Aluminum-Ion Implantation into 4H-SiC (11-20) and (0001)
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Aluminum-Ion Implantation into 4H-SiC (11-20) and (0001) Y. Negoro, T. Kimoto, and H. Matsunami Department of Electronic Science and Engineering, Kyoto University, Kyotodaigaku-katsura, Nishikyo, Kyoto 615-8510, Japan ABSTRACT High-dose aluminum-ion (Al+) implantation into 4H-SiC (11-20) and (0001) has been investigated. Surface morphologies of implanted (0001) samples were improved by annealing with a graphite cap. Implant-dose dependence and annealing-time dependence of electrical properties are examined by Hall-effect measurements. A low sheet resistance of 2.3 kΩ/sq. was obtained in (0001) by high-dose Al+ implantation at 500 °C with a dose of 3.0 x 1016 cm-2 and high-temperature annealing at 1800 °C for a short time of 1 min. In the case of (11-20), even room-temperature implantation brought a low sheet resistance below 2 kΩ/sq. after annealing at 1800 °C. INTRODUCTION Ion implantation into SiC as well as post-implantation annealing still has several problems, especially for highly p-type doping. Although high-dose aluminum (Al+) implantation at an elevated temperature and subsequent annealing at 1700-1800 °C has been employed for forming p+-SiC [1, 2], the sheet resistances of p+-SiC are still not low enough for the use of high-performance power devices. In addition, considerable roughening due to macrostep formation on Al+-implanted p+-SiC after high-temperature annealing is also a critical problem. The 4H-SiC (11-20) face has shown various promising properties such as a superior MOS interface [3] and a low sheet resistance of phosphorus (P+)-implanted n-type region [4,5]. Besides the low sheet resistance, remarkable lattice recovery owing to a fast recrystallization rate along the [11-20] direction and excellent surface flatness could be realized in high-dose P+-implanted (11-20) [5,6]. However, no reports have ever been published on high-dose Al+ implantation into 4H-SiC (11-20). Different characteristics of Al+-implanted SiC can be expected by using different crystal faces. In this study, the authors present the properties of high-dose Al+-implanted 4H-SiC (11-20) layers in comparison with 4H-SiC (0001). EXPERIMENTAL DETAILS N-type 4H-SiC (11-20) and 8° off-axis (0001) epitaxial layers with a net donor concentration of 1 × 1016 cm-3 grown in the authors' group were used in this study. Multiple energy implantation of Al+ (10-160 keV) was carried out at 500 °C or room temperature (RT) to obtain a 0.2 µm-deep box profile of Al. In this study, the total implant dose was varied from 4.0 x 1015 to 6.0 x 1016 cm-2, which corresponds to an Al concentration from 2.0 x 1020 to 3.0 x 1021 cm-3. Some of the samples
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were prepared by utilizing co-implantation of carbon ions (C+) with a 20% or 100% dose of implanted Al+. The implanted samples were then covered with a graphite cap to suppress surface roughening during annealing [7]. Post-implantation annealing was performed in an Ar ambient at 1800 °C for 1-30 min using a CVD reactor. For Hall effect measurements, clover-leaf shaped mesa structures (~4 x
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