Paper PS-TuM11
Evaluation of C5HF7: A High Etch Selectivity Hydrogen-Containing Fluorocarbon Gas for Oxide Etch

Tuesday, November 1, 2011, 11:20 am, Room 201

A high etch selectivity hydrogen-containing fluorocarbon gas, C5HF7, was evaluated for high aspect ratio dielectric etch. Plasma etching with Ar/C5HF7/O2 chemistry was shown to have significant advantages over Ar/C4F6/O2 in terms of oxide-to-organic mask etch selectivity and line-edge roughness. The mechanism behind the high etch selectivity of C5HF7 originated from the different thickness and composition of steady-state fluorocarbon (FC) layers generated on oxide and organic mask materials during plasma etch. We also determined that hydrogen addition to the Ar/C4F6/O2 feedgas did not reproduce C5HF7 etch behavior, presumably due to the difference in atomic hydrogen formation between molecular H2 dissociation versus intramolecular H dissociation (from C5HF7). This latter phenomenon facilitated a wider window for “etch stop” margin. Profile evaluation showed larger bowing for C5HF7, compared to C4F6, and was linked to a higher sticking coefficient of CxFyHz radicals. This was verified and remedied by increasing the substrate temperature, which reduced the radical sticking coefficient and eliminated bowing, while maintaining the high etch selectivity. We also demonstrated reduced low-frequency line-edge roughness when etching with C5HF7. We showed that less surface roughness was generated using C5HF7 since less organic mask thickness was removed. In addition, since a major contribution of line-edge roughness was the transfer of organic mask surface roughness into the sidewalls of the dielectric, overall lower line-edge roughness was observed.