| Hydrogenated microcrystalline silicon (μc-Si:H) films have attracted widely application in the silicon thin film solar cells, because of their good long wave response characteristics, high carrier mobility, and stable behavior under illumination compared with hydrogenated amorphous silicon (a-Si:H). Plasma-enhanced chemical vapor deposition (PECVD), especially excited with very-high frequency (VHF) power source, has become the most widely used method for deposition of device-grade μc-Si:H films. So the research of microcrystalline silicon thin film growth mechanism is great significance in the process of preparation of thin films for regulating the microstructure, optimization of battery performance. In this paper, numerical simulation takes into account electron-impact, gas phase and surface growth reactions of diluted SiH4in H2discharges through the combination of the plasma module of the Comsol software and the AUROR module of the Chemkin software, in which42gas phases and43surface reactions were involved. Plasma parameters such as the electron density (ne) and the electron temperature (Te) are determined through a1D discharge model and used as inputs for the gas phase and surface reaction model, to obtain the concentrations of film precursors and the properties of film. At the same time, the diluted SiH4in H2discharges plasma is monitored online using the optical emission spectrometry (OES), and in order to test the modeling data, the specimen have prepared on the same conditions. The results of simulation and experimention Conform to the well, and the main conclusions are as follows:(1) The increase of power can bring about the increase of ne, Te, which cause the volume density of SiH3, SiH2and H (nSiH3, nsiH2, nH)to increase but nSiH3/nH to plummet; the pressure increase cause Te to plummet, and ne first to increase then to decrease, the nSiH3keeps increasing and becomes saturated gradually, but nSiH3/nH to plummet; the increase of excitation frequency leads to the increase of nSiH3, nSiH3nH, Te and nsiH3/nH to decrease; With the increase of silane concentration, the nSiH3 increases but nsiH3/nH plummets.(2) At low pressure and low silane concentration, SiH3is the major deposition precursor. With the increase of pressure and the content of silane, the gas residence time in the reactor increases, and the generation of silicon hydride clusters is enhanced, which may be incorporated into the film and contribute to the increase of the deposition rate. When the power is too high, ion bombardment effect results in the decrease of thin film deposition rate. At the same time, the plasma characteristic parameters from silane, hydrogen gas mixture or pure hydrogen gas discharge, the result of the simulation and experiment results compared very well, can be simplified model with pure hydrogen plasma discharge.(3) Crystallization (Xc) depends on the ratio of nsiH3/nH. With the decrease of the nSiH3/nH, the hydrogen content (CH) in thin films reduces, and the Xc increases. Thin film growth orientation and the crystal grain size of different crystal planes mainly depend on the relative growth rate. With the deposition temperature increasing, the surface diffusion of the deposition precursors and the fraction of the surface dangling bonds increases, at the same time, it helps<110> crystal orientation to grow. When the deposition precursors concentration is low, the surface growth presents the gas phase diffusion restriction, which leads to an increase deposition rate of<111> crystal orientation, and the increase of grain size; When the deposition precursors concentration at high concentration, the growth changes to limit surface reaction. At this time, an increased CH in plasma enhances the growth of<110> crystal orientation. |
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