The residual damage which was caused by etching with Cl2/Ar plasma, generated by an electron cyclotron resonance source, was investigated. It was found that the residual damage and electrical properties were strong]y affected by changes in etching parameters such as the ion energy, ion flux and temperature. The lattice damage which was caused under all of the processing conditions was in the form of small dislocation loops. Samples which had been etched using 200W of radio-frequency power exhibited a defect density that was 5 times higher than that in samples which had been etched using 20W of radio-frequency power. The enhanced residual damage at higher radio-frequency powers was paralleled by a degradation of the unannealed contact resistance. Higher etching rates, which were associated with the higher power levels, caused the width of the disordered region to contract as the power was increased. Thus, the residual damage was affected by both the generation and removal of defects. Increasing the microwave power or ion flux resulted in an increase in the residual defect density, surface roughness, and unannealed contact resistance. Samples which were etched at about 350C had a lower contact resistance than samples which had been etched at 25C. High-temperature etching increased the defect diffusion which, in turn, decreased the near-surface defect density. This decrease in residual damage was suggested to be responsible for an improvement in the electrical performance at 350C. The electrical measurements were found to be more sensitive to the defect density than to the vertical extent of disorder below the etched surface. The present results demonstrated that, in order to minimize damage and to improve electrical properties, etching with an electron cyclotron resonance source should be carried out at low power and high substrate temperature.

M.W.Cole, K.K.Ko, S.W.Pang: Journal of Applied Physics, 1995, 78[4], 2712-5