Quasi-atomic layer etching of silicon with surface chlorination and removal using Ar or He plasmas

A comparative study of argon (Ar) and helium (He) plasmas is conducted in quasi-atomic layer etching (ALE) processes for silicon (Si). The ALE window is identified to be between 35 and 55 V for Ar and 25–45 V for He, with an etch per cycle of 6.0 Å/cycle for Ar and 7.5 Å/cycle for He. Thirty percent thicker chlorination layers are observed with Cl₂/He ALE than with Cl₂/Ar ALE in the chlorination step. The penetration depth of He ions is twice that of Ar ions, with a standard deviation of 4.5 times greater. This study demonstrates that He ions in the removal steps considerably affect the subsequent modification steps in Si ALE.