Abatement of perfluorocarbons using direct current plasma generated in gas bubbles in water

Yuriko Matsuya, Ryota Miyazawa, Kei Ikeda, Nozomi Takeuchi, Koichi Yasuoka^*

^* The author to whom correspondence should be addressed.

Department of Electrical and Electronic Engineering, Tokyo Institute of Technology, Japan

Abstract

Reducing the use of perfluorocarbons (PFCs) in semiconductors and other industries is a key issue. To this end, to date combustion methods have often been implemented for large abatement systems. However, plasma could potentially be used to develop a compact system that operates at a low gas flow rate. Here, atmospheric direct current (DC) plasma generated in gas bubbles in water was demonstrated to remove C₂F₆ and CF₄. Using nitrogen-based 1% C₂F₆ a removal rate of 90.6% was achieved at 35 mA and 0.071 standard liters per minute (SLM). Fourier-transform infrared spectroscopy (FTIR) analysis indicated that the byproduct ratio of CF₄ to C₂F₆ was below 1%; thus, almost all CF₄ was decomposed by the DC plasma. The decomposition characteristics of CF₄ were studied by changing the base gas, such as nitrogen and argon. The gas temperatures in both plasmas were approximately the same. However, the argon-based plasma showed a higher mean electron energy (by approximately 2 eV) and a higher removal rate at the same plasma power. In conclusion, both thermal and impact collision processes occur during the decomposition of CF₄. The difference in the removal rate was possibly caused by the metastable atoms and ions in the argon-based scrubbers.

Keywords - Abatement, tetrafluoromethane (CF₄), hexafluoroethane (C₂F₆), DC plasma, gas bubble.

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