Simultaneous Formation of n- and p-Type Ohmic Contacts to 4H-SiC Using the Binary Ni/Al System
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1069-D09-01
Simultaneous Formation of n- and p-Type Ohmic Contacts to 4H-SiC Using the Binary Ni/Al System Kazuhiro Ito1, Toshitake Onishi1, Hidehisa Takeda1, Susumu Tsukimoto1, Mitsuru Konno2, Yuya Suzuki2, and Masanori Murakami1 1 Materials Science and Engineering, Kyoto University, Kyoto, 606-8501, Japan 2 Hitachi High-Technologies Corporation, Hitachinaka, 312-0057, Japan
ABSTRACT Fabrication procedure for silicon carbide power metal oxide semiconductor field effect transistors can be improved through simultaneous formation of ohmic contacts on both the nsource 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 mins in an ultra-high vacuum. Ohmic contacts to n-type SiC were found when Al-layer thickness was less than about 5 nm while ohmic contacts to p-type SiC were observed for an Al-layer thickness greater than about 5 nm. Only the contacts with Al-layer thicknesses in the range of 5 to 6 nm exhibited ohmic behavior to both n- and p-type SiC, with specific contact resistances of 1.8 × 10–4 Ωcm2 and 1.2 × 10–2 Ωcm2 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. The distribution in values for the Al/Ni ratio in the δ-Ni2Si(Al) grains which exhibited ohmic behavior to both n- and p-type SiC was the largest. The smallest average δ-Ni2Si(Al) grain size was also observed in these contacts. 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.
INTRODUCTION Compared to Si, silicon carbide (SiC) is better suited to the next generation of highpowered devices due to such excellent intrinsic properties as a higher electric field breakdown strength and a higher saturation electron velocity1. However, several technical issues such as doping at high levels by ion implantation and development of formation techniques to create low resistance ohmic contacts2 must be solved before the application of SiC in high-power devices can be realized. For power metal oxide semiconductor field effect transistor devices with a doubleimplanted vertical structure, the ohmic contacts on both n+ -source region and p-well region are needed3. Nickel4 and Ti/Al5,6 contacts, where a slash symbol “/” indicates the deposition sequence staring with Ti, are well known as the low resistance ohmic contact to n- and p-type SiC, respectively. Thus, the ohmic contacts to n- and p-type SiC are currently fabricated using different contact materials and different annealing processes. Simultaneous formation of ohmic contacts to both n- and p-type SiC using the same contact material and in a one-step annealing process will simplify device fabrication processes and miniaturize the cell size.
Although a variety of ohmic contact materials to SiC have been developed, only a few materials are suitable for ohmic contacts to
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