Dopant redistribution during the formation of iron silicides

Abstract

Iron disilicide (β-FeSi 2) is a semiconducting silicide with a direct bandgap of about 0.87 eV, thus rendering it attractive properties for opto-electronic applications. The compatibility with standard IC-technology is of great importance for future on-chip optical interconnects. This study is focused on the dopant behaviour during processing of iron silicides. The redistribution of dopants during silicide formation was studied utilising SIMS analysis. Different silicide procedures were investigated. The silicides were either formed by reacting a deposited iron film with crystalline silicon or from a bilayer structure consisting of excess silicon on top of the iron film. Cross-sectional TEM micrographs of the bilayer structures showed an epitaxial regrowth of the excess silicon at the crystalline silicon-silicide interface when the system was fully reacted. Arsenic implanted silicon was observed to yield good epitaxial regrowth while boron showed an inferior crystalline regrowth. The dopant redistribution was found to depend on the formation condition. Boron and phosphorus were depleted at the silicide-silicon interface, while arsenic was found to yield a small accumulation at the interface.