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 mum min-1 and 5.0 mum 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 (congruent-to 1.2 Torr) gives rise to good etching anistropy. 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.