| AVS 63rd International Symposium & Exhibition | |
| Plasma Science and Technology | Thursday Sessions |
| Session PS-ThA |
| Session: | Plasma Chemistry and Plasma Surface Interactions |
| Presenter: | Kenji Ishikawa, Nagoya University, Japan |
| Authors: | K. Ishikawa, Nagoya University, Japan T. Tsutsumi, Nagoya University, Japan Y. Zhang, Nagoya University, Japan M. Sekine, Nagoya University, Japan T. Hayashi, Nagoya University, Japan M. Hori, Nagoya University, Japan Y. Horiike, Tsukuba University, Japan |
| Correspondent: | Click to Email |
In chemical dry etching (CDE) of F-based etch chemistry such as CF4, SF6, etc. [1], it has been believed that F atoms transport as long as 1 meters downflow of plasma source and etch Si with etch rates around 500 nm/min [2]. The etch results for SiO2 and SiN films were shown stable even low rates but relevant values regardless of the distance [3,4]. Otherwise, whilst the cases of NO + F2 gas mixture generates F atoms, the etch rates significantly decreases with the distance from the location generated F atoms [5]. These apparently paradoxical results remain an open question, which needs to revisit. In particular of O2 addition, the etch rate-dependence versus distance is evident, thus the the effects of peroxy radicals, OOF, and peroxides, F2O2, are hypothesized. Here, we report the transport mechanism on reactive species in downflow for F-based etch.
The chemical dry etching apparatus was constructed by a long-length quartz tube. A mixture of CF4 and O2 gases was flown into the tube and a microwave cavity (2.45 GHz, 50W) was used for plasma generation. At the downflow, F atom or FOO signals were measured by electron spin resonance (ESR) instrument [6,7]. Quantum-chemical calculations were done with B3LYP/6-311+G(d) by Gaussian 09.
Ground-state of O2 (3Σg) is reacted with F atom and stabilized 0.36 eV to generate OOF. Subsequently, OOF reacts with F atom to form F2O2. The OOF and Si reaction takes place Si + OOF -> SiF + O2(3Σg), rather than Si-oxidation pathways.
Experimentally, concentrations of F atoms at downflow depended on mixture ratio of O2 and distances from the plasma source. The O2 addition enhanced to transport F atom toward further positions. In general, although F atom recombination to F2 is known to be relatively low reaction rate, however the recombination cannot be negligible during transport. Thus, we revisited the radical complex mechanism, i.e., F + O2 -> OOF and OOF -> F + O2, vise verse. In summary, we suggest that the transport of reactive species needs to revisit effects of the radical complex of F atom with O2., in particular of the O2 added F-based chemistry.
[1] Y. Horiike et al. Jpn. J. Appl. Phys. suppl. 15 (1976) 13; [2] N. Hayasaka et al., 11th Proc. DPS (1989), p.57;[3] B. E. E. Kastenmeier et al., J. Vac. Sci. Technol. A 14 (1996) 2802; [4] G. S. Oehrlein et al., Plasma Sources Sci. Technol. 5 (1996) 193; [5] S. Tajima et al., J. Phys. Chem. C 117 (2013) 5118; [6] H. E. Radford et al., Phys. Rev. 123 (1971) 153; [7] A. D. Kirshenbaum et al., J. Am. Chem. Soc. 88 (1966) 2434.