Method for manufacturing polycrystalline silicon
A method for manufacturing polycrystalline silicon with high quality by effectively preventing undesired shape such as giving an rough surface to silicon rods or an irregularity in diameter of the silicon rods. The method for manufacturing polycrystalline silicon includes: an initial stabilizing step of deposition wherein a velocity of ejecting the raw material gas from the gas ejection ports is gradually increased; the shaping step wherein first the ejection velocity is increased at a rate higher than that in the stabilizing step and then the ejection velocity is gradually increased at a rate lower than the previous increasing rate; and a growing step wherein, after the shaping step, the ejection velocity is made slower than that at the end of the shaping step until the end of the deposition.
1. A method for manufacturing polycrystalline silicon, in which a plurality of silicon seed rods stood in a reaction furnace is heated and polycrystalline silicon is deposited on surfaces of the silicon seed rods by a raw material gas ejected from gas ejection ports located in an inner bottom part of the reaction furnace, the method comprising:
a stabilizing step of deposition wherein a velocity of ejecting the raw material gas from the gas ejection ports is gradually increased in a first stage of the deposition of the polycrystalline silicon;
a shaping step wherein first the ejection velocity is increased at an increasing rate higher than that in the stabilizing step and then the ejection velocity is gradually increased at a rate lower than the increasing rate; and
a growing step wherein, after the shaping step, the ejection velocity is made slower than that at the end of the shaping step.
2. The method according to claim 1 , wherein the duration required for the shaping step corresponds to 20 to 35% of the total duration of the deposition of the polycrystalline silicon.
3. The method according to claim 1 , wherein a plurality of the gas ejection ports is branched from a gas supplying pipe, and in the shaping step, an ejection velocity from a part of gas ejection ports is increased by closing the other of the plurality of gas ejection ports.
4. The method according to claim 3 , wherein, in the shaping step, 30% to 55% of the gas ejection ports are closed.
5. The method according to claim 3 , wherein, in the growing step, the velocity of ejecting the raw material gas is decreased by making the number of closed gas ejection ports less than that in the shaping step.
6. The method according to claim 5 , wherein, in the growing step, 10% to 20% of the gas ejection ports are closed.
7. The method according to any one of claim 3 , wherein the gas ejection ports to be closed are switched to the other gas ejection ports, thereby switching between an opened/closed state, at every predetermined duration.