Point defect distributions and their electrical effects on perovskite titanate thin films

Perovskite-structure metal titanate thin films, such as (Ba,Sr)TiO 3 (BST) and Pb(Zr,Ti)O3 (PZT), have attracted considerable interest for possible applications in semiconductor memories. However, their electrical performance is sensitive to the presence of point defects, such as hydrogen interstitials and oxygen vacancies. The purpose of this research is to investigate the relationship between the point defect spatial distributions and their electrical effects on perovskite titanate thin films. In particular, the nature of hydrogen/deuterium interstitials in BST thin films and the oxygen vacancy motion in PZT thin films have been studied.; Hydrogen annealing is routinely used in semiconductor fabrication; however, such annealing causes serious electrical degradations in perovskite titantate films. In this research, deuterium was used to avoid the interference of hydrogen, resulting from the metal organic chemical vapor deposited (MOCVD) film-growth process. Deuterium annealing effects on the electrical properties of BST/Pt interfaces were investigated using electrical measurements and x-ray photoelectron spectroscopy (XPS). Combined with secondary ion mass spectroscopy (SIMS) depth profiling, these results suggest that the majority of incorporated deuterium is electrically inactive. Therefore, there are most likely other contributors, in addition to charged deuterium defects, to the deuterium annealing degradation; possibilities, including the creation of oxygen vacancies and annealing-induced changes in the BST/Pt interface state density are assessed. Furthermore, the incorporation of deuterium defects in BST films was also studied through simulations of the equilibrium point defect distributions; the electrostatic potential and point defect distributions in D2/N2 annealed BST thin films have been derived from static deuterium profiles analyzed by SIMS.; In addition to hydrogen interstitials, mobile oxygen vacancies have been viewed as a major reason for several degradations in ferroelectric titanate thin films, such as retention and endurance failures. However, no quantitative measurements of the mobility and activation enthalpy for oxygen vacancy motion in PZT thin films have been reported. As a first step toward such a quantitative understanding, a systematic analysis of 18O tracer in-diffusion experiments into 100 nm MOCVD PZT films was conducted to monitor oxygen vacancy distributions and to obtain the kinetic parameters associated with vacancy motion.