Process for producing polycrystalline silicon bar

Abstract

A process in which a polycrystalline silicon ingot improved in life time characteristics, which are correlated with the conversion efficiency of solar wafers, is inexpensively produced by the ordinary-pressure hydrogen-atmosphere melt method. In the process, the generation of oxygen and impurities in the silicon melt is inhibited and light-element impurities are removed through reaction or crystallization. Fine crystal grains can be grown at a high rate, and a high-purity polycrystalline silicon ingot having a crystal structure reduced in crystal defect can be grown. A silicon raw material is melted in an atmosphere of 100% hydrogen at ordinary pressure or an elevated pressure to prepare a silicon melt and simultaneously dissolve hydrogen in the silicon melt. The silicon melt containing hydrogen dissolved therein is solidified. Thereafter, the solid is held at a high temperature around the solidification temperature to grow silicon crystal grains in the solid phase and thereby obtain a polycrystalline silicon ingot.

Description

technical field [0001] The invention relates to a method for manufacturing polycrystalline silicon rods used in solar cells and the like. Background technique [0002] As a conventional method for producing polycrystalline silicon ingots for solar cells, a method of melting / solidifying a silicon raw material in an argon atmosphere under reduced pressure is generally known, as in the single crystal pulling method. A melting furnace used in this conventional method will be described with reference to FIG. 2 . FIG. 2 is a schematic explanatory diagram showing an example of a conventional melting furnace. In FIG. 2 , 10 a is a melting furnace, and has a sagger 12 , a heating device 14 for heating the sagger 12 , a support device 16 for placing the sagger 12 to rotate and ascend, a heat insulating material 18 , and a vacuum chamber 20 . The heat insulating material 18 is erected on the inner side of the side wall of the vacuum chamber 20 . Ambient gas, such as argon gas, is in...

AI Technical Summary

Problems solved by technology

However, if the particle growth is promoted, the solidification time needs to be long, and in a decompressed argon atmosphere, there will be problems that the silica sintered body saggar used in the melting vessel, oxygen and carbon from the carbon saggar, and further The amount of carbon produced from the heater is also increased, dissolved in the silicon ingot, and the concentration of oxygen, carbon and other impurities will increase

[0009] As mentioned above, in the conventional method, there are the following problems: (1) In order to promote the particle growth of the polycrystalline silicon melt, a long solidification time is required, and the power cost of the production will increase.

(2) The concentration of oxygen, carbon and other impurities melted in the ingot for a long time will increase, resulting in a decrease in life characteristics

The content of these is to cause a decrease in mechanical strength or a decrease in life characteristics when the plate is thinned.

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