Atomic layer etching of molybdenum with fluorination and ion bombardment

Atomic layer etching (ALE) process for Mo was developed with surface fluorination using CHF3 or C4F8 plasmas and ion bombardment using Ar plasma. The Mo surface was fluorinated with fluorocarbon generated by CHF3 or C4F8 plasmas, and fluorinated Mo was etched by Ar plasma. The C4F8 plasma produced fluorine-rich fluorocarbon layer compared to the CHF3 plasma and etch per cycle (EPC) of Mo was about 3 times higher in C4F8 plasma than in CHF3 plasma. EPC of Mo was investigated by changing the bias voltage of Ar plasma, and ALE window was confirmed in the range of 100 ~ 225 V. The EPC of Mo in the ALE window was determined to be 0.8 nm/cycle for CHF3 plasma and 2.8 nm/cycle for C4F8 plasma, and it was self-limited with increasing Ar plasma time. Fluorine-rich fluorocarbon layer on the Mo surface increases the EPC of Mo.