The atomic mixing and formation of silicides during deposition of a thin film onto a substrate are caused by diffusion processes which are dominated by thermal effects and are also influenced by the energy of the incident particles. Sputter deposition of metal thin films on a silicon substrate shows the formation of silicides at the interface of metal and silicon. This is particularly marked in the case of copper thin films deposited onto silicon. In this paper, the influence of the substrate temperature on broadening of the mixed layer at the interface is discussed and experimental results are presented. The mixing profiles and the compositions of the silicides near the interface are evaluated using Rutherford backscattering spectroscopy. The experimental results show that sputter deposition at a temperature below 550 K causes moderate interfacial mixing (the silicide thickness is about a few tens of nanometres) while at comparatively higher temperatures the intermixed layers are broadened to more than 200 nm.