Effect Of Added Si On The Resistivity Of Co And Ni Films

Chemical and electrical changes in Co/Si and Ni/Si bilayered films on Si02 substrates are investigated. The Si thicknesses chosen correspond to 0 to 11 atomic percent of the total film. After the films were vacuum annealed at 400, 500, 600, 700, 800, and 900°C for 1 hour, they were examined by means of 4He+ backscattering spectrometry, x-ray Read camera and diffractometer, scanning electron and optical microscopy, and four point probe resistivity measurements. At low annealing temperatures, we observe the Ni5Si2, Ni3Si and Co2Si phases. At 800 and 900°C, Si dissolves in the film. The film resistivity increses rapidly as the amount of dissolved Si in the film rises. For example, 2 at.% and 3.6 at.% suffice to double the film resistivity of Co and Ni, respectively. The lattice parameter perpendicular to the plane of the film for films annealed at 900°C was determined at room temperature and found to decrease with increasing Si content. The surface of a pure metal film becomes nonuniform upon 900°C annealing; adding as little as 2.5 at.% Si stabilizes the film morphology.