Measuring Ion Energy Distributions by Retarding Field Energy Analyzer and Using Low-Energy Ions for Si-ALE by Cl2

To minimize etching damage of the underlying material, atomic layer etching (ALE) with low-energy ions was used for structuring silicon. The ion energy distribution was determined using a retarding field energy analyzer. The etching tool achieved a maximal ion energy of 136 eV at 140 W bias power and an average ion energy of 11.1 eV without applied bias power. The plasma-enhanced ALE included a Cl2 adsorption and an Ar desorption step. The bias power was varied between 8 W and 22 W. The observed etch per cycle (averaged over 30 cycles) was minimal (~0.3 nm) at 8 W (~12 eV) and maximal (~14 nm) at 19 W (~23 eV) bias power. Atomic force microscopy measurements revealed rough etch grounds.