Superheterodyning technique in the spatial frequency domain and structure for pattern registration measurement.

摘要

A superheterodyning technique in the spatial frequency domain for pattern registration measurement, a grid structure to be used in such superhetero-dyning techniques and a method for producing such grid structures are provided. To produce an observable fringe pattern with a fringe contrast inversion, two grid structures (7, 8) with a slightly different basic period are superposed leading to a beat modulation pattern. One of the two grid structures has a grid scale reference at its side and one of the two grid structures is supermodulated. The supermodulated grid pattern (8) modulates the beat modulation pattern and generates a virtual pointer to the reference scale. This virtual pointer is the location of the fringe contrast inversion which is determined with respect to the reference scale by human or machine vision. The supermodulated grid structure (8) is a checkerboard and the second grid structure (7) is a line grid. The pair of grid structures is engraved into the surface of an object (1) with subsequent mask processes writing the line edges as a sequence of neighboured pixels of incremental placement. <IMAGE>