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.