Improvement of process uniformity in recessed gate AlGaN/GaN HFET by selective etching of in-situ Si x N y on AlGaN

The effects of in-situ Si x N y 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 Si x N y passivation. By varying O 2 ratio in total gas flow, etch rate and selectivity of Si x N y and AlGaN were changed significantly. The etch rate of AlGaN was reduced by adding O 2 in gas mixture, which caused the formation of AlO x and GaO x on the surface during etching process. The etch rate of in-situ Si x N y was decreased with increasing O 2 ratio. By this relationship, the highest selectivity was obtained with 30% O 2 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.