Low Global Warming C4H3F7O Isomers for Plasma Etching of SiO2and Si3N4Films

In this study, the plasmas of C 4 H 3 F 7 O fluoro-ether and fluoro-alcohol isomers of CF 3 CF 2 CF 2 OCH 3 (HFE-347mcc3), (CF 3 ) 2 CFOCH 3 (HFE-347mmy), and CF 3 CF 2 CF 2 CH 2 OH (PPC) with low global warming potentials (GWPs) were characterized for etching SiO 2, Si 3 N 4, and poly-Si films. The C 4 H 3 F 7 O isomers have a short lifetime (<5 years) and low GWP (<1000) compared to the widely used C 4 F 8, with a lifetime of 3200 years and a GWP 100 of 10,592. Radicals in the plasma of C 4 H 3 F 7 O fluoro-ethers and fluoro-alcohol isomers were analyzed by mass spectroscopy, and HF and CO peaks were identified as major gas-phase products in the plasma phase. The concentration of exhaust gases after plasma etching were analyzed, and the million metric tons of carbon equivalent (MMTCE) were determined relative to conventional perfluorocarbon (PFC), C 4 F 8 . HF, CO, and COF 2 were identified as the major reaction products in exhaust with C 4 H 3 F 7 O isomer plasmas. The MMTCEs of HFE-347mcc3, HFE-347mmy, and PPC were lowered by 82, 74, and 85%, respectively, compared with that of C 4 F 8 . The chemical bonding of the steady-state fluorocarbon film on SiO 2, Si 3 N 4, and poly-Si surfaces was analyzed during the etching process, and a lower F 1s/C 1s ratio was observed for C 4 H 3 F 7 O isomers than for C 4 F 8 . A high etch selectivity of 170 was achieved for SiO 2 etching over poly-Si and 263 for Si 3 N 4 etching over poly-Si with PPC plasma. This high selectivity is attributed to the higher carbon and lower fluorine contents in the steady-state fluorocarbon film. The C 4 H 3 F 7 O isomer plasmas also generate a superior etch profile compared to the C 4 F 8 plasma with an aspect ratio of 7:1 etch of 200 nm hole patterns. This study demonstrates that C 4 H 3 F 7 O isomers can significantly reduce the global warming effect by replacing the conventional PFC in the etching processes of semiconductor device fabrication.