Polycrystalline silicon producing method, apparatus for producing polycrystalline silicon, and polycrystalline silicon

Polycrystalline silicon having a diameter of 100 mm or larger, produced by a producing method comprising:

• supplying electric current to a silicon seed rod in a reactor to make the silicon seed rod to generate heat;
• supplying raw material gas including chlorosilanes to the silicon seed rod;
• and
• depositing polycrystalline silicon on a surface of the silicon seed rod to be grown as a rod,
• wherein a pressure in the reactor is equal to or greater than 0.4 MPa and equal to or less than 0.9 MPa,
• the method includes a first process and a second process,
• in the first process, a surface temperature of the rod is maintained at a predetermined range by adjusting the current value in the silicon seed rod, and the raw material gas is supplied while maintaining a supply amount of chlorosilanes per square millimeter of the surface of the rod to be equal to or greater than 2.0×10−7 mol/sec/mm2 and equal to or less than 3.5×10−7 mol/sec/mm2 until a temperature of the center portion of a rod reaches a predetermined temperature lower than the melting point of the polycrystalline silicon, and
• in the second process, after the temperature of the center portion of the rod reaches a predetermined temperature lower than the melting point of the polycrystalline silicon, a previously determined current value is set corresponding to a rod diameter and the supply amount of the raw material gas per square millimeter of the surface of the rod is decreased to maintain the surface temperature and the temperature of the center portion of the rod to be within predetermined ranges, respectively.

An apparatus for producing polycrystalline silicon, comprising:

• a reactor having a bell jar and a bottom plate closing an opening of the bell jar;
• a plurality of electrodes which are installed on an upper surface of the bottom plate and supply electric current to silicon seed rods attached on the electrodes;
• a plurality of ejection nozzles which are provided on the upper surface of the bottom plate and supply a raw material gas including chlorosilanes into the reactor;
• a plurality of gas discharge ports which are provided on the upper surface of the bottom plate and discharge the gas after the reaction to an outside of the reactor;
• a thermometer which measures temperature of a surface of a rod obtained by depositing polycrystalline silicon on the seed rods;
• a diameter measuring device which measures diameter of the rod;
• and
• a controller which controls a flow of the raw material gas supplied from the ejection nozzles and the electric current flowing through each of the silicon seed rod based on the temperature measured by the thermometer and the diameter of the rod measured by the diameter measuring device,
• wherein the controller is programmed to perform the step of:
• i) controlling a pressure in the reactor is equal to or greater than 0.4 MPa and equal to or less than 0.9 MPa;
• ii) maintaining the temperature of a surface of a rod at a predetermined range and maintaining a supply amount of chlorosilanes per square millimeter of the surface of the rod (R) to be equal to or greater than 2.0×10−7 mol/sec/mm2 and equal to or less than 3.5×10−7 mol/sec/mm2 until a temperature of the center portion of the rod reaches a predetermined temperature lower than the melting point of the polycrystalline silicon;
• and
• iii) setting current value to a previously determined current value corresponding to the diameter of the rod, decreasing the supply amount of the raw material gas per square millimeter of the surface of the rod, and maintaining the surface temperature and the temperature of the center portion of the rod to be within predetermined ranges, after the temperature of the center portion of the rod reaches a predetermined temperature lower than the melting point of the polycrystalline silicon.