Rapid plasma etching of silicon, silicon dioxide and silicon nitride using microwave discharges

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Abstract
Microwave plasma discharges of CF4, SF6 and CHF3 at high pressures (0.5-1.5 Torr) have been used for rapid etching of silicon, silicon dioxide and silicon nitride suitable for single-wafer etching applications. Etch rates and selectivities have been studied as a function of pressure, gas flow and the amount of O2 as the additive gas. Extremely high etch rates of 2.0-3.6 mu m min-1 and 5.0 mu m min-1 for silicon, obtained respectively in an CF4 and a CF4+20% O2 plasma can be useful for deep-trench etching applications. Formation of a sidewall passivation layer in silicon at high CF4 pressure ( approximately=1.2 Torr) gives rise to good etching anisotropy. The variation of etch selectivity between SiO2 and Si3N4 has been studied as a function of gas flow rates in SF6 plasma. The formation of a thin fluorocarbon polymer film on the etching surface in a CHF3 plasma, which has resulted in selective etching of SiO2 over Si3N4, has been observed by X-ray photoelectron spectroscopy.

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