Preparation and Characterization of SrTiO 3 Thin Films Using ECR Plasma Assisted MOCVD
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numerous high dielectric materials, paraelectric SrTiO 3 and (BaSr)TiO.3 have been attracted for particular attention because of their high dielectric cons-tant, good thermal stability and good high frequency characteristics. Several deposition techniques, such as rf-sputtering[1-4], pulsed laser deposition[5]i, metal organic chemical vapor deposition (MOCVD)[6-11], have been reportedl on SrTiO3 films. Among these techniques, MOCVD is often considered to be a best technique due to its magnificent features such as high deposition rate, easy composition control and high coverage of surface irregularities. Sr MO-source (Bis(2,2,6,6-tetramethyl--3,5-heptanedionato) strontium hydrate: Sr(TMiHID)), however, has a low vapor pressure even at high temperature[12]. In order to overcome this weakness, a membrane evaporator has been used in this study. In this paper, we also investigate the effects of depo~sition conditions on the structure and the electrical properties of SrTiO.3 films prepared by the ECR p~lasma assisted MOCVD. EXPERIMENTAL A schematic diagram of the ECR-MOCVD system is shown in Figure 1. Sr(TMHI-D)2 and Ti-isopropoxide (or TIP) were used as the metal organic sources, and oxygen and argon was used as the oxidant and the carrier gas to transport the metalorganic vapors, resp~ectively. The stainless steel bubbler containing TIP was maintained at 45"C in an oil bath. The membrane evap~orator containing Sr(TMHI-D) 2 was 183 Mat. Res. Soc. Symp. Proc. Vol. 4150©1996 Materials Research Society
heated using heating tapes. Membrane consists of 5 p m pores, so that Ar carrier gas can go through it. We deposited films using a boat evaporator but changed to a membrane evaporator in order to maximize the vaporization of Sr(TMt{D)2 by increasing contact surface area with carrier gas. This modification provided increase in the deposition rate of SrO films. The gas lines from the bubbler and the evaporator to the gas ring in the reaction chamber including joint were heated to prevent the condensation of source gas vapor. Oxygen introduced into the plasma generation chamber to generate oxygen plasma was also heated. TIP and Sr(TMIHD)2 vapors were mixed at joint located just before the reaction chamber. Substrates were rotated at 5rpm during the .deposition and heated by a resistance heater. The substrates used here were 4" Si(p-type 100) and Pt(1000 A)/SiO2 (1000A)/Si wafers fabricated by sputtering Pt onto an oxidized Si(100) substrate. The pumping system consisted of a series of a turbomolecular pump (TMP) and a rotary pump (RP). The pressure in the reaction chamber was controlled by conductance controllable valve. The surface morphologies of the films were investigated using a scanning electron microscope(SEM). The film thickness were measured using an ellipsometer and a color chart and confirmed by SEM micrographs of the fracture surface. The crystal structure of the films was evaluated using an X-ray diffraction analyzer, and the composition was analyzed using a wavelength dispersive X-ray spectroscopy (WDXS). The ele
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