Approach to interface roughness of silicide thin films by micro-Raman imaging

Abstract

The rough interface between a silicide film and a Si substrate induces large junction leakage currents in Si-based devices. In this work, we demonstrate that micro-Raman imaging can be used to characterize the interface roughness, without any special sample preparation. Pure metal (Ni and Ti) thin films and the subsequently formed silicide thin films after annealing (NiSi and TiSi2) were investigated using the intensity of the Si Raman band at 520cm−1. Uniformity results of the pure metal films are in good agreement with those obtained using global four-point-probe measurement. In comparison, the signals obtained from the interfaces between Si and NiSi are nonuniform with large variations. The intensity of the major peak of NiSi at 214cm−1 shows a point-to-point correlation with the intensity of the Si peak at 520cm−1, which reveals that the local grain orientation affects the diffusion velocity of Ni atoms and the growth of NiSi. Images of Ti-silicides show that the interface of the C49 TiSi2 phase is much smoother than that of the C54 TiSi2 phase which is due to different formation mechanisms. Simulation was carried out based on two interfacial models, a two-step interface and a sinusoidal interface, to understand the correlation between the average attenuation of the Si Raman signal and the film thickness.