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

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.