Control of electro-chemical etching for uniform 0.1 /spl mu/m gate formation of HEMT

In gate recess etching of a 0.1 /spl mu/m gate HEMT process, an anomalous phenomenon caused by electrochemical etching was found. The isolation region implanted with oxygen ion was etched more deeply than the channel region, which caused a non-flat etched surface. This anomaly affects device performance and its uniformity seriously. We suppressed the anomaly by optimizing the condition of the isolation and the pattern of the device. A flat etched surface was achieved and uniform device characteristics obtained.