Growth kinetics of three Mo-silicide layers formed by chemical vapor deposition of Si on Mo substrate

The growth kinetics of three Mo-silicide layers formed by chemical vapor deposition (CVD) of Si on a Mo substrate using SiCl4-H2 gas mixtures were investigated at temperatures between 950 and 1200 °C. Three Mo-silicide layers (Mo3Si, Mo5Si3, and MoSi2) grew simultaneously with a parabolic rate law after an initial nucleation period, indicating the diffusion-controlled growth. The activation energy (130 kJ/mol) for the MoSi2 layer were in a good agreement with the previous results having low activation energy (130±20∼157 kJ/mol), but its growth rate was higher than the previous results with high activation energy (209∼241±25 kJ/mol). A possible explanation about this difference may be the detrimental effect of impurities such as oxygen on the growth rate of the MoSi2 layer. The activation energy (350 kJ/mol) for growth of the Mo5Si3 layer was consistent with the prior values (297∼360 kJ/mol) obtained by annealing of the MoSi2/Mo diffusion couples, but its growth rate was an order of magnitude lower than the rate measured in the MoSi2/Mo diffusion couples. The activation energy (223 kJ/mol) for the growth of the Mo3Si layer was similar with the value (199 kJ/mol) obtained from annealed Mo5Si3/Mo diffusion couple at temperatures between 1250 and 1350 °C. This value was lower than the value (326 kJ/mol) reported at higher temperatures from 1500–1715 °C. This suggests that the rate-limiting step for growth of the Mo3Si layer is the grain boundary diffusion-controlled process at low temperatures but volume diffusion-controlled process at high temperatures. The growth rates of the Mo3Si layer measured at condition of the simultaneous parabolic growth of three Mo-silicide layers were approximately two orders of magnitude lower than the rates measured in the Mo5Si3/Mo diffusion couples. The differences in the growth rates of the Mo5Si3 and Mo3Si layers depending on the type of diffusion couples were well explained by the multiple layer growth model.