Actinometry of inductively coupled Cl2∕N2 plasmas for dry etching of GaAs

Inductively coupled plasma dry etching of GaAs with Cl2∕N2-containing plasmas and investigations of these plasmas with optical emission spectroscopy and actinometry are presented. The results of actinometry were revised to allow the comparison of relative ground-state densities at different pressures. The obtained relative ground-state densities of N2, Cl2, and Cl (I) are presented as functions of the process parameters [rf power, pressure, and Cl2∕(Cl2+N2) ratio]. Cl (I) relative ground-state densities were found to be linearly connected to the pressure and the Cl2∕(Cl2+N2) ratio. GaAs etch rates up to 3μm∕min were obtained, while etch rates of the photoresist mask did not exceed 0.95μm∕min. The impact of the rf power changes on the etch rates was negligible. Plotting the etch rates against the process parameters revealed a linear relationship between the etch rates and the pressure and between the etch rates and the Cl2∕(Cl2+N2) ratio. Therefore a correlation between the Cl (I) relative ground-state density measured in plasmas without wafer and GaAs and the photoresist mask etch rate was found. All GaAs dry etching examined in this investigation was found to take place in a reactant-limited regime with Cl (I) as the rate-limiting species.