Boron etch-stop in TMAH solutions

Abstract

Etch rates of 〈100〉 single-crystal silicon in tetramethyl ammonium hydroxide (TMAH) solutions have been measured as a function of boron doping concentration with the purpose of studying the feasibility of an etch-stop. The boron concentration has been varied up to 2.5 × 10 20 cm −3. An etch ratio of 1:40 between the heavily and lightly boron-doped silicon has been obtained. This ratio may depend slightly on the temperature of the etch, but no significant variation with etchant concentration has been observed for TMAH concentrations in the range 23–32 wt.%. Preliminary experiments on the effect of adding pyrazine to the etch solution indicate that pyrazine increases the etch rate slightly and seems to have the effect of reducing surface roughness.