Selective atomic layer etching of Al2O3, AlNx and HfO2 in conventional ICP etching tool

Abstract

The atomic layer etching process of Al2O3, AlNx and HfO2 in conventional plasma etching tool was investigated. The etching process is based on surface modification by fluorocarbon film deposition from Ar/CF4/H2 plasma and subsequent activation of etching by Ar ion bombardment from plasma. The study of deposition process showed that varying plasma composition surface kinetics significantly change from deposition to etching. This is associated with the rise of fluorine concentration both in plasma and in deposited fluorocarbon film. Plasma mixture with low CF4 fraction was chosen for modification step of ALE process because it provides low fluorinated film which does not etch SiO2 and TiN improving selectivity to the potential mask material in etch process. The ALE process shows self-limiting characteristics providing the ALE process window at duration of modification step. The etch rate is 0.16 nm/cycle for Al2O3, 0.20 nm/cycle for AlNx and 0.11 nm/cycle for HfO2, which is close to monolayer mode. Relatively short cycle duration provides feasible etch rate in terms of time consumption. The significant selectivity over TiN (more than 20) was achieved allowing employing TiN as mask material for high resolution selective etching.