Effects of Ti-capping on formation and stability of Co silicide I. Solid phase reaction of Ti to Co/Si system

We have investigated the formation and thermal stability of Co silicide on Si using a Ti-cap. We propose that Ti retards the reaction between Co and the Si substrate and also prevents oxygen contamination. The Ti-capped CoSi2 has a higher transformation temperature and thinner film thickness than TiN-capped CoSi2. A 15 nm thick Ti-cap provides a CoSi2 layer with a more uniform interface and higher thermal stability compared to CoSi2, layers with a TiN-cap. The increased uniformity of the silicide/Si interface results from the retarded Go-Si reaction, due to the formation of a CoTi binary phase. The high thermal stability can be explained by a Ti-stuffing model. From analysis of the depth profile, it is likely that surface Ti diffuses rapidly into the CoSi2 grain boundaries and slows the agglomeration process, thereby increasing the thermal stability. As a result, Ti-capped Co silicide formed on a 0.15 mu m wide polycrystalline Si gate shows a thermal budget limit as high as 900 degrees C for 30 min. Based on the results of capacitance-voltage and time-dependent dielectric breakdown measurements, we can conclude that Ti-capped Co silicide is a candidate as a gate electrode for high thermal budget devices such as logic with embedded dynamic random access memory. (C) 2000 The Electrochemical Society. S0013-4651(99)03-089-X. All rights reserved.