Chemical vapor deposition of β-SiC thin films on Si(100) in a hot wall reactor

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Virginia Tech


A systematic method was developed for the deposition of β-SiC thin films on Si(100) substrates in a hot wall reactor, using low pressure chemical vapor deposition (LPCVD). Due to poor adhesion resulting from lattice mismatch and difference in thermal expansion coefficients between the (SiC films and the Si(100) substrates, the feasibility of forming a SiC buffer layer on the Si(100) surface before beginning the chemical vapor deposition (CVD) process was investigated. The SiC buffer layers were formed with either a smooth or porous morphology. A nonporous Si(100) substrate with a 35Å thick SiC buffer layer was formed when the Si surface was heated at 1050°C in an atmosphere of C₂H₂ and H₂. A porous surface was obtained when the Si substrate was heated at 1000°C in C₂H₂ alone. The porous defects were correlated to the out—diffusion of Si in the carburizing process.

On smooth Si(100) substrates, polycrystalline and stoichiometric β-SiC thin films with the (111) planes paralleling the Si(100) substrates were grown from a CH₃SiCl₃ (MTS)—H₂ mixture at 1050°C. At high H₂/MTS ratios and/or low deposition pressures, no etching on the Si substrates of the β-SiC films was observed, resulting in a smooth topography. Degradation in film morphology, changes in the preferred orientation, and etching of the Si substrates were observed at higher pressures, temperatures, and H₂/MTS ratios. The etching of the Si substrate was due to the out—diffusion of Si atoms from the substrate and the presence of Cl—containing radicals, which resulted from the decomposition of MTS molecules before arriving at the substrates. A model of the deposition mechanism is proposed which predicts the deposition rates in a hot wall CVD reactor and agrees very well with the experimental data.

On the Si(100) substrate with a porous topography, epitaxial β-SiC(100) thin films were grown from MTS—H₂ at 1150°C. The crystallinity of the deposited films was influenced by the deposition time. With increasing deposition time, rotational β-SiC(100) crystals and polycrystalline β-SiC with a highly preferred orientation of (100) and/or (111) were obtained. At a lower temperature of 1100°C, poor morphology and polycrystalline β-SiC thin films were observed.

Finally, a new approach to the calculation of the local equilibrium CVD phase diagrams, which represent the most stable phases above the substrates in a hot wall reactor, for SiC deposition from the MTS—H₂ gas mixture by coupling the depletion effects to the equilibrium thermodynamic computer code SOLGASMIX—PV. The calculated CVD phase diagrams were also compared with experimental and the literature data. Although the local equilibrium CVD phase diagrams predicted the deposition of single phase SiC better than established CVD phase diagrams, the experimental regions for depositing single phase SiC are larger than those calculated from local CVD phase diagrams. This may be because of the high linear velocity of the gas flux under low pressure and the polarity of the Si—containing intermediate species.