Thin-oxide degradation along feature edges during reactive ion etching of polysilicon gates

Enhanced leakage current through the gate oxide insulator and degraded oxide breakdown voltages were observed following hexode reactive ion etching and magnetically enhanced reactive ion etching (MERIE) of poly-Si electrodes over thin gate oxides. The degradation was seen to occur along the edges of the etched poly-Si gates and was not aggravated by the amount of poly-Si charge collection area (antenna) over a thick field oxide. Defect densities ranging from 0.02 to 0.3 per meter of perimeter were observed so that significant yield losses could be expected in deep submicron ultralarge scale integrated circuit chips. Interestingly the defect density, as measured at a fixed voltage, was not markedly affected by the gate oxide thickness down to 7 nm. Comparisons of results from the two etching systems showed that the degradation was three times greater in MERIE than with the hexode.