Laser Fizeau interferometer for silicon wafer site flatness testing

摘要

Abstract: Requirements on wafer flatness, like most semiconductor specifications, are becoming increasingly tight, with greater accuracy and resolution needed for measurements. In addition to traditional peak-to-valley surface deviation and root-mean- square roughness measurements, it is desirable to measure the flatness of silicon wafers over a small area, or site flatness. This involves dividing the wafer into many sub- regions and calculating the surface statistics for these smaller regions in addition to the overall wafer statistics. Veeco Metrology has developed a high-resolution phase-shifting laser Fizeau interferometer for site flatness testing. The system is designed with 40 mm $MUL 40 mm square field and a 1000 $MUL 1000 pixel CCD camera. Features as small as 100 micrometer may be measured by the system with high resolution, repeatability, and accuracy. A motorized stage allows any region of the wafer to be measured by the system such that problem areas do not escape measurement. This paper discusses the overall system design and presents data from the wafer flatness tester developed by Veeco. Data on lateral resolution, vertical repeatability and accuracy are presented. In addition, the site flatness statistics of a silicon wafer measured by the instrument are given. !4