Method Of Determining An Amount of Impurities That A Contaminating Material Contributes To High Purity Silicon And Furnace For Treating High Purity Silicon

Abstract

A method of determining an amount of impurities that a contaminating material contributes to high purity silicon comprises the step of partially encasing a sample of high purity silicon in the contaminating material. The sample encased in the contaminating material is heated within a furnace. A change in impurity content of the high purity silicon is determined after the step of heating, compared to an impurity content of the high purity silicon prior to the step of heating. A furnace for heat treating high purity silicon comprises a housing that defines a heating chamber. The housing is at least partially formed from low contaminant material that contributes less than 400 parts per trillion of impurities to the high purity silicon during heating at annealing temperatures for a sufficient period time to anneal the high purity silicon, and the furnace contributes an average of less than 400 parts per trillion of impurities to the high purity silicon under the same heating conditions.

1 . A method of determining an amount of impurities that a contaminating material including the impurities contributes to high purity silicon, said method comprising the steps of:
 optionally, determining the impurity content of the contaminating material;   optionally, determining impurity content of the high purity silicon;   providing the contaminating material;   at least partially encasing a sample of the high purity silicon in the contaminating material;   heating the sample at least partially encased in the contaminating material within a furnace; and   determining a change in impurity content of the high purity silicon after said step of heating the sample at least partially encased in the contaminating material compared to an impurity content of the high purity silicon prior to said step of heating.   
     
     
         2 . A method as set forth in  claim 1  wherein the high purity silicon is further defined as a silicon having an impurity content of less than or equal to 500 parts per trillion atomic. 
     
     
         3 . A method as set forth in  claim 1  wherein the sample at least partially encased in the contaminating material is heated at a temperature of at least 1650° F. for a period of at least 200 minutes. 
     
     
         4 . A method as set forth in  claim 1  wherein the impurities are selected from the group of aluminum, arsenic, boron, phosphorous, iron, nickel, copper, chromium, and combinations thereof. 
     
     
         5 . A method as set forth in  claim 4  wherein the contaminating material comprises at least one ceramic present in an amount of at least 40 percent by weight based on the total weight of the contaminating material. 
     
     
         6 . A method as set forth in  claim 5  wherein the at least one ceramic is selected from the group of aluminium oxide, silicon dioxide, silicon carbide, and combinations thereof. 
     
     
         7 . A furnace for heat treating high purity silicon, said furnace comprising:
 a housing which defines a heating chamber of said furnace and is at least partially formed from low contaminant material that contributes less than 400 parts per trillion of impurities to the high purity silicon during heating of the high purity silicon at annealing temperatures for a sufficient period of time to anneal the high purity silicon;   wherein said furnace contributes an average of less than or equal to 400 parts per trillion of impurities to the high purity silicon during heating of the high purity silicon at annealing temperatures for a sufficient period time to anneal the high purity silicon, as measured at monthly intervals over a period of at least four months.   
     
     
         8 . A furnace as set forth in  claim 7  wherein the annealing temperature is at least 1650° F. and the annealing time is at least 200 minutes. 
     
     
         9 . A furnace as set forth in  claim 7  wherein said low contaminant material comprises a compound selected from the group of aluminium oxide, silicon dioxide, silicon carbide, and combinations thereof. 
     
     
         10 . A furnace as set forth in  claim 9  wherein said low contaminant material comprises aluminium oxide in an amount of at least 40 percent by weight based on the total weight of said low contaminant material. 
     
     
         11 . A furnace as set forth in  claim 10  wherein said low contaminant material comprises aluminium oxide in an amount of at least 90 percent by weight based on the total weight of said low contaminant material. 
     
     
         12 . A furnace as set forth in  claim 9  wherein said low contaminant material comprises a silicon dioxide. 
     
     
         13 . A furnace as set forth in  claim 7  wherein said housing comprises a plurality of components that define the heating chamber with each component having a surface in atmospheric communication with the heating chamber and with at least one of said components formed from said low contaminant material. 
     
     
         14 . A furnace as set forth in  claim 13  wherein each of said components are independently formed from low contaminant material. 
     
     
         15 . A furnace as set forth in  claim 13  wherein one of said components is further defined as a hearth formed from low contaminant material for receiving the high purity silicon. 
     
     
         16 . A furnace as set forth in  claim 15  wherein said hearth is further defined as a layered composite with at least two layers each independently formed from low contaminant material. 
     
     
         17 . A furnace as set forth in  claim 16  wherein one of said layers comprises a ceramic fiber formed from low contaminant material. 
     
     
         18 . A furnace as set forth in  claim 17  wherein another of said layers comprises firebrick coated with low contaminant material, with said ceramic fiber disposed on said coated firebrick. 
     
     
         19 . A furnace as set forth in  claim 7  wherein the heating chamber has a volume of at least 10,000 cm 3 . 
     
     
         20 - 22 . (canceled) 
     
     
         23 . A furnace as set forth in  claim 7  wherein said housing comprises
 a base presenting a hearth for receiving the high purity silicon and 
 a furnace cover separate from said base and defining a cavity with said base abutting said furnace cover thereby sealing said cavity and forming said heating chamber; 
 wherein said base and said furnace cover are separable for enabling said furnace cover to be removed from said base during insertion and removal of the high purity silicon from said heating chamber. 
 
     
     
         24 - 27 . (canceled) 
     
     
         28 . A furnace as set forth in  claim 23  further comprising a frame including an elevating mechanism attached to said furnace cover for raising and lowering said furnace cover. 
     
     
         29 . A furnace as set forth in  claim 28  wherein said elevating mechanism is further defined as at least one elevating screw for raising and lowering said furnace top in response to rotation of said elevating screw. 
     
     
         30 . (canceled) 
     
     
         31 . A furnace as set forth in  claim 23  wherein at least one of said base and said furnace cover is at least partially formed from low contaminant material that contributes less than 400 parts per trillion of impurities to high purity silicon during heating of the high purity silicon at annealing temperatures for a sufficient period of time to anneal the high purity silicon. 
     
     
         32 . (canceled) 
     
     
         33 . A method of heat treating a high purity composition in the furnace as set forth in  claim 23 , said method comprising the steps of:
 disposing the high purity composition on the hearth;   arranging a relative position of the furnace cover to the base with the furnace cover in an elevated position relative to the base;   positioning the base beneath the furnace cover;   lowering the furnace cover onto the base to form the furnace defining the heating chamber with the high purity composition disposed within the heating chamber; and   heating the high purity composition within the heating chamber.   
     
     
         34 - 35 . (canceled)