Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1999-04-19
2001-08-07
Berman, Jack (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S441110, C250S442110, C277S913000, C277S431000, C384S131000
Reexamination Certificate
active
06271530
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an apparatus for reducing the distortion of the bearing surfaces of a fluid bearing such as a gas bearing. The invention relates in particular to an ion implanter having such apparatus.
BACKGROUND OF THE INVENTION
As will be familiar to those skilled in the art, in a typical ion implanter a relatively small cross-section beam of dopant ions is scanned relative to a silicon wafer. Traditionally, a batch of wafers was mechanically scanned in two directions relative to a fixed direction ion beam.
Single wafer processing has several advantages over batch processing, such as increased flexibility of implantation and a reduction in the potential costs should the implantation process fail, requiring the wafer to be discarded. Single wafer processing is particularly preferred for larger wafers having a diameter of 300 mm or more.
For single wafer processing, it is desirable mechanically to scan the silicon wafer in one direction whilst electrostatically or electromagnetically scanning or fanning the ion beam in a second direction.
U.S. Pat. Nos. 5,003,183 and 5,229,615 show examples of a variety of different scanning mechanisms which are known for this purpose. WO-A-99/13488 shows a further device suitable for allowing mechanical scanning of a single wafer. In the device of WO-A-99/13488, the wafer is mounted upon a substrate holder in a process chamber of an implantation device. Attached to, or integral with, the substrate holder is an arm which extends through an aperture in the wall of the vacuum chamber. Mechanical scanning is effected by a scanning mechanism located outside the process chamber. The scanning mechanism is connected with the arm of the substrate holder and allows movement of the arm (and hence the substrate holder) relative to the process chamber.
To facilitate movement of the moving parts of the scanning mechanism, one or more gas bearings are provided. For example, the end of the arm distal from the substrate support may be attached to a first bearing member which moves reciprocally relative to a second bearing member. This allows the wafer to be mechanically scanned in a plane orthogonal to the ion beam of the ion implanter. Movement of the first bearing member relative to the second bearing member is facilitated via a first gas bearing.
Likewise, the second bearing member may itself be rotatable relative to the process chamber to allow tilting of the substrate support relative to the direction of ion beam. The second bearing member rotates against a stator mounted upon a flange adjacent the aperture in the wall of the process chamber; a second gas bearing is employed between the stator and the surface of the second bearing member to facilitate this rotation.
For successful operation of the gas bearings, the bearing surfaces must each be flat. Variations in flatness of more than 10 &mgr;m or so can cause one of the bearing surfaces to touch the other bearing surface. Whilst the bearing surface of the second bearing member and that of the stator may be made flat to this accuracy, the exterior surface of flange on the process chamber wall adjacent to the aperture therein tends to be relatively uneven. Thus, when the stator is bolted or otherwise affixed to that flange, the clamping forces generated can distort the bearing surface of the stator. This problem is exacerbated by the presence of a vacuum within the vacuum chamber: the force of atmospheric pressure on the outside (non-bearing) surface of the second bearing member can also contribute to distortion of the stator.
It is an object of the present invention to address this problem. More generally, it is an object of the invention to reduce the problems associated with distortion of the bearing faces in a fluid bearing.
SUMMARY OF THE INVENTION
These and other objects are achieved by the provision of a fluid bearing comprising: (i) a base; (ii) a stator attached to the base providing a first planar fluid bearing surface extending in a direction of movement; (iii) a moving member having a second planar fluid bearing surface extending over said first surface, said moving member being mounted to be movable relative to said stator in said direction of movement, said first and second bearing surfaces being adapted to allow the second surface to be supported spaced from said first surface by a bearing fluid, one of said stator and said base having a locating member extending normal to the plane of said first bearing surface and the other of said stator and said base having a recess shaped to receive said locating member; (iv) a fluid seal enabling said member to slide in said channel in said normal direction sealing off an enclosed volume between said member and said other of said stator and said base; (v) a plurality of fixtures at respective points distributed in a plane parallel to said first bearing surface to fix said locating member and said other of said stator and said base together at said points to form said enclosed volume, the number of said fixtures being the minimum necessary so that the first planar bearing surface of the said stator remains undistorted, and a fluid controller controlling the supply of a fluid to said enclosed volume to maintain said first planar bearing surface undistorted under the loading of said moving member.
Supplying a fluid to a volume defined between the locating member and the base or the stator provides a “cushion” which minimizes the distortion influence of the base upon the stator. This in turn improves the flatness of the first planar fluid bearing surface of the stator relative to the second planar fluid bearing surface of the moving member. Thus, the moving member may move relative to the stator more easily. This is because the thickness of the fluid bearing layer may be reduced when both bearing surfaces are mutually very flat. Previously, in order to avoid the second bearing surface of the rotor from contacting the first bearing surface of the stator (which tended to be distorted), a thicker fluid bearing layer was necessary. Reducing the fluid bearing layer thickness provides several advantages.
Preferably, the locating member is generally U-shaped in section, and the recess is correspondingly generally U-shaped in section to receive the said locating member. Most preferably, the locating member is arranged substantially perpendicular to said normal direction, and a corresponding base of said generally U-shaped recess is also arranged substantially perpendicular to said normal direction, the said enclosed volume being defined between the said base of the locating member and the said base of the recess. This shape allows the locating member to extend in a normal direction whilst providing a significant area generally perpendicular to that normal direction to provide a corresponding significant volume for the fluid seal.
In one preferred embodiment, the locating member defines an enclosed annulus in a plane perpendicular to said normal direction. For example, the stator may be circular in a plane perpendicular to the normal direction, and the moving member may be a rotor arranged to rotate relative to said stator about an axis parallel to said normal direction.
The use of an annulus is preferred when the movable member is arranged to rotate relative to the stator, as the annular shape is particularly suitable for supporting the stator against any loading forces introduced by the movable member in that configuration.
In that case, it is preferable that there are three of the fixtures distributed about the plane parallel to the first bearing surface. Three represents the optimum number of fixtures in the case where the rotor is arranged to rotate relative to the stator, particularly when they are distributed equidistantly about the enclosed annulus.
Alternatively, the locating member may be enclosed and generally rectangular in a plane perpendicular to said normal direction. Such configuration is preferred when the moving member is moved in one or more linear directions relative to the stator, rather than rotating relativ
Farley Marvin
Ryding Geoffrey
Sakase Takao
Smick Theodore H.
Applied Materials Inc.
Berman Jack
Tennant Boult Wade
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