Purification of a metalloid by consumable electrode vacuum arc remelt process

Abstract

A metalloid such as silicon in the form of a preheated solid electrode is purified by a CEVAR purification process by producing an ingot with controlled heating and cool down after the preheated electrode is melted in a CEVAR furnace system using a short CEVAR open-bottomed crucible.

1 . A CEVAR furnace system for producing a purified silicon ingot from a silicon electrode, the CEVAR furnace system comprising:
 a silicon electrode heating apparatus for preheating the silicon electrode to form a preheated silicon electrode;   a gas-tight CEVAR furnace chamber;   a short CEVAR open-bottomed crucible for containment of an arc zone from a CEVAR purification process melting the preheated silicon electrode, the short CEVAR open-bottomed crucible disposed in the gas-tight CEVAR furnace chamber;   a preheated silicon electrode drive system for lowering the preheated silicon electrode within the short CEVAR open-bottomed crucible as a lower end of the preheated silicon electrode melts in the CEVAR purification process;   an ingot heating apparatus disposed adjacent to the open bottom of the short CEVAR open-bottomed crucible through which the purified silicon ingot formed in the CEVAR purification process passes;   an ingot heating controller for controlling the ingot heating apparatus to provide a temperature-controlled thermal environment for the purified silicon ingot passing through the ingot heating apparatus; and   an ingot withdrawal drive system for alternatively withdrawing the purified silicon ingot from the short CEVAR open-bottomed crucible at a vertical growth rate of the purified silicon ingot during steady state of the CEVAR purification process or raising the short CEVAR open-bottomed crucible, the silicon electrode and the ingot heating apparatus at the vertical growth rate of the purified silicon ingot during steady state of the CEVAR purification process.   
     
     
         2 . The CEVAR furnace system of  claim 1  wherein an interior height of the short CEVAR opened-bottom crucible is at least 60 percent and less than 120 percent of a diameter of the purified silicon ingot formed in the CEVAR purification process. 
     
     
         3 . The CEVAR furnace system of  claim 1  further comprising a vacuum lock chamber connected between the silicon electrode heating apparatus and the short CEVAR opened-bottom crucible in the gas-tight CEVAR furnace chamber to prevent exposure to air of the preheated silicon electrode during transfer from the silicon electrode heating apparatus to the gas-tight CEVAR furnace chamber. 
     
     
         4 . The CEVAR furnace system of  claim 3  wherein the silicon electrode heating apparatus comprises a resistance furnace. 
     
     
         5 . The CEVAR furnace system of  claim 1  further comprising an auxiliary electrode heater disposed within the gas-tight CEVAR furnace chamber to heat the preheated silicon electrode during the CEVAR purification process. 
     
     
         6 . The CEVAR furnace system of  claim 1  further comprising a thermal insulation disposed around the preheated silicon electrode in the gas-tight CEVAR furnace chamber. 
     
     
         7 . The CEVAR furnace system of  claim 6  wherein the thermal insulation comprises a carbon fiber insulating material. 
     
     
         8 . The CEVAR furnace system of  claim 1 , the base having a contour for interlocking contact with the bottom of the purified silicon ingot. 
     
     
         9 . The CEVAR furnace system of  claim 1 , the short CEVAR opened-bottom crucible having an interior wall with a rectangular cross section, the interior height of the short CEVAR opened-bottom crucible being at least 60 percent and less than 120 percent of the length of a rectangular side of the purified silicon ingot formed in the CEVAR purification process. 
     
     
         10 . The CEVAR furnace system of  claim 1 , the ingot withdrawal drive system further comprising a base upon which the bottom of the purified silicon ingot sits and a drive actuator connected to the base to control the rate of withdrawing of the purified silicon ingot from the short CEVAR open-bottomed crucible. 
     
     
         11 . The CEVAR furnace system of  claim 10  further comprising a DC power source having a first output and a second output connected respectively between the preheated silicon electrode and the base or the drive actuator. 
     
     
         12 . The CEVAR furnace system of  claim 1  further comprising a continuous preheated silicon electrode furnace charging apparatus for forming the purified silicon ingot with the CEVAR furnace system as a continuous purified silicon ingot. 
     
     
         13 . A CEVAR furnace system for producing a purified silicon ingot from a silicon electrode, the CEVAR furnace system comprising:
 a gas-tight CEVAR furnace chamber;   a silicon electrode heating apparatus disposed within the gas-tight CEVAR furnace chamber for preheating the silicon electrode to form a preheated silicon electrode;   a short CEVAR open-bottomed crucible for containment of an arc zone from a CEVAR purification process melting the preheated silicon electrode, the short CEVAR open-bottomed crucible disposed in the gas-tight CEVAR furnace chamber;   a preheated silicon electrode drive system for lowering the preheated silicon electrode within the short CEVAR open-bottomed crucible as a lower end of the preheated silicon electrode melts in the CEVAR purification process;   an ingot heating apparatus disposed adjacent to the open bottom of the short CEVAR open-bottomed crucible through which the purified silicon ingot formed in the CEVAR purification process passes;   an ingot heating controller for controlling the ingot heating apparatus to provide a temperature-controlled thermal environment for the purified silicon ingot passing through the ingot heating apparatus; and   an ingot withdrawal drive system for alternatively withdrawing the purified silicon ingot from the short CEVAR open-bottomed crucible at a vertical growth rate of the purified silicon ingot during a steady state of the CEVAR purification process or raising the short CEVAR open-bottomed crucible, the silicon electrode and the ingot heating apparatus at the vertical growth rate of the purified silicon ingot during the steady state of the CEVAR purification process.   
     
     
         14 . The CEVAR furnace system of  claim 13  wherein an interior height of the short CEVAR opened-bottom crucible is at least 60 percent and less than 120 percent of a diameter of the purified silicon ingot formed in the CEVAR purification process. 
     
     
         15 . The CEVAR furnace system of  claim 13  further comprising a thermal insulation disposed around the preheated silicon electrode in the gas-tight CEVAR furnace chamber. 
     
     
         16 . The CEVAR furnace system of  claim 15  wherein the thermal insulation comprises a carbon fiber insulating material. 
     
     
         17 . The CEVAR furnace system of  claim 13 , the base having a contour for interlocking contact with the bottom of the purified silicon ingot. 
     
     
         18 . The CEVAR furnace system of  claim 13 , the short CEVAR opened-bottom crucible having an interior wall with a rectangular cross section, the interior height of the short CEVAR opened-bottom crucible being at least 60 percent and less than 120 percent of the length of a rectangular side of the purified silicon ingot formed in the CEVAR purification process. 
     
     
         19 . The CEVAR furnace system of  claim 13 , the ingot withdrawal drive system further comprising a base upon which the bottom of the purified silicon ingot sits and a drive actuator connected to the base to control the rate of withdrawing of the purified silicon ingot from the short CEVAR open-bottomed crucible. 
     
     
         20 . The CEVAR furnace system of  claim 19  further comprising a DC power source having a first output and a second output connected respectively between the preheated silicon electrode and the base or the drive actuator.