Chemical Vapor Deposition of Polycrystalline Silicon in a Rapid Thermal Processor

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Abstract
The deposition of polycrystalline silicon in a rapid thermal processor was studied in the temperature range of 600-1100°C using a mixture of silane and argon at reduced pressures. The amorphous-to-polycrystalline transition temperature was determined by X-ray diffraction and UV-visible spectrophotometry to be between 650 and 700°C. The activation energy of the deposition was found to be approximately 1.5 eV in the temperature range of 600 to 800°C, in reasonable agreement with LPCVD and APCVD results. At 800°C and above, the deposition rate depended only weakly on temperature, as is characteristic of mass-transport-fimited processes. The partial pressure of silane was found to affect the deposition rate in both surface-limited and gas-transport-limited depositions. A UV-visible spectrophotometer was used as a reflectometer to measure the surface roughness of the samples, which in general increased with increasing deposition temperature and film thickness. At the lower deposition temperatures, the surfaces were very smooth, as is characteristic of amorphous-silicon films. Furthermore, the ability to change temperature rapidly appears to allow smoother films to be obtained by initially depositing at lower temperatures, and then ramping to a higher temperature to increase the deposition rate.