Papers by Keyword: Polysilicon

Abstract: The Siemens CVD reactor should be refined when addressing the low energy consumption requirement for the production of solar grade polysilicon. The object of this paper is to investigate the heat transfer in Siemens reactor, which will provide the theoretical guidance for saving energy of polysilicon scale production. Based on Discrete Ordinates (DO) radiation model, an analysis is presented which studies the radiation exchange between the hot polysilicon rods and the cold reactor wall of four typical reactor configurations, especially the variation of the average power emitted per rod under various conditions of different rod diameter and wall emissivity. The results show that the energy consumption can be reduced by decreasing the emissivity of the reactor wall and enlarging the reactor capacity.

Abstract: The thermal stress field in the polysilicon was simulated and comparatively analyzed at different shapes of crucibes which have different types of a flat, a inverted-conical and concave bottom by COMSOL Multiphysics version 4.3a. The results indicated that: within the flat-bottomed crucible ,the isotherm in the crystal was slightly convex and the area of the maximum thermal stress was distributed in the bottom of the crystal edge and near the top of crystal edge; within the inverted-cone crucible, the isotherm in the crystal was straight and the area of the maximum thermal stress was only distributed in the bottom of the crystal edge; within the bottom of the concave crucible, the isotherm in the crystal was slightly concave and the area of the maximum thermal stress distributed in the bottom of the crystal edge was larger than that of the crystal within the first two kinds of crucibles. To sum up, the inverted-cone crucibe was beneficial to reduce the thermal stress distribution in the polysilicon which could provide theoretical guidance for improving the production process of the polysilicon.

Abstract: The modified Siemens process is the primary technology of polycrystalline production at present. The Siemens reactor, which is the main equipment in the modified Siemens process, consists of a chamber where several high purity silicon slim rods are heated by an electric current flowing through them. The temperature on the rod centre must be under melting temperature of silicon (1687K) in order to avoid its breaking-down because of an uneven temperature profile of the silicon rod. Therefore the temperature profile of the silicon rod heated by direct current (DC) has been investigated by molding. The current density profile of silicon rod has also been studied to investigate the interaction of current density and temperature. The results show that the temperature is not homogeneous in the rod and the temperature in the center of the polysilicon rod is 1750K which is much higher than the melting temperature (1687K) when the temperature is 1423K on the surface of polysilicon and the radius of rod is 5cm. Therefore, the maximum growth radius of the polysilicon rod in Siemens reactor should be less than 5cm when the joule heating generated by DC. The current density increases from the center to the surface of the polysilicon rod.

Abstract: Numerical simulations of transport phenomena is one of the valid methods in investigation of crystal silicon growth by CVD for various types of reactors. The present review provides the key summary on the development of fluid dynamic simulations on polysilicon of CVD and hopefully aid in future improvement of this technology. In the solution of CVD reactor models for polysilicon production, the influence of the deposition process on temperature, the transport phenomena and the surface reactions have to be taken into account when discussing the silicon growth rate.

Abstract: Solar grade silicon (SoG-Si) is the basic material of photovoltaic industry. Metallurgical method as a way of purification isconsidered to reduce the cost of polysilicon production unanimously based on its low cost, short production cycle, relatively simple process, lowpollution and controllable scale size, and it has become a hot topic in the subject research around the world.In this paper Al-Si-Sn alloy is used to purifypolysiliconand influence on the purification efficiency of polysilicon with different compositions of Al-Si-Sn alloy is analyzed. In order to study the segregation of impurity B in purification process, we introduce final segregation coefficient k_B,final and analyze the relation between k_B,final and the content of Al,Snin Al-Si-Sn alloy thermodynamically.

Abstract: A family of alkaline earth aluminosilicate glasses has been introduced in this paper, that exhibit a high strain point temperature in excess of 740°C, the coefficient of thermal expansion of (27~38) ×10-7/°C. The glasses consist of SiO₂ 59-80 mol%, Al₂O₃ 10-25 mol%, CaO 5-10 mol%, SrO 1-4 mol%, ZnO 4-6 mol%, SnO₂ 0.08 mol%, ZrO₂ 0-4 mol%, Y₂O₃ 0-2 mol%. Their properties show that these glasses can be used as substrates with polysilicon (p-Si) thin film coating on their surface, in particular, for flat panel displays.

Abstract: Molecular dynamics model of the polysilicon material under the micro/nanoscale is established by using molecular dynamics method, make variety of the typical defects distribute to the polysilicon model reasonable and relax the simulation model, obtain the system potential energy curves in the relaxation process and the atomic location figure after the relaxation. Conduct molecular dynamics simulation of nanometric cutting process relying on the development of simulation program, get instant atom position image and draw the cutting force curve. Discusses the typical defects impact on the polycrystalline silicon nanometric cutting process, those mainly include cutting force changes in the cutting process, potential energy changes and processed surface quality etc.

Abstract: In order to reduce the production cost of polysilicon, the raw material of the photovoltaic industry, applying heat integrated distillation technology of two towers in trichlorosilane distillation process consisting of removal of light components after removing heavy components. By assistant of a chemical process software, the new energy-saving process is simulated, the main parameters of two towers are optimized and the best implementation solution are provided. The optimum parameters for the first tower are the operation pressure of 500 kPa, the number of theoretical plates of 32, the position of feed plate of 24, reflux ratio of 4.2 and the distillate to feed ratio of 0.8516. For the second tower, the operation pressure, the number of theoretical plates, the position of feed plate, the reflux ratio and the bottoms to feed ratio are 250 kPa, 74, 15, 111 and 0.9652 respectively.The results showed that the new process can save energy consumption up to 50%, the coefficient of recovery for trichlorosilane is up to 98.7% while the high purity of trichlorosilane can ensure the resulted polysilicon excellent photovoltaic properties.

Abstract: The new two-tower process of thrichlorosilane distillation consisting of removal of light components after removing heavy components is analyzed by assistant of a chemical process simulation software. In order to achieve lower energy consumption, the parameters for each tower in the new process are optimized, such as the number of theoretical plates, the position of feed plate, reflux ratio and distillate (bottoms) to feed ratio. The results show that the optimum parameters for the first tower are the number of theoretical plates of 32, the position of feed plate of 24, reflux ratio of 2.5 and the distillate to feed ratio of 0.8516. For the second tower, the number of theoretical plates, the position of feed plate, the reflux ratio and the bottoms to feed ratio are 80, 16, 143 and 0.9652 respectively. Applying the optimized results in practical production, mass fraction of PCl3 in overhead of the first tower is reduced by two orders of magnitude, condenser duty and reboiler duty of the second tower are dropped by more than eight percent while obtaining higher purity trichlorosilane products.

Abstract: Development and utilization of solar and other renewable resources is the development trend on energy. Belong to one of the national industrial policy to support the strategic emerging industries to optimize the power structure, Energy conservation, environmental protection, the development of low-carbon economy has a positive effect. Different monolithic capacity of photovoltaic power generation project, in construction investment, the basic difference between the little and then be able to estimate the construction of photovoltaic power generation project investment, preliminary determination of investment projects in economic rationality.