Etch characteristics of CeO2 thin films as a buffer layer for the application of ferroelectric random access memory

Abstract

Cerium oxide (CeO2) thin film has been proposed as a buffer layer between the ferroelectric film and the Si substrate in metal–ferroelectric–insulator–silicon structures for ferroelectric random access memory applications. In this study, CeO2 thin films were etched with a Cl2/Ar gas combination in an inductively coupled plasma. The etch properties were measured for different gas mixing ratios of Cl2/(Cl2+Ar) while the other process conditions were fixed at rf power (600 W), dc bias voltage (−200 V), and chamber pressure (15 mTorr). The highest etch rate of the CeO2 thin film was 230 Å/min and the selectivity of CeO2 to YMnO3 was 1.83 at a Cl2/(Cl2+Ar) gas mixing ratio of 0.2. The surface reaction of the etched CeO2 thin films was investigated using x-ray photoelectron spectroscopy (XPS) analysis. There is a Ce–Cl bonding by chemical reaction between Ce and Cl. The results of secondary ion mass spectrometer analysis were compared with the results of XPS analysis and the Ce–Cl bonding was discovered at 176.15 (amu). These results confirm that the Ce atoms of the CeO2 thin films react with chlorine and a compound such as CeCl remains on the surface of the etched CeO2 thin films. These products can be removed by Ar-ion bombardment.