Interactive relationships between sidewall and bottom etch rates, as-affected by sidewall angle, during SiO2 etching in a CHF3 plasma

摘要

Relationships between sidewall and bottom etch rates during SiO2 etching in a CHF3 plasma were studied using a Faraday cage system, which permitted the sidewall angle to be controlled with respect to ions incident on the surface and the sidewall and bottom surfaces to be examined on a scale larger than in actual microfeatures. The etch rates for the sidewall were significantly decreased at sidewall angles near 75 degrees and the resulting angular dependence of the etch rates decreased monotonously following an "inversely S-shaped" curve. On the other hand, the degree of sidewall effect (DSE), which represents changes in the bottom etch rates due to the presence of the sidewall, showed a characteristic "W-shaped" curve with respect to sidewall angle, due to a decrease in the bottom etch rates at sidewall angles near 75 degrees. The relationship between the sidewall etch rate and the DSE was affected by a thick, rough steady-state fluorocarbon film formed on the sidewall surface. The thickness, roughness, and F/C ratio of the fluorocarbon film were examined for cases of different sidewall angles, and their contributions to the sidewall etch yield and the bottom etch rate are discussed with respect to energy transferred to the sidewall surface by bombarding ions. (c) 2006 American Vacuum Society.