The authors found that a B Cl3 N2 plasma is very suitable for metal gate patterning and profile control as it produces a passivating film during the etching. On blanket wafers, a boron-nitride-like film is deposited from a boron trichloride/nitride plasma mixture in a standard etch chamber at temperatures as low as 60 °C. Deposition rate can be varied from 10 to more than 100 nmmin depending on the plasma conditions and B Cl3 N2 ratio. The film contains hexagonal boron nitride but is very unlikely to be a stoichiometric BN. It decomposes at elevated temperatures and is water soluble. The latter property makes the postetch clean relatively straightforward. This film can be used for sidewall passivation during the patterning of advanced non-Si gates, e.g., metal gates. They are presenting the use of B Cl3 N2 plasma for patterning of Ge and TaN gates as examples. The Ge gate profile is damaged by a pure B Cl3 plasma during high- k dielectric (Hf O2) etching after the gate patterning. Addition of 10% N2 to the B Cl3 plasma preserves the gate profile while removing the high k. In the other example, a TaN gate is etched isotopically by pure B Cl3 plasma. Addition of 5% N2 prevents the lateral attack providing straight TaN profile.
Shamiryan, D., Paraschiv, V., Eslava, S., Demand, M., Baklanov, M., Beckx, S., & Boullart, W. (2007). Profile control of novel non-Si gates using B Cl3 N2 plasma. Journal of Vacuum Science & Technology B, 25(3), 739-744. https://doi.org/10.1116/1.2731333