Synthesis of Hard Si-C Composite Films by Ion Beam Irradiation of Polymer Films
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SYNTHESIS OF HARD SI-C COIPOSITE FILMS BY ION BEAM IRRADIATION OF POLYMER FILMS T. VENKATESAN, T. WOLF, D. ALLARA, B. 3. WILKENS and G. N. TAYLOR Bell Laboratories, Murray Hill, New Jersey 07974 G.FOTI University of Catania, Catania, Italy
ABSTRACT We propcoe a novel technique to convert polymer films into useful inorganic films by ion beam irradiation. Along the track of an ion the polymer is dissociated into smaller fragments. Vdatile fragments diffuse through the film and escape. Any element which is not removed in the form of volatile species is subsequently enriched with respect to the other elements. We demonstrate this effect in a pdymer pdy(dimethylsilylene-co-methylphenylsilylene), which initially has a C'Si ratio of 45:1. 2 Upon irradiation with 2 MeV Ar+ irns at a dose of 1015 ions/cm the C:Si ratio changes to 3.4:1 as verified by Rutherford backscattering spectrometry. We believe that the effect of the ion beam irradiation is to produce more Si-C bonds at the expeme of the C-H and Si-Si bonds, with < 10% of the original hydrogen being present in the film at high doses. The loss of the H atoms is further confirmed by a nuclear reaction technique. The IR spectra of the film as a function of the irradiation dose shows a progressive loss of fine mdecular features with significant increase of the refractive index. The IR spectrum at the high doses appears to be due to a mixture of various Si and C bonds. However, the irradiated films are very hard and scratch resistant (knocp value > 1300) suggesting an increase in the number of silicon carbide bonds. fItnrodltion
Ion beam interaction with polymers has been studied with the intention of using ions to xtpose resists for high resolution lithography.' Recently, ion beam irradiation has also been shown to reduce 2 the resistivity of organic and pdoymeric` films. The dynamics of the degradation of polymers by ion 4 beam irradiation also has been studied and in this study significant emission of molecular species has been doserved from the irradiated pdymer films. In general, most polymers tend to carbonize with increasing radiation dose and the reason for this is simply that not all the carbon atoms form volatile species during or after the irradiation process. This idea can be generalized to elements other than carbon. One could in principle design a pdymer with elements A, B, C, etc. (Fig. 1) such that when the film is irradiated, of the various molecules formed, A and B are not removed significantly as volatile mdecules, while the other elements are completely volatilized. One can then form an inorganic composite with a large number of A-B bonds. Coupled with the ability to pattern using ion beams, this may enable the patterned synthesis of an inorganic compound from a polymer film. To demonstrate this idea we chose the polymer poly(dimethylsilylene-co-methylphenylsilylene), which is rich in silicon. The polymer is prepared (Fig. 2) by the method of West and co-workers.5 A tcluene-sodium mixture was heated to the reflux temperature resulting in a sodium meta
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