Reactive ion etching damage to the electrical properties of ferroelectric thin films
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Reactive ion etching damage to the electrical properties of ferroelectric thin films W. Pan, C. L. Thio, and S. B. Desua) Materials Science and Engineering Department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0237 (Received 13 May 1996; accepted 13 April 1997)
Reactive ion etching damage to Pt/Pb(Zr,Ti)O3 /Pt ferroelectric capacitors was evaluated under Ar bombardment and CHClFCF3 etch plasmas. The hysteresis and degradation properties, including fatigue and leakage current, were examined systematically to study the mechanism of damage. The damage was measured quantitatively by comparing the relative voltage shift with respect to the initial hysteresis loops. The damage effects were found to be dependent on etching time and mainly due to the physical effect of ion bombardment. The electrical properties of the etched Pt/Pb(Zr,Ti)O3 /Pt capacitors were substantially recovered by annealing at 400 ±C for 30 min.
I. INTRODUCTION
Dry etch rather than wet etch techniques have become one of the important lithographic processes in silicon integrated circuit devices since the very large scale integrated (VLSI) era began in the late 1970s.1 Furthermore, a great deal of attention has been paid to reactive ion etching (RIE) over other dry techniques because it provides a higher degree of anisotropical pattern definition, good selectivity, and excellent process control. However, the detrimental impact of RIE on the electrical properties of devices has been an area of considerable concern and is thought to be due to RIE related surface contamination and displacement damage.2 The physical damage due to the displacement of atoms is believed to be caused by the bombardment of energetic charged particles in the glow discharges. Displacement damage will alter the near-surface region of the material that is exposed to the plasma and change its electrical properties. Nevertheless, this bombardment during RIE substantially enhances the etch rate.1,3 The chemical residue during RIE is often taken advantage of in increasing the selectivity and/or anisotropy of an etching process. These residues usually remain on the exposed materials after completion of the dry etching process and interfere with device processing following RIE.4,5 As the device feature size decreases, the physical damage and chemical residue effects become much more severe. For example, surface residues and lattice damage have been shown to change the Schottky barrier height and reduce the forward leakage current of Schottky barriers formed on dry etched silicon.6 Surface residues and dopant deactivation caused by contact hole etching through SiO2 to the Si substrate have resulted in a a)
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J. Mater. Res., Vol. 13, No. 2, Feb 1998
high contact resistance of ohmic contacts fabricated on the exposed Si surface.7 Surface roughness and mobile ion contamination reduced the quality of silicon dioxide layers that were either present d
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