Effects of Ohmic Metal on Electrochemical Etching of GaAs in pHEMT Manufacturing

Good ohmic metal contact is crucial for optimum device performance for Heterojunction Bipolar Transistors (HBT) and pseudomorphic High Electron Mobility Transistors (pHEMT). Erosion of Gallium Arsenide (GaAs) adjacent to ohmic structure is a common problem and it is generally observed in the compound semiconductor industry. It is believed that electrochemical etching, which has been studied extensively by researchers, is responsible for the phenomenon. Solutions usually focus around the chemistries in the various wet processing steps. In our recent experiments, we have found that galvanic erosion of GaAs can be suppressed or eliminated by optimizing the ohmic metal scheme and alloy condition. This paper will discuss the correlation between ohmic metal composition and electrochemical etching. The improvement in DC and RF parameters as a result of better ohmic contact and lack of erosion will also be presented.