MOCVD of Ferroelectric Thin Films
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MOCVD of Ferroelectric Thin Films C. E. Rice, S. Sun, J. D. Cuchiaro, L. G. Provost, and G. S. Tompa; Structured Materials Industries, Inc., 201 Circle Drive North, Unit 102/103, Piscataway, NJ 08854 ABSTRACT We have examined the growth of a number of important ferroelectric oxides by MOCVD using a rotating disk reactor. Highly uniform and reproducible films over 6” wafers have been routinely achieved. Materials include Lead Zirconate Titanate (PZT, PbZrx Ti1-x O3 ), Lead Lanthanum Zirconate Titanate (PLZT), Strontium Bismuth Tantalate (SBT), CeMnO3 (CMO), and others. Emphasis has been on achieving highly crystalline and oriented films at the lowest deposition temperatures possible, for compatibility with other integrated device materials and processing; and the achievement of optimum ferroelectric and pyroelectric performance. The effects of varying growth parameters, barrier and/or template layers, and post-growth annealing have been studied. The growth process, physical characterization, and ferroelectric film properties will be discussed. Introduction PZT thin films are capable of high pyroelectric, IR sensitivity and ferroelectric switching. The preferred device structures have limited thermal budgets. For highest sensitivity, crystalline films are required. Typically, to achieve a high degree of crystallinity this requires relatively high deposition and/or annealing temperatures. PZT deposition methods must be devised for high pyroelectric coefficient films at low temperatures, uniformly and at high rates. In this paper we describe our recent efforts at lowering film deposition temperatures, while maintaining film quality sufficient for devices in a production scale reactor. There are several approaches to oxide film deposition; however as reviewed in Table I, specific needs must be met in order to effectively deposit such films. As shown schematically in Figure 1, MOCVD fills these needs. Table I. Oxide Film Deposition Needs. The deposition technology must address simple to complex oxide film deposition on flat and shaped geometries. Sputtering Difficult to produce epitaxy, thin films suffer from pinholes, high volume production below 0.35 µm difficult. PLD Deposition plane limited in scalability and deposition rates, good for rapid prototyping. MBE Very difficult for oxides. Spin-on/mist Limited with respect to complex geometries, film density and defect density. MOCVD Ideal for producing epitaxial, conformal, uniform, scalable, low defect, pinhole-free films, and offers ability to functionally grade the composition
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Liquid Flow
Crack / Short Pinhole
Cracks Riser Substrate
Voids
Entrapped Voids
(a)
(b) Showerhead Reactant Inert Purge Oxidizer Inert Purge Reactant Substrate
Inert Purge Oxidizer DEPOSITING FILM Substrate
(d) (c) Figure 1. Comparison of the deposition techniques. (a) MBE or PVD Deposition, (b) Spin Mist Deposition, (c) MOCVD, and (d) AL(CV)D, a form of CVD. In analyzing the different approaches, only MOCVD readily meets the film deposition goals of conformality, den
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