Silicon Oxide Selective Etching Employing Dual Frequency Superimposed Magnetron Sputtering of Carbon Using F2/Ar Gases

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We have demonstrated environmentally friendly silicon oxide (SiO2) selective etching by dual-frequency magnetron sputtering of carbon using NF3/Ar or F2/Ar gases. In the NF3/Ar plasma, a selectivity of 8 for the etching rate of SiO2/Si was obtained by increasing residence time. The ratio of N atoms in the polymers deposited on the etched Si surface increased with increasing residence time. In the F2/Ar plasma, two different power sources with frequencies of 13.56 MHz and 450 kHz were supplied to the top electrode of the carbon target. The amount of C-based species in the plasma was able to be controlled by the bias voltage on the carbon target. The electron density was controlled by the 13.56 MHz power source, and the target bias voltage $V_{\text{pp}}$ was controlled by the 450 kHz power source. The density of the CF3 radicals was the highest among CFx ($x=1--3$) radicals. The density of the CF2 radicals was precisely controlled by increasing the target bias voltage. A vertical etching pattern profile with a selectivity for the etching rate of SiO2 over resist films was realized by increasing the target bias voltage.
2007-02-15