Optimization of the processing parameters for pulsed laser deposition of nickel silicide ohmic contacts on SiC
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Optimization of the processing parameters for pulsed laser deposition of nickel silicide ohmic contacts on SiC C. J. K. Richardson, M. H. Wisnioski, J. B. Spicer Department of Materials Science & Engineering, The Johns Hopkins University, Baltimore, MD 21218 J. D. Demaree, M. W. Cole, C. W. Hubbard, P. C. Joshi, J. K. Hirvonen Weapons and Materials Research Directorate, Army Research Laboratory, APG, MD 21005 H. Kim, A. Pique and D. B. Chrisey Naval Research Laboratory Code 6370, Washington DC 20375
ABSTRACT This research investigates the potential of pulsed laser deposition to create reliable high current ohmic contacts of Ni 2Si on single crystal 4H-SiC. Since this stoichiometry is the stable interphase in the nickel-silicon carbide diffusion couple, direct deposition eliminates the detrimental excess carbon normally formed by direct sintering Ni on SiC, the surface roughening that results from this sintering as well as the need for post-deposition high-temperature (900'C) anneals that are required in complex multi-component contacts. This study examines the processing parameters that must be used during deposition to obtain the desired microstructural characteristics for the contact. Pulsed laser deposition of nickel silicide produces smooth films with an amorphous or nanocrystalline structure interspersed with macroparticles. Macroparticle formation on the resulting films appear in the form of solidified droplets of the eutectic composition nickel silicide (3:1) that form during the long term target processing. The dependence of the number and size distributions of these droplets on laser fluence sample temperature is examined. INTRODUCTION High quality single crystal silicon carbide (SiC) has enormous promise as a large bandgap semiconductor for applications in high-temperature, high-current load applications.[ ] The promise of SiC for these applications arises from its material properties and its ability to be processed by the same techniques as silicon. Perhaps the largest obstacle impeding the practical application of SiC is the inability to fabricate stable ohmic contacts. The difficulty in fabricating stable metallizations on SiC for pulsed power applications evolves from the electrical requirements of matching band structures, while maintaining a physically distinct contact. Most metals form silicide or carbides, thus making it very difficult to maintain device structure integrity at elevated temperatures.[2] Previous research has revealed nickel-based metallizations as having the most potential. Unfortunately, nickel reacts with SiC to produce Ni 2 Si[3] which leaves excess carbon through the interaction region.[4] During this reaction the interface becomes rough and in some cases voids may form.[5] By directly depositing Ni 2Si, the thermodynamically stable interphase between Ni and SiC, onto 4H-nSiC an ohmic contact can be produced without producing the unwanted free carbon. To achieve this goal, Ni 2Si was deposited on SiC using pulsed laser deposition (PLD).
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