 Tetramethylammonium hydroxide (TMAH) presents a safer alternative than EDP, with a 37X selectivity between {100} and {111} planes in silicon.Etching a (100) silicon surface through a rectangular hole in a masking material, for example a hole in a layer of silicon nitride, creates a pit with flat sloping {111}-oriented sidewalls and a flat (100)-oriented bottom.The {111}-oriented sidewalls have an angle to the surface of the wafer of