| 摘要 |
1289645 Workpiece positioning INTERNATIONAL BUSINESS MACHINES CORP 15 April 1970 [1 May 1969] 17936/70 Heading G2J [Also in Division H4] A method for aligning a semiconductor wafer 18 with respect to a photo-mask 26 comprises the following steps: providing, by techniques employed during the fabrication of the wafer, two reference patterns having a spatial frequency content distinct from the rest of the wafer, providing in a predetermined positional relationship to the mask 26, a complex spatial filter 35 representing the patterns and responsive to light of a preselected wavelength; directing a beam of coherent monochromatic infrared light 15 of this wavelength through the wafer 18 and the filter 35 to form two recognition spots of light which fall on two infrared photodetectors 41, 42 at positions thereon dependent on the relative degree of alignment of the wafer and the filter; producing error signals 54 etc., indicative of the relative displacement between each spot and its associated reference position (e. g. 49); and adjusting the respective position of the wafer 18 by servomotors 21-24 responsive to the error signals. The patterns are such that they can be rotated by any amount without disturbing the integrity of the recognition spots, and the filter 35 is attuned to their Fourier Transform. The photo-detector (e.g. 41) are divided into two vertical (45, 47) and two horizontal (46, 48) sectors generating corresponding signals 52, 51 and 56, 57. The mask 26 and the filter 35 may be placed on the same mask holder or substrate 70, Fig. 3 (not shown) to eliminate alignment problems. |
