Deposition of High Purity Silicon Via High Surface Area Gas-Solid or Gas-Liquid Interfaces and Recovery Via Liquid Phase

Abstract

Solid silicon is deposited onto electrically heated deposition plates by the reduction reaction of gaseous trichlorosilane and hydrogen which are mixed and pumped across the surfaces of the plates. The plates can have a number of high-surface area geometries such as concentric cylinders, spirals, or repeating S-shapes. Once the desired amount of silicon has been deposited, the deposition plates are heated to above the melting point of silicon causing the deposited silicon to slide off the plates in the form of a crust due to gravitational force. The plates are left coated with a thin film of liquid silicon which contains any impurities leached from the plates. This film is melted off separately from the main silicon crust to avoid contamination of the latter and the plates are then ready for the next deposition cycle.

1 - 4 . (canceled) 
     
     
         5 . A method for producing high-purity silicon comprising the steps of: a. creating at least two vertically oriented deposition plates compatible with silicon and the vertically oriented deposition plates have a geometry chosen to increase surface area to the volume of space occupied by the vertically oriented deposition plates toward the theoretical maximum wherein the vertically oriented deposition plates are electrically heated and each vertically oriented deposition plate has a surface, b. Placing said plates in a reactor vessel, c. flowing a pressurized mixture of a deposition gas mixture into the reactor vessel to deposit a reduced silicon onto the plate surface wherein the pressurized mixture flows through the spaces between the vertically oriented deposition plates and the vertically oriented deposition plates are heated to a surface temperature to optimize the reduction reaction of the silicon-bearing gas but below a temperature that would effect the structural properties of the solid silicon, d. Heating the vertically oriented deposition plates quickly after the desired amount of reduced silicon is deposited so as to form a liquid silicon, e. Collecting the liquid silicon in an appropriate container within the reactor with the vertically oriented deposition plates partially submerged in the liquid silicon to provide the necessary heating f extracting the liquid silicon in a controlled manner. g. Continuing to heat the vertically oriented deposition plates after they have been separated from the deposited silicon so that the thin layer of liquid silicon is removed and disposed wherein the plate surface becomes clean and may be used for another deposition cycle. 
     
     
         6 . The method for producing high-purity silicon in  claim 5  wherein the silicon deposition gas mixture is selected from hydrogen and the group consisting of trichlorosilane, silicon tetrachloride, other silanes, and mixtures thereof. 
     
     
         7 . The method for producing high-purity silicon in  claim 5  wherein the least two vertically oriented deposition plates are made from materials with the appropriate structural, conductivity, heat resistance, and silicon compatibility characteristics. 
     
     
         8 . The method for producing high-purity silicon in  claim 7  wherein the least two vertically oriented deposition plates are made from materials selected from the group consisting of silicon carbide, silicon nitride, tungsten, certain graphite composites, and mixtures thereof. 
     
     
         9 . The method for producing high-purity silicon in  claim 8  wherein extracting the liquid silicon in a controlled manner comprises removal of the vertically oriented deposition plates in a controlled manner including reducing the temperature of the vertically oriented deposition plates so as to result in crystallization of the liquid silicon into an ingot of polycrystalline silicon. 
     
     
         10 . The method for producing high-purity silicon in  claim 8  wherein extracting the liquid silicon in a controlled manner comprises pumping the liquid silicon out of the container and reactor, through appropriately constructed piping, to a Czokralski crystal puller for production of monocrystalline silicon. 
     
     
         11 . A method for producing high-purity silicon comprising the steps of: a. creating at least two vertically oriented deposition plates compatible with silicon and the vertically oriented deposition plates have a geometry chosen to increase surface area to the volume of space occupied by the vertically oriented deposition plates toward the theoretical maximum wherein the vertically oriented deposition plates are electrically heated and each vertically oriented deposition plate has a surface a serrated lower edge, b. Placing said plates in a reactor vessel, c. flowing a pressurized hydrogen gas and liquid silane into the reactor vessel to deposit a reduced silicon on the coated surface wherein the pressurized mixture is sufficient to flow through the spaces between the vertically oriented deposition plates and the vertically oriented deposition plates are heated to a surface temperature to optimize the reduction reaction of trichlorosilane and above a melting point of reduced silicon, d. Removing the liquid reduced silicon from the vertically oriented deposition plates by allowing the liquid reduced silicon to drip from the serrated edges such that it forms droplets, 
     
     
         12 . The method for producing high-purity silicon in  claim 11  wherein the liquid silianes is selected from the group of liquids consisting of trichlorosilane, silicon tetrachloride, other silanes, and mixtures thereof. 
     
     
         13 . The method for producing high-purity silicon in  claim 11  wherein the least two vertically oriented deposition plates are made from materials with the appropriate structural, conductivity, heat resistance, and silicon compatibility characteristics. 
     
     
         14 . The method for producing high-purity silicon in  claim 13  wherein the least two vertically oriented deposition plates are made from materials selected from the group consisting of silicon carbide, silicon nitride, tungsten, certain graphite composites, and mixtures thereof. 
     
     
         15 . The method for producing high-purity silicon in  claim 14  wherein the serrated lower edge has a geometry to effect formation of evenly sized and spaced droplets. 
     
     
         16 . The method for producing high-purity silicon in  claim 15  wherein the droplets have sufficient time to form individual silicon beads wherein such cooling is effected by contact of the downward-traveling droplets with silicon deposition-hydrogen gas mixtures and/or contact of the droplets with a pool of liquid trichlorosilane and/or silicon tetrachloride at the bottom of the reactor. 
     
     
         17 . A method for producing high-purity silicon comprising: a. Coupling an electrical base heater that is electrically heated to a reactor vessel, b. Coupling a liquid-gas inlet to allow a hydrogen-liquid silane mixture to flow into the reactor vessel; c. Heating the a hydrogen-liquid silane mixture to a temperature at which the vaporized silane and hydrogen react to form high-purity silicon in bubble that are formed in a liquid state; and d. Shutting off the hydrogen-silane mixture; and e. removing the high purity silicon. 
     
     
         18 . The method for producing high-purity silicon in  claim 17  wherein removing the high purity silicon is accomplished by cooling the pool of liquid silane to form solid of polycrystalline silicon which may then be removed from the reactor vessel. 
     
     
         19 . The method for producing high-purity silicon in  claim 17  wherein removing the high purity silicon is accomplished by pumping the liquid silicon out of the container and reactor, through appropriately constructed piping, to a Czokralski crystal puller for production of monocrystalline silicon. 
     
     
         20 . The method for producing high-purity silicon in  claim 17  wherein the liquid silane is selected from the group of liquids consisting of trichlorosilane, silicon tetrachloride, other silanes, and mixtures thereof.