Estimation of activation energy and surface reaction mechanism of chlorine neutral beam etching of GaAs for nanostructure fabrication

To understand the etching mechanisms of GaAs materials through the neutral beam etching (NBE) process developed in our laboratory, we investigated the effect of substrate temperature on etching conditions. The etch rate as a function of wafer temperature was found to increase with temperature. The apparent activation energy was calculated to be an average of about 8.6±1.4kJmol^-1. However, as the vapour pressure of the etch product (GaCl_x) was above the chamber pressure, the etching mechanism was assumed to be temperature independent. It has been suggested that residual Ga₂₃ oxide on the GaAs surface is responsible for the temperature dependence of the etch rate. A comparison with reactive ion etching (RIE) was done and a lower activation energy was calculated (4.0±0.3kJmol ^-1). We argue that etching of residual oxide on the GaAs surface is more efficient with RIE because of the energetic ions and ultraviolet photons. It should be noted that when substrate temperature was increased, the etching rate ratio between NBE and RIE decreased, suggesting a stronger effect of chemical etching on the etching mechanism.