Effects of electron temperature in high-density Cl₂ plasma for precise etching processes

Silicon etching characteristics are investigated by using radio-frequency (rf) biased ultrahigh frequency (UHF) and other conventional plasmas (electron cycotron resonance plasma, inductive coupled plasma, surface wave plasma) determined by using a Cl₂ etchant. The silicon etching rate and its pattern dependence are significantly improved by decreasing the electron temperature when supplying a 600-kHz rf bias. In particular, use of the UHF plasma allows high-rate and microloading-free silicon trench etching. It is suggested that a larger number of negative ions are generated in the UHF plasma because of the extremely low electron temperature. The low-frequency bias accelerates the negative and positive ions alternately to the substrate surface. As a result, the low-frequency biased UHF plasma reduces the charge accumulation on the substrate.