Apparatus and method for washing polycrystalline silicon
Disclosed is a polycrystalline silicon washing apparatus that sequentially immerses polycrystalline silicon into a plurality of acid baths each of which is filled with an acid to wash the polycrystalline silicon. The temperatures of the acids in the acid baths are set such that the temperature of the acid in a later acid bath of adjacent acid baths is equal to or lower than that of a former acid bath and the temperature of the acid in the last acid bath is lower than that of the acid in the first acid bath. Each of the acid baths is provided with a temperature adjusting unit that controls the temperature of the acid at a constant value.
1. A polycrystalline silicon washing apparatus comprising:
a plurality of acid baths each of which is filled with an acid and into which polycrystalline silicon is sequentially immersed,
a transporting unit that sequentially transports the polycrystalline silicon to each of the acid baths,
a device that flows clean air through the polycrystalline silicon washing apparatus in the direction opposite to the transport direction of the polycrystalline silicon by the transporting unit,
a temperature adjusting unit which set such that a temperature of the acid in a later acid bath in which the polycrystalline silicon is immersed later in adjacent acid baths is equal to or lower than that of a former acid bath in which the polycrystalline silicon is immersed earlier and a temperature of the acid in a last acid bath is lower than that of the acid in a first acid bath; and
liquid transferring units which are provided between adjacent acid baths among the acid baths, each of which transfers the acid in the later bath of two adjacent acid baths to the former acid bath, wherein
the liquid transferring units are formed by overflow passages,
the overflow passage provided in the last acid bath where the polycrystalline silicon is immersed into acid lastly is disposed at a highest position,
the heights of the overflow passages are sequentially lowered from the later acid bath to the former acid bath,
the acid in the later acid bath of two adjacent acid baths overflows to the former acid bath,
a hydrofluoric acid supply system provided to supply hydrofluoric acid to the acid baths, and
a nitric acid supply system provided to supply nitric acid to the last acid bath and a second-to-last acid bath.
2. The polycrystalline silicon washing apparatus according to claim 1 , wherein each of the acid baths is provided with a temperature adjusting unit that controls the temperature of the acid charged in the acid bath at a predetermined range.
3. The polycrystalline silicon washing apparatus according to claim 1 , further comprising:
an acid supply unit that is provided in at least the last acid bath among the acid baths that are connected to each other by the liquid transferring units; and
a liquid discharge system that is connected to the first acid bath.
4. The polycrystalline silicon washing apparatus according to claim 1 , further comprising: a pure water bath which is supplied with pure water and into which the polycrystalline silicon that has been immersed into the last acid bath and brought out therefrom is immersed.
5. The polycrystalline silicon washing apparatus according to claim 1 , further comprising: at least one intermediate pure water bath which is provided between the first acid bath and the last acid bath and is supplied with pure water and into which the polycrystalline silicon is immersed.
6. The polycrystalline silicon washing apparatus according to claim 1 , wherein,
the temperature adjusting unit includes heat exchangers, heating medium supply systems, and liquid temperature measuring units,
the heat exchanger is provided on a bottom of each of the acid baths,
the heat exchanger is connected to the heating medium supply system,
each of the acid baths is provided with the liquid temperature measuring unit, and
heating medium or cooling medium is supplied from the heating medium supply system to the heat exchanger on the basis of the measurement result of the liquid temperature measuring unit.
7. The polycrystalline silicon washing apparatus according to claim 1 , wherein the nitric acid supply system is provided to a fourth acid bath and a fifth acid bath.
8. The polycrystalline silicon washing apparatus according to claim 1 ,
wherein the transporting unit sequentially transports the polycrystalline silicon to each acid bath in a direction in which the acid baths are arranged,
the transporting unit includes baskets which are arranged in a direction orthogonal to the arranged direction of the acids baths,
the baskets include a large size polycrystalline silicon basket and a small size polycrystalline silicon basket,
the large size polycrystalline silicon basket in which large lumps of the polycrystalline silicon are charged is arranged at a position close to the hydrofluoric acid supply system, and
the small size polycrystalline silicon basket in which small lumps of the polycrystalline silicon are charged is arranged at a position far from the hydrofluoric acid supply system.