Ge effects on silicidation
Nickel and cobalt silicides have formation and/or stability issues when forming in the presence of Ge. Additions of Ge increase the temperature at which a low resistance CoSi2 is formed due to phase separation into CoSi2 and Ge-rich SiGe grains. With Ni, additions of Ge decrease the temperature at which NiSi converts to a NiSi2, lead to agglomeration at a lower temperature and lead to germanosilicide formation. Nickel has a must not exceed critical temperature that decreases with increasing Ge concentration, and Co has a minimum critical temperature that increases with increasing germanium concentration. Neither silicide is ideal for doped SiGe contacts, where the germanium compositions are in excess of 20%. The insertion of a layer of pure Si above the SiGe is a promising integration option for forming a robust silicide on SiGe substrates. The phase formation and stability of pure Co on Si-20%Ge substrates with Si caps of thickness from 200 to 1000 were studied and it was shown that a 400 Si cap on Si-20%Ge leads to low resistance CoSi2.
silicide cobalt silicide agglomeration si-ge nickel silicide