Whole film inspection using an extended source

Currently, one measures dielectric thin film thickness on a wafer surface b y sampling a predetermined number of points across the wafer. Point measure ments do not provide accurate information on the trend in thickness variati on across the wafer surface. Such information could be quite useful while d eveloping new coating, deposition, etching, or polishing processes. Hence, a system that can map single layer film thickness across the whole wafer or a large area of the wafer will be very useful to process developers. In th is article, we will discuss a technique that can map film thickness across a large area in a relatively short amount of time. It takes about 4 s to de termine about 23 000 thickness values across the wafer. The approach has be en breadboarded and demonstrated. Using a single wavelength, this technique makes it possible to characterize single layer film thickness without havi ng to know optical constants of the substrate material. (C) 1998 American V acuum Society. [S0734-211X(98)16106-1].