Impurity Activation in N + Ion-Implanted 6H-SiC with Pulsed Laser Annealing Method
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Impurity Activation in N+ Ion-Implanted 6H-SiC with Pulsed Laser Annealing Method O. Eryu, K. Aoyama, K. Abe, and K. Nakashima Department of Electrical and Computer Engineering Nagoya Institute of Technology, Nagoya 466-8555, Japan ABSTRACT We have succeeded in pulsed laser annealing of N+ ion-implanted n-type 6H-SiC for increasing the carrier density near surface in order to decrease contact resistance, which induces little redistribution of implanted impurities after laser irradiation. By repeated laser irradiation at low energy density, the ion-implanted impurities were electrically activated without melting the surface region. SiC substrates with impurity concentration of 2x1018 /cm3 were implanted with 30 keV N+ ions with dose of 4.7x1013 /cm2. After pulsed laser annealing, a contact resistance was measured to be 5.7x10-5 Ωcm2 using Al electrode on the N+-implanted layer. INTRODUCTION SiC material has the excellent characteristics that can be applied to an ultraviolet (UV) ray detection, a MESFET, and power electric devices for the purpose of use in the high temperature environment. But, both ion-implantation followed with high temperature annealing of about 1500 ºC and ion-implantation to high temperature substrates are necessary for electrical activation of impurities to control SiC device properties [1,2]. There are serious problems in high temperature processing. The surface becomes rough and the stoichiometry near surface layer of SiC changes by the high temperature treatment. Therefore, a low temperature process should be made. Especially, the low temperature process be in urgent need of development the device structure using surface layer such as the electrode formation. We have shown that the formation of the p-n junction [3], the formation of ohmic electrode [4-6] and annealing of ion-implanted defects [7] become possible by pulsed laser processing at the room temperature. It should be noted that the pulsed laser annealing (PLA) for the activation of impurities introduced by ionimplantation near surface layer could become an indispensable process in the point of the application to form the UV ray sensor and ohmic electrodes. Ahmed showed that laser irradiation to SiC substrate at about 1.5 J/cm2 causes melt within an ion-implanted layer. The impurities were activated, however, the impurity distribution was changed [8]. It is not desirable that impurity distribution has been changed by PLA. So, we have developed a method with an excimer laser annealing in the low energy density to activate ionimplanted impurities, which has not much affected the impurity distribution. Furthermore, we have succeeded to measure the time resolved optical reflectivity (TROR) during PLA in order to monitor the PLA process with no surface damage. The present paper shows the instantaneous high temperature condition induced by pulsed laser irradiation anneals the ion-implanted defects, and impurity activation was achieved. EXPERIMENTAL DETAILS A schematic diagram of PLA and TROR measurement system is shown in figure 1. N+ ions
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