Research On Preparation, Property And Device Of Hydrogenated Silicon Films

Hydrogenated silicon film attracts extensively attention due to its application on many kinds of microelectronic devices, such as infrared imaging system, solar cell and thin film transistor. Plasma enhanced chemical vapor deposition (PECVD) technique is the primary method which is used to prepare hydrogenated silicon film.In this dissertation, we changed the PECVD technique parameters, and deposited amorphous, microcrystalline and polymorphous silicon films. The microstructure, optical, electrical and thermal properties of hydrogenated silicon films were characterized by a series method. Polymorphous silicon film was selected to be thermal-resistance layer of micro-bolometer, and we optimized the structure of micro-bolometer through optical and thermal design.The refractive index and optical band gap of amorphous silicon were obtained by spectroscopy ellipsometry in FB model. The resuts demonstrate the value of refractive index and optical band gap of amorphous silicon film depends on substrates' temperature. The variation of total gas pressure also influences the deposition rate, optical band gap and extinctive coefficient of amorphous silicon film. Fourier-transform infrared spectrometer (FTIR) was used to characterize the information of Si-H in silicon film deposited on KBr substrate. The effect of substrate temperature and total gas pressure on hydrogen content in silicon film was confirmed.With the increasing of pure silane total gas pressure, we use XRD, Raman and FTIR method to demonstrate the phase transition of the produce of PECVD process occurred as a formation of amorphous silicon→polymorphous silicon→agglomeration→powder formation. However, when using strong hydrogen dilution silane as source gas, the phase transition is microcrystalline silicon→polymorphous silicon→agglomeration→powder formation. The crystalline mechanism difference of microcrystalline and polymorphous silicon was investigated by thermal gradient theoretical and hydrogen etching model. The volume crystalline fraction of microcrystalline silicon increases with the increasing of film thickness, and there is no such relation in polymorphous silicon film. The resistivity, squared resistance and temperature coefficient of resistance in hydrogenated silicon film decrease with the increasing of boron doping concentration. The resistance of amorphous silicon increases with the increment of measurement time for the surface oxide. The crystalline in silicon film results in the decreasing of resistivity and squared resistance, and the resistance decreases with Joule effect and exposed in light. The measurement of 1/f noise in amorphous, microcrystalline and polymorphous silicon film was performanced with a self-design semiconductor system. The results demonstrate microcrystalline and polymorphous silicon films have low 1/f noise for their crystallization make them better ordered than amorphous silicon film.The thermal conductivity measurement results of silicon films show thermal conductivity of amorphous silicon increase with the increment of substrate temperature, and the vibrational bonds in silicon film were demonstrated to reduce the thermal conductivity. The crystalline in silicon films increases the thermal conductivity of hydrogenated silicon films. There is a thermal conductivity gradient in microcrystalline silicon film similar as the crystalline gradient. The thermal conductivity of polymorphous silicon is nearly silimar as that of microcrystalline silicon film. Both nanocrystal and high hydrogen content contribute to the increment of thermal conductivity in polymorphous silicon film.Polymorphous silicon film was used to thermal-resistance layer in micro-bolometer. According to optical admittance matrix theory, relation between sensing film thickness, resonant cavity height of microbolometer and infrared absorptivity was simulated using FEA (Finite Element Analysis) MatLab software. Optimal film thickness and resonant cavity height for high infrared absorptivity ranging from 3～5 to 8～14μm atmosphere window infrared bands were achieved, which provides reliable evidence to improve the sensitivity of microbolometer.