Coating silicon pellets with dopant for addition of dopant in crystal growth
AssigneeRWE Schott Solar, Inc.
InventorBernhard P. Piwczyk
Life of this patent
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Abstract
An inexpensive method of coating silicon shot with boron atoms comprises (1) immersing silicon shot in an aqueous solution comprising a boric acid and polyvinyl alcohol, and (2) heating the solution so as to evaporate water and form a polymerized polyvinyl alcohol coating containing boron on the shot. A precise amount of this coated shot may then be mixed with a measured quantity of intrinsic silicon pellets and the resulting mixture may then be melted to provide a boron-doped silicon melt for use in growing p-type silicon bodies that can be converted to substrates for photovoltaic solar cells.
Claims16
Method of coating silicon pellets with a selected dopant for use in adding that dopant to a silicon melt comprising the steps of:
- forming an aqueous solution comprising a compound containing a selected dopant and polyvinyl alcohol;
- combining said aqueous solution with a measured quantity of silicon pellets in a container so as to form a mixture thereof;
- heating said mixture to a temperature at which the aqueous solution evaporates and the polyvinyl alcohol polymerizes, whereby the pellets are coated with a dopant-containing coating of polymerized polyvinyl alcohol;
- and
- discontinuing the heating after the dopant-containing coating of polymerized polyvinyl alcohol is dry and the coated silicon pellets are free-flowing.
Method of coating silicon pellets with boron dopant for use in adding boron dopant to a silicon melt comprising the steps of:
- forming an aqueous solution comprising a compound containing boric acid and polyvinyl alcohol;
- combining said aqueous solution with a measured quantity of silicon pellets in a container so as to form a mixture thereof;
- heating said mixture to a temperature at which the aqueous solution evaporates and the polyvinyl alcohol polymerizes, whereby the pellets are coated with a boron-containing coating of polymerized polyvinyl alcohol;
- and
- discontinuing the heating after the boron-containing coating of polymerized polyvinyl alcohol is dry and the coated silicon pellets are free-flowing.
Method of coating silicon shot with boron dopant for use in adding dopant to a silicon melt comprising the steps of:
- combining in a container (1) a solution comprising boric acid and polyvinyl alcohol having a pH of between about 8 and about 9 and (2) a measured quantity of clean silicon pellets so as to form a mixture thereof;
- heating said mixture to a temperature sufficient to removal of the solution by evaporation;
- moving the pellets as they are being heated so as to prevent agglomeration thereof;
- and
- terminating the heating after the solution has been fully evaporated and the pellets are dry and free moving.
Silicon pellets having a coating comprising polymerized PVA and a selected dopant from the class consisting of boron, phosphorus and arsenic.
Dependencies are inferred from the claim text.