Simultaneous Formation of Ni/Al Ohmic Contacts
to Both n- and p-Type 4H-SiC |
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Authors: | Kazuhiro Ito Toshitake Onishi Hidehisa Takeda Kazuyuki Kohama Susumu Tsukimoto Mitsuru Konno Yuya Suzuki Masanori Murakami |
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Affiliation: | (1) Department of Materials Science and Engineering, Kyoto University, Kyoto 606-8501, Japan;(2) Nanotechnology Products Business Group, Hitachi High-Technologies Corporation, Ibaraki-ken 312-0057, Japan;(3) The Ritsumeikan Trust, Nakagyo-ku, Kyoto 604-8520, Japan |
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Abstract: | The fabrication procedure for silicon carbide power metal oxide semiconductor field-effect transistors can be improved through
simultaneous formation (i.e., using the same contact materials and a one-step annealing process) of ohmic contacts on both
the n-source and p-well regions. We have succeeded in the simultaneous formation of Ni/Al ohmic contacts to n- and p-type SiC after annealing at 1000°C for 5 min in an ultrahigh vacuum. Ohmic contacts to n-type SiC were found when the Al-layer thickness was less than about 6 nm, while ohmic contacts to p-type SiC were observed for an Al-layer thickness greater than about 5 nm. Only the contacts with an Al-layer thickness in
the range of 5 nm to 6 nm exhibited ohmic behavior to both n- and p-type SiC, with a specific contact resistance of 1.8 × 10−4 Ω cm2 and 1.2 × 10−2 Ω cm2 for n- and p-type SiC, respectively. An about 100-nm-thick contact layer was uniformly formed on the SiC substrate, and polycrystalline
δ-Ni2Si(Al) grains were formed at the contact/SiC interface. In the samples that exhibited ohmic behavior to both n- and p-type SiC, the distribution of the Al/Ni ratios in the δ-Ni2Si(Al) grains was larger than that observed for any of the samples that showed ohmic behavior to either n- or p-type SiC. Furthermore, the grain size of the δ-Ni2Si(Al) grains in the samples showing ohmic behavior to both n- and p-type SiC was smaller than the grains in any of the samples that showed ohmic behavior to either n- or p-type SiC. Thus, the large distribution in the Al/Ni ratios and a fine microstructure were found to be characteristic of the
ohmic contacts to both n- and p-type SiC. Grains with a low Al concentration correspond to ohmic contacts to n-type SiC, while grains with a high Al concentration correspond to ohmic contacts to p-type SiC. |
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Keywords: | Ni/Al ohmic contacts simultaneous formation 4H-SiC |
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