Nucleation and diffusion during growth of ternary Co_1-xNi_xSi₂ thin films studied by complementary techniques in real time

The growth kinetics of ternary Co_1-xNi_xSi₂ thin films was studied in real time. The “Kissinger” method was applied to the results of ramped sheet resistance measurements to extract the apparent activation energy for the growth process. By simultaneously acquiring sheet resistance, x-ray diffraction and laser light scattering data on one hand and combining resistance measurements and Rutherford backscattering spectrometry on the other hand, we could distinguish between the initial, nucleation controlled thin film growth, and the subsequent diffusion controlled growth. The apparent activation energy for the initial growth decreases with increasing Ni concentration as a result of a lower nucleation barrier for the ternary disilicide. The markedly different microstructure of the ternary Co_1-xNi_xSi₂ films with respect to pure CoSi₂ layers lies at the origin of a lower activation energy for the diffusion controlled growth of the ternary films. Despite the low activation energy, these films grow at a much slower rate than CoSi₂ films due to the large grain size and consequently lower density of grain boundary diffusion paths. These results explain the unexpected high thermal budget required for the formation of low resistivity Co_1-xNi_xSi₂ thin films.