SIO2 MASK EROSION AND SIDEWALL COMPOSITION DURING CH4/H-2 REACTIVE ION ETCHING OF INGAASP/INP

SiO2 mask erosion has been studied during CH4/H-2 reactive ion etching of InGaAsP/InP double heterostructures. The amount of mesa mask narrowing at a pressure of 100 mT, normalized for an etch depth of 3.5 mum, is approximately 0.4-0.6 mum and decreases slightly with increasing self-bias voltage. It is not strongly dependent on the sidewall angle of the mask or CH4 concentration. Mask residue deposits on the etched sidewall under conditions of relatively high CH4 concentration and low power density. Auger electron spectroscopic analysis of the sidewall shows that the deposit contains a significant amount of elemental Si, which suggests a mechanism for mask erosion in which SiO2 is reduced to Si in the hydrogen/hydrocarbon-rich environment of the plasma.