Electricity: motive power systems – Positional servo systems
Reexamination Certificate
1999-11-10
2001-08-07
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Positional servo systems
C318S560000, C318S625000, C318S648000, C318S649000
Reexamination Certificate
active
06271640
ABSTRACT:
FIELD OF INVENTION
The present invention relates, in general, to electro-mechanical alignment and isolation and, more particularly, to such method and apparatus for supporting and aligning a wafer in a microlithographic system and isolating the system from its own reaction forces and external vibrations.
BACKGROUND OF THE INVENTION
Various support and positioning structures are known for use in microlithographic instruments. Typically, in the prior art, XY guides, including a separate X guide assembly and Y guide assembly, are utilized with one guide assembly mounted on and movable with the other guide assembly. Often, a separate wafer stage is mounted on top of these guide assemblies. These structures require high precision and many parts. Typically, external forces directed to parts of the positioning assembly and reaction forces due to movement of different parts of the assembly are coupled directly to the image forming optics and reticle handling equipment resulting in unwanted vibration.
U.S. Pat. No. 5,120,036 to Van Engelen et al. describes a two-step positioning device using Lorentz forces and a static gas bearing for an opto-lithographic device.
U.S. Pat. No. 4,952,858 is directed to a microlithographic apparatus utilizing electro-magnetic alignment apparatus including a monolithic stage, a sub-stage and isolated reference structure in which force actuators imposed between the monolithic stage and the sub-stage are used for suspending and positioning monolithic stage in space. In this apparatus a Y frame or stage is mounted on an X frame and the monolithic stage is positioned from and supported in space from the Y frame.
SUMMARY OF THE INVENTION
Broadly stated, the present invention is directed to method and apparatus utilizing a guideless stage for supporting an article and incorporating a reaction frame which isolates both external forces as well as reaction forces created in moving the object from other elements of the system such as a lens system which produces an image that is exposed on the photoresist of a wafer object surface.
The present invention incorporates an object stage, a reaction frame mounted on a base and substantially free from transferring vibrations between itself and the object stage, means for supporting the object stage in space independent of the reaction frame and cooperating force type linear actuator means mounted on the object stage and the reaction frame for positioning of the object stage. The object stage can be mounted for movement in a given direction or can constitute a XY, stage for movement in the X and Y directions while being supported in space in the Z direction.
A feature, an advantage of this invention is the provision of a support, positioning and isolation assembly which allows the positioning function of the object or wafer stage to be accomplished while minimizing vibrations coupled to the stage and lens systems from the reaction stage faster and with fewer parts while minimizing vibrations coupled to the stage and isolating the stage from undesired reaction forces.
In accordance with another aspect of the present invention, a positioning method and apparatus are provided for an XY stage with an independently moveable X follower and independently moveable Y follower and cooperating linear force actuators mounted between the stage and followers whereby the movement of either follower does not effect the movement of the other follower.
Another aspect of this invention is the provision on at least one follower of a pair of arms on the follower with each arm supporting a drive member and wherein the arms are positioned and movable in spaced apart planes above and below the center of gravity of the object stage.
In accordance with another aspect of the present invention, the guideless stage incorporates at least three linear force actuators with two of those actuators driving in one of the X or Y directions and the third actuators driving in the other of the X and Y directions. In accordance with the preferred embodiment of this invention the guideless stage incorporates at least four linear actuators operating between the XY stage and a reaction frame assembly with each actuator including a drive member on the XY stage so that a pair of X drive members serve to drive the XY stage in an X direction and a pair of Y drive members serve to drive the XY stage in the Y direction. The linear actuators and their drive members are constructed, positioned and controlled such that the vector sum of the moments of force at the center of gravity of the XY stage due to the positioning forces of cooperating drive members is substantially equal to zero.
These features and advantages of the present invention will become more apparent upon perusal of the following specification taken in conjunction with the following drawing wherein similar characters of reference refer to similar parts in each of the several views.
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patent:
Nikon Corporation
Oliff & Berridg,e PLC
Ro Bentsu
Smith Tyrone W
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