Laser Direct Write and Gas Immersion Laser Doping Fabrication of SiC Diodes
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Laser Direct Write and Gas Immersion Laser Doping Fabrication of SiC Diodes Z. Tian, N.R. Quick1 and A. Kar Laser-Aided Manufacturing, Materials and Micro-Processing Laboratory (LAMMP) School of Optics/CREOL, University of Central Florida Orlando, FL 32816-2700, USA 1 AppliCote Associates, LLC, 894 Silverado Court Lake Mary, FL 32746, USA ABSTRACT Laboratory prototype SiC diodes are fabricated using a combination of gas immersion laser doping (GILD) and laser direct write (LDW) in situ metallization in a commercial SiC wafer. Trimethylaluminum (TMA) and nitrogen are the precursors used to produce p-type and n-type SiC, respectively. Using these techniques, a 150 nm p-type doped junction is fabricated in semiinsulating 6H-SiC and n-doped 4H-SiC wafers. Ohmic contacts are created by laser direct metallization producing carbon rich conductive phases in these doped materials. Alternatively an excimer laser can be used to create silicon rich Schottky contacts. The geometry of the diodes can be vertical or planar to the wafer surface and the laser processes are thought to reduce defect densities in the irradiated areas. These laser-processed diodes are intended for use in high temperature, high voltage and high frequency switching and sensing applications. INTRODUCTION The current technology barriers for silicon carbide device fabrication include micropipe defects in the substrate and processing limitations (e.g., dielectric deposition, etching, oxidation, metallization, and doping) [1]. One of these challenges is metallization for source, drain and gate contacts on devices. Metal conductors generate strains due to thermal expansion coefficient mismatch resulting in debonding, or can create charge carrier traps, particularly dislocations, which decrease the device efficiency. Also, metal conductors can oxidize and react with chemical species in hostile environments degrading their conductive properties and further creating chemical products that can eventually affect the device [2]. Doping is another challenge in SiC processing due to its hardness, chemical inertness, the requirement of the use of dry etching techniques, and the low diffusion coefficient of most impurities[3]. Current doping techniques in SiC device fabrication include epilayer doping and ion implantation. Epilayer doping refers to in situ doping during the chemical vapor deposition (CVD) epitaxial growth, which is primarily accomplished through the introduction of nitrogen (N) or phosphorous (P) for n-type, aluminum (Al) or boron (B) for p-type and vanadium (V) for semi-insulating epilayer. The traditional ion implantation technique 1) generates implantationinduced defect centers in the substrate, and therefore, requires high annealing temperatures to remove the implantation damage and to electrically activate the dopants, 2) generates defects that remain in the material up to 1700°C annealing and 3) changes the stoichiometry, which may affect the diffusion of dopants or enhance the formation of intrinsic-related defect centers [4-6]. A laser con
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