High purity, environmentally clean method and apparatus, for high rate, liquid anisotropic etching of single crystal silicon or etching of polycrystalline silicon, using an overpressure of ammonia gas above aqueous ammonium hydroxide

摘要

A high purity, non-toxic, environmentally friendly method for anisotropically etching single crystal silicon and etching polysilicon, suitable for microelectronics, optoelectronics and microelectromechanical (MEMS) device fabrication, using high purity aqueous ammonium hydroxide (NH4OH) solution generated at the point of use, is presented. The apparatus of the present invention supports generation of high purity aqueous NH4OH solution from ammonia NH3 gas dissolved into distilled/deionized water and maintained in equilibrium with an overpressure of NH3, within a hermetically enclosed chamber at the optimal temperature between 70-90° C., preventing evaporation of NH3 gas from aqueous NH4OH solution for achieving a high anisotropic etching rate. Other liquid anisotropic etching methods for silicon may use tetramethylammonium hydroxide (TMAH). In contrast to carbon containing TMAH, the NH3 gas and H2O precursors of NH4OH etchant eliminate risk for solid residues to be deposited on silicon due to being composed entirely of elements having a gaseous form at room temperature.

主权项

1. A method for liquid anisotropically etching a single crystal silicon semiconductor wafer substrate for, optoelectronic devices using ammonium hydroxide (NH4OH) anisotropic etching solution generated directly at the immediate time and point of use by chemically reacting semiconductor grade deionized water (H2O) with semiconductor grade ammonia (NH3) gas to form said ammonium hydroxide (NH4OH) 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 (H2O), wherein said semiconductor grade deionized water (H2O) 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 (H2O), wherein said semiconductor grade deionized water (H2O) remains in a liquid state contained within said inert liner and wherein said optimal temperature of said semiconductor grade deionized water (H2O) is provided by an electric heater coupled to the exterior surface of said base plate flange; and introducing said semiconductor grade ammonia (NH3) gas into said hermetically sealed pressure chamber at higher than atmospheric pressure, wherein said semiconductor grade ammonia (NH3) gas chemically reacts with said semiconductor grade deionized water (H2O) contained within said inert liner, thereby forming said ammonium hydroxide (NH4OH) anisotropic etching solution, and wherein said semiconductor grade ammonia (NH3) gas overpressure above said ammonium hydroxide (NH4OH) anisotropic etching solution prevents evaporation of said semiconductor grade ammonia (NH3) gas in said ammonium hydroxide (NH4OH) 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 (NH4OH) anisotropic etching solution; and withdrawing said single crystal silicon semiconductor wafer substrate from said ammonium hydroxide (NH4OH) anisotropic etching solution immediately after completion of said liquid anisotropic etching.