Effect of high temperature deposition on CoSi2 phase formation

Abstract

This paper discusses the nucleation behaviour of the CoSi to CoSi2 transformation from cobalt silicide thin films grown by deposition at elevated substrate temperatures ranging from 375 °C to 600 °C. A combination of channelling, real-time Rutherford backscattering spectrometry, real-time x-ray diffraction, and transmission electron microscopy was used to investigate the effect of the deposition temperature on the subsequent formation temperature of CoSi2, its growth behaviour, and the epitaxial quality of the CoSi2 thus formed. The temperature at which deposition took place was observed to exert a significant and systematic influence on both the formation temperature of CoSi2 and its growth mechanism. CoSi films grown at the lowest temperatures were found to increase the CoSi2 nucleation temperature above that of CoSi2 grown by conventional solid phase reaction, whereas the higher deposition temperatures reduced the nucleation temperature significantly. In addition, a systematic change in growth mechanism of the subsequent CoSi2 growth occurs as a function of deposition temperature. First, the CoSi2 growth rate from films grown at the lower reactive deposition temperatures is substantially lower than that grown at higher reactive deposition temperatures, even though the onset of growth occurs at a higher temperature, Second, for deposition temperatures below 450 °C, the growth appears columnar, indicating nucleation controlled growth. Elevated deposition temperatures, on the other hand, render the CoSi2 formation process layer-by-layer which indicates enhanced nucleation of the CoSi2 and diffusion controlled growth. Our results further indicate that this observed trend is most likely related to stress and changes in microstructure introduced during reactive deposition of the CoSi film. The deposition temperature therefore provides a handle to tune the CoSi2 growth mechanism.