Thermal and ion-induced reaction of Ni–Au dilute alloys on Si

Abstract

Redistribution of Au in Ni silicide formation by thermal annealing or ion beam mixing of Ni films with 1.4 at. % Au deposited on 〈100〉 Si was investigated using Rutherford backscattering spectrometry and glancing-angle x-ray diffraction. Annealing at temperatures of 300–350 °C results in the formation of Ni2Si with accumulation of Au at the Ni2Si/Ni interface. A similar redistribution of Au has also been found when the samples are irradiated with Xe ions at doses ≥2×1015 ions/cm2. This accumulation is contrary to the dispersion that one would anticipate in ballistic collisions and we believe that the Au accumulation is a result of thermodynamic forces in ion-induced reactions. In thermal annealing, the accumulation of Au impedes the supply of Ni and the second phase NiSi begins to form before the Ni film is consumed. With ion beam mixing, however, the accumulation of Au does not block silicide formation and Ni2Si continues to grow. We attribute the continued growth of Ni2Si to Au–Ni demixing within the collision cascade.