Etch-stop characteristics of heavily B/Ge-doped silicon epilayer in KOH and TMAH

Abstract

This paper describes the characterization of a heavily boron/germanium (B/Ge)-doped silicon layer as an etch-stop in tetramethyl ammonium hydroxide (TMAH) and potassium hydroxide (KOH). We investigated the etch rate variation of heavily B/Ge-doped silicon epilayer as a function of varying temperature and/or concentration of the etchants. To facilitate the investigation, we described etch-stop performance by the etch-rate ratio of lightly phosphorous-doped and heavily boron/germanium-doped 〈1 0 0〉silicon. Results show that the etch-stop performance of boron/germanium-doped silicon is not as good as the heavily boron-only doped silicon with a similar boron doping level. However, the heavily B/Ge-doped silicon still exhibits good etch-stop performance. Tetramethyl ammonium hydroxide (TMAH) is recommended as an etchant of choice when B/Ge-doped silicon layer is used as an etch-stop layer. Specifically, experimental conditions with low concentrations and temperatures of TMAH lead to a good etch-stop ratio on the heavily B/Ge-doped silicon.