Characterization of Highly Selective SiO_2/Si_3N_4 Etching of High-Aspect-Ratio Holes

概要

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The pattern size dependence of SiO_2 etch Si_3N_4 etch rates of contact holes (RIE-lag) in C_4F_8 + CO plasma was studied, It was found these etch rates can be characterized by the aspect ratio, regardless of the pattern size. SiO_2 etch rate decreased with increasing aspect ratio and became 0 at an aspect ratio of 6. Si_3N_4 etch rate also decreased; however, etching still occurred at an aspect ratio of 30. From ion current measurements through capillary plates (CPs), it was deduced that etch rates decreased because of decreasing ion current. XPS analyses revealed that fluorocarbon film deposited on the Si_3N_4 surface at the bottom of a hole was more F-rich than that deposited on a flat si_3N_4 surface. This explained why Si_3N_4 is etched even in high-aspect-ratio holes. A small amount of O_2 addition to the C_4F_8 + CO plasma resolved the RIE-lag. It was found that the ion current density at high aspect ratio increased with O_2 addition, which would enhance SiO_2 etching and contribute to suppressing RIE-lag.
社団法人応用物理学会の論文
1996-04-30