KINETICS OF GAAS DISSOLUTION IN H2O2-NH4OH-H2O SOLUTIONS

GaAs, a compound semiconductor commonly used in optoelectronic devices , is often subjected to wet-etching techniques during microelectronic device manufacture. In this work we investigated the wet etching of Ga As by H2O2-NH4OH-H2O solutions using a batch stirred-tank reactor and determined the intrinsic kinetics of the dissolution reaction. Increas ing the NH4OH content produced a constant rate above a minimum concent ration. The reaction rate was found, in the presence of excess NH4OH, to fit a rate equation r = k[H2O2](0.75) at 15, 25, and 40 degrees C w ith an activation energy of 33.7 kJ/mol. Using NaOH instead of NH4OH r esulted in greatly reduced reaction rates, and it was concluded that t he presence of the ammonium ion increases the rate by forming soluble compounds with oxidized species of Ga and As. Analysis of the surface by X-ray photon spectroscopy confirmed that samples etched in solution s containing NH4OH had considerably less oxide content on the surface than that etched in H2O2-H2O only. NH4OH does not directly react with GaAs but incorporates a second step into the overall etch reaction, fa cilitating the oxidation by H2O2 and the formation of soluble compound s.