Highly selective and vertical etch of silicon dioxide using ruthenium films as an etch mask

Highly selective and vertical profile etching of thermally grown SiO2 films using thin metallic Ru mask films was investigated in a commercial inductively coupled plasma etcher. The effects of varying chamber pressure, substrate bias, and gas composition on etch performance were all investigated. Selectivities (measured as the SiO2 etch rate divided by the Ru etch rate) ranging from 50 to as high as 370 were measured under various process conditions without compromising the etch profile quality. It was found that fluorocarbon gas mixtures (CF4/CHF3 and CF4/C4F8) gave the best results. The addition of SF6 to the gas mixture dramatically reduced selectivity, resulting in significant Ru mask faceting and necking in the etched pillars and is not recommended for use in a standard Ru/SiO2 etch process.