THE REACTION OF EXTREMELY THIN CO-ZR AND PD-TA LAYERS WITH SI(100)

Co-Zr films with thicknesses in the range 2.5-40 nm and with different compositions were electron-gun deposited on Si(100) substrates. In situ annealing, Auger analysis, and Rutherford backscattering spectrometry were performed to monitor the arrival of Si at the surface of the film. The temperature at which Si was observed at the film surface was found to vary quite considerably with the composition. A few experiments were performed on the Pd-Ta system as well. Both for the Co-Zr and Pd-Ta system the annealing temperature at which Si was detected at the surface was much higher for the amorphous than for the crystalline alloys. From the temperature dependence at which Si was observed at the surface as a function of thickness, an approximate activation energy for Si diffusion was derived of 1.0 +/- 0.2 eV for amorphous Pd0.4Ta0.6; the figures found for amorphous Co0.8Zr0.2 and Co0.2Zr0.8 were 2.3 +/- 0.2 eV and 2.7 +/- 0.2 eV, respectively. These values are valid for films with a thickness of 5 nm or more. For thinner amorphous films the activation energy was considerably lower, indicating that inhomogenities, e.g., in the thickness, start to play a role. For polycrystalline Pd0.7Ta0.3, pure Co, and pure Zr no values were derived because there was considerable scatter in the data points. Resistivity measurements on Co and C0.8Zr0.2 layers on SiO2 indicated that the early growth of amorphous films is more homogeneous than that of the crystalline Co film.