L. A. Chuprov

High-resolution Fourier-transform IR spectroscopic determination of impurities in silicon tetrafluoride and silane prepared from it

The impurity compositions of silicon tetrafluoride and silane prepared from it have been determined by high-resolution Fourier-transform IR spectroscopy. In the spectra of SiF4 samples differing in purity, we have identified rovibrational bands arising from Si2F6O, SiF3OH, HF, SiF3H, SiF2H2, SiH3F, CH4, CO2, and CO impurities. Their detection limits lie in the range 9 × 10−5 (CO2) to 3 × 10−3 mol % (Si2F6O). In the spectra of SiH4 samples of different purity, we have detected CH4, CO2, SiF3H, SiF2H2, and SiF4 impurities. Their detection limits lie in the range 8 × 10−5 (CO2) to 1 × 10−3 mol % (SiF4).

Integral Intensities of Absorption Bands of Silicon Tetrafluoride in the Gas Phase and Cryogenic Solutions: Experiment and Calculation

The spectral characteristics of the SiF4 molecule in the range 3100–700 cm−1, including the absorption range of the band ν3, are studied in the gas phase at P = 0.4–7 bar and in solutions in liquefied Ar and Kr. In the cryogenic solutions, the relative intensities of the vibrational bands, including the bands of the isotopically substituted molecules, are determined. The absorption coefficients of the combination bands 2ν3, ν3 + ν1, ν3 + ν4, and 3ν4 are measured in the solution in Kr. In the gas phase of the one-component system at an elevated pressure of SiF4, the integrated absorption coefficient of the absorption band ν3 of the 28SiF4 molecule was measured to be A(ν3) = 700 ± 30 km/mol. Within the limits of experimental error, this absorption coefficient is consistent with estimates obtained from independent measurements and virtually coincides with the coefficient A(ν3) = 691 km/mol calculated in this study by the quantum-chemical method MP2(full) with the basis set cc-pVQZ.

Application of High-Resolution IR and Microwave Spectroscopies for Investigation of the Impurity Composition of Silicon Tetrafluoride

The possibility of combined application of gas chromatography, high-resolution IR spectroscopy, and transient microwave gas spectroscopy (TMGS) for investigation of the impurity composition of silicon tetrafluoride is studied. Using high-resolution IR Fourier spectroscopy, the lines of a number of impurities are observed in the region from 4500 to 550 cm−1. The absorption lines of some of the main well-known impurities in silicon tetrafluoride in the 2-mm wavelength range are analyzed. The advantages of the TMGS method for investigating the multicomponent SiF4-impurities system are demonstrated. Using the TMGS method, the freons CHF3, CH2F2, and CH3F are experimentally detected in silicon tetrafluoride.

Molecular analysis of isotopically enriched 28SiF4 and 28SiH4 prepared from it

We have developed analytical techniques for the determination of impurities in isotopically enriched 28SiH4 and 28SiF4. The impurities in SiF4 were first determined by IR spectroscopy, and those in SiH4, by gas chromatography/mass spectrometry. High-sensitivity determination of organic impurities in SiH4 and SiF4 was performed by gas chromatography. SiF4 was found to contain C1–C4 hydrocarbons, hexafluorodisiloxane (Si2F6O), hydrogen fluoride, trifluorosilanol (SiF3OH), fluorosilanes, water, and carbon oxides. The impurities identified in SiH4 include C1–C4 hydrocarbons, disilane (Si2H6), inorganic hydrides, Si2H6O, alkylsilanes, and fluorinated and chlorinated organics. The detection limits of IR spectroscopy were 3 × 10−3 to 5 × 10−5 mol %, those of gas chromatography/mass spectrometry were 8 × 10−6 to 10−8 mol %, and those of gas chromatography were 6 × 10-6 to 2 × 10−7 mol %.

Impurities in monosilanes synthesized by different processes

Using high-resolution IR spectroscopy, we have compared the impurity compositions of monosilane (SiH4) fractions enriched in impurities in the process of cryofiltration and low-temperature distillation of monosilanes derived from silicon tetrafluoride (SiF4) and trichlorosilane (SiCl3H). The results demonstrate that the more volatile impurities present in both monosilanes are methane (CH4) and carbon dioxide (CO2), whereas the impurities specific to the fluoride-derived monosilane are SiF4, SiF3H, and SiF2H2. The less volatile impurities common to both monosilanes are ethane (C2H6), disiloxane (Si2H6O), and disilane (Si2H6); the impurities specific to the fluoride-derived monosilane are tetrafluoroethylene (C2F4) and monofluorosilane (SiFH3); and those specific to the chloride-derived monosilane are hydrogen chloride (HCl) and the chlorosilanes SiClH3, SiCl2H2, and SiCl3H.

Hydrocarbon impurities in SiF4 and SiH4 prepared from it

Using gas chromatography and high-resolution Fourier-transform IR spectroscopy, we have determined the concentrations of C1–C4 hydrocarbon impurities in isotopically unmodified silicon tetrafluoride before and after fine purification and in 28Si-enriched SiF4. The concentrations of C1–C4 hydrocarbon impurities in silicon tetrafluoride for SiH4 synthesis have been shown to correlate with those in the synthesized silane.