Improvement of process uniformity in recessed gate AlGaN/GaN HFET by selective etching of in-situ SixNy on AlGaN

The effects of in-situ SixNy etching were investigated by comparing the uniformity of threshold voltage on recessed gate AlGaN/GaN heterostructure field effect transistor (HFET) devices with in-situ grown SixNy passivation. By varying O2 ratio in total gas flow, etch rate and selectivity of SixNy and AlGaN were changed significantly. The etch rate of AlGaN was reduced by adding O2 in gas mixture, which caused the formation of AlOx and GaOx on the surface during etching process. The etch rate of in-situ SixNy was decreased with increasing O2 ratio. By this relationship, the highest selectivity was obtained with 30% O2 ratio in total gas flow and selectivity was increased from 5 : 1 to 100 : 1. Using this optimized etching condition, the standard deviation of threshold voltage on AlGaN/GaN recess gate HFET was improved from 0.60 to 0.18 on 6-in. processed wafer.