Low-temperature Preparation of Crystallized Zirconia Films by ECR Plasma MOCVD
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Low-temperature Preparation of Crystallized Zirconia Films by ECR Plasma MOCVD Hiroshi Masumoto and Takashi Goto Institute for Materials Research, Tohoku University, Sendai, 980-8577, Japan. ABSTRACT Zirconia (ZrO2) thin films were deposited at low temperatures on quartz and polyamidoimide substrates by electron cyclotron resonance (ECR) plasma MOCVD. Zr-hexa-fluoro-acetylacetonato [Zr(Hfac)４] solution was used as a precursor. Substrate temperature (Tsub) was from 300 to 973 K by a water-cooling holder and an infrared lamp heater. Cubic and monoclinic zirconia films were obtained on polyamidoimide substrates at 300 K. The ECR plasma was significantly effective to prepare crystallized ZrO2 films at low temperatures. INTRODUCTION It is known that zirconia (ZrO2) has excellent thermal and chemical stability and oxide ion conduction. Therefore, zirconia is expected to be used as oxide ion conducting materials, catalytic materials[1], optical mirror materials[2] and heat-resistant materials[3]. Zirconia films have been prepared by PVD (ex. sputtering[4] and laser-ablation[2]), chemical vapor deposition (CVD)[3] and sol-gel methods[5]. Usually, high substrate temperature is required for fabricating crystallized zirconia films. If crystallized zirconia films are prepared below 550 K on low melting point substrates, such as aluminum alloys and thermally stable polymers, the application of zirconia film will be expanded. CVD method is capable to prepare high quality zirconia films with excellent conformal coverage; however, deposition temperature of conventional CVD was usually higher than that of PVD. On the other hand, an electron cyclotron resonance (ECR) plasma is high-active plasma[6] and high quality crystalline films can be obtained at low temperatures. In the present study, zirconia films were deposited at low temperatures on quartz and polyamidoimide substrates by ECR plasma MOCVD.
EXPERIMENTAL Figure 1 shows a schematic diagram of the ECR plasma MOCVD apparatus. A Zr-hexa-fluoro-acetylacetonate (Zr(Hfac)４) was used as a Zr precursor. The solution which dissolved Zr(Hfac)４ (0.4 g) in anhydrous ethyl alcohol (2 ml) was ultrasonically atomized. The Zr source was carried into the reactor by Ar gas (25 cm3/min). Quartz (10mm x 10mm x 0.5mm) and polyamidoimide (φ10mm x 1.0mm) were used as substrates. The heatproof temperature of the polyamidoimide substrate is 523 K. An infrared lamp was used for controlling the substrate temperature (Tsub) in the range of 473 - 973 K. When ZrO2 film was prepared without heating by the infrared lamp, the substrate was heated up to about 423
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Figure 1. Schematic diagram of ECR plasma CVD apparatus. K by the ECR plasma irradiation. In order to prevent an increase in Tsub by the ECR plasma irradiation, the substrate was placed on a water-cooled substrate holder, and ZrO2 films were prepared at 300 K. The substrate temperature was measured by a Pt-13%PtRh thermocouple. A microwave (2.45 GHz) was introduced into the plasma chamber through a rectangular wave gui
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