A Study of Nucleation and Growth in MOCVD: The Growth of Thin Films of Alumina
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A Study of Nucleation and Growth in MOCVD: The Growth of Thin Films of Alumina M.P. Singh, S. Mukhopadhayay, Anjana Devi*, and S.A. Shivashankar Materials Research Centre, Indian Institute of Science, Bangalore 560 012, India (* Presently at Lehrstuhle fuer Anorganische Chemie-II, Ruhr-Universitaet Bochum, Germany) ABSTRACT We have studied the nucleation and growth of alumina by metalorganic chemical vapor deposition (MOCVD). The deposition of alumina films was carried out on Si(100) in a horizontal, hot-wall, low pressure chemical vapor deposition (CVD) reactor, using aluminum acetylacetonate{Al(acac)3}as the CVD precursor. We have investigated growth of alumina films as a function of different CVD parameters such as substrate temperature and total reactor pressure during film growth. Films were characterized by optical microscopy, X-ray diffractometry (XRD), scanning electron microscopy (SEM), cross-sectional SEM, and secondary ion mass spectrometry (SIMS) compositional depth profiling. The chemical analysis reveals that the carbon is present throughout the depth of the films. INTRODUCTION The MOCVD process has been developed for the deposition of thin films of a wide variety of materials, such as GaAs, Si, Cu, Al, W etc. But, except in a few cases such as GaAs and Si, nucleation and growth by MOCVD has not been studied in much detail. We have attempted to study these aspects of the MOCVD process using the deposition of alumina as an illustration, because alumina coatings are technologically important in various fields, such as dielectric mirrors, electronics devices, optical-wave guides, abrading coatings and passivation layers for metal surfaces [1-3]. Alumina is also the prospective gate oxide material for MOSFET devices in ultra large scale integrated (ULSI) circuits of the next generation. In the present study, we have examined the nucleation and growth of alumina thin films deposited by MOCVD using Al(acac)3 on Si(100) and TiN/WC (CVD-grown polycrystalline TiN on cemented WC substrates used as cutting tool inserts) under different CVD conditions. The microstructural investigation was carried out using optical microscopy, XRD, SEM, crosssectional SEM, and SIMS. EXPERIMENTAL DETAILS The deposition of alumina thin films was carried out in a custom-built, horizontal, hot-wall, fused quartz reactor evacuated by a two-stage rotary pump. The carrier gas (argon) flow was
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controlled by an electronic mass flow controller (MFC) and the total reactor pressure measured by a capacitance manometer. Finely powdered, polycrystalline Al(acac)3, synthesized and purified in our laboratory, was used as the source material. Films were deposited under growth conditions in the range given in table I. Average film thickness was calculated from the weight gained by the substrate (measured on a microbalance) due to the film, assuming uniform film thickness and bulk alumina density. Table I. Conditions used for film deposition. Substrate Si(100), TiN/WC Substrate temperature 450-900°C Precursor vaporization temperature 120-1
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