The Effects of Titanium Silicide Formation on Dopant Redistribution

Abstract

This paper reports on boron and arsenic redistribution during the self‐aligned silicide process as applied to shallow (<0.2 μm) junctions. Dopant loss was seen to occur through evaporation from the silicide surface, segregation into the Ti‐rich outer layer which is subsequently removed, and diffusion into the silicide layer. Depending on the silicide and junction annealing temperatures, up to 99% of the implanted dopant dose can be lost via these three mechanisms. Dopant loss is particularly acute when the silicide is formed concurrently with recrystallization/annealing of the junction implant, before the dopant diffuses into the silicon. Germanium preamorphization, to eliminate channeling of the ion implanted dopants, further aggravates the loss of boron but has a slightly beneficial effect with arsenic. Oxide capping of the silicide before annealing reduces dopant evaporation and increases the dopant concentration at the silicide contact, but at the expense of increased junction depth.