Unraveling the complex chemistry using dimethylsilane as a precursor gas in hot wire chemical vapor deposition

Abstract

The gas-phase reaction chemistry when using dimethylsilane (DMS) as a source gas in a hot-wire chemical vapor deposition (CVD) process has been studied in this work. The complex chemistry is unraveled by using a soft 10.5 eV single photon ionization technique coupled with time-of-flight mass spectrometry in combination with the isotope labelling and chemical trapping methods. It has been demonstrated that both free-radical reactions and those involving silylene/silene intermediates are important. The reaction chemistry is characterized by the formation of 1,1,2,2-tetramethyldisilane (TMDS) from dimethylsilylene insertion into the Si-H bond of DMS, trimethylsilane (TriMS) from free-radical recombination, and 1,3-dimethyl-1,3-disilacyclobutane (DMDSCB) from the self dimerization of either dimethylsilylene or 1-methylsilene. At low filament temperatures and short reaction time, silylene chemistry dominates. The free-radical reactions become more important with increasing temperature and time. The same three products have been detected when using tantalum and tungsten filaments, indicating that changing the filament material from Ta to W does not affect much the gas-phase reaction chemistry when using DMS as a source gas in a hot-wire CVD reactor.

Effect of pressure on the gas-phase chemistry when using monomethylsilane and dimethylsilane in hot-wire chemical vapor deposition

“…Investigation of the secondary gas-phase reactions of 0.12 Torr of DMS on a tantalum filament revealed a competition between free radical reactions and silylene−silene reactions. 21 This competition was found to be dependent on reaction time and filament temperature. At a relatively low filament temperature of 1200°C, the gas-phase chemistry was dominated by the formation of TMDS (m/z 118), which resulted from the insertion reaction of dimethylsilylene into the Si−H bond of the parent DMS molecule.…”

“…As was described in our previous study, 14,21 the room temperature 10.5 eV SPI TOF mass spectrum of DMS is predominated by the parent ion peak at m/z 60 ((CH 3 ) 2 SiH 2 + ) and its photofragment at m/z 58 ((CH 3 ) 2 Si + ). Investigation of the secondary gas-phase reactions of 0.12 Torr of DMS on a tantalum filament revealed a competition between free radical reactions and silylene−silene reactions.…”

“…In addition to this peak, it has been demonstrated that DMDSCB (m/z 116) was also formed at higher filament temperatures. 21 This molecule was the product of both cyclodimerization of 1-methylsilene and dimethylsilylene dimerization.…”

“…At this temperature, the secondary gas-phase reaction when using 0.12 Torr of DMS at a short reaction time (t ≤ 25 min) was dominated by the formation of TMDS (m/z 118 and its photofragment ions at m/z 103 and 73) resulting from the silylene insertion reaction. 21 When the DMS pressure was increased 10-fold and after 5 min of filament-on time, the dominant product peaks became TriMS (m/z 73) formed by a free radical recombination reaction and DMDSCB (m/z 116) generated from silene−silylene dimerization reactions. This change in dominant peaks with an increasing pressure is also observed when using 12 Torr of 4% DMS−He (p(DMS) = 0.48 Torr).…”

“…When 1.2 Torr of DMS was used, this temperature was determined to be 1000°C, which was slightly lower than the 1100°C obtained using 0.12 Torr of DMS. 21 Figure 1 shows a comparison between the mass spectra recorded using 0.12 and 1.2 Torr of DMS in the HWCVD reactor at a filament temperature of 1300°C. The increase in the source gas pressure resulted in a greater number of products, as indicated by the increase in the number of mass peaks.…”