Effect of impurities on growth of Ti silicides in bulk Ti/Si diffusion couple

Abstract

Reaction diffusion and the Kirkendall effect in Ti-Si binary system have been studied by using sandwich-type bulk diffusion couples consisting of 99.99% Ti, 99.9999% Ti plates and a 〈111〉 oriented Si wafer. The results have been compared with our previous one obtained by using 99.99% Ti/Si and 99.5% Ti/Si couples. The faster growth of TiSi2 formed in these Ti/Si diffusion couples, the higher the purity of titanium. To identify the element which slows down the growth rate of TiSi2, the effects of oxygen, nitrogen, carbon and iron were studied by adding oxygen and nitrogen into 99.9999% Ti or by depositing carbon and iron on the Ti surface. It has been clarified that iron atoms slow down the growth of TiSi2. Silicon atoms diffuse 50 to 100 times faster than titanium atoms in TiSi2. Iron affects the diffusivity of Si more effectively than that of Ti. On the basis of these results the role of iron in the Ti/Si bulk reaction diffusion couple has been discussed by taking into account a possibility of diffusion barrier effect or grain boundary diffusion.