Silicide formation and interdiffusion effects in Si-Ta,SiO2-Ta AND Si-PtSi-Ta thin film structures

The formation of TaSi₂ in the Si-PtSi-Ta and Si-Ta systems has been studied using Auger spectroscopy, x-ray diffraction and electron diffraction techniques. The reaction of tantalum with PtSi was observed by Sinha, et al.^l to take place with high temperature (800°-900°c) annealing of thin film systems consisting of Si-PtSi-Ta-W¹. In the present investigation, it is shown that tantalum reacts with PtSi at approximately 600°C to form a mixture of Ta₅Si₃ and TaSi₂ and predominantly TaSi₂ at 785°C. Platinum is displaced at the refractory metal (Ta)-PtSi interface, whereupon the more stable refractory metal-silicide is formed. The displaced platinum reacts further with the excess silicon which diffuses from the Si-PtSi interface. The Si-PtSi-Ta reaction is similar to the Si-PtSi-W reaction. However, unlike tungsten which migrates very little in the Si-PtSi-W system, tantalum appears to interdiffuse with the PtSi at temperatures as low as 600°C. In the case of the Si-Ta couple, TaSi₂ forms at approximately 750°C as determined by transmission electron microscopy (TEM) measurements. The kinetics of TaSi₂ formation at the Si-Ta interface are compared to that which takes place at the PtSi-Ta interface to determine the influence of the PtSi layer. Silicide formation was not observed in SiO₂-Ta specimens. after anneals up to 800°c. At 750°C Ta₂O₅ formed as observed by electron diffraction.