Stage counter mass system

• US 20040158427A1
• Filed: 02/11/2003
• Published: 08/12/2004
• Est. Priority Date: 02/11/2003
• Status: Active Grant

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Ueta, Toshio, Binnard, Michael, Yuan, Bausan, Novak, W. Thomas
• Granted Patent: US 6,963,821 B2
• Time in Patent Office: Days
• US Class Current: 702/169
• CPC Class Codes: B23Q 11/0032 Arrangements for preventing or isolating vibrations in parts of the machine B23B29/022, B23D47/005 take precedence; means for damping or suppressing vibrations, in general F16F
• CPC Class Codes: G03F 7/70725 control
• CPC Class Codes: G03F 7/70766 Reaction force control means, e.g. countermass

Abstract

A wafer stage countermass assembly generally includes a base supporting one or more stages and first and second countermasses. The first and second stages move in one or more degrees of freedom. The countermasses move in at least one degree of freedom and, under ideal conditions, move to counter the movement of the stages in operation and thus preserve the systems center of gravity to avoid unwanted body motion. However, under actual conditions the countermasses may under travel or over travel their ideal trajectory. To more closely track the ideal trajectory, a controller actuates trim motors to apply small forces to the countermasses to push them towards a reference position in the Y direction. A second embodiment also takes into account the X position the stage(s) to cancel torque.

Claims

1. A method for maintaining a center of gravity for a stage and a countermass system in a fixed location comprising at least one moving stage and at least two countermasses, the method comprising the steps of:

calculating a target position for said at least two countermasses according to a position of said at least one stage; and

pushing said at least two countermasses towards said target position based on said calculating step.

2. The method according to claim 1, wherein said pushing step includes applying predetermined forces to the at least two countermasses to push the at least two countermasses towards said target position.

3. The method according to claim 2, wherein the applying of the predetermined forces substantially eliminates residual velocities, and maintains conservation of momentum.

4. The method according to claim 2, wherein the applying of the predetermined forces does not require advance knowledge of a trajectory of the at least one moving stage.

5. The method according to claim 2, wherein the predetermined forces are equal but opposite forces applied to each of the at least two countermasses.

6. The method according to claim 1, wherein the system comprises at least two stages and said target position is given as:

7. The method according to claim 6, wherein the predetermined forces are equal but opposite forces applied to each of the at least two countermasses and further maintain a combined center of gravity of the at least two stages and countermasses constant.

8. The method according to claim 1, wherein said at least two countermasses are first and second countermasses which move substantially symmetrically around said target position.

9. The method according to claim 1, wherein said at least one stage is one stage and said target position is given as:

10. The method according to claim 1, wherein said target position is an average position of the at least two countermasses at any time.

11. The method according to claim 10, wherein any additional motion of said at least two countermasses is substantially symmetrical about the average position maintains conservation of momentum and eliminates substantially all of the center of gravity shift of the stage.

12. A control method for maintaining a center of gravity for a stage and a countermass system comprising a moving stage and at least two countermasses having different target positions, the method comprising the steps of:

calculating the target positions for said at least two countermasses according to a position of said stage, said calculating step allowing for a weight factor to trade off torque cancellation for reduced countermass stroke; and

pushing said at least two countermasses towards said different target positions.

13. The method of claim 12, wherein said different target positions are given as:

14. The method according to claim 13, wherein the weight factor, w, is between 0 and 1.

15. The method according to claim 13, wherein:

when w=0, y1=y2 and when the stage moves in the Y direction, torque is transferred to ground;

when w=1, the different target positions of the two countermasses are unequal and when the stage moves in the Y direction, there will be no net torque transferred to ground.

16. The method according to claim 14, wherein w=0.5.

17. A system for maintaining a center of gravity for a stage and a countermass system in a fixed location comprising at least one moving stage and at least two countermasses, the system comprising:

a controller that calculates a target position for said at least two countermasses according to a position of said at least one stage; and

a motor that pushes said at least two countermasses towards said target position based on said calculating.

18. The system according to claim 17, wherein said motor applies a predetermined forces to the at least two countermasses to push the at least two countermasses towards said target position.

19. The system according to claim 18, wherein the predetermined forces substantially eliminates residual velocities, and maintains conservation of momentum.

20. The system according to claim 18, wherein the motors apply equal but opposite forces to each of the at least two countermasses.

21. The system according to claim 17, wherein the system comprises at least two stages and said target position is given as:

22. The system according to claim 17, wherein said at least one stage is one stage and said target position is given as:

23. A control system for maintaining a center of gravity for a stage and a countermass system comprising a moving stage and at least two countermasses having different target positions, the system comprising:

a controller that calculates the target positions for said at least two countermasses according to a position of said stage, said calculating step allowing for a weight factor to trade off torque cancellation for reduced countermass stroke; and

a motor that pushes said at least two countermasses towards said two different target positions.

24. The control system of claim 23, wherein said different target positions are given as:

25. The control system according to claim 24, wherein the weight factor, w, is between 0 and 1.

26. The control system according to claim 23, wherein the stage includes a stage assembly comprising:

a wafer stage supported by a base;

a wafer table supported by the wafer stage;

an interferometer mirror IM mounted to the wafer table; and

a wafer chuck mounted on the wafer table, the wafer chuck adapted to hold a wafer.

27. A system for maintaining a center of gravity for a stage and a countermass system in a fixed location comprising at least one moving stage and at least two countermasses, the system comprising:

means for calculating a target position for said at least two countermasses according to a position of said at least one stage; and

means for pushing said at least two countermasses towards said target position based on said calculating step.

28. A system for maintaining a center of gravity for a stage and a countermass system in a fixed location, comprising:

at least two countermasses;

at least one guide bar having at least one stage disposed thereon, respectively, said at least one guide bar being mounted to the at least two countermasses;

a controller that calculates a target position for said at least two countermasses according to a position of said at least one stage; and

a motor that pushes said at least two countermasses toward said target positions.

29. An exposure apparatus, comprising:

an illumination system that projects radiant energy through a mask pattern on a reticle R; and

a system that reduces a stroke of at least two countermasses in an assembly comprising at least one moving stage and the at least two countermasses, the radiant energy being projected on a wafer positioned on the at least one moving stage, the system comprising;

a controller that calculates a target position for said at least two countermasses according to a position of said at least one stage; and

a motor that pushes said at least two countermasses towards said target position based on said calculating.

30. A device manufactured by a lithographic process using the exposure apparatus of claim 29.

31. A wafer on which an image has been formed by the exposure apparatus of claim 29.