Laser Processing, Characterization, and Modeling of Epitaxial Si/TiN/Si (100) Heterostructures
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LASER
PROCESSING, CHARACTERIZATION, AND MODELING EPITAXIAL Si/TiN/Si (100) HETEROSTRUCTURES
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RINA CHOWDHURY, X. CHEN, K. JAGANNADHAM AND J. NARAYAN North Carolina State University, Department of Materials Science and Engineering, Raleigh, NC 27695-7916. ABSTRACT We have successfully deposited multilayer Si/ITiN/Si(100) epitaxial heterostructures at a substrate temperature of 600'C in a chamber maintained at a vacuum of -10-7 torr using pulsed laser (KrF: X= 248 nm, r = 25 ns) deposition. This silicon-on-conductor device configuration has potential applications in three-dimensional integrated circuits and radiation hard devices.The two interfaces were quite sharp without any indication of interfacial reaction between them. The epitaxial relationship was found to be Si II TiN II Si. In the plane, four unit cells of TiN matched with three unit cells of silicon with less than 4.0% misfit. This domain matching epitaxy provides the mechanism of epitaxial growth in systems with large lattice mismatch. Energetics and growth characteristics of such domain matching epitaxy in the high lattice mismatch Si/TiN/Si(100) system and possible device implications are discussed. INTRODUCTION Silicon-on-conductor (SOC) device configurations have currently been investigated [1-3] as potential materials systems for radiation hardened devices and for three-dimensional integration of advanced semiconductor devices. Epitaxial TiN is a promising material for use as a conductor in metal-base transistors and as interconnects in 3-D integrated circuits. TiN has several advantages [4]: high thermal and mechanical stability, diffusion barrier characteristics etc. TiN also has good etch-stop capability, therefore, a chlorine-based dry-etch chemistry can be used to etch TiN without undercut or post etch corrosion. Laser ablation is one of the most desirable low-temperature processing techniques to grow single crystal epitaxial Si and TiN films. We recently reported [5] the formation of single crystal TiN (a = 4.24173 A) by laser physical vapor deposition (LPVD) on high lattice mismatch Si(100) substrate (a = 5.43088A), where it was shown that 4 unit cells of TiN match with 3 unit cells of silicon within 4% misfit with TiN II Si epitaxial relationship. Domain epitaxial growth has become possible in this large mismatch system. We have calculated the energy associated with the epilayer in the Si/TiN/Si structure and found that it is minimized via domain epitaxial growth. EXPERIMENTAL RESULTS A pulsed KrF excimer laser (wavelength 248 nm, pulse duration 25 ns) was used to ablate titanium nitride from a stoichiometric hot pressed TiN pellet at a repetition rate of 5 Hz followed by ablation of silicon from a single crystal Si(100) target at a repetition rate of 1 Hz [6]. 2 The 2 cm-diam laser beam was focussed onto the target to obtain an energy density of -10 J cmat a 45* angle of incidence. The silicon substrates were cleaned prior to introduction in the vacuum chamber by ultrasonically degreasing in acetone for 5 minutes, and then in methanol fo
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