Method for removing phosphorus and boron impurity from industrial silicon melt by secondary refining

Abstract

A method for removing phosphorus and boron impurities in an industrial silicon melt by secondary refining is provided. According to the present disclosure, inorganic zinc chloride is adopted as an impurity removal medium and is quickly decomposed into zinc and chloride ions at high temperatures; the phosphorus and boron impurities can react with the zinc and chloride ions to yield low-melting and high-melting compounds during contact with a silicon melt, the low-melting compounds volatilize and escape from the industrial silicon melt at the high temperature of the secondary refining. The high-melting compounds are segregated at the grain boundary along with silicon solidification and removed by crushing and pickling, or sink to the very bottom of the silicon melt and are removed by cutting off a deposition layer at a bottom of a silicon ingot after the silicon melt is solidified.

Claims

1. A method for removing phosphorus and boron impurities from an industrial silicon melt by a secondary refining, comprising steps of: introducing a carrier gas to a ladle, and vaporizing and adding zinc chloride to the industrial silicon melt by means of the carrier gas, wherein the zinc chloride is slowly and uniformly added to the industrial silicon melt with the carrier gas after the vaporizing and a temperature of the industrial silicon melt is controlled to be greater than or equal to 1,700° C., letting the industrial silicon melt stand for a reaction for 30 min to 60 min, and allowing low-melting compounds yielded by a reaction of chloride and zinc ions generated by a decomposition of the zinc chloride with the phosphorus and boron impurities in the industrial silicon melt to volatilize and escape; and cooling and solidifying the industrial silicon melt, and removing high-melting compounds by means of crushing and pickling or cutting off a deposition layer at a bottom of a silicon ingot.

2. The method for removing the phosphorus and boron impurities from the industrial silicon melt by the secondary refining according to claim 1, wherein a mass of the zinc chloride added is 1% to 5% of a mass of the industrial silicon melt.

3. The method for removing the phosphorus and boron impurities from the industrial silicon melt by the secondary refining according to claim 1, wherein the carrier gas is a compressed argon.

4. The method for removing the phosphorus and boron impurities from the industrial silicon melt by the secondary refining according to claim 1, wherein the carrier gas is introduced at a pressure of 0.2 MPa to 0.3 MPa and a flow rate of 800 L/h to 1,200 L/h for 20 min to 60 min.

5. The method for removing the phosphorus and boron impurities from the industrial silicon melt by the secondary refining according to claim 1, wherein the temperature of the industrial silicon melt is controlled at 1,700° C.

6. The method for removing the phosphorus and boron impurities from the industrial silicon melt by the secondary refining according to claim 1, wherein the cooling is intended to cool the industrial silicon melt to room temperature at a rate of 1 K/min to 5 K/min.

7. The method for removing the phosphorus and boron impurities from the industrial silicon melt by the secondary refining according to claim 3, wherein the carrier gas is introduced at a pressure of 0.2 MPa to 0.3 MPa and a flow rate of 800 L/h to 1,200 L/h for 20 min to 60 min.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) The present disclosure will be further described below in conjunction with examples, and the protection scope of the present disclosure is not limited to the following descriptions:

Example 1: A Method for Removing Phosphorus and Boron Impurities from an Industrial Silicon Melt by Secondary Refining

(2) Compressed argon as a carrier gas was introduced to a ladle at a pressure of 0.2 MPa and a flow rate of 800 L/h for 20 min. Zinc chloride was vaporized and added to a silicon melt by means of the carrier gas. The vaporized zinc chloride was slowly and uniformly added to the silicon melt along with the carrier gas. The mass of the zinc chloride added was 1% of that of industrial silicon. The temperature of the silicon melt was controlled at 1,700° C. The silicon melt was let stand for a reaction for 30 min after ventilation, and low-melting compounds yielded by a reaction of the zinc chloride with the phosphorus and boron impurities in the silicon melt volatilized and escaped; after the silicon melt was cooled and solidified, high-melting compounds were removed by means of crushing and pickling or cutting off a deposition layer at a bottom of a silicon ingot. The cooling was intended to cool the silicon melt to room temperature at a rate of 1 K/min.

(3) Before impurity removal, the content of phosphorus in the silicon melt was 35 ppm, and that of boron was 25 ppm; after impurity removal, the content of phosphorus was 25 ppm, and that of boron was 20 ppm.

Example 2: A Method for Removing Phosphorus and Boron Impurities from an Industrial Silicon Melt by Secondary Refining

(4) Compressed argon as a carrier gas was introduced to a ladle at a pressure of 0.2 MPa and a flow rate of 800 L/h for 20 min. Zinc chloride was vaporized and added to a silicon melt by means of the carrier gas. The vaporized zinc chloride was slowly and uniformly added to the silicon melt along with the carrier gas. The mass of the zinc chloride added was 3% of that of industrial silicon. The temperature of the silicon melt was controlled at 1,700° C. The silicon melt was let stand for a reaction for 30 min after ventilation, and low-melting compounds yielded by a reaction of the zinc chloride with the phosphorus and boron impurities in the silicon melt volatilized and escaped; after the silicon melt was cooled and solidified, high-melting compounds were removed by means of crushing and pickling or cutting off a deposition layer at a bottom of a silicon ingot. The cooling was intended to cool the silicon melt to room temperature at a rate of 1 K/min.

(5) Before impurity removal, the content of phosphorus in the silicon melt was 35 ppm, and that of boron was 25 ppm: after impurity removal, the content of phosphorus was 20 ppm, and that of boron was 15 ppm.

Example 3: A Method for Removing Phosphorus and Boron Impurities from an Industrial Silicon Melt by Secondary Refining

(6) Compressed argon as a carrier gas was introduced to a ladle at a pressure of 0.2 MPa and a flow rate of 800 L/h for 20 min. Zinc chloride was vaporized and added to a silicon melt by means of the carrier gas. The vaporized zinc chloride was slowly and uniformly added to the silicon melt along with the carrier gas. The mass of the zinc chloride added was 5% of that of industrial silicon. The temperature of the silicon melt was controlled at 1,700° C. The silicon melt was let stand for a reaction for 30 min after ventilation, and low-melting compounds yielded by a reaction of the zinc chloride with the phosphorus and boron impurities in the silicon melt volatilized and escaped; after the silicon melt was cooled and solidified, high-melting compounds were removed by means of crushing and pickling or cutting off a deposition layer at a bottom of a silicon ingot. The cooling was intended to cool the silicon melt to room temperature at a rate of 1 K/min.

(7) Before impurity removal, the content of phosphorus in the silicon melt was 35 ppm, and that of boron was 25 ppm: after impurity removal, the content of phosphorus was 15 ppm, and that of boron was 10 ppm.

Example 4: A Method for Removing Phosphorus and Boron Impurities from an Industrial Silicon Melt by Secondary Refining

(8) Compressed argon as a carrier gas was introduced to a ladle at a pressure of 0.2 MPa and a flow rate of 800 L/h for 20 min. Zinc chloride was vaporized and added to a silicon melt by means of the carrier gas. The vaporized zinc chloride was quickly added to the silicon melt in a short time along with the carrier gas. The mass of the zinc chloride added was 5% of that of industrial silicon. The temperature of the silicon melt was controlled at 1,800° C. The silicon melt was let stand for a reaction for 30 min after ventilation, and low-melting compounds yielded by a reaction of the zinc chloride with the phosphorus and boron impurities in the silicon melt volatilized and escaped; after the silicon melt was cooled and solidified, high-melting compounds were removed by means of crushing and pickling or cutting off a deposition layer at a bottom of a silicon ingot. The cooling was intended to cool the silicon melt to room temperature at a rate of 1 K/min.

(9) Before impurity removal, the content of phosphorus in the silicon melt was 35 ppm, and that of boron was 25 ppm; after impurity removal, the content of phosphorus was 10 ppm, and that of boron was 6 ppm.

Example 5: A Method for Removing Phosphorus and Boron Impurities from an Industrial Silicon Melt by Secondary Refining

(10) Compressed argon as a carrier gas was introduced to a ladle at a pressure of 0.2 MPa and a flow rate of 800 L/h for 40 min. Zinc chloride was vaporized and added to a silicon melt by means of the carrier gas. The vaporized zinc chloride was quickly added to the silicon melt in a short time along with the carrier gas. The mass of the zinc chloride added was 5% of that of industrial silicon. The temperature of the silicon melt was controlled at 1,800° C. The silicon melt was let stand for a reaction for 30 min after ventilation, and low-melting compounds yielded by a reaction of the zinc chloride with the phosphorus and boron impurities in the silicon melt volatilized and escaped; after the silicon melt was cooled and solidified, high-melting compounds were removed by means of crushing and pickling or cutting off a deposition layer at a bottom of a silicon ingot. The cooling was intended to cool the silicon melt to room temperature at a rate of 1 K/min.

(11) Before impurity removal, the content of phosphorus in the silicon melt was 35 ppm, and that of boron was 25 ppm; after impurity removal, the content of phosphorus was 8 ppm, and that of boron was 5 ppm.

Example 6: A Method for Removing Phosphorus and Boron Impurities from an Industrial Silicon Melt by Secondary Refining

(12) Compressed argon as a carrier gas was introduced to a ladle at a pressure of 0.2 MPa and a flow rate of 800 L/h for 40 min. Zinc chloride was vaporized and added to a silicon melt by means of the carrier gas. The vaporized zinc chloride was slowly and uniformly added to the silicon melt along with the carrier gas. The mass of the zinc chloride added was 5% of that of industrial silicon. The temperature of the silicon melt was controlled at 1,800° C. The silicon melt was let stand for a reaction for 30 min after ventilation, and low-melting compounds yielded by a reaction of the zinc chloride with the phosphorus and boron impurities in the silicon melt volatilized and escaped; after the silicon melt was cooled and solidified, high-melting compounds were removed by means of crushing and pickling or cutting off a deposition layer at a bottom of a silicon ingot. The cooling was intended to cool the silicon melt to room temperature at a rate of 5 K/min.

(13) Before impurity removal, the content of phosphorus in the silicon melt was 35 ppm, and that of boron was 25 ppm; after impurity removal, the content of phosphorus was 12 ppm, and that of boron was 6 ppm.

Example 7: A Method for Removing Phosphorus and Boron Impurities from an Industrial Silicon Melt by Secondary Refining

(14) Compressed argon as a carrier gas was introduced to a ladle at a pressure of 0.25 MPa and a flow rate of 800 L/h for 40 min. Zinc chloride was vaporized and added to a silicon melt by means of the carrier gas. The vaporized zinc chloride was slowly and uniformly added to the silicon melt along with the carrier gas. The mass of the zinc chloride added was 5% of that of industrial silicon. The temperature of the silicon melt was controlled at 1,800° C. The silicon melt was let stand for a reaction for 60 min after ventilation, and low-melting compounds yielded by a reaction of the zinc chloride with the phosphorus and boron impurities in the silicon melt volatilized and escaped; after the silicon melt was cooled and solidified, high-melting compounds were removed by means of crushing and pickling or cutting off a deposition layer at a bottom of a silicon ingot. The cooling was intended to cool the silicon melt to room temperature at a rate of 5 K/min.

(15) Before impurity removal, the content of phosphorus in the silicon melt was 35 ppm, and that of boron was 25 ppm; after impurity removal, the content of phosphorus was 9 ppm, and that of boron was 5 ppm.

Example 8: A Method for Removing Phosphorus and Boron Impurities from an Industrial Silicon Melt by Secondary Refining

(16) Compressed argon as a carrier gas was introduced to a ladle at a pressure of 0.2 MPa and a flow rate of 1,000 L/h for 40 min. Zinc chloride was vaporized and added to a silicon melt by means of the carrier gas. The vaporized zinc chloride was slowly and uniformly added to the silicon melt along with the carrier gas. The mass of the zinc chloride added was 5% of that of industrial silicon. The temperature of the silicon melt was controlled at 1,800° C. The silicon melt was let stand for a reaction for 60 min after ventilation, and low-melting compounds yielded by a reaction of the zinc chloride with the phosphorus and boron impurities in the silicon melt volatilized and escaped; after the silicon melt was cooled and solidified, high-melting compounds were removed by means of crushing and pickling or cutting offa deposition layer at a bottom of a silicon ingot. The cooling was intended to cool the silicon melt to room temperature at a rate of 1 K/min.

(17) Before impurity removal, the content of phosphorus in the silicon melt was 35 ppm, and that of boron was 25 ppm; after impurity removal, the content of phosphorus was 5 ppm, and that of boron was 3 ppm.

Example 9: A Method for Removing Phosphorus and Boron Impurities from an Industrial Silicon Melt by Secondary Refining

(18) Compressed argon as a carrier gas was introduced to a ladle at a pressure of 0.3 MPa and a flow rate of 1,200 L/h for 40 min. Zinc chloride was vaporized and added to a silicon melt by means of the carrier gas. The vaporized zinc chloride was slowly and uniformly added to the silicon melt along with the carrier gas. The mass of the zinc chloride added was 5% of that of industrial silicon. The temperature of the silicon melt was controlled at 1,800° C. The silicon melt was let stand for a reaction for 45 min after ventilation, and low-melting compounds yielded by a reaction of the zinc chloride with the phosphorus and boron impurities in the silicon melt volatilized and escaped; after the silicon melt was cooled and solidified, high-melting compounds were removed by means of crushing and pickling or cutting off a deposition layer at a bottom of a silicon ingot. The cooling was intended to cool the silicon melt to room temperature at a rate of 3 K/min.

(19) Before impurity removal, the content of phosphorus in the silicon melt was 35 ppm, and that of boron was 25 ppm; after impurity removal, the content of phosphorus was 7 ppm, and that of boron was 5 ppm.

COMPARATIVE EXAMPLE

(20) Compressed argon as a carrier gas was introduced to a ladle at a pressure of 0.25 MPa and a flow rate of 1,000 L/h for 20 min. The silicon melt was let stand for a reaction for 30 min after ventilation. No zinc chloride was added to the ladle.

(21) Before impurity removal, the content of phosphorus in the silicon melt was 35 ppm, and that of boron was 25 ppm; after impurity removal, the content of phosphorus was 33 ppm, and that of boron was 24 ppm.

(22) The above description is only preferred embodiments of the present disclosure, but the protection scope of the present disclosure is not limited thereto. Any equivalent substitution or alteration made within a technical scope of the present disclosure by a person skilled in the art according to the technical solution of the present disclosure and inventive concepts thereof shall fall within the protection scope of the present disclosure.