MEDIUM ENERGY ION-SCATTERING STUDY OF NI ON ULTRATHIN FILMS OF SIO2 ON SI(111)

The structure of thin Ni films (approximately 7 angstrom) deposited at room temperature on ultrathin SiO2 layers on Si(111) has been studied using medium energy ion scattering. Our results indicate that the Ni films deposited at room temperature are not uniform. The data have been fitted with two model approximations. In one, the overlayer structures are characterized by spherical caps with a radius of 39 and height of 22 angstrom, while in the second they are characterized by a thickness distribution function with an average thickness of 14 and deviation of 7 angstrom. Above 750 K, Ni atoms start to diffuse through the SiO2 layer and subsequently into the near-surface region of the crystalline Si substrate. After annealing to 1075 K, some of the Ni has diffused into the substrate to a depth of at least 800 angstrom. In this final state, the SiO2 is completely desorbed and nickel silicides are formed.