Self-seeding conversion of polycrystalline silicon sheets to macrocrystalline by zone melting

A self-seeding process for converting an unsupported, substrate-free polycrystalline semiconductor silicon sheet to a macrocrystalline semiconductor silicon sheet, which comprises:

• (a) forming a region of said sheet having a small width compared to the width of the remainder of said sheet,
• (b) heating said small width region in an oxidizing atmosphere to form a molten zone in said small width region of said sheet,
• (c) allowing a portion of said molten zone to solidify into a seed crystal of the semiconductor silicon material substantially coextensive with the small width of said region at the portion of the molten zone so solidified,
• (d) expanding and axially moving the molten zone to encompass the full width of the sheet, and continuing axially moving moving the molten zone along the remainder of said sheet,
• (e) allowing said sheet to solidify successively as said molten zone passes along it, said molten zone having a trailing boundary which is arcuate shaped with a centrally located portion of said trailing boundary extending further along said sheet in the direction of travel of said molten zone than portions of said trailing boundary proximate to the edges of said sheet, whereby said single seed crystal propagates into the remainder of said sheet through which said molten zone passes.