Magnetic positioning device - Patent Review 5196745

Claims

What is claimed is:

1. A device for positioning a movable member having a first surface relative to a stationary member having a second surface, said first and second surfaces being adjacent each other, the device comprising:

a magnetic array mounted in one of said surfaces, said array having adjacent magnetic elements in the direction of movement which are adapted to be of opposite polarity;

a multiphase coil array mounted in the other of said surfaces, said other surface being formed of a material having low magnetic permeability;

said magnetic array and coil array being mounted so as to provide smooth, mating adjacent surfaces spaced from each other by a substantially uniform gap; and

means for selectively applying controlled currents to each phase of said coil array in a phase, amplitude and polarity to interact with said magnetic array to drive said movable member to a selected position relative to aid stationary member.

2. A device as claimed in claim 1 wherein said magnetic array is an array of permanent magnets, with adjacent magnets being oppositely poled.

3. A device as claimed in claim 2 wherein said array of permanent magnets are flush mounted in said first surface.

4. A device as claimed in claim 1 wherein each of said arrays has a pitch, and wherein said pitches are integral multiples of each other.

5. A device as claimed in claim 4 wherein said pitches are substantially equal.

6. A device as claimed in claim 1 wherein forces generated when currents are applied to said coil array have a component parallel to the arrays and a component perpendicular to the arrays, wherein the parallel component is operable to move the movable member to the selected position, and including means for utilizing the perpendicular component to support the movable member, and to thereby maintain said gap.

7. A device as claimed in claim 6 wherein said moving member has a weight which may vary, and including means for varying the perpendicular force applied to the moving member to maintain a desired gap between said first and second surfaces.

8. A device as claimed in claim 7 including a ferrous backing sheet for said coils, said means for varying including means for varying the spacing between the backing sheet and the coil array.

9. A device as claimed in claim 1 including means for maintaining a desired gap between said first and second surfaces.

10. A device as claimed in claim 9 wherein said gap maintaining means includes first and second magnetic elements mounted respectively to said moving member and said stationary member, said elements being adjacent mounted and being poled to counteract the effects of gravity on the moving member.

11. A device as claimed in claim 10 wherein the first magnetic element is mounted to the bottom surface of the moving member and the second magnetic element is mounted to the adjacent surface of the stationary member; and

wherein said magnetic elements are poled to repel.

12. A device as claimed in claim 10 wherein the moving member has a weight which may vary, and wherein at least one of said magnetic elements is movable in a direction perpendicular to said gap to permit a desired gap to be maintained regardless of variations in moving member weight.

13. A device as claimed in claim 10 wherein one of said magnetic elements is sufficiently larger than the other so that said magnetic elements are fully coupled regardless of any allowed movement of said platen.

14. A device as claimed in claim 1 wherein said coil array is at least a three phase array.

15. A device as claimed in claim 1 wherein the relative movement between said members is in at least a first degree of freedom parallel to said surfaces; and

including means for controlling the relative position of said members in other selected degrees of freedom.

16. A device as claimed in claim 15 wherein said means for controlling includes means for indicating a desired relative position for each of said degrees of freedom, means for detecting deviations from desired position for the degrees of freedom, and means responsive to a detected deviation for applying an electromagnetic force to the moving member in a direction to move the moving member to the desired relative position.

17. A device as claimed in claim 16 wherein said means for applying an electromagnetic force includes electromagnet elements mounted to the stationary member, a ferrous element mounted to the moving member adjacent each electromagnet element, each said electromagnet element/ferrous element pair being positioned to move the moving member in at least one degree of freedom when the electromagnet element is energized, and means responsive to a detected deviation for selectively energizing the electromagnet elements.

18. A device as claimed in claim 15 wherein there are at least two magnetic array/coil array pairs for controlling motion in said first degree of freedom.

19. A device as claimed in claim 18 wherein for each magnetic array/coil array pair on one side of the moving member, there is a corresponding magnetic array/coil array pair on the opposite side of the moving member

20. A device as claimed in claim 18 wherein the first surface is the bottom surface of the moving member, and wherein there are two symmetrically positioned magnetic arrays in said first surface, there being an adjacent corresponding coil array for each of said magnetic arrays.

21. A device as claimed in claim 20 wherein there is a magnetic array in the top surface of the moving member substantially opposite each magnetic array in the bottom surface, there being an adjacent corresponding coil array for each of said magnetic arrays.

22. A device as claimed in claim 18 wherein there is at least one magnetic array in the bottom surface of said moving member and a magnetic array in each of the two side surfaces of the member parallel to said first degree of freedom, there being an adjacent corresponding coil array for each of said magnetic arrays.

23. A device as claimed in claim 15 wherein said means for controlling includes at least one magnetic array/coil array pair for controlling relative movement between said members in a second degree of freedom.

24. A device as claimed in claim 23 wherein there are two symmetrically positioned magnetic arrays oriented parallel to the first degree of freedom and two symmetrically positioned magnetic arrays oriented parallel to the second degree of freedom in at least one of the top and bottom surfaces of the moving member, there being an adjacent corresponding coil array for each magnetic array.

25. A device as claimed in claim 23 wherein one array of each magnetic array/coil array pair for controlling motion in the first degree of freedom is sufficiently wider in the direction of the second degree of freedom than the other array so that the arrays fully overlap regardless of any allowed movement in the second degree of freedom, and wherein one array of each magnetic array/coil array pair for controlling motion in the second degree of freedom is sufficiently wider in the direction of the first degree of freedom than the other array so that the arrays fully overlap regardless of any movement in the first degree of freedom.

26. A device as claimed in claim 23 wherein said magnetic arrays are in the bottom surface of the moving member.

27. A device as claimed in claim 1 including means for detecting the relative position of the members in at least a first degree of freedom, means for indicating a selected relative positions in said first degree of freedom, and wherein said means for selectively applying includes means responsive to the detected relative position and the selected relative positions for producing control currents to move the movable member in said first degree of freedom toward the selected relative position.

28. A device as claimed in claim 27 wherein said means for producing control current includes a linear feedback compensator.

29. A device as claimed in claim 27 wherein said means for producing control current includes a nonlinear geometric compensator to compensate for changes in relative positions of the center of mass of the moving member as it is moved relative to the stationary member.

30. A device as claimed in claim 27 wherein said means for producing control current includes a commutation circuit to compensate for nonlinearities in the control currents as a function of relative position.

31. A device as claimed in claim 27 wherein said means for detecting and said means for indicating are for two degrees of freedom, wherein there is at least one magnetic array/coil array pair for controlling relative movement in each of said two degrees of freedom, and wherein said means for producing control currents produces control currents to the coil arrays to move the movable member in said two degrees of freedom to the selected relative position.

32. A device as claimed in claim 31 wherein there are two symmetrically positioned magnetic array/coil array pairs for each degree of freedom, each magnetic array being oriented in the direction of the degree of freedom it controls and being in at least one of the bottom and top surfaces of the moving member, and wherein the means for producing control currents produces appropriate control currents for each coil array to move the movable member to the selected relative position.

33. A device as claimed in claim 27 wherein said means for detecting includes interferometric detectors for detecting relative movement and capacitive detectors for detecting relative positions.

34. A device as claimed in claim 1 wherein at least said movable member is formed of a cellular composite material.

35. A device as claimed in claim 1 including a damping fluid in said gap.

36. A device as claimed in claim 35 wherein said gap damping fluid is a ferrofluid.

37. A device as claimed in claim 1 wherein said device is a fine positioning stage of a positioning system, the stationary member being mounted to a movable frame of a system coarse positioning stage.

38. A device as claimed in claim 1 wherein the adjacent mating surfaces of said magnetic array and said coil array are planar surfaces.

39. A device as claimed in claim 1 wherein at least selected ones of said coil arrays are formed of a plurality of independently energized coil arrays spaced in the direction of movement by a distance less than the extent in the direction of movement of the corresponding magnetic arrays.

40. A device for positioning in at least two degrees of freedom a movable member having a top and bottom surface relative to a stationary member having corresponding surfaces adjacent to at least one of said top and bottom surfaces, the device comprising:

at least one magnetic array mounted in one of said member surfaces for each of said degrees of freedom, each of said arrays having adjacent magnetic elements in the direction of the degree of freedom which elements are of opposite polarity;

a multiphase coil array for each magnetic array mounted in the surface adjacent said one surface of the other member;

each magnetic array/coil array pair being mounted so as to provide smooth, mating adjacent surfaces spaced from each other by a substantially uniform gap; and

means for applying controlled currents for each phase of each of said coil arrays in a phase, amplitude and polarity to interact with the corresponding magnetic array to drive the movable member in said at least two degrees of freedom to a selected position relative to said stationary member.

41. A device as claimed in claim 40 wherein there are two symmetrically oriented magnetic arrays in at least one of said top and bottom surfaces for each of a first and a second degree of freedom, there being corresponding adjacent coil arrays in adjacent surfaces of said stationary member; and

wherein said means for applying includes, means for detecting the relative positions of said members in six degrees of freedom, means for indicating desired relative positions for the members in said six degrees of freedom, and means responsive to a detected relative position in a degree of freedom being different than the desired relative position in such degree of freedom for applying currents to at least selected ones of said coil arrays to move the movable member to the desired position.

42. A device as claimed in claim 41 said first and second degrees of freedom are both substantially parallel to the surfaces spaced by said gap and are substantially perpendicular to each other.

FIELD OF THE INVENTION

This invention relates to precision positioning devices, and more particularly to a device which provides for extended movement in one or two degrees of freedom while maintaining precision control in multiple degrees of freedom.

BACKGROUND OF THE INVENTION

There are many applications where an object must be positioned in multiple degrees of freedom, for example six degrees of freedom, with high precision in the nanometer range, while also being movable, generally in one or two such degrees of freedom, over a greater range, for example 200 to 300 millimeters with, for example, 10 nm accuracy Such applications might include scanned probe microscopy; however, the primary application would be in precision, mechanically suspended linear slides in XY stages, such as those used in the motion control subsystem of a photolithographic machine for producing semiconductor integrated circuits.

Current wafer stepping machines use compound axes in coarse/fine stages to achieve travels of about 200 mm in X and Y with resolution better than 100 nm. The camera head may be moved on flexures to provide Z-axis focusing motion. Such devices are relatively large and heavy and achieve positioning in six degrees of freedom through use of numerous actuators, including rack and pinion or ball screws for the coarse motion and piezoelectric or miniature hydraulic actuators for the fine motion. Thus, the overall system is complex and is also very expensive. It is also difficult to design each stage to be free of resonances, and thus to provide fast settling times as the stage moves from one chip site to another.

In order to reduce complexity both in the system itself and in the design thereof, magnetically-suspended XY stages have been proposed for such applications. Copending application Ser. No. 632,965, filed Dec. 20, 1990, teaches a magnetic bearing which may be utilized for maintaining the position of an object with a high degree of precision and for making small position adjustments which would typically not exceed 250 microns in any direction. Such a stage could therefore be used only for very fine positioning, and one or more additional coarse positioning stages would be required to achieve the degree of movement required for XY positioning applications such as in photolithographic machines for semiconductor fabrication.

A need therefore exists for an improved positioning device which would provide positioning control in the 10 nm range, preferably in six degrees of freedom, while permitting movement with good acceleration and settling time over a range of several hundred mm, for example 200 to 300 mm, preferably in both the X and Y direction. Such magnetic positioning device might also provide the capability for controlled movement in the Z direction (i.e. in a direction perpendicular to a work surface), also with precision in the 10 nm range.

While many magnetic linear positioning devices are described in the literature, most of these devices provide for motion in only a single direction. Further, such devices employ toothed magnetic elements and/or toothed or slotted electromagnetic actuators. This results in a cogging when no actuating current is applied to the device, or, in other words, in detenting occurring at certain preferred positions. This means that the only way a precision position can be maintained which is not one of the detent positions is to maintain current in the coils, which current must be sufficient to overcome the detent effect This cogging effect thus makes it far more difficult to achieve precise positioning with fine resolution, makes it harder to maintain stability of the device at a precisely determined position, and increases the time required to stabilize the device at a desired position. Teeth on the magnets and/or on the coils are therefore undesirable.

Further, where coils are in slots or on an iron core, as is the case for most prior art linear actuators, the device has a narrower frequency response, and also has a non-linear hysteresis curve which makes the device harder to control and results in some energy losses. Such hysteresis losses, in conjunction with eddy currents which also exist in such cores, reduce the high frequency response and power efficiency of the device. All of this results in poor stiffness for the device, or in other words, in decreased stability.

Existing devices also normally operate in a stepping mode. However, there are applications, for example in semiconductor fabrication, where a scanning mode of operation is desirable wherein movement from a first point to a second point is accomplished at a precisely controlled speed. This permits exposure to be performed along a strip which allows a simpler optical design in the exposing lens.

A need therefore exists for an improved positioning device which is preferably capable of positioning an object in the X and Y degrees of freedom with travel in the 200 to 300 mm range with 10 nm resolution, and with good acceleration and stabilization times. The device should also be capable of maintaining a desired position for the object in six degrees of freedom with the same level of resolution, should be of lower cost than existing systems and should permit operation in either a stepping mode or a scanning mode.

SUMMARY OF THE INVENTION

In accordance with the above, this invention provides a device for positioning a movable member relative to a stationary member, which members have at least one pair of adjacent surfaces. A magnetic array is mounted in one of the adjacent surfaces, the array having a plurality of adjacent magnetic elements aligned in the direction of movement, which elements are oppositely poled. The magnetic elements are preferably permanent magnets, with adjacent magnets being oppositely poled and the array of permanent magnets is preferably mounted in the adjacent surface of the moving member. A multiphase coil array is also provided which is mounted in the other adjacent surface in a position to electromagnetically interact with the magnetic array The magnetic array and the coil array are preferably mounted so as to provide smooth, mating adjacent surfaces spaced from each other by a substantially uniform gap. Controlled currents are selectively applied to each phase of the coil array in a phase, amplitude and polarity to interact with the magnetic array to drive the moveable member to a selected position relative to the stationary member.

Each of the arrays has a pitch, which pitches are a substantially integral multiple of each other and are preferably substantially equal. The forces generated when currents are applied to the coil array have a component parallel to the arrays and a component perpendicular to the arrays. The parallel component is preferably operable to move the moveable member to the selected position while the perpendicular component may be utilized to support the weight of a moveable member and thereby to maintain the gap between the members. Where the weight of the moveable member may be varied, a means may also be provided for varying the perpendicular force applied to the moving member to maintain a desired gap between the adjacent surfaces of the members. The means for varying the perpendicular force may include varying the spacing between a ferrous backing sheet for the coils and the coil array.

A desired gap between the adjacent surfaces may be maintained in a number of ways including providing first and second magnetic elements mounted respectively to the moving member and the stationary member, which elements are adjacent mounted and poled to counteract the effects of gravity on the moving member. The first magnetic element is preferably mounted to the bottom surface of the moving member, and the second magnetic element is preferably mounted to the adjacent surface of the stationary member with the magnetic elements being poled to repel. Where the moving member has a weight which may be varied, at least one of the magnetic elements may be moveable in a direction perpendicular to the gap to permit a desired gap to be maintained regardless of variations in the weight of the moving member.

The coil array preferably has at least three phases. The relative movement between the members is in at least a first degree of freedom parallel to the adjacent surfaces, with the relative position of the members also being controlled in other selected degrees of freedom. The control in other selected degrees of freedom may be accomplished by indicating a desired relative position for each of the degrees of freedom, detecting deviations from desired position for the degrees of freedom, and applying an electromagnetic force to the moving member in response to a detected deviation in a direction to move the moving member to the desired relative position. For some embodiments, electromagnetic force is applied to the moving member by electromagnetic elements mounted to the stationary member, with a ferrous element being mounted to the moving member adjacent each electromagnetic element. Each electromagnetic element/ferrous element pair is positioned to move the moving member in at least one degree of freedom when the electromagnetic element is energized, the electromagnetic elements being energized in response to a detected deviation.

For preferred embodiments, there are at least two magnet array/coil array pairs for controlling motion in a first degree of freedom. For one embodiment, there is a magnetic array/coil array pair on one side of the moving member for each such pair on the opposite side. The adjacent surface for the moving member is preferably its bottom surface, and there are preferably two symmetrically positioned magnetic arrays on such bottom surface for each degree of freedom in which the array is to be driven, with an adjacent corresponding coil array on the stationary member for each of the magnetic arrays. Other possible configurations include having like numbers of magnetic arrays on the top and bottom surfaces of the moving member, and having magnetic arrays on opposite sides of the moving member along with a magnetic array on the bottom of the member. For all embodiments there are one or more corresponding adjacent coil array on the stationary membe