Transmission electron microscopy study of PtSi/Si (p-type) composites grown on Si(111) substrates

A transmission electron microscopy (TEM) study was made of PtSi/Si (p-type) composite films grown on Si(111) substrates. The films, 3-μm thick, were prepared by sputtering from a Pt–Si target consisting of 81 at.% Si and 19 at.% Pt. They were subsequently annealed in argon at 575°C for 7.5 h. TEM indicated a dense aggregation of PtSi particles 50 nm and smaller in size, concentrated in a surface region about 500 nm thick. Resistivity measurements on this segregated layer showed that it was p-type with a resistivity of 3×10−3 Ω cm. Below this the structure is constant right down to the Si(111) substrate and consists of PtSi particles 10 nm in size clustered around the Si matrix. The Si is partly crystalline (10 nm particles) and partly amorphous. The resistivity of this layer is on the order of 100 Ω cm. These results are attributed to the movement of the PtSi particles in the bulk composite film toward the surface where they exist in a lower energy configuration. A microprobe analysis of these films showed 78 at.% Si and 22 at.% Pt.