Stationary vibration isolation system and method for controlling a vibration isolation system

Abstract

The invention relates to a stationary vibration isolation system and to a method for controlling such a system which comprises a damper effective in a horizontal direction which includes a fluid of variable viscosity.

Claims

1. A stationary vibration isolation system, comprising: a load that is anti-vibration mounted in a horizontal direction and vertical direction on a base and which comprises a moving mass; wherein the vibration-isolated load is coupled to the base via a first damper which is effective in the horizontal direction and which comprises a first fluid of variable viscosity, and wherein viscosity of the first fluid of variable viscosity increases as a direct consequence of changes in motion of the load in a horizontal direction.

2. The stationary vibration isolation system as claimed in claim 1, wherein the fluid is a non-Newtonian fluid.

3. The stationary vibration isolation system as claimed in claim 1, wherein the vibration isolation system which is an active vibration isolation system comprises at least one sensor for detecting vibrations of the anti-vibration mounted load and/or of the ground, and at least one actuator for actively reducing vibrations.

4. The stationary vibration isolation system as claimed in claim 3, wherein the actuator is a magnetic actuator.

5. The stationary vibration isolation system as claimed in claim 1, wherein the vibration-isolated load is coupled to the base via a second damper which is effective in the vertical direction and which comprises a second fluid of variable viscosity.

6. The stationary vibration isolation system as claimed in claim 1, wherein the first damper, which comprises the first fluid of variable viscosity, is arranged in a vibration isolator.

7. The stationary vibration isolation system as claimed in claim 6, wherein the vibration isolator is a pneumatic spring that is effective in vertical and horizontal directions.

8. The stationary vibration isolation system as claimed in claim 7, wherein the pneumatic spring comprises a piston that has an extension which is immersed in a chamber containing the fluid of variable viscosity.

9. A method for controlling a vibration isolation system, wherein said vibration isolation system comprises a lithography apparatus including a moving mass, wherein the method comprises: (a) passively damping, via a fluid of variable viscosity, at least some vibrations sourced from horizontal motion of the lithography apparatus; and (b) actively controlling, via actuators, at least some vibration sourced from an external environment, wherein, either directly or indirectly, due to said some vibrations sourced from horizontal motion of the lithography apparatus, viscosity of the fluid increases thereby stiffening the vibration isolation system and reducing an amount of vibration control provided by the actuators.

10. The method for controlling a vibration isolation system as claimed in claim 9, wherein the lithography apparatus is a stepper.

11. The method for controlling a vibration isolation system as claimed in claim 9, wherein the moving mass is a displaceable table.

12. The method for controlling a vibration isolation system as claimed in claim 9, comprising detecting vibrations of the lithography apparatus or of the ground by at least one sensor, and controlling at least one actuator for active vibration isolation based on the detected vibrations.

13. The method for controlling a vibration isolation system as claimed in claim 12, wherein in calculating a signal for controlling the actuator, both the vibrations of the ground or of the lithography apparatus detected by the at least one sensor and the detected motion of the mass are considered.

14. A stationary vibration isolation system, comprising a load that is anti-vibration mounted in a horizontal direction and vertical direction on a base and which comprises a moving mass; a damper that comprises a fluid of variable viscosity, wherein the damper is effective in the horizontal direction for coupling at least some vibrations from the load to the base; and an actuator that actively reduces at least some vibrations sourced from an external environment and introduced into the stationary vibration isolation system, wherein the damper functions independently of the actuator.

15. The stationary vibration isolation system of claim 14 and further wherein viscosity of the fluid increases as a direct consequence of changes in motion of the load.

16. The stationary vibration isolation system of claim 14 and further wherein the fluid of variable viscosity comprises an electrorheological fluid or a magnetorheological fluid, and wherein the stationary vibration isolation system further comprises: a sensor for sensing motion of the load; and a control circuit that controls viscosity of the fluid of variable viscosity.

17. The stationary vibration isolation system of claim 14 and further wherein the damper and the actuator are co-located in a vibration isolator.

18. The stationary vibration isolation system of claim 14 wherein the vibration isolator is a pneumatic spring that is effective in vertical and horizontal directions.

19. The stationary vibration isolation system of claim 14 and further wherein the damper is arranged so that it wherein the damper is effective in the vertical direction for coupling at least some vibrations from the load to the base.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically illustrates an exemplary active vibration isolation system.

(2) FIG. 2 illustrates the anti-vibration mounted load 2 coupled with the base or ground 4 via dampers 9.

(3) FIG. 3 schematically illustrates a vibration isolator 3 in which the fluid of the damper is integrated in the vibration isolator 3.

(4) FIG. 4 shows another schematic view, in which the illustrated vibration isolator is configured as a pneumatic spring including a working space 13.

(5) FIG. 5 shows another exemplary embodiment of a vibration isolator 3 which is likewise configured as a pneumatic spring including a working space 13.

(6) FIG. 6 shows a sectional view of a practical vibration isolator 3.

DETAILED DESCRIPTION

(7) The subject matter of the invention will now be explained in more detail with reference to the drawings of FIGS. 1 to 6 by way of schematically illustrated exemplary embodiments.

(8) FIG. 1 schematically illustrates an exemplary active vibration isolation system.

(9) In this vibration isolation system, the ground 4 is used as a base for receiving an anti-vibration mounted load 2. The anti-vibration mounted load 2 is coupled with the ground 4 via vibration isolators 3 which are typically configured as a pneumatic spring.

(10) Furthermore, the vibration isolation system comprises sensors. In this exemplary embodiment, sensor 5 is provided as a position sensor, sensor 6 as a speed or acceleration sensor of the anti-vibration mounted load 2 in the vertical direction, and sensor 7 as a sensor effective in the horizontal direction.

(11) By virtue of sensors 5, 6, 7 it is possible to use compensating signals to control an actuator 23, by means of a control device (not shown).

(12) In this exemplary embodiment, actuator 23 is integrated in vibration isolator 3. In particular a Lorentz motor is used as the actuator.

(13) Actuator 23 is effective both in the horizontal and vertical directions in this exemplary embodiment.

(14) The anti-vibration mounted load 2 comprises a lithography apparatus 1 which in this exemplary embodiment is configured as a displaceable table of a stepper that changes its direction of movement 8. Due to the acceleration caused thereby, forces are applied to the anti-vibration mounted load 2.

(15) The vibrations or motions of the anti-vibration mounted load 2 in form of a table together with components placed thereon may be counteracted by controlling actuator 23. However, with increasing size of the lithography apparatus 1, bigger and bigger actuators are required.

(16) Therefore, according to the invention, the anti-vibration mounted load 2 may be coupled with the base or ground 4 via dampers 9, as shown in FIG. 2.

(17) Dampers 9 comprise a fluid of variable viscosity (not shown), so that the damping effect is variable.

(18) Forces applied by the lithography apparatus 1 as a result of a motion of the displaceable table may now be diverted to the ground 4, due to a frictional connection via dampers 9, so that the requirements on the actuators of the system are reduced.

(19) FIG. 3 schematically illustrates a vibration isolator 3 in which the fluid of the damper is integrated in the vibration isolator 3.

(20) Vibration isolator 3 is configured as a pneumatic spring and includes a working space 13.

(21) A preferably controllable valve 14 may be used to control the pressure in the working space 13.

(22) Vibration isolator 3 further comprises a piston 11 on which the anti-vibration mounted load rests.

(23) Working space 13 is sealed on the piston side by a membrane 12 which is secured on the housing of working space 13 by means of a clamping ring 10.

(24) Above membrane 12, a seal 15 is arranged which enables to introduce a fluid between membrane 12 and seal 15, in particular a liquid of variable viscosity.

(25) Fluid 16 may be a non-Newtonian fluid, for passively changing the damping effect, or an electrorheological or magnetorheological fluid, for actively changing the damping effect.

(26) If now, due to a change of motion of a displaceable table, a force, in particular a horizontal force, is applied to the piston 11 which is rigidly connected to the anti-vibration mounted load, the viscosity of fluid 16 can be increased, whereby a frictional connection is established between piston 11 and clamping ring 10.

(27) At least horizontal force components may be diverted to the base in this manner, at least partially.

(28) FIG. 4 shows another schematic view, in which the illustrated vibration isolator substantially corresponds to the vibration isolator shown in FIG. 3, being configured as a pneumatic spring including a working space 13.

(29) A fluid 16 of variable viscosity is arranged between piston 11 and clamping ring 10. In this exemplary embodiment, the fluid is an electrorheological fluid 16.

(30) When installed in a vibration isolation system, isolator 3 is controlled by a control device 21. Control device 21 is connected to the lithography apparatus 1. Changes in the direction of movement 8 of the displaceable table are communicated from lithography apparatus 1 to control device 21. Based on this change of motion, the control device determines the force generated by lithography apparatus 1 and based thereon controls the power source 22 by means of which the viscosity of fluid 16 is controlled.

(31) Thus, the vibration isolation system comprises a feed-forward control which in the event of forces caused by the lithography apparatus, preliminarily achieves a frictional connection between the anti-vibration mounted load and the base.

(32) It will be understood that control device 21 moreover may be part of an active control and may additionally control actuators for active vibration isolation (23 in FIG. 1).

(33) FIG. 5 shows another exemplary embodiment of a vibration isolator 3 which is likewise configured as a pneumatic spring including a working space 13.

(34) This vibration isolator 3 likewise comprises a piston 11.

(35) Working space 13 is sealed by a membrane 12, which is secured on the housing of the working space by means of clamping ring 10.

(36) In this exemplary embodiment, piston 11 has an extension 18 which projects into the working space 13 of the isolator.

(37) Within working space 13, a chamber 17 is provided which is filled with a fluid 16 of variable viscosity.

(38) If the fluid is an electrorheological fluid, the viscosity of the fluid 16 may be controlled by applying a voltage between the wall of chamber 17 and extension 18.

(39) FIG. 6 shows a sectional view of a practical vibration isolator 3.

(40) It comprises working space 13.

(41) Piston 11 is movable relative to the working space both in the horizontal and vertical directions and may be fixed to the anti-vibration mounted load by means of fastening element 19.

(42) Furthermore, clamping ring 10 can be seen, by means of which the working space is sealed using a membrane.

(43) The piston now comprises extension 18 which projects into the preferably sealed chamber 17 which is arranged within the working space and which comprises a fluid 16 of variable viscosity.

(44) Vibration isolator 3 further comprises a foot 20 by means of which it may be fixed on the ground or on a base.

(45) By increasing the viscosity of fluid 16, a frictional connection may be achieved between piston 11 and the housing of working space 13 and thus ultimately between the anti-vibration mounted load and the base.

(46) The invention permits in a very simple manner to divert forces which are caused by an anti-vibration mounted load, in particular by a stepper, to the ground, at least partially, so that they do not need to be completely counteracted by actuators.

LIST OF REFERENCE NUMERALS

(47) 1 Lithography apparatus 2 Load 3 Vibration isolator 4 Ground 5 Sensor 6 Sensor 7 Sensor 8 Direction of movement 9 Damper 10 Clamping ring 11 Piston 12 Membrane 13 Working space 14 Valve 15 Seal 16 Fluid 17 Chamber 18 Extension 19 Fastening element 20 Foot 21 Feedback control device 22 Power source 23 Actuator