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A study of the etch characteristics of a thermally grown silicon dioxide etch in RITEs 2406 PLASMATRAC RIE was performed for a C2F6 / CHF3 / C02 gas mixture. Correlations between the amount of CHF3 and C02 introduced and Si02 etch rates and selectivity to polysilicon were investigated using a statistical experimental design. Si02 etch rates as high as 1018 A/mm were achieved with a corresponding selectivity to polysilicon of 2.84:1. At a gas flow of 60 sccm C2F6, 171 sccm CHF3, 48 sccm C02, 255 watts & 150 mtorr, an optimized etch for selectivity was found to give an Si02 etch rate of 910 A/mm with a corresponding selectivity of 5.29:1. Uniformity of the etch rate across the wafer was found to be good for the Si02 etch with etch rates varying less than 5% across the wafer. Helium additions were found to improve the uniformity of polysilicon etch rates from their nominal value of 25% to 11% across the wafer.

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