During the fabrication of refractory gate MESFET devices, sputter deposition of a WSix gate and reactive ion etching of the gate pattern could lead to surface damage and contamination. In order to study these effects, material with a shallow Si implant was subjected to reactive ion etching alone, or to both WSix sputter deposition and reactive ion etching, before annealing. The surface damage, due to WSix sputter deposition and reactive ion etching at self-bias under 200V, was healed by capped (SiNx) furnace annealing at 800C. It was found that sheet resistance and Hall mobility measurements could be correlated with the diffusion of compensating impurities into the bulk. Secondary ion mass spectrometry profiles indicated that the major contaminants (Fe, Cr, Ni, Cu, V) were already present in the W targets and were thus present in the WSix layers. These contaminants were left on the surface of the GaAs after gate reactive ion etching and were driven into the bulk during capped annealing. An HCl etch was found to remove the contaminants; thus resulting in lower sheet resistances for implanted and processed GaAs. Refractory gate sub-micron MESFET devices which were fabricated by using an HCl etch after gate reactive ion etching exhibited a reduced access resistance.

H.Baratte, A.J.Fleischman, G.J.Scilla, T.N.Jackson, H.J.Hovel, F.Cardone: Journal of the Electrochemical Society, 1991, 138[1], 219-22