SURFACE DAMAGE THRESHOLD OF SI AND SIO2 IN ELECTRON-CYCLOTRON-RESONANCE PLASMAS

Damage thresholds of Si and SiO2 during reactive ion etching (RIE) were measured in an electron cyclotron resonance plasma reactor equipped with an energy-analyzed mass spectrometer, Faraday cup, and in situ ellipsometer. Si damage was monitored by the minority-carrier lifetime measured by the noncontact microwave reflection technique. The threshold ion energy of displacement damage is very low near 20 eV but the RIE damage threshold for Si devices is found to be about 100 eV. This means that a RIE process with the bias voltage lower than 100 V(dc) can fabricate Si devices with no serious damage effect as long as surface contamination by reactive radicals is carefully avoided. In a SF6 plasma, the threshold energy of SiO2 RIE is 15 (+/-2) eV, independent of a substrate temperature, while the physical sputtering threshold is roughly 40 eV in Ar plasmas.