In this work we used Raman spectroscopy to investigate the structural characteristics of as-deposited amorphous and micro-crystalline silicon films. For amorphous silicon films, the order (or disorder) of the silicon network was quantified using properties of the Raman spectra that were related to key deposition conditions. We found that a strong relationship exists between the structural order of the silicon matrix and the deposition temperature and deposition rate. A quantitative model was proposed relating the intensity ratio of transverse optical phonon peak to longitudinal optical phonon peak to the surface diffusion length, a parameter that was calculated from available data. It was found that optimization of the as-deposited silicon microstructure is possible by selecting deposition conditions yielding peak–ratio values in the vicinity of 0.53. For as-deposited micro-crystalline silicon films, Raman spectroscopy was used to estimate the initial crystalline fraction of the film and monitor the crystallization process during annealing. These data were used to confirm the crystallization mechanism in mixed-phase silicon films and identify the effect of different process parameters on the crystallization time of the annealed films.

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In this work we studied the effect of the deposition temperature, total pressure, source gas dilution, and deposition rate on the structure of the as-deposited silicon films. Depositions were performed by low pressure chemical vapor deposition (LPCVD) in the temperature range of 530 to 600~ and in the pressure range of 2 to 300 mTorr. For a fixed deposition temperature a phase transition from polycrystalline to amorphous silicon was shown to occur when the deposition rate exceeded a critical value. The critical value for the deposition rate was found to depend only upon the deposition temperature and to decrease as the temperature was decreased. By controlling the rate, as-deposited polycrystalline silicon was obtained by conventional LPCVD at temperatues as low as 530~ A relationship between the ,deposition rate and the partial pressure of the source gas was established via a kinetic model for the decomposition of silane and used to provide a simple model for the dependence of the structure of the as-deposited silicon films upon the deposition parameters. This " model was subsequently used to provide guidelines for both the expected structure of the as-deposited films and the grain size of the as-deposited polycrystalline silicon films over an extensive range of deposition conditions. Polycrystalline silicon is an important material for the semiconductor industry with a vast variety of applications in the microelectronics area. Recently, thin (_<200 nm) polycrystalline silicon films deposited by low pressure chemical vapor deposition (LPCVD) on glass substrates have received considerable interest for application in active matrix liquid crystal displays. 1'2 For such an application the deposition temperature must be below the strain point of the glass and for low cost glass substrates below 600~At moderate pressures (0.5 Torr) the transition temperature between as-deposited amorphous and polycrystalline silicon is about 600~ 3 It has been shown previously that high quality polysilicon films can be formed at temperatures less than 600~ by first depositing the silicon in the amorphous phase and then crystallizing the material by a low temperature thermal anneal. 4 The crystallization time of the as-deposited amorphous silicon film was found to depend upon the deposition and annealing temperatures and to increase as both temperatures decrease.Some previous studies ~-7 have shown that it is possible to obtain as-deposited polycrystalline silicon films at temperatures lower than 600~ if the deposition pressure is reduced below 0.5 Torr. Bisaro et al. ~ have identified a qualitative relationship between the deposition pressure, the deposition temperature, and the structure of the as-deposited silicon films. However, they performed the bulk of their experiments at temperatures above 560~ and pressures above 0.2 Tort. Joubert et al. 7 have also studied the structure and the texture of the as-deposited silicon films as a function of the deposition temperature and pressure and noted that the key pressure characterizing the...

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