Low Global Warming C₄H₃F₇O Isomers for Plasma Etching of SiO₂and Si₃N₄Films

Abstract

In this study, the plasmas of C4H3F7O fluoro-ether and fluoro-alcohol isomers of CF3CF2CF2OCH3 (HFE-347mcc3), (CF3)2CFOCH3 (HFE-347mmy), and CF3CF2CF2CH2OH (PPC) with low global warming potentials (GWPs) were characterized for etching SiO2, Si3N4, and poly-Si films. The C4H3F7O isomers have a short lifetime (<5 years) and low GWP (<1000) compared to the widely used C4F8, with a lifetime of 3200 years and a GWP100 of 10,592. Radicals in the plasma of C4H3F7O 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), C4F8. HF, CO, and COF2 were identified as the major reaction products in exhaust with C4H3F7O isomer plasmas. The MMTCEs of HFE-347mcc3, HFE-347mmy, and PPC were lowered by 82, 74, and 85%, respectively, compared with that of C4F8. The chemical bonding of the steady-state fluorocarbon film on SiO2, Si3N4, and poly-Si surfaces was analyzed during the etching process, and a lower F 1s/C 1s ratio was observed for C4H3F7O isomers than for C4F8. A high etch selectivity of 170 was achieved for SiO2 etching over poly-Si and 263 for Si3N4 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 C4H3F7O isomer plasmas also generate a superior etch profile compared to the C4F8 plasma with an aspect ratio of 7:1 etch of 200 nm hole patterns. This study demonstrates that C4H3F7O isomers can significantly reduce the global warming effect by replacing the conventional PFC in the etching processes of semiconductor device fabrication.

Dissociation of Hydrofluorocarbon Molecules after Electron Impact in Plasma

“…The goal of these simulations will be to understand the rules, which should enable us to predict products of dissociation and, therefore, enable control of the chemical composition of plasma. Our effort to find simple rules of dissociation of molecules after electron impact supports that of recent works, 28,29 where dissociation of molecules in low temperature plasma have been investigated experimentally.…”

“…Hydrofluorocarbons and other organofluorine molecules are broadly used in the microelectronics industry for various plasma technologies. Recently they came under scrutiny due to their potential environmental damage, and the importance of finding new less environmentally damaging molecules has recently been highlighted. , We demonstrate that simulations of the dynamics of their dissociation are possible and can be done in a manner similar to how simulations of photodissociation were done previously. Also, perhaps, simple rules that allow predictions of dissociation channels can be found, improving plasma modeling for applications.…”

Plasma Atomic Layer Etching of SiO2 and Si3N4 with Low Global Warming C4H3F7O Isomers

“…The CH 3 peaks in the HFE-347mcc3 and HFE-347mmy plasmas are attributed to −OCH 3 in the molecules. The −OCH 3 induced an inductive effect at the center of the HFE-347mmy molecule and weakened adjacent C–C bonds, resulting in the generation of trifluoromethyl (CF 3 ) and (1,2,2,2-tetrafluoroethoxy)­methyl (C 3 H 3 F 4 O) radicals, as indicated by the dashed lines in Figure . Because hydrogen decomposed in the CH 3 radical combined with fluorine in the HFE-347mmy plasma to form HF, the HFE-347mcc3 plasma generated relatively large amounts of C x F y radicals as compared with the HFE-347mmy plasma. − In the PPC plasma, the CF peak was dominant, but H, CHO, and CF 3 peaks were also detected.…”

“…The CH 3 peaks in the HFE-347mcc3 and HFE-347mmy plasmas are attributed to −OCH 3 in the molecules. The −OCH 3 induced an inductive effect at the center of the HFE-347mmy molecule and weakened adjacent C−C bonds, resulting in the generation of trifluoromethyl (CF 3 ) and (1,2,2,2-tetrafluoroethoxy)methyl (C 3 H 3 F 4 O) radicals, as indicated by the dashed lines in Figure2 57.…”

Etching Mechanism Based on Hydrogen Fluoride Interactions with Hydrogenated SiN Films Using HF/H2 and CF4/H2 Plasmas

“…This phenomenon is particularly significant for Si and SiO 2 etching, as they are generally considered to have no reaction with gaseous HF. ,, Based on the proposed model, it is evident that HF can react with the hydrogenated SiN surface. This leads us to consider the following scenario: In the CF 4 /H 2 plasma case, HF molecules, generated from the plasma and released from the hydrofluorocarbon layer deposited on the film surface via ion bombardment, are expected to increase, based on the numerical simulations and experiments. ,, The HF molecules spawned from the hydrofluorocarbon are highly likely to react with the hydrogenated SiN surface, resulting in the formation of the AFS phase, particularly when the H 2 concentration in plasma is increased. This could potentially explain the fact that a small amount of AFS phase formation occurs at higher hydrogen content, as observed in the XPS spectra.…”