PLANAR VACUUM SEAL FOR ISOLATING AN AIR BEARING

Abstract: A graded planar seal is provided between opposing planar surfaces (62, 64) for isolating an air bearing in a vacuum environment (16). The air bearing (22, 24, 26, 62, 64) supports a structure (20) such as a semiconductor mask or wafer and functions in a vacuum environment without severely degrading the quality of the vacuum. The air bearing is isolated from the vacuum by the use of the graded planar seal which establishes a pressure gradient from the level of the air which supports the air bearing (22, 24, 26, 62, 64) to the level of the vacuum environment (16). The gradient is established across the seal by evacuating gas through successive orifices (42, 44. 46, 52) in opposing planar members (12, 14).

Description: PLANAR VACUUM SEAL FOR ISOLATING AN AIR BEARING Background of the Invention This invention relates to treating materials under high vacuum conditions, e.g., in electron beam lithography. In electron beam lithography, a substrate to be written on is supported in high vacuum on an x/y table. As the writing proceeds, the vacuum must be maintained while the motion of the table is accurately controlled in the x/y plane. Summary of the Invention My invention features a vacuum chamber de¬ fined by means including two closely spaced planar portions which in turn define a planar seal for the chamber. One of the planar portions at least partially encloses an interior volume of the chamber. Further, one of the planar portions, and with-it the work ele¬ ment, is movable along the plane of the seal toward and away from tha ' interior volume. Means are provided for evacuating gas from between the planar portions along a direction transverse to the plane to provide the seal. In preferred embodiments the seal is a graded seal between lapped surfaces of said planar portions, and a gas bearing is provided between said surfaces outwardly of said seal. Both seal and bearing are highly effective, despite the pressure differential and despite the relative movement of the planar portions across the boundary of the vacuum chamber. Description of the Preferred Embodiment I turn now to the structure and operation of preferred embodiments of the invention, after firsn briefly describing the drawings. - 2 - Drawings • Fig. 1 is a diagrammatic elevation, partly in section of 'electron beam lithography apparatus embody¬ ing the invention. • 'Fig. 2 is a fragmentary plan view taken along 2-2 of Fig ' . 1. .Fig. 3 is a sectional view through 3-3 of Fig. 2. Fig. 4 is a sectional view through 4-4 of 0 Fig. 2. Fig. 5 is an enlarged view taken along 5-5 of Fig. 4. ; Fig. 6 is a view similar to Fig. 1, of another embodiment. 5 Fig. 7 is a view similar to Fig. 1, of another embodiment. Structure Referring to Figs. 1-5, electron beam column assembly 10, including " rectangular plate 12, is mounted 0 for planar movement along x and y axes above rectangu¬ lar plate 14. Recess 16 in plate 14 is evacuated through channel 18, to provide (with plate 12) a vacuum chamber. orkpiece 20 is supported in chamber 16. Figs. 2-5 show an air bearing and seal be- 5 tween plates 12 and 14. Around the perimeter of the plate 14 are two spaced rows of air delivery holes 22 and 24. Each hole 22 and 24 communicates with a shallow air distribution groove 26 extending parallel to an edge of plate 14. 0 Bent metering rods ' 28 fit in holes 22 and 24, which are .005 inch in diameter larger than the rods. Each rod •,:s * ^ι s a groove 30 at its top. Air pumps 32 and 34 supply pressurized air through manifolding 36 and 38 to holes 22 and 24. Air filters 40 are located between pumps 5 32 and 34 and holes 22 and 24. Three spaced air evacuation channels 42, 44,- and 46 surround the perimeter of chamber 16 inwardly of air supply holes 24. Channel 42 (1/2 inch deep and 1/8 inch wide) is connected directly by manifolding 48 to vacuum pump 50. Channels 44 and 46 (each 3/8 inch wide, and 3/8 inch deep) are connected by spaced holes 52 (5/16 inch diameter, spaced on 7/16 and 1/2 inch centers, respectively) through the channel floors, and manifolds 54 and 56 to vacuum pumps 58 and 60. The facing surfaces 62 and 64 of plates 12 and 14 are lapped to a surface finish variation of no more than 4 micro-inches and to a flatness tolerance variation of no more than .0002 inch. In the embodiment of Fig. 6, electron beam column assembly 100, including plate 112, is station¬ ary. Vacuum chamber and recess 114 is in the upper plate 116, which is movable along x and y axes. Plate 112 has two spaced rows of air delivery holes and three spaced air evacuation channels, respectively manifolded to air supply and vacuum pumps, all generally as in plate 14 of Figs. 1-5. Plate surfaces 118 and 120 are lapped ana correspond to surfaces 62 and 64 of plates 12 and 14. In the embodiment of Fig. 7, electron beam column assembly 130, including plate 132, is station¬ ary and supported by means not shown. Plate 132 has an opening 133 into vacuum chamber 134, which is evacuated through channel 136. Workpiece holder 138 in chamber 134 is connected by colur-n 140 to plate 142, in turn supported from below for movement along x and y axes. A light pressure, sliding mechanical . seal 144 is preferably provided between workpiece holder 138 and the upper surface 146 of plate 132 overhangs and is lapped with the upper surface 150 of plate 142. These surfaces correspond to surfaces 62 and 64 of plates 12 and 14. Plate 132 has the spaced rows of air delivery holes and air evacuation channels, respectively manifolded to air supply and vacuum pumps, all generally as in plate 14 of Figs. 1-5. •5 Operation Referring now to Figs. 1-5, pressurized air flows through holes 22 and 24 and around the outside of rods 28 to form an air cushion (pressurized at about 3 atm. or 2280 torr in the embodiment disclosed, 0 and preferably from 1 to 10 micrometers thick) which acts as an air bearing between plates 12 and 14. Air filters 40 remove dust from the pressurized air to protect the mating plate surfaces. Grooves 26 and 30 help distribute the air. The overall air supply ar- *5 rangement promotes highly stable operation. Channels 42, 44, and 46 provide an effective graded seal between the vacuum chamber and the air bearing, even though there is relative movement of the sealed plates across the vacuum chamber boundary with - the air bearing. In the embodiment disclosed, the outermost air evacuation channel 42 reduces the air pressure to about 46.6 torr, the middle channel 44 further reduces pressure to about .180 torr, and the innermost channel 46 reduces the pressure to about -5 3.2 x 10 torr. The pressure in the vacuum chamber 16 is typically about 5 x 10 " ° torr. In general, the air bearing pressure must be enough to at least counteract the tendency of plates 12 and 14 to approach each other because of the 3 vacuum in chamber. The electron beam assembly 10 is moved along the x and y axes to write on workpiece 20 as desired. In the embodiment of Fig. 6 movement of the electron beam assembly 100 is avoided. • " In the embodiment of Fig. 7, che overhang of downardly facing surface 148 protects the graded seal from dust accumulation. Sliding seal 144 acts to seal the vacuum chamber when the graded seal is shut down for repair or maintenance. Other embodiments are in the following claims Claims What is claimed is:

Claims: - - What is claimed is: 1. Apparatus for treating a work element in high vacuum, comprising means defining a vacuum chamber, said means having first and second closely spaced planar portions defining a planar seal for said chamber, one of said portions at least partially enclosing an interior volume of said chamber, one of said portions being movable relative to the other said portion parallel to the plane of said seal toward and away from said volume, means for supporting said work element in said chamber for movement parallel to said plane with said movable portion, means for treating said work element upon said movement, and means for evacuating gas from between said planar portions along a direction transverse to said plane to provide said seal. 2. The apparatus of claim 1 wherein said means for evacuating comprises first and second portions spaced apart in a direction parallel to said plane, to provide a graded seal. 3. The apparatus of claim 1 wherein said means for evacuating comprises three portions spaced apart in a direction parallel to said plane to provide graded seal. 4. The apparatus of claim 2 or 3 wherein said evacuation portion closest to said vacuum chamber has the largest capacity. 5. The apparatus of claim 2 or 3 wherein said air evacuation portions comprise channels in one of said planar portions, said channels extending around the perimeter of said vacuum chamber and being adapted for connection to a vacuum pump. 6. The apparatus of claim 5 wherein one of said channels is adapted for connection to said pump through spaced, manifolded bores through the channel floor. 7. The apparatus of claim 1 further compris¬ ing means for providing a gas bearing between said planar portions, said means for evacuating being be¬ tween said vacuum chamber and said means for providing a gas bearing. 8. The apparatus of claim 7 wherein said means for providing a gas bearing comprises gas supply openings in one of said planar portions, spaced around said vacuum chamber outwardly of said means for evacuating. 9. The apparatus of claim 8 wherein said gas supply openings are arranged in a plurality of rows spaced along a direction parallel to said plane. 10. The apparatus of claim 8 wherein each said gas supply opening communicates with a groove in said one planar portion, said grooves forming a border around said vacuum chamber. 11. The apparatus of claim 10 wherein said grooves are spaced from one another so that said border is discontinuous. 12. The apparatus of claim 8 wherein each said gas supply opening has a bent metering rod therein. 13. The apparatus of claim 12 wherein said rods are grooved at the surface of said one planar portion. 14. The apparatus of claim 1 wherein the opposing surfaces of said planar portions are lapped. 15. The apparatus of claim 14 wherein said surfaces are lapped to a surface finish variation of no more than 4 micro inches. - 3 - 16. The apparatus of claim 14 wherein said surfaces are lapped to a flatness tolerance variation of no more than .0002 inch. 17. The apparatus of claim 1 wherein said means for treating comprises an electron beam column in communication with said vacuum chamber. 18. The apparatus of claim 1 wherein said planar portion facing said movable portion is recessed to provide said volume.

Inventors: FOX WAYNE L
Applicants: VARIAN ASSOCIATES
Application year: 1980
Main classification: F16J15
IPC codes: F16C29, F16C32, F16J15, H01J37, H01L21