Electrochemical Etching of Ion Implanted Channel Regions in GaAs
Electrochemical etching or corrosion of GaAs in the vicinity of metal contacts is a well known phenomenon in the compound semiconductor device and IC manufacturing industry. Corrosion of GaAs has been most frequently reported for situations where wafers with bare regions GaAs and metal contacts are exposed to de-ionized water for extended periods of time. The corrosion typically manifests only in close proximity to the edge of the metal contacts. Recently we determined that some MSAG wafer losses, characterized by FETs with abnormally low drain current under positive gate bias, were caused by electrochemical oxidation and etching of the implanted near-surface region of the FETs. Investigation traced the source of the problem to a dump rinse step where oxidation was taking place followed by etch removal of the oxide in the FET channel at a subsequent acid-exposure step. This paper will discuss some of the abnormal corrosion behavior we observed in comparison to that reported in the literature. Discussion will also be presented regarding beneficial FET attributes that can be obtained from a controlled amount of corrosion/etching in the process sequence that was causing the problem that led to this investigation.