Monitoring of the Intermediate Products in the Thermal Decomposition of SiH 4 , Si 2 H 6 , SiF 4 and SiH 2 F 2
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2 F2 and Si2 H6 diluted in H2 as the reactant mixture. They also used SiH 2F 2 and SiH 4 as the reactants. However, the reaction mechanism of SiH 2 F2 pyrolysis has not been studied in detail yet, and therefore we have studied experimentally the pyrolysis properties of silanes, difluorosilane and their mixtures under isothermal conditions. The partial pressures of the intermediate species produced by the gas-phase reaction have been measured by FTIR and mass spectroscopy following proper analysis procedures. The experimental conditions have been selected so that they are similar to those used by Nishida et al.[7] who obtained a crystalline Si film from the fluorosilane mixture at low temperatures. We have proposed the pyrolysis mechanism of silanes, difluorosilane and their mixtures based on the experimental observations of the intenriediates produced in the process. We expect that the results of this study will provide guidelines to selection of experimental conditions for obtaining crystalline Si films by decomposition of fluorosilanes at low temperatures. EXPERIMENT SiH 4, Si2 H6, SiF 4 and SiH 2 F2 diluted in H2 , were used as reactants for the pyrolysis experiments. H2 was of ultra-high purity grade, and SiH 4 and Si 2 H6 were of electronic grade. SiH 2 F2 purchased from Mitsui Chemicals included about 5% of SiHF 3 and insignificant amounts of SiH 4 and SiF 4 as analyzed with infrared spectroscopy. The gas mixture was pyrolyzed in a hot-wall stainless-steel batch reactor whose
internal volumne was about 12 crn3, and the product gases were analyzed with a
quadruple mass spectrorneter (Sensorlab 200, VG Instrument). Gas in the reactor was 39 Mat. Res. Soc. Symp. Proc. Vol. 406 0 1996 Materials Research Society
sampled by a capillary tube connected to the mass spectrometer chamber maintained at 10-r bar so that the mass spectrum of the pyrolysis gas was measured. Table I lists the location and the intensity of the characteristic mass spectroscopic peaks of the Si-containing species considered in this study. Table I. Mass spectroscopic peaks of Si-containing species Species
Location" (Relative Intensity)")
Ref. Peak
(m/e) SiH 4 28(0.94), 29(1), 30(2.86), 31(2.14), 32(0.2) Si 2H6 30(0.22), 31(0.30), 58(0.71), 59(0.30), 60(1), 61(0.39), 62(0.46) SiH 2F2 47(0.33), 49(1), 66(0.18), 67(1.21), SiF 4 33(0.015), 47(0.061), 85(1), 86(0.05) SiHF 3
47(0.35), 66(0.15), 67(1), 85(1.52)
29 60 49 85 67
SiF 3 47(0.5), 66(1), 85(0.2) SiF 2 47(1), 66(0.1) 1). Unit : rn/e 2). Defined as peak intensity/reference peak intensity
66 47
The peak intensity is given in relative magnitude with respect to a reference peak seleced for each species. The amounts of each species were estimated from the intensity of the peaks which were unique to the individual species. For example, the amounts of SiH 2F2 was estimated from the peak at m/e = 49. As the peak at m/e = 67 appeared only with SiH 2 F2 and SiHF 3, the amount of SiHF 3 was obtained from the difference between the observed peak intensity and the intensity corresponding to the
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