N2 effect on GaAs etching at 150 mTorr capacitively-coupled Cl2/N2 plasma

The role of N-2 on GaAs etching at 150 mTorr capacitively-coupled Cl-2/N-2 plasma is reported. A catalytic effect of N-2 Was found at 20-25% N-2 composition in the Cl-2/N-2 discharges. The peak intensities of the Cl-2/N-2 plasma were monitored with optical emission spectroscopy (OES). Both atomic Cl (725.66 nm) and atomic N (367.05 nm) were detected during the Cl-2/N-2 plasma etching. With the etch rate and OES results, we developed a simple model in order to explain the etch mechanism of GaAs in the high pressure capacitively-coupled Cl-2/N-2 plasma as a function of N-2 ratio. If the plasma chemistry condition became positive ion-deficient at low % N-2 or reactive chlorine-deficient at high % N-2 in the Cl-2/N-2 plasma, the GaAs etch rate is reduced. However, if the plasma had a more balanced ratio Of Cl-2/N-2 (i.e. 20-25% N-2) in the plasma, much higher etch rates (up to 150 nm/min) than that in pure Cl-2 (50 nm/min) were produced due to synergetic effect of neutral chlorine adsorption and reaction, and positive ion bombardment. Pure Cl-2 etching produced 14 nm of RMS surface roughness of GaAs. Introduction of >= 20% N-2 gas in Cl-2/N-2 discharges significantly reduced the surface roughness to 2-4 nm. SEM photos showed that the morphology of photoresist mask was strongly degraded. Etch rate of GaAs slightly increased from 10 to 40 nm/min when RIE chuck power changed from 10 to 150 W at 12 sccm Cl-2/8 sccm N-2 Plasma condition. The surface roughness of GaAs etched at 12 sccm Cl-2/8 sccm N-2 plasma was 2-3 nm. (C) 2009 Elsevier B.V. All rights reserved.