Method for producing silicon using microwave, and microwave reduction furnace

Abstract

A microwave reduction furnace including a reaction furnace provided with a refractory chamber of silica or silicon carbide for storing a material therein, a supply section for supplying the material into the refractory chamber, the material being a mixture of a silica powder and a graphite powder or a mixture of a silica powder, a silicon carbide powder and a graphite powder, a discharge section for discharging molten silicon, obtained through reduction, out of the chamber, and a microwave oscillator for outputting microwave toward the refractory chamber in the reaction furnace with a degree of directionality by virtue of a helical antenna or a waveguide.

Claims

1. A microwave reduction furnace comprising: a reaction furnace provided with a refractory chamber of silica or silicon carbide for storing a material therein; a supply section for supplying the material into the refractory chamber, the material being a mixture of a silica powder and a graphite powder or a mixture of a silica powder, a silicon carbide powder and a graphite powder; a discharge section for discharging molten silicon, obtained through reduction reaction, out of the chamber, said discharge section having a tapping hole, provided at the chamber, through which the molten silicon flows and a weir whose tip is configured to be immersed in the molten silicon to prevent an SiO gas produced in the chamber from leaking out of the chamber; and a microwave oscillator for outputting a microwave toward the refractory chamber in the reaction furnace with a degree of directionality by virtue of a helical antenna or a waveguide.

2. The microwave reduction furnace according to claim 1, wherein the weir includes a cutout at a position along a center line of a tapping pipe that includes the tapping hole, and wherein the cutout serves as a molten silicon outlet with a remaining portion other than an outlet serving to block an outflow of the molten silicon.

3. The microwave reduction furnace according to claim 2, wherein the weir extends from a side wall inner surface of the chamber and bends toward a bottom surface of the chamber.

4. The microwave reduction furnace according to claim 3, wherein the weir includes a drooping end, and wherein at the drooping end of the weir, opposing side portions of the weir beside the outlet are in contact with the bottom surface of the chamber and supported by the bottom surface, with the portion of the weir corresponding to the outlet being positioned so as to be immersed in the molten silicon as the molten silicon fills a bottom portion of the chamber.

5. The microwave reduction furnace according to claim 1, wherein the mixture material consists essentially of the silica powder, the silicon carbide powder and the graphite powder.

6. The microwave reduction furnace according to claim 1, wherein the mixture material consists essentially of the silica powder and the graphite powder.

7. The microwave reduction furnace according to claim 1, wherein the mixture material consists of the silica powder, the silicon carbide powder and the graphite powder.

8. The microwave reduction furnace according to claim 1, wherein the mixture material consists of the silica powder and the graphite powder.

9. The microwave reduction furnace according to claim 1, wherein the mixture material comprises the silica powder, the silicon carbide powder and the graphite powder.

10. The microwave reduction furnace according to claim 1, wherein the mixture material comprises the silica powder and the graphite powder.

11. The microwave reduction furnace according to claim 1, wherein the weir comprises a refractory material and is provided on a portion of the tapping hole.

12. The microwave reduction furnace according to claim 1, wherein the weir includes an outlet with an upper end of the outlet of the weir immersed in the molten silicon when the molten silicon starts flowing out continuously by a siphon-action.

13. The microwave reduction furnace according to claim 12, where immersion of the upper end of the outlet of the weir in the molten silicon prevents the SiO gas in the chamber from leaking out through the outlet.

14. The microwave reduction furnace according to claim 1, wherein the tip of the weir is out of contact with a bottom surface of the chamber.

15. A microwave reduction furnace comprising: a reaction furnace provided with a refractory chamber of silica or silicon carbide, the reaction furnace being capable of storing a material therein and preventing a generated gas from escaping; a supply section for supplying the material into the refractory chamber, the material being a mixture of a silica powder and a graphite powder or a mixture of the silica powder, a silicon carbide powder and the graphite powder; a discharge section for discharging molten silicon, obtained through reduction reaction, out of the chamber, said discharge section having a tapping hole, provided at the chamber, through which the molten silicon flows and a weir whose tip is configured to be immersed in the molten silicon to prevent an SiO gas produced in the chamber from leaking out of the chamber; and a microwave oscillator for outputting a microwave toward the refractory chamber in the reaction furnace with a degree of directionality by virtue of a helical antenna or a waveguide, wherein the SiO gas is produced as an intermediate product through the reduction reaction between the silica powder and the silicon carbide powder and/or the graphite powder, and the SiO gas is allowed to be in contact with the silica, graphite and/or silicon carbide powders while preventing the SiO gas from escaping out of the refractory chamber, thus reducing the silica powder through the reduction reaction, thereby allowing for continuous production of the molten silicon.

16. A microwave reduction furnace comprising: a reaction furnace provided with a refractory chamber of silica or silicon carbide for storing a material therein; a supply section for supplying the material into the chamber, the material being a mixture of a silica powder and a graphite powder or a mixture of a silica powder, a silicon carbide powder and a graphite powder; a discharge section for discharging molten silicon, obtained through reduction reaction, out of the chamber, said discharge section having a tapping hole, provided at the chamber, through which the molten silicon flows and a weir whose tip is configured to be immersed in the molten silicon to prevent an SiO gas produced in the chamber from leaking out of the chamber; and a microwave unit arranged on an inner surface of a circumferential surface surrounding the refractory chamber for radiating a microwave beam toward a particular point in the refractory chamber; and a main reflection mirror arranged above the refractory chamber, the main reflection mirror having a paraboloid whose focal point coincides with the particular point and which paraboloid serves as a reflection surface for a microwave.

17. A microwave reduction furnace comprising: a reaction furnace provided with a refractory chamber of silica or silicon carbide for storing a material therein; a microwave window surrounding the reaction furnace; a melting furnace top plate supported by the microwave window for covering the refractory chamber so as to prevent a generated gas from escaping; a supply section for supplying the material into the refractory chamber through the melting furnace top plate, the material being a mixture of a silica powder and a graphite powder or a mixture of the silica powder, a silicon carbide powder and the graphite powder; a discharge section for discharging molten silicon, obtained through reduction reaction, out of the chamber, said discharge section having a tapping hole, provided at the chamber, through which the molten silicon flows and a weir whose tip is configured to be immersed in the molten silicon to prevent an SiO gas produced in the chamber from leaking out of the chamber; a microwave unit arranged on an inner surface of a circumferential surface surrounding the refractory chamber for radiating a microwave beam toward a particular point in the refractory chamber; and a main reflection mirror arranged above the refractory chamber, the main reflection mirror having a paraboloid whose focal point coincides with the particular point and which paraboloid serves as a reflection surface for a microwave, wherein the SiO gas is produced as an intermediate product through the reduction reaction between the silica powder and the silicon carbide powder and/or the graphite powder, and the SiO gas is allowed to be in contact with the silica powder, graphite powder and/or silicon carbide powder while preventing the SiO gas from escaping out of a housing constructed by the refractory chamber and the melting furnace top plate, thus reducing the silica powder through the reduction reaction, thereby allowing for continuous production of the molten silicon.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 A vertical-sectional view showing a microwave reduction furnace for use with a method for producing silicon using microwave according to an embodiment of the present invention.

(2) FIG. 2 A partial plan view showing a weir portion thereof.

(3) FIG. 3 A vertical-sectional view showing a melting furnace of a microwave reduction furnace according to another embodiment of the present invention.

(4) FIG. 4 A diagram showing a stepped reflection mirror thereof.

(5) FIG. 5 A perspective view showing the entire microwave reduction furnace.

REFERENCE SIGNS LIST

(6) 2: Material mixture powder (SiO.sub.2+SiC+C or SiO.sub.2+C)

(7) 3: Molten silicon

(8) 12, 51a: Silica reaction chamber

(9) 13, 62: Tapping hole

(10) 16, 63: Tapping pipe

(11) 17, 18, 64: Heater

(12) 31: Reaction furnace

(13) 32: Furnace body

(14) 33: Microwave oscillator

(15) 34: Microwave transmitting antenna

(16) 41: Support plate

(17) 42: Semiconductor 500 W module

(18) 43: Microwave unit

(19) 50: Melting furnace

(20) 51: Reaction furnace

(21) 51b, 52: Heat-insulating material

(22) 53: Main reflection mirror

(23) 53a: Microwave mirror surface

(24) 54: Microwave window

(25) 55: Stepped reflection surface

(26) 56: Sub-reflection mirror

(27) 57: Auxiliary reflection mirror