Patent ID: 8790531

Claim:
A method for liquid anisotropically etching a single crystal silicon semiconductor wafer substrate for, optoelectronic devices using ammonium hydroxide (NH 4 OH) anisotropic etching solution generated directly at the immediate time and point of use by chemically reacting semiconductor grade deionized water (H 2 O) with semiconductor grade ammonia (NH 3 ) gas to form said ammonium hydroxide (NH 4 OH) anisotropic etching solution, whereby (111 ) planes of said single crystal silicon semiconductor wafer substrate are etched more slowly than (100) planes of said single crystal silicon semiconductor wafer substrate, comprising the steps of: immersing said single crystal silicon semiconductor wafer substrate into only said semiconductor grade deionized water (H 2 O), wherein said semiconductor grade deionized water (H 2 O) is contained within an inert liner and wherein said inert liner is contained within a hermetically sealed pressure chamber, said hermetically sealed pressure chamber comprising a base plate flange coupled to said inert liner; and setting an optimal temperature of said semiconductor grade deionized water (H 2 O), wherein said semiconductor grade deionized water (H 2 O) remains in a liquid state contained within said inert liner and wherein said optimal temperature of said semiconductor grade deionized water (H 2 O) is provided by an electric heater coupled to the exterior surface of said base plate flange; and introducing said semiconductor grade ammonia (NH 3 ) gas into said hermetically sealed pressure chamber at higher than atmospheric pressure, wherein said semiconductor grade ammonia (NH 3 ) gas chemically reacts with said semiconductor grade deionized water (H 2 O) contained within said inert liner, thereby forming said ammonium hydroxide (NH 4 OH) anisotropic etching solution, and wherein said semiconductor grade ammonia (NH 3 ) gas overpressure above said ammonium hydroxide (NH 4 OH) anisotropic etching solution prevents evaporation of said semiconductor grade ammonia (NH 3 ) gas in said ammonium hydroxide (NH 4 OH) anisotropic etching solution according to Henry's law; and etching away silicon anisotropically from the surface of said single crystal silicon semiconductor wafer substrate immersed in said ammonium hydroxide (NH 4 OH) anisotropic etching solution; and withdrawing said single crystal silicon semiconductor wafer substrate from said ammonium hydroxide (NH 4 OH) anisotropic etching solution immediately after completion of said liquid anisotropic etching.