Dopant redistribution during titanium silicide formation

Abstract

For advanced metal-oxide-semiconductor structures it is highly desirable to have a self-aligned silicide structure on source and drain regions as well as on the gate in order to simplify lithography while reducing parasitic resistances. The reproducible formation of metal silicides on highly doped n+ and p+ regions with shallow junctions is required for those structures. Therefore, it is essential to understand the dopant behavior, silicide phase formation, and grain growth during high-temperature annealing. Titanium silicides were formed on arsenic and boron difluoride implanted and annealed Si substrates. Arsenic atoms showed a significant redistribution and loss during titanium silicide formation. Arsenic atoms diffused out of the silicide surface with an activation energy of 0.95 eV. Boron atoms segregated to the silicide surface, and some boron atoms were lost from the surface; on the other hand, fluorine atoms were retained in the silicide layer. After prolonged 900 °C annealing, the thin titanium disilicide layers were converted into discontinuous structures.