Anisotropic etching rates of single-crystal silicon for TMAH water solution as a function of crystallographic orientation

We evaluated orientation dependence in the etching rate of single-crystal silicon for tetramethyl-ammonium-hydroxide (TMAH) water solutions. Etching rates for a number of crystallographic orientations were measured for a wide range of etching conditions, including TMAH concentrations of 10–25% and temperatures of 70–90°C. We found significantly different characteristics from those for KOH water solutions. Firstly, different types of orientation dependence in etching rate were found around (111) between TMAH and KOH. This means the bonding energy of the silicon crystal lattice is not a single factor that dominates orientation dependence, and there exist different etching mechanisms for the two etchants. Secondly, effects of the circulation of etchants on the etching rates were not negligible in TMAH in contrast to KOH system.