Co2 laser photosensitised (SF6) decomposition of diethylsilane proceeds via molecular extrusion of ethene and affords solid Si/C/H materials wbich possess both Si-C and Si contributions, contain some fluorine from the sensitising sulphur hexafluoride, and react with ambient atmosphere to incorporate oxygen. INI'RODUCTIONStudies of the gas-phase decomposition of various organosilanes are important due to possible applications in chemical vapour deposition of silicon (Si) and silicon carbides (SiC l-.x) f11m5. The examinations of these processes under various conditions (structurally different precursors, different techniques ofthe initiation ofthe decomposition) are ofinterest due to correlation between the mechanism of the gas-phase reactions and properties of the deposited films. Of the infrared laser-induced processes, those using monoorganylsilanes have attracted most attention. 15 Infrared multiphoton decompositions of RSiH3 (R = C2H5 and n-C4H9) proceed3 via a four-centre activated complex involving H atoms 3 to silicon, while those of (HnF3nC)SiH3, n=O-2) are dominated4'5 by a dyotropic rearrangement or by a series of carbene cleavage/insertion reactions. Diethylsilane (DES) is a safe potential precursor for preparation of the Si or (SiC i) films, but its decomposition has been studied only under conditions of heterogeneous thermolysis' and infrared multifoton dissociation7. We report on cw CO2 laser-induced and SF6 photosensitised decomposition (LPD) of DES and investigate both mechanism of this decomposition and properties of the deposited layers. EXPERIMENTALContinuous-wave CO2 laser photosensitised decomposition of DES was carried out by the irradiation (laser output 10 W, incident radiation energy 30 W.cm2) of DES (0.3 -0.7 kPa) -SF6 (sensitizer, 2.7 -5.4 kPa) mixtures in a glass tube (10 cm x 3.6 cm ID.) reactor furnished with two KBr windows. The cw CO2 laser was operated at the P(20) line of the l-+ 1 transition (944. 1 9 cnc l) where absorptivities of DES (3 .3 x 1 -2 kPa 1 cm l) and SF6 (1 .4 kPa 1 cnr l) infer that absorption in the sensitizer was dominant. The mixtures were irradiated for measured intervals (time 5 -60 sec) and analysed using a Nicolet Impact FTIR spectrometer, a Shiniadzu QP-1000 mass spectrometer (70 eV, Porapak P, programmed temperature) and gas chromatograph Chrom 5 (Alumina). Properties of the deposit were measured by the FTIR spectrometer, a VG ESCA 3 Mk II electron spectrometer and SEM Tesla BS 350 ultrahigh vacuum instrument equipped with an EDAX dispersive analyser of X-radiation. Sulphur hexafluoride (Fluka) and DES (ABCR) were commercial samples. O-8194-1813-7/95/$6.OO SPIE Vol. 2461 / 121 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 05/30/2015 Terms of Use: http://spiedl.org/terms

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