Shallow Si N + P junction diodes realized via molecular monolayer doping

Abstract

A conformal and controlled semiconductor doping is needed for applications in next generation nanoscale devices, low contact resistivity metal semiconductor junctions such as selective emitters in solar cells. Molecular monolayer doping (MLD) in silicon is a novel technique based on the formation of self-assembled monolayer of dopant – containing molecules on surface of crystalline silicon, followed by rapid thermal anneal. The technique is capable of forming ultra-shallow junctions with high atomic accuracy and minimum defects in silicon. A container and process was developed which successfully doped 6in. diameter silicon wafers using MLD for the in-house CMOS fabrication facility. The phosphorus monolayer is grafted on hydrogen terminated p-type silicon followed by rapid thermal anneal. Average sheet resistance ~670Ω/sq. and junction depth ~25nm are achieved. N+P junctions are fabricated using MLD and current-voltage characteristics are measured and analyzed using unified diode model.