Abstract:
A stage for processing a substrate, especially useful for vacuum applications, has a recess just large enough to hold a substantially flat substrate and a chuck or holder but not much more. The perimeter of the recessed side has an air bearing surface separated from the recess by differentially pumped groves and seal lands. The air bearing lands are urged against a reference plate guide surface and the seal lands being substantially coplanar create a resistance to flow between the groves and recess, on the other side of the base reference plate mounts the radiation source. The VCS may operate in a vacuum environment itself, or in another preferred embodiment, it provides the possibility for multiple stages moving between process or inspection steps within the same tool or process sequence.

Description:
REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims the benefit of U.S. Provisional Patent Application No. 60/602,339, filed Aug. 18, 2004, and U.S. Provisional Patent Application No. 60/697,973, filed Jul. 12, 2005, whose disclosures are hereby incorporated by reference in their entireties into the present disclosure. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates generally to equipment used in the manufacturing of semiconductor devices and masks and more particularly to equipment used in vacuum processes. Applications are anticipated in areas including, but not limited to, ion implant and milling, deposition, etch, ash, clean, lithography and inspection.  
       DESCRIPTION OF RELATED ART  
       [0003]     Because of the shrinking feature sizes in semiconductor wafers, greater degrees of precision are required in the stages used to provide the necessary motions. Because air-bearing stages allow for higher precision, they are commonly used to pattern and inspect semiconductor wafers. A point has been reached where optical techniques are limiting because of the width of the wavelength of light. Deep UV and even electronic beam processing will be required because of their shorter wavelength. The same or higher degree of precision is required in these processes, but they also require a vacuum environment. There are technical difficulties in attempting to use air-bearing stages in vacuum, as the escaping air increases the pressure in the vacuum chamber.  
         [0004]     Many techniques have been employed to effect motion inside a vacuum chamber. Use of rolling element or plane bearing technology has been used, but it is difficult to achieve the required precision. Air bearing systems with differentially pumped scavenge grooves have been employed inside a vacuum chamber. The difficulty here is that the stages quickly become very large to provide the required travels, necessitating large vacuum chambers, and because there is so much scavenging groove perimeter, it is difficult to achieve the low pressures required in the chamber. Another complicating factor in both these methods is that drives, encoders and services all have to be contained inside the vacuum chamber, causing problems with particulation and out gassing.  
         [0005]     Methods to keep the mechanization outside of the vacuum chamber have been employed. These include linear and rotary contact seals, rotary ferro fluidic seals, expanding and contracting bellows. Also used are air bearings structures separated from the vacuum chamber by integral differentially pumped grooves that support some sort of a moving member through an aperture in the vacuum chamber wall. (Note U.S. Pat. No. 4,726,689 February 1988 Pollack, Varian; U.S. Pat. No. 5,898,179 April 1999 Smick, Applied Materials; U.S. Pat. No. 6,515,288 February 2003 Ryding, Applied Materials) have been tried and are the current state of the Art in ion implantation. However, the above-noted problems with the prior art have not all been successfully overcome.  
       SUMMARY OF THE INVENTION  
       [0006]     It is therefore an object of the invention to overcome the above-noted problems of the prior art.  
         [0007]     To achieve the above and other objects, an important design feature in this invention is that instead of trying to build a stage inside a vacuum chamber or reach through a chamber wall, the stage itself becomes the vacuum chamber. Such a stage is called a vacuum chamber stage (VCS). By having the primary or only vacuum chamber completely contained inside the moving stage, all motion systems can exist outside of the vacuum. Because the vacuum chamber size can be reduced to little more than the volume of the substrate, the vacuum pumping requirements and pump down times are dramatically reduced, and the requirement for a large conventional vacuum chamber is eliminated. At the same time, the structural loop between the source and the substrate, say a wafer, is dramatically shortened and stiffened. The stage is guided by its topside, which runs directly on the underside of the base reference member to which the optics, ion source or electron source would mount. Guidance of the stage in the plane established by the X and Y-axis is achieved with an annular air bearing separated from the vacuum section of the stage by differentially pumped groves. This type of stage would be very appropriate for electron beam writing or inspection, Deep UV lithography or ion implantation. This stage architecture may also be useful for many non-vacuum processes because of improvements in the structural loop.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     Preferred embodiments of the present invention will be set forth in detail with reference to the drawings, in which:  
         [0009]      FIGS. 1   a - 1   c  show a first preferred embodiment;  
         [0010]      FIGS. 2   a - 2   c  show a second preferred embodiment;  
         [0011]      FIGS. 3   a  and  3   b  show a third preferred embodiment;  
         [0012]      FIGS. 4   a - 4   c  show a fourth preferred embodiment; and  
         [0013]      FIGS. 5   a - 5   c  show other preferred embodiments.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     Preferred embodiments of the present invention will now be set forth in detail with reference to the drawings.  
         [0015]      FIG. 1   a  is a side view sectional schematic of a vacuum chamber stage  100  used for precision positioning of the semiconductor wafer or substrate  103  while the substrate is maintained in a vacuum chamber  117 . The object of the apparatus is to expose the substrate to some sort of a manufacturing, processing or inspection for the purpose of manufacturing microelectronics circuits there on. Typically the substrate is exposed to some sort of radiation; examples of the many species of radiation would include but are not limited to Ions, x-rays, ultraviolet or extreme ultraviolet, electron beams, DUV (deep ultraviolet), extreme ultraviolet (soft x-rays) and visible light. Often this radiation needs to be conditioned by such devices as analyzers, magnets, mirrors or optics. This conditioning of radiation in this illustration is provided for in the area indicated by  119 . This conditioning assembly is connected directly to the base reference member  104  with its output aperture  118  aligned with a consummate aperture  101  in the first reference plate  104 .  
         [0016]     Vacuum ports  225  for high vacuum conductance can be arrayed around the aperture  202  and connected on the opposite side of the base reference plate  206  to a manifold  203  connected to a cryopump or other low-pressure device. This arrangement allows for excellent conductance of pressure away from the area of interest. The ports may breakthrough into the wall of the aperture as in  102 , or they may be completely through base reference plate  206  and arrayed around the aperture  202 , as in  FIG. 2   a . Alternatively, or in addition, ports  102  could be used for directing radiation on an angle rather than normal to the surface of the substrate  103  with appropriate detectors arranged as needed, as for example is often the case in thin film measuring (ex. scatterometry and ellipsometry). The first reference plate  104  may be made from hard coated or nickel coated aluminum, nickel coated steel or stainless steel. Other materials such as ceramics or carbon fiber could also be considered. Important considerations are that the material be vacuum compatible, and the undersurface  106  may be made suitably flat to be used as an air bearing surface, and that the material have the structural strength to withstand the significant atmospheric pressures that may be applied to it without experiencing unaccepted distortions. The first reference plate  104  is shown as a simple plate for simplicity. It could easily be designed with structural ribs on the back; these ribs could also couple to additional mounting points for the radiation conditioning device providing a stiffer, firmer mount than the flange mount shown for simplicity. Avoiding distortions from atmospheric pressures is not a trivial issue; thousands of pounds of force will be equally distributed across a face of the vacuum chamber which will move around on the base reference plate. It is important that the reference base plate  104  remain flat because the smaller the air gap that can be used in the air bearing without contact the more efficient the lands between the differentially pumped grooves become. Engineering techniques for calculating and modeling these forces, including finite element analysis, are well-known in the art and need not be repeated here.  
         [0017]     The vacuum chamber stage  114  with air bearing  115  and differentially vacuum pumped grooves  116  is urged against the lower surface  106  of the first reference plate  104  by thousands of pounds of atmospheric pressure. As air bearing surfaces  115  on the vacuum chamber stage  114  come within a thousandth of an inch of the reference base plate surface  106 , pressure builds up in the gap  156  between them until equilibrium is reached. The stage then rides on this pressurized film of air, using atmospheric pressure as a preload force to create a very stiff, well damped air bearing free to translate in X, Y and theta. As with the first reference base plate  104 , it is important that the vacuum chamber stage  114  have the requisite stiffness not to deform from the thousands of pounds of atmospheric pressure urging it toward the reference plate  104 . The air bearing surface  115  in this preferred embodiment employs porous media compensation. Other air bearing compensation may be employed including but not limited to orifice and step compensation. Air bearings are a widely accepted art, much has been written about orifice and porous type air bearings, for porous media air bearings (see  FIG. 1   b ). Porous media air bearings are most commonly made from porous carbon or graphite but may be made from porous alumina or silicon carbide. Carbon and graphite have excellent crash resistance and are very tolerant of inadvertent bearing face contact. Differentially pumped grooves are also well known in the art and are illustrated in  FIG. 1   b . Notice that in this preferred embodiment the grooves get wider and deeper progressively with lower air pressures. This is consistent with minimizing restriction and maximizing conductance of pressure away from the air bearing land areas.  
         [0018]     This embodiment can be arranged so as to make it relatively simple to get a wafer  103  in and out of the vacuum chamber stage  114 . A 25 mm×325 mm aperture  105  can be arranged in the side of a vacuum chamber stage  114 , the vacuum chamber stage  114  can be physically docked against the load-unload station  107  see  FIGS. 1   c  and  2   c  for the passing of wafers  103  in and out of the chamber without the introduction of atmospheric pressure to the chamber. Commercially available, but not shown, vacuum gates will be required.  
         [0019]     By allowing for X and Y motions in a single plane it becomes convenient to use reference mirrors in the plane of the wafer and to drive the vacuum chamber stage through its center of mass. It is also possible to use reaction masses and service stages to improve the stage performance.  
         [0020]     It is not necessary but it would be wise to provide another mechanism to urge the vacuum chamber stage  114  against the first reference plate  104 . In the event that the vacuum chamber stage  114  loses the vacuum in the chamber  117 , gravity would separate the vacuum chamber stage  114  from the first reference plate  106 . This would result in a temporary unrecoverable situation. To avoid this situation, air bearings  111  acting upon a second reference plate or base  110  can be employed to urge the vacuum chamber stage  114  against the first reference plate  104  through a constant force springs mechanism  112 .  
         [0021]     The chuck  109  may be an electrostatic chuck or another chuck technology appropriate for vacuum. The chuck  109  may be mounted on a Z actuator or lifter mechanism  108  for the purpose of raising or lowering the substrate  103  in the VCS, for instance to facilitate substrate changes or to achieve a depth of field adjustment or fine planerization of the substrate. Many techniques known in the art are possible including piezos, super Z&#39;s, flexures or other mechanical lifters.  
         [0022]      FIG. 2   a  shows a side view sectional view of a second preferred embodiment. This embodiment allows for the VCS  210  to contain an isolated vacuum chamber  223  as before but also operate in a vacuum  207 . This can be a important feature minimizing problems which could occur regarding water vapor adhering to the first  222  or second  216  reference surfaces while the VCS is not over that area. This is accomplished by repeating the air bearing  214  and differentially pumped grooves  211  on the underside of the vacuum chamber stage  210 . This is essentially two opposed mirror images.  
         [0023]     A radiation source  201  can have a high conductance manifold  203  arrayed around the interface with the base reference plate  206 . This manifold is attached to a vacuum pump via large aperture tube  204 . Ports  225  through the first reference plate  206  surround the area of interest for good conduction, but are not necessary in all applications. The annular air bearing  214  is separated from the vacuum chamber  223  by differentially pumped grooves and seal lands  211  which are serviced by tubes from the motion system. This pattern is repeated exactly on the opposite side of the vacuum chamber stage  210 . This second set of air bearing lands and differentially pumped grooves bear on surface  216  which is the top of the second reference plate  209 . The opportunity exists to make the air bearing land area  214  smaller because in this embodiment the opposite pressures in the air bearing lands, grooves and chamber are exactly equal due to the fact that they are ported through common connections  217 ,  218 ,  220  and  221  to their source through  250 ,  251 ,  252  and  253 . The pressurized air gaps  215  are preloaded against each other only. The air bearing  214  running on the second reference base  209  will be carrying the gravity load of the vacuum chamber stage  210  which would likely be 20 lbs. plus or minus an order of magnitude. The preload force between the bearings can easily be 10 times (one order of magnitude more than this gravity force), making the gravity force inconsequential. This allows the VCS to operate in a vacuum with the lowest pressure inside the VCS and isolated from contamination or pressure.  
         [0024]      FIGS. 3   a  and  3   b  are sectional views of an X and Y vacuum chamber stage with rotation, and a differentially pumped port for transfer of the wafers or substrates and or high conductance pumping port, as in a third preferred embodiment.  
         [0025]     Some applications, like thin film characterization, often employ rotation of the wafer. The embodiment of  FIGS. 3   a  and  3   b  provides for rotation inside of an XY stage. By employing annular 360 degree radial air bearing surfaces isolated from the pass though by 360 degree radial differential pumped grooves and lands. As the XY stage is moved about, the radial bearings keep the rotating part centered. The XY stage carries a rotary actuator to spin the rotation part of the stage; it is possible to add an encoder. It is possible with differentially pumped grooves on outside of these bearings to operate the whole assembly in a vacuum environment. It will be necessary to vent the volume that the upper and lower  3  bearing set commonly leak into, it will also be necessary to vent the area under the rotating member to avoid pressure build up. An area  314  is provided for the motor and the encoder.  
         [0026]      FIG. 4    a, b, c  show a device and method for ion implantation of substrates such a semiconductor wafers as in a fourth preferred embodiment. Ion implantation has moved from batch processing to serial processing. Serial processing provides more flexibility in the recipe that is administered to each wafer and more flexibility in the attitude of the wafer to the ion radiation, being able to pitch and rotate the wafer so as to dope or expose the sides of the via and the trenches equally. In order to keep throughput high, makers of ion implantation equipment have been migrating from spot or point beams that were scanned across the wafer in batch process to “ribbon” type beams. Ribbon type beams are slightly wider than the substrate or wafer being processed. The substrate may then be passed through the ribbon beam, exposing the whole substrate surface to the radiation. The beam may be a thin ribbon; 0.25 in, or a thick ribbon; 4 in. The thickness of the ribbon beam has an effect on the required travel of the wafer, which must pass though the entire ribbon before reversal.  
         [0027]      FIG. 4   a  represents the preferred embodiment of the vacuum chamber stage device and method for modern ion implantation. The beam  409  in this case comes from below with the first reference plate  405  and vacuum chamber stage  403  nominally horizontal, although this could easily be reversed or at 45 degrees. The vacuum chamber stage  403 , as in previous embodiments is urged against the opposite side  413  of the first reference plate  405  from the radiation source by atmospheric pressure  
         [0028]     The vacuum chamber stage  403  is actuated by a motion system  417  outside of the vacuum area  402 . The guidance for the motion system  418  could be from air bearings or rolling element bearings. In ion implantation motion characteristics are not as critical as in other precision applications and roller bearings would be an appropriate choice. The connection between the vacuum chamber stage  403  and the motion system  417  and actuators  418  could be with a blade flexure  450  which would decouple the vacuum chamber stage  403  from the drive and guide system in the Z direction which is constrained by the air bearing and atmospheric pressure against the vacuum chamber stage as in  FIG. 4   c . In this embodiment is not necessary to run vacuum services to the vacuum chamber stage  403 . Because the motion on the vacuum chamber stage is linear only with respect to the base reference plate  405 , holes or ports  415  through the first reference plate which aligned to the grooves  411  can be used to conduct pressure out of the grooves  411 . Holes or ports  414  through the first reference plate  405  may also be used to conduct pressure from the chamber directly around the area of interest. These holes may be on an angle to clear the beam  409  during tilting. The chuck  406  holding the substrate or wafer  407  is mounted to a rotary actuator  401  through a Ferro fluidic, mechanical contact seal or air bearing with differentially pumped grooves. Continuous rotation is not required in this embodiment, only the ability to index 90 or 180 degrees, 90° in order to be able to get all the orthogonal groves and trenches, and 180 degrees in order to avoid tilting the plate in both directions as shown in  FIG. 4   b . Notice the whole reference plate may be tilted with respect to the Ion or radiation source. This tilting action, combined with a rotary motion allows complete coverage of all surfaces on the substrate including the sides of the via and trenches. This embodiment also allows for constant focus or distance from the Ion or radiation source providing the most uniform doping of the substrate.  
         [0029]     Still further embodiments are possible, as will be described with reference to  FIGS. 5   a - 5   c .  FIG. 5   a  shows two VCS&#39;s on reference members on opposite sides of a cylindrical member.  FIG. 5   b  shows a VCS on a reference member incorporating components for writing and measuring a workpiece.  FIG. 5   c  shows two VCS&#39;s on opposite sides of an opening in a single reference member.  
         [0030]     While preferred embodiments have been set forth in detail above, those skilled in the art who have reviewed the present disclosure will readily appreciate that other embodiments can be realized within the scope of the invention. For example, the invention can be used in a variety of applications other than those set forth in detail, such as display screens and MEMS. Therefore, the present invention should be construed as limited only by the appended claims.