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MATERIALS RESEARCH

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Metallization schemes for dielectric thin film capacitors H. N. Al-Shareef, D. Dimos, B. A. Tuttle, and M. V. Raymond Sandia National Laboratories, Albuquerque, New Mexico 87185 (Received 9 May 1996; accepted 11 October 1996)

A detailed analysis of Pt/Ti, Pt/TiO2 , and Pt/ZrO2 electrodes was carried out to develop a bottom electrode stack for sol-gel derived thin film capacitors. For the Pt/Ti stack, the choice of layer thickness and deposition temperature is found to affect adhesion to the SiO2 /Si substrate as well as the extent of hillock formation and Pt–Ti interaction. By using elevated temperature deposition, Pt films close to 1 mm in thickness can be produced with relatively good adhesion and morphological stability using Ti adhesion layers. In addition, Pt films grown on ZrO2 and TiO2 adhesion layers exhibit little morphological change and no degradation in sheet resistance after annealing at 650 ±C. However, neither ZrO2 nor TiO2 are as effective as Ti metal in promoting Pt adhesion. Experiments aimed at establishing a correlation between hillock formation and capacitor yield revealed two important results. First, the behavior of Pt/Ti stacks during annealing in air is markedly different from their behavior during PZT film crystallization. Second, preannealing of the Pt/Ti in air prior to PZT film growth actually improves capacitor yield, even though hillock formation occurs during the preannealing treatment. Implications of these results regarding the role of hillocks in controlling capacitor yield are discussed.

I. INTRODUCTION

Pt metal is the most promising electrode material in the processing of thin film capacitors based on high permittivity materials such as Ba1–x Srx TiO3 and (Pb, La)(Zr, Ti)O3 . This is due to a combination of the low resistivity and excellent stability of Pt against oxidation and reaction with the dielectric material during elevated temperature processing. However, there are some drawbacks associated with using Pt. These include hillock formation due to stress relief and poor adhesion of Pt to SiO2ySi, the most commonly used substrate material.1–5 Therefore, a Ti layer has typically been used to promote adhesion between Pt and SiO2 . The effectiveness of Ti as an adhesion promoter stems from its ability to reduce SiO2 .6 Unfortunately, the Ti adhesion layer has been found to diffuse into Pt during high temperature processing (600–700 ±C) of the dielectric thin film, leading to formation of Pt–Ti alloys and/or TiOx . This process, as will be shown in this paper, degrades the sheet resistance and enhances hillock formation in the PtyTi stack. Our work has focused on developing an electrode material for applications such as thin film decoupling capacitors. For this application, the electrode material issues involved are somewhat different from applications such as ferroelectric random access memories (FRAM’s) and dynamic random access memories (DRAM’s). For example, the electrode sheet resistance (Rs ) must be minimized in order to redu