High aspect ratio SiO₂/SiN (ON) stacked layer etching using C₃HF₅, C₄H₂F₆, and C₄H₄F₆

Abstract

Abstract High aspect ratio SiO 2 /SiN (ON) stacked layer etching using hydrofluorocarbon gases was conducted with various ratios of H, F, and C to achieve higher etching rates and precise profile control. The experimental gases were C 3 HF 5 , C 4 HF 5 , C 4 H 2 F 4 , C 4 H 2 F 6 , C 4 H 4 F 6 and C 5 H 2 F 10 . The oxygen gas flow rate and mixing ratio were optimized to maximize mask selectivity while avoiding clogging at the top of the mask. For comparison, C 4 F 6 /CH 2 F 2 /Ar/O 2 , and C 4 F 6 /C 4 F 8 /CH 2 F 2 /Ar/O 2 were used as reference gas mixtures. The initial screening narrowed the candidate pool to 3 gases: C 3 HF 5 , C 4 H 2 F 6 , and C 4 H 4 F 6 . At equivalent power, the C 3 HF 5 condition achieved a 15% faster ON etch rate, and C 4 H 2 F 6 achieved a 9% faster ON etch rate compared to the reference condition. Only C 4 H 4 F 6 showed a worse ON etch rate than the reference (∼33%) due to severe mask clogging. Furthermore, C 3 HF 5 achieved a 29% faster ON etch rate under high power conditions. It also achieved a 57% faster ON etch rate without excessively compromising selectivity or bow CD expansion after optimization. We report detailed comparisons of etch rate and clogging while controlling the CD profile in the ON stack process.