Papers by Keyword: Aluminum Ion Implantation

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Authors: Takashi Tsuji, T. Tawara, Ryohei Tanuma, Yoshiyuki Yonezawa, Noriyuki Iwamuro, K. Kosaka, H. Yurimoto, S. Kobayashi, Hirofumi Matsuhata, Kenji Fukuda, Hajime Okumura, Kazuo Arai
Abstract: The authors fabricated pn diodes with Al+ implantation in p-type epitaxial layers, and investigated the influence of the implantation dose on reverse leakage currents. Only in the highest dose with the Al concentration of 2x1020cm-3, more than 90% of the devices showed high leakage currents above 10-4A at the maximum electric field of 3MV/cm. In such devices, almost all of the emissive spots corresponded to threading screw dislocations (TSDs) by the analysis of emission microscopy and X-ray topography. These TSDs were defined as killer defects with the estimated density of 500cm-2 in the case of the highest dose. The emissions were supposed to be due to microplasmas, since the spectra of the emissions were different from those of heat radiation. Condensation of Al atoms, nitrogen atoms and DI defects were excluded as the origin of the emissions by secondary ion mass spectrometry and low temperature photoluminescence analyses.
Authors: Masataka Satoh, Shohei Nagata, Tohru Nakamura, Hiroshi Doi, Masami Shibagaki
Abstract: Electrical properties of p+n 4H-SiC(0001) diode formed by Al ion implantation to n-type epitaxial layer have been investigated as a function of Al doping concentration ranging from 1 x 1020 to 6 x 1020 /cm3 and the operation temperature. The n-type 4H-SiC(0001) epitaxial layer with a net donor concentration of 1 x 1016 /cm3 are multiply implanted by Al ions in the energy range from 30 to 170 keV at elevated temperature of 500 oC with a implantation layer thickness of 350 nm, followed by the annealing at 1900 oC for 1min using EBAS. On-state resistance of diode with Al concentration of 1 x 1020 /cm3 is estimated to be about 4.5 mcm2, while that for diode with Al concentration of 6 x 1020 /cm3 is 1.8 mcm2 at 25 oC. In the sample with Al concentration of 6 x 1020 /cm3 shows the positive temperature coefficient of on-state resistance of diode, while that for sample with Al concentration less than 3 x 1020 /cm3 is negative. The diode formed by Al implantation at the concentration of 6 x 1020 /cm3 is able to operate at the constant current density of 80 A/cm2 at the bias of 2.9 V independent to operation temperature.
Authors: Ming Hung Weng, Fabrizio Roccaforte, Filippo Giannazzo, Salvatore Di Franco, Corrado Bongiorno, Mario Saggio, Vito Raineri
Abstract: This paper reports on the electrical activation and structural analysis of Al implanted 4H-SiC. The evolution of the implant damage during high temperature (1650 – 1700 °C) annealing results in the presence of extended defects and precipitates, whose density and depth distribution in the implanted sheet was accurately studied for two different ion fluences (1.31014 and 1.31015 cm-2) by transmission electron microscopy. Furthermore, the profiles of electrically active Al were determined by scanning capacitance microscopy. Only a limited electrical activation (10%) was measured for both fluences in the samples annealed without a capping layer. The use of a graphite capping layer to protect the surface during annealing showed a beneficial effect, yielding both a reduced surface roughness and an increased electrical activation (20% for the highest fluence and 30% for the lowest one) with respect to samples annealed without the capping layer.
Authors: Tomokatsu Watanabe, Sunao Aya, Ryo Hattori, Masayuki Imaizumi, Tatsuo Oomori
Abstract: Effects of implantation temperature on electrical properties of heavily-Al-doped 4H-SiC layer formed with Al implantation have been investigated. To form the p++ 4H-SiC with the original 4H-stacking structure, the implantation temperature above 175 °C is needed. A decrease in the implantation temperature below 250 °C leads to an increase in the NA-ND. It is suggested that an increase in the density of vacancies with a decrease in the implantation temperature promotes the Al substitution to lattice sites during activation annealing. The lower-temperature implantation also causes a decrease in activation energy for the p-type electrical conduction and a decrease in p-type ohmic contact resistivity. We presume that the increase in the Al acceptors at low-implantation temperatures gives expansion of the impurity bands and formation of valence band tail-states, causing the decrease in the impurity binding energy. The properties obtained with the lower-temperature implantation are desirable for practical applications especially at low temperatures.
Authors: Shigeru Hirono, Hironori Torii, Tetsuya Tajima, Takao Amazawa, Shigeru Umemura, Tomoyuki Kamata, Yasuo Hirabayashi
Abstract: A high dose impurity doping process for 4H-SiC crystals has been developed using electron cyclotron resonance (ECR) sputtered carbon cap film and ECR plasma ashing. ECR-sputtered carbon films are newly found crystalline carbon films of which the hardness is comparable to that of diamonds. Since this carbon film showed such a high thermal tolerance that the hardness did not change after 1900oC annealing, this carbon cap film worked well for suppressing roughening during annealing for aluminum-ion implanted 4H-SiC. Cap carbon film can be removed successfully by using high density ECR plasma ashing.
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