Reactions of thin molybdenum films on silicon induced by argon and xenon irradiation

Abstract

Irradiation of molybdenum films on silicon by 80 keV argon and xenon ions has been used to investigate the mechanisms involved in altering the interface and in the formation of molybdenum disilicide. The films were bombarded at room temperatures by Ar 2+ and Xe 2+ ions up to doses in the range 2 × 10 15 – 2 × 10 16 ions cm −2, and at temperatures ranging from room temperature to 350°C by 2 × 10 16 ions cm −2 Ar 2+ ions. Backscattering of 2 MeV helium was used to determine the degree of Mo-Si mixing and the composition of the resulting films. Interfacial mixing was shown to occur with Ar 2+ and Xe 2+ bombardment at all temperatures and exhibited a linear dependence on the dose. Below 150°C, the mixing showed no detectable dependence on temperature but, at irradiation temperatures above 150°C, there was a strong dependence of mixing on temperature. At temperatures above 250°C and for Ar 2+ doses in excess of 2 × 10 16 ions cm −2 a region, appearing to have the stoichiometric composition of MoSi 2, was formed at the interface and its formation was found to have a linear dependence on the dose. The thermally activated contribution of the mixing, derived from the temperature dependence of mixing, gives rise to an activation energy of 0.9 eV and the reaction kinetics appear to be very similar to those for the Nb/Si system. At the lowest irradiation temperatures the efficiency of mixing was found to be an order of magnitude higher than the theoretical collisional mixing predictions. This difference is attributed to the relaxation processes occurring immediately after the cascade. Subsequent annealing of films bombarded at room temperature did not lead to any detectable interfacial change.