Polycrystalline silicon and process and apparatus for producing the same
Foamed polycrystalline silicon having bubbles therein and an apparent density of 2.20 g/cm 3 or less. This silicon generates an extremely small amount of fine grains by crushing and can be easily crushed. There is also provided a method of producing foamed polycrystalline silicon. There is further provided a polycrystalline silicon production apparatus in which the deposition and melting of silicon are carried out on the inner surface of a cylindrical vessel, a chlorosilane feed pipe is inserted into the cylindrical vessel to a silicon molten liquid, and seal gas is supplied into a space between the cylindrical vessel and the chlorosilane feed pipe.
1. Foamed polycrystalline silicon which has bubbles therein and an apparent density of 2.20 g/cm 3 or less.
2. The foamed polycrystalline silicon of claim 1 which is in the form of an assembly of independent grains or an agglomerate of independent grains.
3. The foamed polycrystalline silicon of claim 2 , wherein the assembly of independent grains contains independent grains each having a weight of 0.2 to 2 g in an amount of 50 g or more based on 100 g.
4. The foamed polycrystalline silicon of claim 2 , wherein the assembly of independent grains is formed by breaking up the agglomeration of an agglomerate of independent grains.
5. The foamed polycrystalline silicon of claim 1 , wherein a plurality of independent bubbles are contained and are existent in a center portion of a grain.
6. A crushed product of the foamed polycrystalline silicon of claim 1 .
7. The crushed product of claim 6 which has an average grain diameter in the range of greater than 200 μm to 5 mm.
8. A method of producing foamed polycrystalline silicon comprising dropping droplets of silicon containing hydrogen which has been molten in the presence of hydrogen in 0.2 to 3 seconds and cooling the droplets until hydrogen bubbles are locked up in the droplets.
9. The method of claim 8 , wherein dropping is carried out for 0.2 to 2 seconds.
10. The method of claim 8 , wherein a silicon deposition reaction between hydrogen and a chlorosilane and a reaction for melting the deposited silicon in the presence of hydrogen are carried out simultaneously to prepare silicon droplets containing the hydrogen.
11. A polycrystalline silicon production apparatus comprising:
(a) a cylindrical vessel having an opening which is a silicon take-out port at the lower end;
(b) a heater for heating the inner wall from the lower end to a desired height of the cylindrical vessel at a temperature equal to or higher than the melting point of silicon;
(c) a chlorosilane feed pipe which is composed of an inner pipe having a smaller outer diameter than the inner diameter of the cylindrical vessel and constituted such that one opening of the inner pipe faces down in a space surrounded by the inner wall heated at a temperature equal to or higher than the melting point of silicon; and
(d) a first seal gas feed pipe for supplying seal gas into a space defined by the inner wall of the cylindrical vessel and the outer wall of the chlorosilane feed pipe.
12. The apparatus of claim 11 , which further comprises (e) a hydrogen gas feed pipe for supplying hydrogen gas into the above cylindrical vessel.
13. The apparatus of claim 11 , wherein a cooling acceptor for receiving droplets falling from the lower end of the cylindrical vessel is disposed in a lower portion of the cylindrical vessel with a space therebetween.
14. The polycrystalline silicon production apparatus of any one of claims 11 to 13 further comprising a closed vessel which covers at least a lower end portion of the cylindrical vessel, forms a space in the lower portion of the cylindrical vessel and is provided with an exhaust gas discharge pipe, and a second seal gas feed pipe for supplying seal gas into a space defined by the outer wall of the cylindrical vessel and the inner wall of the closed vessel.