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-H-2 gas mixtures were investigated at temperatures between 950 and 1200 degreesC. 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 similar to 157 U/mol), but its growth rate was higher than the previous results with high activation energy (209 similar to 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 MoSi2 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 U/mol) obtained from annealed Mo5Si3/Mo diffusion couple at temperatures between 1250 and 1350 degreesC. This value was lower than the value (326 kJ/mol) reported at higher temperatures from 1500-1715 degreesC. 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 MoSi2 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. (C) 2002 Elsevier Science B.V. All rights reserved.