Gravimetric Investigation of the Deposition of SiC Films Through Decomposition of Methyltrichlorosilane

Abstract

A comprehensive study of the deposition kinetics of SiC films from methyltrichlorosilane (MTS) at subambient presures is presented. A hot-wall reactor, coupled with an electronic microbalance, has been used to gravimetrically investigate the dependence of the deposition rate on temperature, pressure, flow rate, and feed composition in a relatively o 3 broad region of experimental conditions: 775-1075 C temperature, 20-600 Torr pressure, 100-400 cm/rain flow rate, and 0.025-0.33 MTS mole fraction in the feed. Deposition rate data are presented at different locations in the deposition reactor, and results on composition and morphology are reported. The results are discussed and qualitatively explained in the context of past experimental and theoretical studies on SiC deposition and MTS decomposition.

Hydrogen Chloride Effects on the CVD of Silicon Carbide from Methyltrichlorosilane

“…For the other combinations of operating parameters, it is rather difficult to discern any consistent trends in the variation of the limiting mole fraction of HCl in the feed. This behavior agrees both with the complex dependence of the deposition rate on the operating parameters (e.g., pressure) that was observed in past studies [9] and with the fact that the concentration of HCl at the deposition location (the position of measurement) depends not only on the inlet concentration of HCl, but also on the rates of the various homogeneous and heterogeneous reactions that lead to production of HCl in the section of the reactor that precedes the location of deposition.…”

“…One can easily verify that the activation energies that are extracted from the slope of these curves at different temperatures cover a range of almost one order of magnitude in breadth (27-270 kJ/mol). Values reported in the literature [3,6,7,10] as well as activation energy values obtained at different locations in our CVD reactor [9] fall within the same range. The strong effects of increasing hydrogen chloride concentration on the deposition rate and its temperature dependence indicate that the varying concentration of hydrogen chloride at the point of measurement in the CVD reactor can be a major reason for the wide discrepancies in the reactivity data and the kinetic parameters (activation energy and reaction order) reported in the literature.…”

“…Moreover, the activation energy values computed from reactivity results in the temperature range 1048-1123 K were always significantly higher than those obtained for temperatures between 1123 and 1373 K. Variable dependence of deposition rate on the temperature of operation was also observed in other studies, [6,7,10] and it was attributed to the overall reaction rate becoming diffusion limited with increasing temperature. Previous experimental results [9] showed that the deposition rate decreased with increasing residence time (increasing distance at fixed flow rate or decreasing flow rate at fixed distance) away from the beginning of the hot zone of the reactor. Since the precursor species for solid deposition are formed through homogeneous decomposition of MTS, and therefore their concentrations are generally expected to increase with increasing residence time, it was concluded that this decrease was probably the result of the negative influence of the increasing concentration of the gaseous products of the deposition process (such as HCl) on the deposition rate.…”

“…The strong effects of increasing hydrogen chloride concentration on the deposition rate and its temperature dependence indicate that the varying concentration of hydrogen chloride at the point of measurement in the CVD reactor can be a major reason for the wide discrepancies in the reactivity data and the kinetic parameters (activation energy and reaction order) reported in the literature. [2,3,6,9] Increasing the concentration of hydrogen chloride in the feed stream is, in a way, equivalent to carrying out the kinetic measurements for larger residence times in the hot zone of the reactor. The residence time of the mixture in the reactor can also be increased by increasing the distance of the location of the substrate from the beginning of the hot zone, using lower reactive mixture flow rates, or using a CVD reactor of larger cross section.…”

“…In an experimental study of SiC deposition from MTS conducted in a hot wall, gravimetric CVD reactor under subambient pressures, [9] it has been found that the deposition rate exhibits strong dependence on the residence time in the CVD reactor and (equivalently) on the distance from the entrance of the reactor. The analysis of the experimental data showed that the apparent activation energy for the deposition reaction and the reaction order with respect to the concentration of methyltrichlorosilane are strongly dependent on the residence time of the reacting mixture in the hot zone of the reactor, as well as on the temperature of operation.…”