Lead zirconate titanate (PZT) is a ferroelectric material which has perovoskite structure. PZT has been studied for application to capacitors in memory devices, such as dyanmic random access memory (DRAM) and non - volatile ferroelectric random access memory (FRAM), because of its high dielectric constant, high electrical breakdown strength and hysteresis properties. However, problems still remain concerned with integration process, such as the damage that may occur during the etching process of the ferroelectric capacitor and electrode materials, interdiffusion through the electrode on which the ferroelectric capacitor are integrated and the stability of ferroelectric materials in the silicon process. One of the severe problems of Pt/PZT/Pt capacitor is the disappearance of polarization hysteresis characteristics during annealing in hydrogen contained ambient. It has been well known that the annealing in hydrogen contained ambient such as post-metal annealing, ILD(interlevel dielectric) deposition, passivation film deposition and forming gas annealing may cause severe degradation of ferroelectric thin film. The hydrogen concentration in the annealing affects the ferroelectric capacitor characteristics. The PZT film itself is not damaged by annealing in a hydrogen contained ambient even at 400℃, whereas the Pt/PZT/Pt ferroelectric capacitor loses its polarization hysteresis characteristics at 300℃. The top Pt electrode was found to induce degradation of electrical properties(C-V, P-E).
However, the mechanism of damage by hydrogen annealing has not been studied sufficiently. In this study, the C-V and P-E of the Pt/PZT/Pt were measured before and after hydrogen annealing. The hydrogen paths into the PZT film was investigated.
Perovskite PZT film was fabricated on the Pt/Ti/$SiO_2$/Si substrate by DC magnetron multi-target reactive sputtering method. Pt top electrode was deposited on PZT film by RF magnetron single-target sputtering method. The Pt/PZT/Pt was annealed in 200℃-400℃ for 20min in 5%$H_2$/$N_2$ ambient. Then, the change of electrical properties(C-V, P-E) before and after hydrogen annealing were investigated. The hydrogen pathway into the PZT film was investigated by the SIMS. The electrical properties(C-V, P-E) were degraded after hydrogen annealing.
The higher the annealing temperature was, the more the electrical properties were degraded. The Pt top electrode was peeled off after 400℃ hydrogen annealing. The RTA(rapid thermal annealing) for Pt/PZT/Pt capacitor structure before hydrogen annealing reduced the degradation. The higher the pre-RTA temperature was, the more the degradation of Pt/PZT/Pt reduced. The SIMS depth profiles showed that the hydrogen concentration in the PZT increased when the electrical properties were degraded. The SIMS image mapping stated that the hydrogen penetrated into the PZT through the special part of the Pt surface. The RTA process after hydrogen annealing recovered the electrical properties of Pt/PZT/Pt. However, for the recovering of electrical property this RTA should be conducted in oxygen ambient. In conclusion, the degradation of the Pt/PZT/Pt after hydrogen annealing was found to be related with the hydrogen penetration through the special part of the Pt surface and the oxygen.
