Chemical etching of silicon wafer.

An etching technique for obtaining a silicon wafer with very little thickness variation is described in this paper. The etchants used in this experiment consist of nitric acid, hydrofluoric acid and diluents, such as water and glacial acetic acid. Rate limiting processes are segregated into two categories, one is the diffusion-rate-limiting process, where the etching rate is affected by etchant agitation. The other is the reaction-rate-limiting process, which is scarcely affected by etchant agitation. As a result, etching in the reaction-rate-limiting process can easily result in extremely smaller wafer thickness variation, about 1 μm, than that by diffusion-rate-limiting process. Furthermore, water ratio to nitric acid is an important factor to determine the category in which the rate-limiting process is classified.