Metallization of Large Silicon Wafers. Final Report.

摘要

A metallization scheme has been developed which allows selective plating of silicon solar cell surfaces. The system is comprised of three layers. Palladium, through the formation of palladium silicide at 300 exp 0 C in nitrogen, makes ohmic contact to the silicon surface. Nickel, plated on top of the palladium silicide layer, forms a solderable interface. Lead-tin solder on the nickel provides conductivity and allows a convenient means for interconnection of cells. To apply this metallization, three chemical plating baths are employed. Palladium is deposited with an immersion palladium solution and an electroless palladium solution, and nickel is deposited with an electroless nickel solution. Solder is applied with a molten solder dip. Extensive development work has been performed to achieve an effective immersion palladium solution formulation, leading to reproducible formation of the palladium silicide contact layer. This metallization system has been repeatedly demonstrated to be extremely effective. Current-voltage characteristic curve fill factors of 78% are easily achieved. This has been done while maintaining metal contact adhesion at such a strength as to fail by fracturing silicon upon perpendicular pull testing rather than be delaminating the metal system. Process specifications and procedures have been prepared. (ERA citation 04:056244)