Lead Zirconate titanate (PZT) is a ferroelectric material which has perovskite structure. The PZT film is one of the promising materials 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.
In this study, perovskite PZT films were fabricated on platinized Si substrates by ECR plasma enhanced DC magnetron multi-target reactive sputtering method. The multi-target sputtering method leads to better control of the process in the case of multi-component films. The effect of activation of oxygen by ECR plasma on the composition and structure of the film was examined. The effect of each element on the formation of nucleation sites for the perovskite phase was also investigated. On the basis of these results, the early stage process condition which leads to the formation of the perovskite phase films with good crystallinity and electrical properties is suggested.
The effect of deposition condition of the Pt electrode on the properties of the PZT capacitors within the MFM structure was studied. Microstructual changes of the Pt electrode deposited at various conditions were investigated. The crystalline structure and electrical properties of the PZT films deposited on Pt/Ti/SiO2/Si substrate were also examined as a function of deposition condition of the Pt film.
Activation of oxygen by ECR plasma enhanced the incorporation of Pb into the PZT film so that stable stoichiometric composition was obtained at very high Zr/Ti concentration ratios and high deposition temperatures above 500℃. This is because the oxygen molecules activated by ECR plasma are so reactive that not only titania but also zirconia reacts readily with the lead oxide molecules, leading to the enhanced Pb incorporation into the PZT film.
Stable incorporation of Pb at the early stage of film formation is very important to the formation of nucleation sites for the perovskite-phase PZT films, because Pb incorporation into A site of the perovskite structure helps the incorporation of Zr and Ti atoms into B sites, resulting in a stable stoichiometric PZT film. Pb incorporation at the early stage was enhanced more effectively by lowering the Zr/Ti flux ratio than by simply supplying Pb excessively.
The structure and electrical properties of PZT films deposited on Pt/Ti/SiO2/Si electrode were sensitively changed by the deposition condition of the Pt film. As the deposition temperature of the Pt film increased or the deposition rate decreased, the Pt film became dense and the out-diffusion of Ti and the deformation of the Pt film were suppressed. During the high temperature process, Ti diffused out through the grain boundaries of the Pt overlayer. The out-diffused Ti helped the formation of nucleation sites for the perovskite PZT films. However, excessive Ti out-diffusion not only decreased the total capacitance of the PZT capacitor by forming an interfacial layer of low dielectric constant, but also degraded the leakage current characteristics of the PZT film by deforming the Pt electrode.
