Interfacial reactions of the Co/Si_1-xGe_x system

Thermal reactions of Co(200 Å)/Si_0.76Ge_0.24(1500 Å)/Si and Co(200 Å)/Si_0.54Ge_0.46(1000 Å)/Si systems in a vacuum of 1-2 ×10^-6 Torr were studied. At temperatures above 200°C Ge segregation appeared even though no suicides and/or germanosilicides were formed. At a temperature of 225-550°C Co(Si_1-y,Ge_y) was formed, in which the Ge concentration was deficient. The formation temperatures of CoSi₂ in the Co/Si_1-xGe_x systems, where x = 0.24 and 0.46, were above 575°C, being relatively higher than that in the Co/Si system. At temperatures above 500°C the island structure, Ge segregation to the surface of the exposed Si_1-xGe_x films, and the penetration of reacted layer into the Si substrate occurred. At temperatures above 700°C a SiC layer was grown on the film surface. For the Si_0.54Ge_0.46 films the penetration of the reacted layer into the Si substrate occurred even at 350°C owing to the wave structure of the as-grown Si_0.54Ge_0.46 films. A Si layer interposed between Co and Si_0.76Ge_0.24 films is an effective scheme to grow a continuous CoSi₂ contact at 550-600°C without inducing Ge segregation and hence the strain relaxation in the Si_0.76Ge_0.24 films.