Abstract

A wafer-bearing chuck, an annular reference plate, a copy lens system, and a mask-bearing holder are mounted on a floating unit so that the copy lens system produces an image of a pattern-bearing surface of the mask at a plane positioned between the annular reference plate and the wafer chuck and produces an image of a selected pattern-bearing region of a photosensitive-film-bearing surface of the wafer at the pattern-bearing surface of the mask. The wafer chuck is movably mounted for positioning the photosensitive-film-bearing surface of the wafer in abutment with the annular reference plate in a plane parallel to the image plane of the pattern-bearing surface of the mask and for subsequently positioning the selected pattern-bearing surface region of the wafer in the image plane of the pattern-bearing surface of the mask. A stop mechanism may be employed to automatically stop the wafer chuck when the selected pattern-bearing surface region of the wafer is substantially positioned in the image plane of the pattern bearing surface of the mask. Alternatively, the wafer chuck may be manually adjusted, while viewing the pattern-bearing surface of the mask and the image of the selected pattern-bearing surface region of the wafer through a microscope of an optical unit, to precisely position the selected pattern-bearing surface region of the wafer in the image plane of the pattern-bearing surface of the mask. The mask holder is movably mounted for thereafter aligning the pattern of the mask with the image of pattern of the selected surface region of the wafer while they are viewed through the microscope. The floating unit is floatingly supported within a base unit on three balls and coupled to the base unit by a parallelogram linkage so that the floating unit may be scanned relative to the microscope without rotating relative to the base unit to facilitate and verify alignment of all portions of the pattern of the mask with the image of the pattern of the selected surface region of the wafer. A vacuum clamping mechanism may be employed to clamp the floating unit in any position to which it may be scanned, whereupon the mask holder may be moved to further align the pattern of the mask with the image of the pattern of the selected surface region of the wafer. Upon completion of the pattern alignment operation, the floating unit is unclamped and a centering mechanism employed to automatically return the floating unit to a central position at which an exposure lens system of the optical unit may be employed for exposing the photosensitive film on the selected surface region of the wafer in accordance with the pattern of the mask. A loading arm is mounted on a movable stage secured to the floating unit and is rotated in a plane orthogonally intersecting the first optical axis to move the wafer between a loading station and the wafer chuck. The movable stage is stepped to a plurality of different positions arranged in orthogonal rows and columns so that the loading arm may be employd to move the wafer to a corresponding plurality of different positions on the wafer chuck. This permits a corresponding plurality of different regions of the photosensitive-film-bearing surface of the wafer to be aligned and exposed in accordance with the pattern of the mask.