Structural properties of thin films of high dielectric constant materials on silicon

We have used Medium Energy Ion Scattering (MEIS) and other techniques to investigate the structure and formation mechanisms of ultrathin (less than 10 nm) layers of Ta2O5 on Si. We find that a compositionally graded oxide with 2 nm effective thickness can be formed. The him degenerates at high annealing temperatures both by roughening at the outer surface. and reacting at the interface, hut a buffer layer of Si3N4 can prevent the latter effect to a certain extent. Introducing a TiN/Ti layer between Ta2O5 and Si (which may be desirable for DRAM applications) has an adverse effect on the thermal stability of the Ta2O5 overlayer due to migration and subsequent reaction of oxygen with titanium.