BORON ETCH-STOP IN TMAH SOLUTIONS

Each rates of (100) single-crystal silicon in tetramethyl ammonium hyd roxide (TMAH) solutions have been measured as a function of boron dopi ng concentration with the purpose of studying the feasibility of an et ch-stop. The boron concentration has been varied up to 2.5 x 10(20) cm (-3). An etch ratio of 1:40 between the heavily and lightly boron-dope d silicon has been obtained. This ratio may depend slightly on the tem perature oi the etch, bur no significant variation with etchant concen tration has been observed for TMAH concentrations in the range 23-32 w t.%. Preliminary experiments on the effect of adding pyrazine to the e tch solution indicate that pyrazine increases the etch rate slightly a nd seems to have the effect of reducing surface roughness.