Excimer laser-induced doping of crystalline silicon carbide films
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M. I. Chaudhryc) Department of Electrical Engineering and Computer Engineering, Clarkson University, Potsdam, New York 13699
S.V. Babu Center for Advanced Materials Processing and Department of Chemical Engineering, Clarkson University, Potsdam, New York 13699 (Received 22 July 1994; accepted 31 July 1995)
0.25 /Am thick, single crystal, n-type, silicon carbide (/3-SiC) films thermally grown on p-type Si(100) were doped with boron by using KrF excimer laser radiation and a spin-on dopant with a boron concentration of 10 20 /cm 3 . The threshold fluence for the doping to occur was approximately 0.08 J/cm 2 . Similarly, /?-SiC/w-SiC diodes were fabricated by laser-induced doping of single-crystal /3-SiC (ra-type, 6 /im thick) films on n-type Si(100). The diodes obtained at 0.25 J/cm 2 showed good rectifying characteristics. The threshold fluence for surface modification and/or ablation was approximately 0.3 J/cm 2 , indicating that doping and diode formation have to be accomplished within the fluence window of 0.08 J/cm 2 -0.3 J/cm 2 for these films.
I. INTRODUCTION /3-SiC is an important electronic device material for high temperature, high power, and high frequency applications due to its unique combination of properties of high thermal conductivity (5.0 Wcm" 1 K™1), large bandgap (2.2 eV at 300 K), high breakdown electric field (3 X 106 V/cm), and high saturated drift velocity (2 X 107 cm/s). 1 Its large bandgap allows /3-SiC/Si heterojunction devices to be utilized as high efficiency solar cells and high-speed heterojunction bipolar transistors (HBTS).2 Semiconductor device fabrication requires the incorporation of dopants and formation of high-quality doped layers. Thermal diffusion, ion implantation, and doping during growth are some of the most commonly used methods of doping SiC. Thermal diffusion of dopants into SiC requires high processing temperatures of 2000 K or more and long processing times.3 However, high-temperature processing causes impurity contamination, resulting in nonabrupt heterojunctions, degradation of minority carrier lifetimes in the substrate, and deterioration of the crystallinity of the substrate.4"7 Ion implantation was also investigated for doping SiC. During implantation each dopant ion displaces several a) Now
with Ultra Clean Technology, 150 Independence Drive, Menlo Park, California 94025. b:iNow with Praxair Corp., White Plains, New York. c) Now with CHEMI Laboratories, Watervliet, New York 12189. J. Mater. Res., Vol. 10, No. 11, Nov 1995 http://journals.cambridge.org
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lattice atoms, severely damaging the lattice structure. Restoration of the lattice structure is essential if the electrical effects of the defects are not to dominate those of the implanted ions. Typically, thermal or laser annealing is employed for restoring the lattice structure. However, thermal annealing at temperatures as high as 2000 K did not completely restore the lattice structure of SiC layers implanted with boron and aluminum ions.14 Furthermore, thermal annealing results in
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