Preparation of zirconia thin films by metalorganic chemical vapor deposition using ultrasonic nebulization
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Preparation of zirconia thin films by metalorganic chemical vapor deposition using ultrasonic nebulization Dong-Young Kim Department of Inorganic Materials Engineering, Seoul National University, Shillim-dong, Kwanak-gu, Seoul 151-742, Korea
Choon-Ho Lee Department of Materials Engineering, Keimyung University, Nam-gu, Taegu 705-701, Korea
Soon Ja Park Department of Inorganic Materials Engineering, Seoul National University, Shillim-dong, Kwanak-gu, Seoul 151-742, Korea (Received 18 December 1995; accepted 27 March 1996)
Zirconia (ZrO2 ) thin films were prepared by metalorganic chemical vapor deposition (MOCVD) using ultrasonic nebulization with new source materials, Zr(OBu)4 , Zr(OBu)3 (acac), Zr(OBu)2 (acac)2 , and Zr(OBu) (acac)3 . This process is a simple and economic method to prepare oxide thin films. Zr(OBu)4 was successfully reacted with acetylacetone at a molar ratio of 1 : 3. Polycrystalline thin films were deposited at a substrate temperature range from 300 to 550 ±C. The substitution of alkoxy radicals by acetylacetone made the deposition rate higher and insensitive to substrate temperature. The films deposited below 450 ±C mostly had a monoclinic structure, and those deposited above 450 ±C had a tetragonal structure. The measured optical energy band gap of zirconia film was 5.32 eV.
I. INTRODUCTION
Zirconia (ZrO2 ) films are of current interest due to such unique properties as high melting point, chemical inertness, high refractive index, wide band gap, high dielectric constant, and high elecrical resistivity.1 Therefore, zirconia thin films can be used for optical, dielectric, mechanical, insulating, and refractory applications.2 Zirconia is also a component of ferroelectric Pb(Zr, Ti)O3 which has recently become a hot issue in applications to integrated circuits. So the demand for the developemnt of a stable precursor for ZrO2 film is increasing. Zirconia is known to be crystallized into three different structures: monoclinic, tetragonal, and cubic. The monoclinic form is stable at room temperature. The tetragonal form is produced by heating to 1100 ±C. A cubic form with fluorite structrue is stable above 1900 ±C.3 The cubic or tetragonal forms can be stabilized at room temperature by the addition of CaO and Y2 O3 .4 Mechanical properties can be improved by the toughening associated with the monoclinic-to-tetragonal phase transformation in this material.5 Zirconia thin films have been prepared by various fabrication techniques such as pulsed laser deposition,6 ion assisted deposition,2 chemical vapor deposition (CVD),7 and metalorganic chemical vapor deposition (MOCVD).8 Recently, MOCVD using the ultrasonic nebulization technique has been developed in this laboratory for the J. Mater. Res., Vol. 11, No. 10, Oct 1996
preparation of high quality ferroelectric thin oxide films.9 This method is very simple in concept. Heating the gas lines, which is essential in conventional MOCVD, is not required. It is a very economic method to prepare thin films. Drop
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