Ion Implantation Induced Deep Defects in n-type 4H-Silicon Carbide
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Ion Implantation Induced Deep Defects in n-type 4H-Silicon Carbide A. O. Evwarayea, S. R. Smithb, W. C. Mitchel, and M. A. Capanoc Air Force Research Laboratory, Materials Directorate, MLPS 3005 P Street, Wright-Patterson Air Force Base, OH 45433-7707 a University of Dayton, Physics Department, 300 College Park, Dayton, OH 45469-2314 b University of Dayton Research Institute, 300 College Park, Dayton, OH 45469-0178 c Purdue University, Department of ECE, West Lafayette, IN 47907 ABSTRACT Aluminum (Al) and argon (Ar) ions were implanted into n-type 4H-SiC epitaxial layers at 600 0C. The energy of the ions was 160 keV at a dose of 2 x 1016 cm-2. After annealing at 1600 0C for 5-60 minutes, Schottky diodes were fabricated on the ion implanted samples. Deep Level Transient Spectroscopy (DLTS) was used to characterize ion implantation induced defects. A defect at EC-0.18 eV was observed in the Al+ implanted devices annealed for five and fifteen minutes. However, annealing for 30 minutes produced an additional deeper defect at EC -0.24 eV. This defect annealed out after a sixty minute anneal. DLTS studies of Ar+ implanted devices showed six defect levels at EC -0.18 eV, EC -0.23 eV, EC -0.31 eV, EC -0.38eV, EC -0.72 eV, and EC -0.81eV. These defects are attributed to intrinsic-related defects. It is suggested that “hot” implantation of Al+ inhibits the formation of intrinsic-related defects. While “hot” implantation of Ar+ into 4H-SiC does not reduce the concentration of the vacancies and interstitials.
INTRODUCTION
In silicon carbide technology, ion implantation has become a standard technique of selectively doping areas of silicon carbide with either donors or acceptors. Nitrogen (N) and phosphorous (P) and other donor ions [1, 2] have been successfully implanted into p-type 4H-SiC substrates to obtain an n-type region. Aluminum (Al) and boron (B) ions have also been implanted into n-type substrates to obtain a p-type region. The implanted species are normally at interstitial sites where they are not electrically active. Severe lattice damage and local stoichiometric imbalance [3] occur as a result of the implantation of energetic, heavy ions. Therefore, to activate the implanted species and to repair the lattice damage, the ion-implanted samples are annealed at high temperatures (1200 – 1700 0C) for various times. A high donor activation has been reported [4] but acceptor activation in silicon carbide is still an issue. Various attempts have been made to increase the acceptor activation in silicon carbide; these attempts include co-implantation of ions and implantations at elevated temperatures (the so called “hot” implants). “Hot” implant is the preferred method in the industry. Ion implantation of inert ions has been used as edge termination of Schottky devices. This reduces the field crowding at the periphery of the Schottky devices [5] and a subsequent anneal reduces considerably the reverse leakage current. The inert ions such
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as Ar+ are not known to be electrically active in silicon carbide; t
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