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 GaAs by H 2 O 2 −NH 4 OH−H 2 O solutions using a batch stirred-tank reactor and determined the intrinsic kinetics of the dissolution reaction. Increasing the NH 4 OH content produced a constant rate above a minimum concentration. The reaction rate was found, in the presence of excess NH 4 OH, to fit a rate equation r = k [H 2 O 2 ] 0.75 at 15, 25, and 40 °C with an activation energy of 33.7 kJ/mol. Using NaOH instead of NH 4 OH resulted in greatly reduced reaction rates, and it was concluded that the 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 solutions containing NH 4 OH had considerably less oxide content on the surface than that etched in H 2 O 2 −H 2 O only. NH 4 OH does not directly react with GaAs but incorporates a second step into the overall etch reaction, facilitating the oxidation by H 2 O 2 and the formation of soluble compounds.