Hydrogenation effects during high-density plasma processing of GaAs MESFETS

GaAs MESFETs may be exposed to -containing plasmas during various etch and deposition steps. We have found that both inductively coupled plasma (ICP) and electron cyclotron resonance (ECR) plasmas create severe reductions in MESFET mutual transconductance and reverse breakdown voltage through reductions in channel layer doping and surface stoichiometry changes. While changes in channel sheet resistance and diode ideality factor may be minimized by limiting the plasma exposure time, and are still reduced by up to a factor of two even for 30 s exposures. The results show that there are no conditions under which there are not substantial changes in device performance, and unless -free plasma chemistries are used, post-plasma annealing will always be necessary to restore the device characteristics.