Inductively coupled plasma etching of InP using CH4/H2 and CH4/H2/N2

Inductively coupled plasma etching of InP in CH4/H2 and CH4/H2/N2 gas mixtures was studied to understand the etching mechanisms and the influence of etching gas composition on etching rate, etching profile, and surface morphology. CH4/H2 plasmas generally had higher etching rates than CH4/H2/N2 plasmas. Deterioration of InP surfaces, following etching, reflected the preferential loss of P over In due to the diffusivity and reactivity of H being higher than CH3 on InP surfaces, and also since PH3 is more volatile than In(CH3)3. In extreme circumstances, this can lead to the formation of In-rich droplets on the surface, with associated surface roughening. This was supported by the opposing trends of surface roughness (measured using atomic force microscopy) and P/In ratio (from x-ray photoelectron spectroscopy) as a function of the CH4 gas concentration for CH4/H2 gas mixtures. The addition of N2 to the CH4/H2 plasmas improved the surface morphology as N radicals reduced the rate of P removal by reacting with H radicals. However, an inevitable increase in the N+ and N2+ concentrations led to erosion of the SiO2 masks and caused sloping sidewalls.