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Electronic chemicals
advanced critical dimension dielectric etching process-
es now employ these two etching chemistries.
A study has been published examining the per-
formance of these gases in fluorocarbon plasma. The
rate of polymer film formation is two times faster for
C4F6 than c-C5F8, and 50 times faster than c-C4F8.5
In addition, this study suggests there is more cross-
linked carbon present in the films made from c-C5F8
and C4F6 than the films made from cyclic-C4F8.
This is believed to be a direct consequence of the
large abundance of highly unsaturated poly-carbon
species present in polyunsaturated plasmas. Higher
cross-linking implies a more durable film that is bet-
ter able to resist ion sputtering and/or plasma etch-
ing and therefore, offer better protection of pho-
toresists and channel side walls.
We were unable to find any information about
cyclic hexafluorobutene (c-C4F6, 4) as an etchant
gas but we imagine that such a molecule should
also be of interest. Vapour phase reaction studies on
C4F6 indicate that there is a rapid rearrangement to
the cyclic isomer.6,7 Many of these reactions are
probably also occurring in the plasma.
Conclusion
The industry will continue to move to smaller and
smaller resolution. The trends towards lower fluo-
rine-to-carbon ratios may possibly continue. If so,
then molecules like c-C4F4 or c-C5F8 might be of
interest as they combine three degrees of unsatura-
tion with even lower fluorine-to-carbon ratios.
Another approach might be to substitute one or
more of the fluorine molecules with hydrogen. One
thing is certain: the electronics industry will continue
to make smaller and smaller devices.
Speciality Chemicals Magazine June 2009 37
he dry etching of electronic chips
F
F F
F
F F
F F
1
F
F
F
F
F F
2
F
F
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F
4
F
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F F
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3
References:
1. G.E. Moore, Electronics 1965, 38 (8), 1003-1006
2. J.W. Coburn & H.F. Winters, J. Appl. Phys. 1979, 50,
3189
3. R. Chatterjee, R. Reif, T. Sparks, V. Vartanian, B.
Goolsby & L. Mendicino, Proceedings - Electrochemical
Society, 2002, 99
4. M. Nakamura, M. Hori, T. Goto, M. Ito & N. Ishii, J.
Vacuum Science & Technology A 2001, 19, 2134
5. B. Ji, S.A. Motika, P.R. Badowski, S. Dheandhanoo,
J.R. Stets & E.J. Karwacki, Solid State Technology 2005,
48, 11
6. E.W. Schlag & W.B. Peatman, J. Am. Chem. Soc.
1964, 86, 1676-1679
7. R.N. Zitter, D.F. Koster & K. Cheung, J. Phys. Chem.
1985, 89, 944Figure 2 - Etchant gas structures
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