Lead zirconate titanate (PZT) is a ferroelectric material which has perovskite structure. The PZT film is one of the promising material applicable to capacitors in memory devices, such as dynamic random access memory (DRAM) and ferroelectric non-volatile memory (FRAM), because of its high dielectric constant, high breakdown strength, and hysteresis properties. For the application of PZT film to memory devices, it is necessary to fabricate the PZT film which has superior electrical properties. The electrical properties of PZT film are affected by the bulk of PZT film and the interfaces between PZT film and electrodes. The effects of the bulk of PZT film and the interface between PZT film and bottom electrode on electrical properties of PZT film have been intensively studied, while the influence of the top electrode deposition process have not been. In this study, the effects of deposition conditions of top electrodes on the electrical properties of PZT thin films were investigated.
Perovskite PZT films were fabricated on $Pt/Ti/SiO_2/Si$ substrates by DC magnetron multi-target reactive sputtering method. Pt and $RuO_2$ top electrodes were deposited on PZT film in many deposition conditions. Then, the changes of electrical properties with the deposition condition of top electrodes, such as deposition temperature, rf power, and pressure, were investigated.
When the Pt top electrodes were deposited at substrate temperatures of 200℃ or above, the ferroelectric properties of the PZT thin film under the Pt electrode were severely degraded. Whereas those of the PZT film where the Pt electrodes were not deposited were not degraded. Water vapors which remained in the vacuum chamber were dissociated into hydrogen atoms by the catalysis of Pt top electrode, and those hydrogen atoms diffused into the PZT film and produced oxygen vacancies at high substrate temperature, resulting in the degradation of the ferroelectric properties of the PZT film under the Pt electrode. Since the water vapors could not be dissociated into hydrogen atoms without the catalysis of Pt, the degradation of the PZT film did not take place where the Pt electrode were not deposited. The degraded feroelectric properties could be recovered by RTA(rapid thermal annealing) treatment. On the other hand, leakgage current characteristics were improved with increasing the deposition temperature of Pt top electrodes. When $RuO_2$ top electrodes were used as top electrodes, the degradation of ferroelectric properties was not observed at high temperatures, which may be due to the difference of chemical reactivity of Pt from $RuO_2$.
The electrical properties of PZT films were not affected by the variation of deposition rf power and pressure of top electrodes.
