Interferometric total thickness variation measurement of glass wafer

摘要

Total thickness variation (TTV) is one of the important specifications of glass wafer. Glass wafers are thin and transparent parallel plates. In order to measure a flat surface by interferometer, at least one reference flat of same size is required. And the interference between two reflected wavefronts by the front and rear surfaces of the glass wafer also exists. Therefore interferometric measurements of thin glass wafers are not easy. So TTV is mainly measured not by interferometer, but by thickness gauge devices. But these devices measure only the TTV of several positions of glass wafer and don't measure the whole area. To measure the whole area or sufficient points, it requires more time. We developed a relatively simple and inexpensive interferometric TTV measurement method using Haidinger interferometer. This method can be applied to large glass wafers without large reference flat.