Paper PS-TuM9
Etch Mechanisms of Silicon Gate Structures Patterned in SF₆/CH₂F₂ Inductively Coupled Plasmas

Tuesday, October 21, 2008, 10:40 am, Room 304

Patterning sub-40 nm gates presents several challenges among which maintaining a tight CD control is one of the most challenging. To succeed, understanding the etching mechanisms in gate patterning processes is one of the challenge. In this work we have investigated the different physical phenomena involved during the patterning of silicon structures in SF₆/CH₂F₂ based plasmas. The experimental work has been carried using a 200 mm etch platform connected, under vacuum, to an x-ray photoelectron spectroscopy surface analysis system. We have studied the impact of the SF₆/CH₂F₂ ratio on the silicon etch rate, thickness and composition of the reactive layer formed on the bottom silicon surfaces of the etched structures, thickness and composition of the sidewall passivation layer formed on the silicon sidewalls and silicon profiles. Our results demonstrate that there are very good correlations between the silicon etch rates and reactive layers formed on the bottom silicon surfaces. Contrary to previous studies performed using HBr/Cl₂/O₂ chemistries our results indicate that there is no simple correlation between the thickness of the CF_x passivation layer formed on the sidewalls and the final slope obtained in silicon. Our results demonstrate on the contrary, that even if very thin CF_x based passivation layers are formed on the silicon sidewalls, significant slopes can be generated in silicon. Other experimental results will be shown to elucidate the etch mechanism driving the silicon gate etch profiles during SF₆/CH₂F₂ plasma etching.