Examination of barrier layers for lead zirconate titanate thin films

Abstract

The selection of a suitable electrode and barrier layer are important in the integration of Lead Zirconate Titanate (PZT) into memory circuits. Five materials were evaluated using physical analysis techniques as possible barrier layers. Glancing-angle x-ray diffraction was used as the initial assessment to determine the structure of the PZT. With either silicon or MoSi₂ as a base layer, it was not possible to obtain a perovskite PZT structure under the conditions investigated. Although the desired crystal structure could be obtained with TiN as a base material, the oxygen-rich sputtering conditions for PZT had transformed this layer to an oxide making it unsuitable as electrode. PZT grown on an indium tin oxide (ITO) coated glass substrate also had a perovskite structure and good electrical properties. Scanning electron microscopy showed good adhesion between the layers, but transmission electron microscopy and secondary ion mass spectroscopy revealed Pb-rich areas residing in the glass beneath the ITO. PZT on platinum appeared to be the only promising barrier layer studied as there was no indication of Pb diffusion into the underlying layers and the desired crystal structure was obtained.