Engineering Electrical Interfaces to Silicon via Indium Solder

This paper provides engineering models of a simple and robust approach for creating electrical connections to silicon using reduced temperature (<;200 °C substrate) soldering. This removes a significant hurdle to the fabrication of high performance, custom silicon piezoresistors. The approach focuses on reducing the resistance of diodes that are undergoing reverse bias behavior, commonly considered to be unacceptable for electrical connections. Reverse bias Schottky barrier analytical models based on quantum mechanical first principles are developed to explain how the behavior is affected by doping, soldering temperature, and geometry. This understanding is encapsulated within parametric models that enable rapid design and optimization of the electrical contacts to silicon. Using this model, one may design contacts for practical applications that do not require the conventional microfabrication processing or the high-temperature processing. Indium solder is found to be the best solder for this process, with ohmic contact resistances of ≈1 Ω-cm² for (110) p-type wafers at 10¹⁷ cm^-3 doping.