Studies of electron energy loss near edge structure at the interface between Si and amorphous carbon films deposited by
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Studies of electron energy loss near edge structure at the interface between Si and amorphous carbon films deposited by direct carbon ion beams M.H. Sohn and S.I. Kim SKION Corporation, 50 Harrison Street, Hoboken, New Jersey 07030
K. Siangchaew Department of Materials Science and Engineering, Stevens Institute of Technology, Hoboken, New Jersey 07030 (Received 20 April 1998; accepted 5 May 1999)
Using direct carbon ion beam deposition, in situ surface modification was performed by an energetic C− beam (400 and 500 eV) prior to amorphous carbon film growth to enhance adhesion of the film. It has been found from high-resolution electron microscopy that the C and Si mixing layer at the interface causes strong adhesion of the film. Electron energy loss spectroscopy was used to investigate chemical states of the C and Si mixing layer at the interface. The carbon composition profile in silicon showed that the thickness of the mixing layer was about 30 nm for 500 eV modification (at 200 °C). Silicon L-edge study at the C/Si interface found C–Si bond formation only at the surface of silicon over 2–3-nm-thick layers. The C–Si bond formation is a function of C− ion impingement energy. The thickness of the bonding layer decreased to less than 1 nm for 400 eV surface modification. When the substrate was modified by a 500-eV C− beam at 800 °C, the thickness of the SiC layer was about 10 nm. C–Si bond formation was enhanced by the supplemental thermal energy.
I. INTRODUCTION −
Direct C ion beam deposition has previously been studied.1 The adhesion of amorphous carbon films to silicon substrates was greatly enhanced by in situ surface modification using 400 and 500 eV C− beams.1 Highresolution electron microscopy has illustrated that the interface between the film and silicon substrate is damaged by the energetic beam bombardment. The silicon lattice at the interface is collapsed, and amorphous pockets are developed in the silicon lattice. The energetic C− ion beam formed a C/Si mixing layer which plays a role in enhancing the adhesion of the film. In this work, the chemical bonding state in the carbon and silicon mixing layer is investigated to determine if carbon is merely compositionally mixed with silicon or if C–Si bonds are formed by the C− beam energy. Recently, the possibility of carbon nitride formation by nitrogen ion implantation into graphite has been reported.2–4 C–N bond formation is accommodated by the kinetic energy of implants even at low substrate temperature. For silicon carbide film growth, very high substrate temperature (>1200 °C) must be supplied to achieve C–Si bonding in thermal processes.5–8 However, in an energetic process using a C− beam, carbon may form chemical bonds with silicon at very low temperature (200 °C) because of the kinetic energy of the beam. J. Mater. Res., Vol. 14, No. 8, Aug 1999
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This paper discusses the chemical composition at the C/Si interface as well as C–Si chemical bond form
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