Comparison between etching in Cl2 and BCl3 for compound semiconductors using a multipolar electron cyclotron resonance source

Abstract

Controllable dry etching of GaAs and InP using a multipolar electron cyclotron resonance (ECR) source and a radio frequency (rf)-powered electrode was investigated. The etch characteristics were studied as a function of microwave power, rf power, distance from the ECR source, pressure, and temperature. Etch rate is found to increase with microwave power initially, then decrease at higher microwave power due to reduction in ion energy. Surface morphology becomes rougher and etch profile is more undercut at higher microwave power, but can be improved using higher rf power or by Ar addition. As the ECR source distance increases, the concentration of ions and neutral species decrease, but the ion energy increases. Therefore, when etching is limited by the arrival rate of reactive radicals, etch rate decreases with source distance. When the process is limited by the ion-enhanced reaction or removal rates, etch rate increases with source distance. Etch rate and self-induced dc bias voltage (‖Vdc‖) typically increase with pressure. The increase in ‖Vdc‖ is believed to be caused by the lower ion flux at higher pressure. However, when the reactive species concentrations and the ion energy are low, etch rate decreases with pressure. Low pressure was observed to favor smooth surface morphology and vertical etch profile. Etch rates for both GaAs and InP increase with temperature, with InP etch rate exceeding GaAs at 380 °C. Using a Cl2/Ar mixture with 10% Cl2, 70 W rf power and 25 W microwave power at 0.5 mTorr, 0.1 μm wide features that are 1 μm deep have been fabricated in GaAs with vertical profile and smooth surface morphology.