Method for cleaning polysilicon

Abstract

A method for cleaning polysilicon comprises steps of cleaning solid or granular polysilicon with an aqueous solution of dissolved ozone, and of cleaning with hydrofluoric acid the polysilicon receiving the above cleaning based on an aqueous solution of dissolved ozone, wherein the above steps are executed once in this order, or the above steps are repeated once or more in this order. Subsequent to the last cleaning step using hydrofluoric acid, a still other step of cleaning the polysilicon with pure water and then drying it is preferably added. This method for cleaning polysilicon allows organic materials, particles and metal impurities adsorbed on the surface of polysilicon to be removed at a low cost, and to increase the freeing rate.

What is claimed is:  
     
         1 . A method for cleaning polysilicon comprising steps of cleaning solid or granular polysilicon with an aqueous solution of dissolved ozone, and of cleaning with hydrofluoric acid the polysilicon which has undergone the cleaning step using the aqueous solution of dissolved ozone, wherein the above steps are executed once in this order, or the above steps are repeated once or more in this order.  
     
     
         2 . A method for cleaning polysilicon of  claim 1  which further comprises, following the last cleaning step using hydrofluoric acid, steps of cleaning polysilicon with pure water and of drying said cleaned polysilicon.  
     
     
         3 . A method for cleaning polysilicon of  claim 1  or  2  wherein the concentration of ozone of the aqueous solution of dissolved ozone is 3 to 20 ppm, and the concentration of hydrofluoric acid is 0.1 to 5 wt. %.  
     
     
         4 . A method for cleaning polysilicon of anyone of claims  1  through  3  wherein the cleaning step using an aqueous solution of dissolved ozone comprises, steps of jetting an aqueous solution of dissolved ozone at solid or granular polysilicon contained in a chemically resistant basket, and of immersing the basket containing the polysilicon in an aqueous solution of dissolved ozone.  
     
     
         5 . A method for cleaning polysilicon of  claim 4  wherein the cleaning step using hydrofluoric acid comprises a step of immersing polysilicon which is kept in a chemically resistant basket and has been cleaned with an aqueous solution of dissolved zone, in hydrofluoric acid.