Thermal stability of highly textured iridium thin films grown on silicon substrates
Résumé
Integration of ferroelectric materials on platinum-coated silicon is problematic due to the difficulty in controlling
phenomena occurring at the interfaces. Therefore, the type of bottom electrode on which the ferroelectric material is
deposited is very important in determining the final properties of the ferroelectric thin film. The growth of iridium thin
films on titanium buffered silicon substrates by DC magnetron sputtering and their stability at high temperature in an
oxidizing environment were investigated. Highly textured (111)Ir thin films of various thicknesses (30 nm∼100 nm)
were grown on titanium buffered Si wafers at 400 oC and 700 oC substrate temperature. These thin films showed a
different behaviour during heat treatment at 700 oC in oxygen atmosphere. The AFM image of the 30nm thick Ir film,
after the thermal treatment, revealed significant changes in the surface morphology. While the initial Ir film surface is
smooth and without surface features having a root-mean-square (rms) roughness of 0.7 nm, after thermal annealing, the
Ir film shows an increased surface roughness by formation of agglomerations up to 30 nm in height. According to the
XPS results, it can be concluded that these changes are due to the diffusion and oxidation of titanium. The 100 nm thick
iridium layer, annealed in the same conditions shows, a good thermal stability with only a slight modification of the
surface morphology. The measured electrical resistivity, before and after thermal annealing, was 11.8 cm and 12.3
cm, respectively. The XPS-survey spectrum showed no sign of titanium on the Ir thin film surface. The obtained
results allowed us to affirm that the Ir(100 nm)/Ti(9 nm)/SiO2/Si structure is electrically and morphologically stable and
can be successfully used as bottom electrode in ferroelectric thin films devices.