Measurement of registration of overlaid test patterns by the use of

Abstract

Two identical test patterns are overlaid upon each other on a planar substrate of semiconductor material A. Each pattern consists of a plurality of spaced parallel lines. The lines are arranged in two sets of horizontal lines and two sets of vertical lines. The line/space periodicity is known. The lines of the two test patterns are made of two different materials, B and C, respectively. Thus, the target pattern formed by the two test patterns and the substrate has four reflecting regions defined by the different layers in each region: A, AB, AC and ABC. Adjacent the overlaid patterns are four macro-zones each containing a different one of the four layers, A, AB, AC and ABC. Each macro-zone is illuminated by a broad spectrum light, such as that from an incandescent lamp, and the reflected light intensity from each macro-zone is measured. Then, the reflected light intensities from the two sets of horizontal lines are separately measured, as are the reflected intensities from the two sets of vertical lines. One then can calculate both the horizontal and vertical overlay error from the known periodicity and the measured light intensities. Instead of reflected intensities, one can use transmitted intensities. Depending upon the materials used, the illumination can be provided by sources of other electromagnetic radiations, such as infrared, ultraviolet and x-ray.