Saturated perfluorocarbons (PFCs) such as CF 4 , C 2 F 6 , C 3 F 8 and c-C 4 F 8 are used as dry-etch gases in the semiconductor industry. They have a significant greenhouse effect. Unsaturated fluorocarbons can be alternated with these PFCs because of their easy decomposition in the atmosphere. The authors have diagnosed the plasmas generated from straight-chain unsaturated gases such as C 3 F 6 , C 4 F 6 , C 4 F 8 and C 5 F 8 in an inductively coupled plasma reactor and have compared their etch properties. It was found that high selectivity has been obtained in a C 4 F 6 or C 5 F 8 plasma without mixing any specific gases. Fine contact holes of approximately 100 nm in diameter also have been obtained using C 4 F 6 or C 5 F 8 with or without adding Ar or O 2 . These good etch properties of C 4 F 6 and C 5 F 8 have been achieved as a consequence of the appropriate balance between the lower density of fluorocarbon polymers and the dominant etching species CF + with lower etching efficiency. It can be concluded that C 4 F 6 and C 5 F 8 can be used as PFC replacements for the dry-etch gas.
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Nakamura et al. (2003) studied this question.