Process damage and contamination effects for shallow Si implanted GaAs

During the fabrication of refractory gate MESFET's, the sputter deposition of a WSi_x gate and Reactive Ion Etching (RIE) of the gate pattern can lead to surface damage and contamination. To study these effects, GaAs with a shallow silicon implant was subjected to RIE alone or to both a WSi_x sputter deposition and RIE at self-biases under 200V was healed out by 800°C SiN₄ capped furnace annealing. Sheet resistance and Hall mobility measurements correlated with the diffusion of compensating impurities into the bulk of the GaAs. The SIMS profiles indicated that the major contaminants (Fe, Cr, Ni, Cu, V,...) were initially present in the W targets and were thus present in the WSi_x layers. These contaminants were left on the surface of the GaAs after the gate RIE and were driven into the bulk on capped annealing. An HCI etch was found to remove the contaminants, resulting in lower sheet resistances for implanted and processed GaAs. Refractory gate submicron MESFET's with reduced access resistances were fabricated.