Method and apparatus for measuring the shape and thickness variation of polished opaque plates

摘要

The present invention consists of a technique and device for measuring the thickness variation and shape of wafers or other polished opaque plates. A combination of two improved phase-shifting Fizeau interferometers (20,40) is used to simultaneously measure the single-sided distance maps between each side (61 or 62) of the wafer (60) and the corresponding reference flat (32 or 52), with the thickness variation and shape being calculated from these data (at 38,58). Provisions are made to determine and eliminate the shape and tilt of the reference surfaces, and also to facilitate the correct overlay of the two single-sided measurements for the calculation of thickness variation and shape.