slidably coupled to a linear guide.

[0022]

[0023] 3 and 5, the beam 21 has a substantially H-shaped cross section perpendicular to the beam length. This H-shaped cross section is constant along most of the beam's entire length. In a preferred embodiment, the beam 21 is made of aluminum or an aluminum alloy. It is advantageous to provide a series of adjacent openings 27 arranged along the entire length of the beam and extending from the top to the bottom of the beam in order to, on the one hand, reduce the weight while maintaining high beam stiffness, and, on the other hand, increase the heat exchange surface for efficiently dissipating heat generated by the Y linear motor 40 arranged on the beam for driving the Y stage 50 in the Y direction along the beam.

[0023]

[0024] 2 and 3, Y stage 50 includes Y carriage 52 with upper portion 54 configured to fixedly receive a load of semiconductor processing equipment. As shown in FIG. 3, the lower portion of cross beam 21 includes rectangular parallelepiped-shaped longitudinal space 28 to which magnetic track 42 of Y linear motor 40 is fixed. Glider 44, which includes a set of coils, is fitted inside motor magnetic track 42 and is connected to carriage 52 of Y stage 50 by connecting bracket 68 to drive carriage 52 along the cross beam. This connecting bracket 68 has an L-shaped portion extending below a portion of cross beam 21 to connect a portion of glider 44 to side wall 56 of Y carriage 52.

[0024]

[0025] Y-stage 50 also includes an air bearing 60 mounted on the same side wall 56 of Y-carriage 52 such that a flat pad surface 62 of air bearing 60 faces guide surface 23 of cross beam 21, as shown in Figures 4 and 4a. In the illustrated embodiment, another air bearing 58 is mounted to the bottom of Y-carriage 52 to create an air gap between a pad surface 59 of the air bearing and top surface 13 of granite base 12.

[0025]

[0026] The XY positioning system 10 further includes a weighing hollow beam 70 having a rectangular cross section. The weighing beam is positioned to extend along the longitudinal rectangular parallelepiped space above the cross beam 21 without contacting the cross beam 21, as shown in Figure 3. Both ends of the weighing beam 70 are connected to the respective carriages 30a, 30b, as shown in Figure 1. The weighing beam 70 is preferably made of alumina (Al2O3), silicon carbide, or another material with a low thermal expansion coefficient.

[0026]

[0027] The XY positioning system 10 includes a linear encoder for positioning the Y stage 50 along the cross beam 21. The encoder includes an encoder scale 72 mounted along the upper side of the weigh beam 70. In a preferred embodiment, the encoder scale 72 is a 1D+ scale type featuring incremental tracks along the Y direction and additional tracks that provide the information necessary for vertical and angular compensation. Accordingly, as shown in FIG. 2, first and second optical readers 74, 76 are mounted on the Y carriage 52 to read the incremental and additional tracks, respectively.

[0027]

[0028] 4 and 4a, the air bearing 60 includes a duct 64 for exhausting pressurized air from the pad surface 62. In a preferred embodiment, the air bearing further includes a suction channel 67 communicating with a suction means for sucking air from the central portion of the pad surface 62. The force of the pressurized air impinging on the guide surface 23 is sufficient to lift the air bearing off the guide surface. By using both the pressurized air and the suction means, an equilibrium state can be created in which the gas supply rate equals the gas leakage rate, generating an air film 66 having a laminar flow of a predetermined thickness between the pad surface 62 and the guide surface 23. Air bearings configured to operate with pressurized air and suction systems are well known in the art and are described, for example, in New Way, "Air Bearing Application and Design Guide," Rev. E, January 2006, https: / / www.newwayairbearings.com / sites / default / files / new_way_application_and_design_guide_%20Rev_E_2006-01-18.pdf.

[0028]

[0029] The thickness of this air film is of paramount importance because a thinner film increases the stiffness of the air bearing, thereby improving the accuracy of the XY positioning system. Therefore, to minimize the thickness of the air film, the flatness of the guideway must be minimized. As a general rule of thumb, the flatness of the guideway 23 corresponds to approximately one-third of the thickness of the air film. To make its surface as flat as possible, the guideway 23 is provided with a ceramic coating 25 having a flatness between 1 and 2 micrometers over the area defined by the length L and width W of the guideway 23, as shown in FIG. 5. This flatness therefore results in an air film 66 having a thickness between 3 and 6 micrometers when the XY positioning system is in operation.

[0029]

[0030] To achieve this flatness, the cross beam 21 is first machined from a block of, for example, 6082 aluminum alloy to obtain at least one lateral side of the beam with a flatness of less than 15 microns, preferably about 10 microns. A sanding process is then performed only on the area defined by the length L and width W of the guideway (FIG. 5) to provide a surface with a predetermined roughness and ensure optimal adhesion of the first layer 24 of nickel or nickel alloy (FIGS. 4 and 4b). This first layer is applied by an air plasma spray (APS) process. The process parameters are set to obtain a layer thickness between 30 and 200 microns, preferably between 40 and 60 microns. The grain size of the nickel or nickel alloy should preferably be in the range of 15 to 90 μm.

[0030]

[0031] Once the first layer 24 has been applied, a ceramic coating 25 is applied thereon, for example using the same APS process, by setting the process parameters to obtain a ceramic coating thickness comprised between 200 micrometers and 1 millimeter, preferably between 500 micrometers and 700 micrometers. The ceramic is preferably alumina (Al2O3), although other types of ceramic may also be used. The particle size of the Al2O3 should preferably be comprised in the range of 5 to 45 μm.

[0031]

[0032] The role of the first layer is to prevent cracks in the ceramic coating 25. In fact, alumina has a small thermal expansion coefficient, which may cause cracks due to the thermal expansion of the cross beam 21 caused by the heating generated by the Y linear motor 40. Nickel or nickel alloy has a thermal expansion coefficient intermediate to that of aluminum and alumina. Therefore, the first layer of nickel or nickel alloy partially absorbs the expansion of the aluminum beam, thereby reducing the mechanical stress in the ceramic coating and preventing cracks in the ceramic.

[0032]

[0033] In other embodiments, the first layer of nickel or nickel alloy in the guideway may be replaced with a layer of another material having a thermal expansion coefficient lower than aluminum but higher than alumina or other types of ceramic.

[0033]

[0034] The ceramic coating 25 is then polished and then lapped to a flatness comprised between 1 and 2 micrometers. More specifically, the ceramic coating may first be polished to a flatness comprised between 5 and 10 microns and then lapped to a final flatness. Lapping can be performed using silicon carbide or diamond abrasive grains, the size of which is comprised between 15 and 45 microns.

[0034]

[0035] In one embodiment, the ceramic coating may be impregnated with a resin, such as a phenolic resin, which advantageously fills the voids between the ceramic grains. The resin may be sprayed onto the ceramic coating or applied with a paint brush, preferably prior to lapping.

[0035]

[0036] In a preferred embodiment (not shown), the XY positioning system includes a cross beam with two longitudinally opposing guideways provided with the ceramic coating and interlayer described above. In this case, the Y-carriage includes two air bearings mounted facing each guideway of the cross beam. This design offers the advantage of symmetrical weight distribution while facilitating bilateral guidance. Additionally, this design does not require suction to generate the preload force of the air bearings, allowing the use of air bearings that contain only pressurized air.

[0036]

[0037] While the present invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are exemplary or representative and should not be considered restrictive. It will be understood that changes and modifications may be made by those skilled in the art within the scope of the appended claims. For example, the mechanical bearings of the X-stage may be replaced with air bearings attached to both ends of the cross beam so as to face guide surfaces disposed along the sides of the stationary linear guide extending in the X direction. Such guide surfaces may comprise an intermediate layer and a ceramic coating having the same properties as those described in connection with the guide surfaces of the cross beam. [Explanation of symbols]

[0037] 10 XY positioning system 12 base 13 Top side 14a, 14b Stationary linear guide 15 Rail 16 x Linear Motors 17 Magnetic Track 18 Glider 20x Stage 21 Crossbeam 22 frames 23 Guide surface 24 nickel layer 25 Ceramic Coating 26 Heat exchanger 27 Opening 28 Lower groove 30a, 30b X carriage 32 Encoder scale of linear encoder 34 Linear Encoder Optical Reader 40 Y linear motor 42 Magnetic Track 44 Glider 50 Y Stage 52 Y carriage 54 upper side 56 Side wall 58 Air bearing section 59 Pad surface 60 Air bearing section 62 Pad surface 64 Duct 65 pressurized air channels 66 Air membrane 67 Suction Channel 68 Connecting bracket 70 Measurement beam 72 Encoder scale for linear encoder 74 First Optical Reader of Linear Encoder 76 Secondary Optical Reader of Linear Encoder

Claims

1. An XY positioning system (10) for positioning a load in semiconductor processing equipment, comprising: a fixed base (12); Two stationary linear guides (14a, 14b) fixed to the base (12) and extending along the X direction of a Cartesian coordinate system; an X-stage (20) including a cross beam (21) extending along the Y direction of the Cartesian coordinate system between the two stationary linear guides (14a, 14b), and two carriages (30a, 30b) connected to each end of the cross beam (21) and slidably engaged with each stationary linear guide (14a, 14b), wherein the cross beam (21) includes a frame (22) and a guide surface (23) made of a first material; a carriage (52) configured to fixedly receive the load; and a Y stage (50) comprising at least one air bearing (60) connected to the carriage (52) and including a pad surface (62) facing the guide surface (23) of the cross beam (21), wherein the at least one air bearing comprises a duct (64) for discharging pressurized air from the pad surface (62) to generate an air film (66) of a predetermined thickness between the pad surface (62) and the guide surface (23); at least one X linear motor (16) configured to move the X stage (20) along an X direction; a Y linear motor (40) configured to move the Y stage (50) along the Y direction; Equipped with 1. An XY positioning system (10) according to claim 1, wherein the guide surface (23) comprises a ceramic coating (25) and a layer (24) of a second material between the ceramic coating (25) and the frame (22) of the cross beam (21), the second material having a thermal expansion coefficient smaller than that of the first material and larger than that of the ceramic coating.

2. 2. The XY positioning system (10) of claim 1, wherein the Y linear motor (40) comprises a magnetic track (42) connected to the cross beam (21) and a glider (44) fitted inside the magnetic track (42), the track (42) extending between two longitudinal sides of the beam (21) along the Y direction.

3. 3. The XY positioning system (10) of claim 1 or 2, wherein the flatness of the ceramic coating (16) over an area defined by the length (L) and width (W) of the guideway is within the range of 1 to 2 micrometers.

4. 4. The XY positioning system (10) according to claim 1, wherein the thickness of the air film (66) between the pad surface (62) and the guide surface (23) is comprised between 3 micrometers and 6 micrometers.

5. The coating is made of alumina (Al ２ O ３ The XY positioning system (10) according to any one of claims 1 to 4, which is manufactured by

6. The XY positioning system (10) according to any one of claims 1 to 5, wherein the second material is nickel or a nickel alloy.

7. The XY positioning system (10) according to any one of claims 1 to 6, wherein the thickness of said ceramic coating is selected in the range of 200 micrometers to 1 millimeter.

8. An XY positioning system (10) according to any of the preceding claims, wherein the thickness of said second material is selected in the range of 30 micrometers to 200 micrometers, preferably between 40 micrometers and 60 micrometers.

9. The XY positioning system (10) according to any of the preceding claims, wherein the ceramic coating (25) is impregnated with a resin, for example a phenolic resin.

10. The XY positioning system (10) according to any one of claims 1 to 9, wherein the frame (22) of the cross beam (21) is made of aluminum or an aluminum alloy.

11. 11. The XY positioning system (10) according to any one of claims 1 to 10, wherein the second material and the ceramic coating (25) are applied to the frame (22) of the cross beam (21) and the second material, respectively, by an air plasma spray (APS) process.

Images