AVS 46th International Symposium
    Thin Films Division Monday Sessions
       Session TF+VM-MoA

Paper TF+VM-MoA10
Polymerization in Remote Hydrocarbon Deposition Plasmas

Monday, October 25, 1999, 5:00 pm, Room 620

Session: Advances in Hard and Superhard Coatings II
Presenter: M.C.M. van de Sanden, Eindhoven University of Technology, The Netherlands
Authors: A. de Graaf, Eindhoven University of Technology, The Netherlands
M.F.A.M. van Hest, Eindhoven University of Technology, The Netherlands
M.C.M. van de Sanden, Eindhoven University of Technology, The Netherlands
K.G.Y. Letourneur, Eindhoven University of Technology, The Netherlands
D.C. Schram, Eindhoven University of Technology, The Netherlands
Correspondent: Click to Email
The chemistry of expanding argon plasmas into which either methane (CH@sub 4@) or acetylene (C@sub 2@H@sub 2@) is injected for fast deposition of a-C:H, DLC and diamond films was studied by means of mass spectrometry, Fourier transform infrared absorption and in situ ellipsometry. The measurements reveal that the plasma chemistry of the expanding Ar/C@sub 2@H@sub 2@ and Ar/CH@sub 4@ plasmas is dominated by argon ion induced dissociation of the precursor gas. For acetylene injection the ion-induced dissociation is very efficient leading to complete depletion under certain conditions. For methane injection however, even under conditions of highest reactivity 100% dissociation of the precursor gas can not be reached. In an Ar/CH@sub 4@ plasma under certain conditions up to 40% of the injected precursor flow is transformed into C@sub m@H@sub n@ (m>1) polymers. In an Ar/C@sub 2@H@sub 2@ plasma the polymerization is much less (maximum 4%) and preferentially C@sub 2m@H@sub n@ polymers are formed. This suggests that in an Ar/C@sub 2@H@sub 2@ plasma the C@sub 2@H radicals are the main building blocks in the polymerization process and that they are probably also the dominant radicals in the deposition process. In the case of acetylene injection the deposition rate as measured in situ by ellipsometry is proportional to the depletion of the precursor gas. For methane injection however this proportonality does not hold even when the polymerization is taken into account. The difference in the polymerization rate and the dependence of the deposition rate on the gas depletion for the two plasmas is attributed to the different loss probabilities of the radicals formed in the dissociation. It is suggested that the large amount of C@sub 2@H@sub 2@ formed in the Ar/CH@sub 4@ plasma may lead to formation of radicals which, due to their relatively high loss probability, may become the dominant growth precursors.