Analysis of the stress and interfacial reactions in Pt/Ti/SiO2/Si for use with ferroelectric thin films

The microstructure of the Pt/Ti/SiO2/Si structure has been investigated by scanning and transmission electron microscopy. Pt films of 100 nm thickness deposited by sputtering or evaporation onto unheated substrates gave complete coverage of the underlying Ti layer and showed a granular and faceted structure with grains similar to 20 nm in diameter. They did not exhibit hillocks or surface TiOx formation. X-ray diffraction was used to examine the film stress through use of the sin(2) psi method with bulk values for the elastic constants (v = 0.39, E = 162 GPa). The as-deposited sputtered film had a compressive stress of similar to 540 MPa, while the evaporated films had tensile stresses of similar to 630 MPa. The films then received a 400 degrees C rapid thermal anneal (RTA) for 90 s and a subsequent RTA of 650 degrees C for 30 s. Further investigation of the film stresses and microstructure were made after each annealing step. After the low temperature anneal, the film stress for the sputtered film became tensile. Plan-view sections examined by transmission electron microscopy (TEM) showed that the as-deposited sputtered films were dense but became porous after annealing. Initially, the evaporated films had a less dense microstructure, but were more stable with annealing. Little change in the stress for the evaporated film was observed after this initial low temperature annealing step. Additional annealing of the evaporated and sputtered samples caused complete consumption of the Ti layer including some TiOx formation from the underlying SiO2 layer and marked interaction with the Pt; however, Little change in the stress was found. The surface of the Pt film revealed larger grains, but otherwise remained unaffected. The underlying phase changes were minimized once the Ti layer had reacted with the Pt. Due to the ratio of the layers, Pt:Ti of 2:1, the surface of the Pt was unaffected.