Multi-axis gas bearing stage assembly

A method of achieving orthgonality between X and Y axes of motion in an apparatus having an X-Y stage located with respect to a first Y-axis positioning elememt and a second Y-axis positioning element spaced apart by a distance L, comprising the steps of:

• a. recording a position Y.sub.1 (old) corresponding to a Y-axis coordinate of said first Y-axis positioning element relative to a first reference, and recording a position Y.sub.2 (old) corresponding to a Y-axis coordinate of said second Y-axis positioning element relative to a second reference;
• b. Calculating a differential value, Y(old), defined by
• .delta.Y(old)=Y.sub.1 (old)-Y.sub.2 (old);
• c. aligning a first alignment mark on said X-Y stage with a measurement standard while keeping .delta.Y(old) a constant;
• d. measuring X and Y displacement between said first alignment mark and said measurement standard, said measurements hereinafter called .delta.X.sub.a and .delta.Y.sub.a ;
• e. aligning a second alignment mark on said X-Y stage with said measurement standard while keeping .delta.Y(old) a constant, said second alignment mark being displaced a distance l in the X-direction from said first alignment mark;
• f. measuring X and Y displacement between said first alignment mark and said measurement standard, said measurements hereinafter called .delta.X.sub.b and .delta.Y.sub.b ;
• g. aligning a third alignment mark on said X-Y stage with said measurement standard while keeping .delta.Y(old) a constant, said third alignment mark being displaced a distance l in the Y-direction from said second alignment mark;
• h. measuring X and Y displacement between said first alignment mark and said measurement standard, said measurements hereinafter called .delta.X.sub.c and .delta.Y.sub.c ;
• i. calculating an orthogonality error angle, .delta..theta., defined by
• .delta..theta.=(.delta.Y.sub.b -.delta.Y.sub.a +.delta.X.sub.b -.delta.X.sub.c)/1;
• j. calculating a differential value, .delta.Y(new), defined by
• .delta.Y(new)=.delta.Y(old)-L.delta..theta.,
• where
• .delta.Y(new)=Y.sub.1 (new)-Y.sub.2 (new),
• where Y.sub.1 (new) is a new Y-axis coordinate for said first Y-axis positioning element, and Y.sub.2 (new) is a new Y-axis coordinate for said second Y-axis positioning element;
• and
• k. moving said first and second Y-axis positioning elements to Y.sub.1 (new) and Y.sub.2 (new), respectively, to reduce .delta..theta. to zero.

An X-Y-.theta. stage apparatus comprising:

• a base for guiding said X-Y-.theta. stage apparatus along an Y-direction and supporting said X-Y-.theta. stage apparatus along an orthogonal Z-direction;
• stage means for holding a workpiece;
• intermediate stage means for guiding said stage means along an X-direction orthogonal to said Z-direction and approximately orthogonal to said Y-direction, and supporting said stage means in said Z-direction, said intermediate stage means being oriented in said approximately orthogonal direction with respect to said Y-axis, and having a first end and a second end opposite said first end;
• bearing means for guiding said first end of said intermediate stage means along said Y-direction with respect to said base;
• X.sub.i -axis drive means for moving said stage means along said intermediate stage means in said X.sub.i -direction;
• first Y-axis drive means, positioned proximate to said first end of said intermediate stage means, for moving said intermediate stage means in said Y-direction;
• second Y-axis drive means, positioned proximate to said second end of said intermediate stage means, for moving said intermediate stage means in said Y-direction, said second Y-axis drive means operable independently of said first Y-axis drive means;
• and
• control means for controlling said first Y-axis drive means and said second Y-axis drive means for moving said intermediate stage means along a .theta.-direction, measured from an X-direction orthogonal to both said Y-direction and said Z-direction, about said Z-direction in a plane of motion comprising said X-direction and said Y-direction.

A method of achieving rotational alignment of a semiconductive wafer positioned on an apparatus having a stage guided and supported by an intermediate stage means, wherein said intermediate stage means is positioned in a Y-direction and a .theta.-direction, about a Z-direction orthogonal to a plane of motion of said intermediate stage element and including said Y-direction, by a first Y-axis positioning element and a second Y-axis positioning element spaced apart by a distance L, comprising the steps of:

• a. positioning said first and second Y-axis positioning elements such that said .theta.-direction orientation of said intermediate stage element is zero;
• b. load said semiconductive wafer on said stage of said apparatus;
• c. aligning a first alignment mark on a first side of said semiconductive wafer with a measurement standard, while keeping said .theta.-direction orientation of said intermediate stage element at zero, the alignment position coordinates hereinafter called X.sub.d and Y.sub.d ;
• d. aligning a second alignment mark on a second side of the semiconductor wafer, opposite said first alignment mark in a nominal X-direction, said X-direction also being in said plane of motion, being orthogonal to said Y-direction and said Z-direction, on said semiconductive wafer, with said measurement standard, while keeping said .theta.-direction orientation of said interminate stage element at zero, the alignment position coordinates hereinafter called X.sub.f and Y.sub.f ;
• e. calculating a new .theta.-direction orientation of said intermediate stage element, .theta.(new), defined by
• .theta.(new)=arctan (Y.sub.f -Y.sub.d)/(X.sub.f -X.sub.d);
• f. calculating a differential value, .DELTA.Y, determined by
• .DELTA.Y=L tan .theta.(new),
• where
• Y(new)=Y.sub.1 (new)-Y.sub.2 (new),
• where Y.sub.1 (new) is a new Y-axis coordinate for said first Y-axis positioning element, and Y.sub.2 (new) is a new Y-axis coordinate for said second Y-axis positioning element;
• and
• g. moving said first and second Y-axis positioning elements to Y.sub.1 (new) and Y.sub.2 (new), respectively, to position said intermediate stage element at .theta.(new).

A kinematic system for positioning a multi-axis stage apparatus within a utilization device such that an object mounted on said multi-axis stage apparatus is positioned coincident with a selected first plane, without lateral motion or rotation, relative to said utilization device, said system comprising:

• a base structure of said utilization device;
• three spaced drive means for supporting said multi-axis stage apparatus for translational movement along a first axis normal to a second plane of said base structure, parallel to said selected first plane, and for rotational movement about second and third axes orthogonal to the first axis and parallel to said second plane of the base structure;
• and
• constraining means, including the drive means, for kinematically constraining said multi-axis stage apparatus to move along the first axis and about the second and third axes and preclude lateral motion or rotation relative to said base structure at said selected first plane.

A kinematic system for positioning a multi-axis stage apparatus within a utilization device such that an object mounted on said multi-axis stage apparatus is positioned coincident with a selected first plane, without lateral motion or rotation, relative to said utilization device, said system comprising:

• a base structure of said utilizing device;
• three spaced drive means for supporting said multi-axis stage apparatus for translational movement along a selected first axis normal to a second plane of said base structure, parallel to said selected first plane, and for rotational movement about second and third axes orthogonal to the first axis and parallel to said second plane of the base structure, said three spaced drive means located equally spaced at 120.degree. at a radius R from said selected first axis, with a first positioning set positioned in front, a second positioning set positioned to the left, and a third positioning set positioned to the right, and adapted for positioning said multi-axis stage apparatus at distances Z.sub.1, Z.sub.2 and Z.sub.3, respectively from said second plane;
• position transducer means for transmitting signals representative of three distances Z.sub.1, Z.sub.2 and Z.sub.3 to said chuck means from said first, second and third positioning sets, respectively, to computer means;
• constraining means, including the drive means, for kinematically constraining said multi-axis stage apparatus to move along said first axis and about said second and third axes and to preclude lateral motion in an X-direction or a Y-direction, orthogonal to one another and both orthogonal to said first axis, or rotation relative to said base structure at a third plane of said base structure, also parallel to said selected first plane, and spaced apart from said selected first plane by a distance H;
• use of said computer means for calculating Abbe offset errors in lateral positioning in said X- and Y-directions, .delta.X and .delta.Y, of the multi-axis stage apparatus in said selected first plane, said Abbe offset errors being determined by a pitch angle, .gamma., and a roll angle, .phi., defined by ##EQU11## where said Abbe offset errors are determined by
• .delta.X.perspectiveto.H(.phi.)
• and
• .delta.Y.perspectiveto.H(.gamma.);
• and
• control means for countermanding said Abbe offset errors in lateral positioning by moving a stage of said multi-axis stage apparatus by -.delta.X and -.delta.Y distances in said X- and Y-directions, respectively.

An X-Y-.theta. stage apparatus comprising:

• a base;
• an X-Y-.theta. stage assembly with workpiece holding means moveable along orthogonal X and Y axes and rotatable about an orthogonal third axis for moving said workpiece along said orthogonal X and Y axes and about said orthogonal third axis, said workpiece holding means having a first, second, and third retroreflector, with each retroreflector fixedly mounted thereto;
• and
• control means for controlling movement of said workpiece holding means, said controlling means comprising:
• first interferometer means, separated an optical distance W from said first retroreflector, for measuring changes in a first parameter associated with changes in said distance W and for providing a first signal corresponding to changes in said distance W;
• second interferometer means, separated an optical distance U from said second retroreflector, for measuring changes in a second parameter associated with changes in said distance U and for providing a second signal corresponding to changes in said distance U;
• third interferometer means, separated an optical distance V from said third retroreflector, for measuring changes in a third parameter associated with changes in said distance V and for providing a third signal corresponding to changes in said distance V;
• transport means responsive to a first circuit means for moving said first, second, and third interferometer means to provide optical coupling between said first, second, and third interferometer means and said first, second, and third retroreflectors, respectively;
• and
• second circuit means for causing said stage means to move to a preselected X-Y position and a preselected angular orientation, .theta., about said third axis in response to said first, second, and third signals.