| dc.description.abstract | The single crystallize-silicon (sc-si) is a major material for solar cell. Oxygen, one of the most important impurities in Czochralski (CZ) system, affects the efficiency of solar cells. There are three general methods to reduce the oxygen concentration in the melt: (1) The magnitude of oxygen released from the quartz crucible is decreased by reducing the temperature of the wall of the quartz crucible. (2) The oxygen transports from the crucible sidewall to the melt-crystal interface is prevented by controlling the flow pattern of the melt. (3) The magnitude of evaporated silicon oxide at the free surface has to be enhanced. In this study, the numerical simulation has been performed to clear the mechanism of oxygen transportation, such as the distribution of oxygen concentration in the melt is related to the crystal rotation rate and crucible rotation rate. The dimensionless Richardson number (Ri) of crucible rotation is smaller than that of crystal one. It means that the crucible rotation rate affects on the distribution of oxygen concentration in the melt very much. The temperature of the crucible is increased by the higher crucible rotation rate, and it is not good for reducing the oxygen concentration in the melt. When the crucible rotation rate is lower, the oxygen is carried from the crucible to the melt-crystal interface by the flow motion of the melt, and it is also not benefit for reducing the oxygen concentration in the melt. Hence, the optimum rotation rate of the crucible can be found to control the flow pattern of the melt for the conventional Cz furnace. Besides, the quantity of the oxygen transportation on the free surface can be increased by increasing the gas flow rate. The magnitude of evaporated silicon oxcide on free surface can be increased by decreasing the furnace pressure. Except the previous methods of adjusting the growth parameters of the conventional Cz furnace, the methods of modifying the hot zone also are proposed in the present study. The shape of the heat shield is modified to carry more quantity of the silicon oxide on the free surface outside the furnace. And the position of the heater is lift in order to reduce the temperature of the crucible. The optimum growth parameters and the modified designs are integrated to a new furnace, and it does not only reduce more oxygen concentration but also control the oxygen concentration. Furthermore, the design of saving power is also developed in this study, and the dipping power is reduced 55% in comparison with the conventional CZ furnace. The new furnace can reduce the oxygen concentration in the crystal 29.3% in comparison with the conventional CZ furnace. In addition, to improve the crystal quality is another concerned issue in this study. The OISF-ring generated by micro-defects is combined with the oxygen, and it becomes a stacking fault and is harmful to the electric property of the solar cell. The new furnace can not only reduce the oxygen concentration 29.3% but also extend the OISF-ring outward the edge of crystal 23.3% in comparison with the conventional CZ furnace.
| en_US |