Alignment apparatus

Abstract

This describes an apparatus and method especially adapted for positioning a semiconductor wafer in a preferred plane with respect to a photomask so as to achieve improved photolithographic focusing. The apparatus comprises a holder, provided with a surface for receiving a semiconductor wafer thereon, mounted in a chuck which mates with an adaptor ring containing both driver mechanisms and sensors for sensing and positioning the wafer. The sensors define a reference plane and converts the spacing between the reference plane and the front surface of the semiconductor wafer into electrical signals which can be fed to the driver mechanisms to position, with both rotational or translational motion, the plane of the wafer by moving the holder until all the signals from the sensors are nulled. Once the wafer is properly aligned, the sensors continually monitor the position of the wafer and the driver mechanisms continually provide loading to the wafer holder to continually maintain the wafer in its preferred position with respect to the established reference plane.

What is claimed is: 
     
       1. A mechanism for positioning the surface of an object in a selected position with respect to a reference plane comprising: means for holding said object,   means for defining said reference plane.Iadd., an adapter ring for mating with said holding means, .Iaddend.   driver means .Iadd.mounted on said adapter ring and .Iaddend.aligned with said holding means, and   sensor means coupled to said driver means and spaced from said object for sensing the surface of said object with respect to said reference plane and controlling respective ones of said driver means to engage and move the holding means to position the sensed surface of said object in said selected position with respect to said reference plane.[...]. .Iadd.said holding means comprising a chuck enclosing a spring loaded mounting means provided with means for holding an object having a flat surface thereon, and   said driver means being aligned with said mounting means to position the sensed surface of the object by moving said mounting means against said spring. .Iaddend.   
     
     
       2. A mechanism for positioning and maintaining the plane surface of a unit in a selected attitude with respect to a reference plane comprising: a unit having a plane surface to be positioned,   .Iadd.a spring loaded mounting .Iaddend.means for holding said unit,   a carrier adapted to mate with said holding means,   driver mechanisms on said carrier aligned with said holding means when mated with said carrier,   means coupled to said carrier defining said reference plane, and   sensors on said carrier being coupled to said driver mechanisms and spaced from said surface of said unit for sensing the position of said surface and controlling said driver mechanisms to engage and move said holding means to position and maintain the sensed surface of the unit in said selected attitude with respect to said reference plane. .[.3. The mechanism of claim 1 wherein there is further provided an adaptor ring supporting said driver means and said sensor means,   said driver means and said sensor means being equally spaced on said   
     
     
        ring..]. 4. The mechanism of claim .[.3.]. .Iadd.1 .Iaddend.wherein said adaptor ring has an inner step, said step being provided with means for securing said means for holding said object in said adaptor ring. .[.5. The mechanism of claim 4 wherein said means for holding said object comprises a cup shaped chuck enclosing   
     
     
        a spring loaded, moveable mounting means..]. 6. The mechanism of claim .[.5.]. .Iadd.1 .Iaddend.wherein said mounting means comprises a disc provided with a plurality of radial and circular channels connected to a 
     
     
        vacuum source for holding an object having a flat surface thereon. 7. The mechanism of claim .[.5.]. .Iadd.6 .Iaddend.wherein said mounting means is spring loaded by a diaphragm spring that provides translational and 
     
     
        rotational freedom of motion to said mounting means. 8. The mechanism of claim 7 wherein each of said sensor means comprises a dual action air switch which can establish the surface of the object parallel to said 
     
     
        reference plane. 9. The mechanism of claim 8 wherein each of said sensors 
     
     
        are coupled to respective driver means through a controller circuit. 10. A mechanism for positioning the plane surface of a unit in a selected position parallel to a reference plane comprising: a unit having a surface to be positioned,   a chuck,   a moveable mounting means in said chuck for holding the unit, said moveable mounting means being provided with a plurality of lugs around its periphery,   a carrier adapted to mate with the chuck,   a plurality of driver mechanisms on said carrier each of which is aligned with a respective one of said lugs on the periphery of said mounting means when the carrier is mated with the chuck, and   means on said carrier defining a reference plane,   a plurality of sensors being spaced from the surface of the unit when the carrier is mated with the chuck for sensing the position of the surface relative to the reference plane, each sensor being coupled to and controlling respective one of said driver mechanisms to engage and drive the lugs on the mounting means to position and maintain the sensed plane surface of the unit parallel to the reference plane,   said moveable mounting means being spring loaded in said chuck providing translational and rotational freedom of movement to said mounting means in   
     
     
        said chuck. 11. In a photoalignment tool a wafer positioner for positioning a wafer in a predetermined plane comprising: an adaptor ring supporting spaced driver mechanisms and sensor units,   a chuck housing mated with said adaptor ring, and   means having translational and rotational freedom of movement mounted in said chuck housing, for holding a wafer adjacent to said sensor units,   said sensor units detecting the distance between the wafer surface and the adaptor ring,   said sensors being coupled to said driver mechanisms to control the driver mechanisms to engage and drive the means mounted in said housing to position and maintain the wafer in a selected plane with respect to the adaptor ring.