Orientation control in PZT/Pt/TiN multilayers with various Si and SiO2 underlayers for high performance ferroelectric memories

Abstract

To suppress fluctuation in capacitor characteristics, highly oriented lead zirconate titanate (or PbZrxTi1−xO3 (PZT) films are required in ultralarge scale ferroelectric memories whose capacitor size is comparable to PZT grain size. The (111) orientation, which is closely related to spontaneous polarization, is achieved when PZT film is grown on highly (111) oriented platinum film. The degree of Pt(111) orientation is dependent on the crystallinity of the underlying TiN barrier metal. Furthermore, the crystallinity of the TiN is strongly dependent on the type of underlying material. The crystallinity of the TiN film grown on amorphous Si is much better than the crystallinity achieved on thermally oxidized Si. The surface energy difference between the TiN and underlayer may affect the growth mode of the TiN films. The crystallinity of the TiN film on rougher Si surfaces, such as in situ crystallized poly-Si, is inferior to the crystallinity observed on amorphous Si. Therefore, a smooth Si buffer layer is required underneath the capacitor to improve performance of the PZT/Pt/TiN capacitor. The modified planarized stacked structure presented in this article uses a postannealed crystalline Si as a buffer layer underneath the capacitor.