Growth of highly textured iridium thin films and their stability at high temperature in oxygen atmosphere
Résumé
The growth and thermal stability of textured iridium thin films used as bottom
electrode in electronic devices based on ferroelectric materials were investigated.
The thin films were grown using the dc magnetron sputtering technique.
The Ir layers directly deposited on SiO2/Si substrates present a mixed (111) and
(200) orientations, while the films grown on Ti seed layers exhibit a strong
preferred (111) orientation favoured by good matching with the titanium lattice.
The substrate temperature during the growth of iridium/titanium stack has a
significant effect on the surface morphology of the iridium layer and its thermal
stability. The as-grown surface of 20-nm-thick Ir films is smooth, having a rootmean-
square (rms) roughness of 0.7 nm. After thermal annealing the Ir film
shows an increased surface roughness due to the formation of agglomerations.
The change in the surface morphology of the Ir layer is due to titanium diffusion
and its oxidation. Thicker and better crystallised iridium thin films annealed in
oxygen atmosphere at 700 C show a good thermal stability with only a slight
modification of the surface morphology. Within the limits of experimental error,
there is no change in the electrical resistivity before and after thermal annealing.
The rms roughness has not varied significantly and the XPS investigation shows
no traces of titanium oxide on iridium surface. Ir/Ti stack deposited under the
optimum conditions could be successfully used as electrode in devices based on
oxide thin films.