Substrate and temperature effects in lead zirconate titanate films produced by facing targets sputtering
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The growth of ferroelectric lead zirconate titanate (PZT) films by rf-sputtering using a facing targets geometry is described. This study focuses on the influence of the substrate on PZT thin film composition, structure, and electrical properties. The deposition temperatures ranged from room temperature to 700 °C and the process gas was a mixture of argon and oxygen. Effects of deposition conditions and post-deposition annealing on film composition, microstructure, and properties were evaluated using Rutherford backscattering spectroscopy (RBS), x-ray diffraction, electron microscopy, and measurements of the permittivity and polarization. The microstructure, composition, and permittivity of the films were found to be strongly dependent on the substrate temperature and on the preparation history of the films.
I. INTRODUCTION rf-sputtering, 1-9
Vapor deposition methods such as magnetron sputtering,5"12 ion beam sputtering,13 and laser ablation14'15 are suitable for deposition of thin PZT films ranging in thickness from several tens of nanometers to several micrometers. For films less than 1 //m thick, the influence of the film substrate can be increasingly important in determining film properties. In this paper we describe the synthesis of PZT thin films using facing targets sputtering. We will compare films prepared at both low (unheated) and high substrate temperature. Film composition, microstructure, and electrical properties are examined as a function of thermal treatment and film thickness. The aim is to find how varying substrates and thermal history affect the formation of the desired film microstructure and properties. Particular attention is paid to films deposited on Pt electrodes so that electrical properties, microstructure, and composition can all be measured on a single substrate, which is representative of a typical memory device configuration. We will discuss our findings in terms of several thermally induced processes including substrate/film interdiffusion, crystallization, volatilization, and film roughening. II. EXPERIMENTS AND ANALYSIS Films were deposited in a diffusion-pumped rfsputtering system that was equipped with opposed top and bottom electrodes powered by separate rf-generators. The substrate platen is mounted on a radiant heater positioned in a plane normal to the plane of the two opposed targets. This configuration or similar variation has been employed for metal deposition and synthesis of perovskite-type superconducting films.16'17 We found it necessary to adopt this arrangement because of resputtering effects that were encountered using the more J. Mater. Res., Vol. 7, No. 6, Jun 1992
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common diode geometry. Films were deposited in an argon/oxygen mixture where the argon concentration was 90% and the total pressure was 1.3 Pa. Substrates included MgO, Si/SiO 2 , and the former substrates coated with 200 nm thick evaporated Pt. The film deposition rate varied from 0.5 to 2.0 nm/min and the final thickness ranged from 30 to 50
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