Simultaneous Formation of Ohmic Contacts for Both N- and P-Type 4H-Sic Using Nial-Based Contact Materials
- PDF / 1,240,168 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 91 Downloads / 163 Views
0911-B11-05
SIMULTANEOUS FORMATION OF OHMIC CONTACTS FOR BOTH N- AND PTYPE 4H-SIC USING NiAl-BASED CONTACT MATERIALS Susumu Tsukimoto, Toshitake Onishi, Kazuhiro Ito, and Masanori Murakami Materials Science & Engineering, Kyoto University, Sakyo-ku, Kyoto, 606-8501, Japan
ABSTRACT In order to simplify a fabrication process of silicon carbide power MOSFETs (metal oxide semiconductor field effect transistors), development of a simultaneous formation process of ohmic contacts to both the p-well and n-source regions of the SiC devices using same contact materials and one step annealing was challenged. We succeeded to develop NiAl-based contact materials which provided ohmic behaviors for both n- and p-type 4H-SiC after one step annealing. The Ni/Al and Ni/Ti/Al ohmic contacts were prepared by depositing sequentially Ni, (Ti) and Al layers with various layer thicknesses onto the n- and p-type SiC substrates which were doped with N at 1×1019 cm-3 and with Al at 8×1018 cm-3, respectively. The Ni(50 nm)/Al(5 ~ 6 nm) contacts showed ohmic behaviors for both the n- and p-type SiC substrates after annealing at 1000 ˚C. The Ni(20 nm)/Ti(50 nm)/Al(50 ~ 70 nm) contacts showed ohmic behaviors for both the n- and p-type SiC substrates after annealing at a lower temperature of 800 ˚C. The specific contact resistances of these contacts were measured to be in the order of 10-3 Ωcm2 for both p- and n-type SiC, and were found to have strong dependence of the Al layer thicknesses of materials. The interfacial microstructures of the NiAl-based contacts were also observed by transmission electron microscopy (TEM) to understand the current transport mechanism through the metal/SiC interfaces. INTRODUCTION Development of reliable ohmic contacts is one of key issues to realize the high-power SiC devices [1]. For power MOSFET devices with a double implanted vertical structure, the ohmic contacts on both the n+-source region and p-well region are needed [2]. Currently, the ohmic contacts for n- and p-type SiC are fabricated using different contact materials and different annealing processes. In order to simplify the fabrication process, simultaneous formation of ohmic contacts for both n- and p-type semiconductors using same contact materials and annealing temperature is mandatory, which results in miniaturizing the cell sizes, possibly leading to wide applications for the SiC devices. Although a variety of the ohmic contact materials to SiC have been developed, only a few materials are suitable ohmic contacts for both n- and p-type SiC [3-5]. Fursin et al. [3] reported that a nickel contact, which was known as a typical ohmic contact material for n-type SiC [6], showed ohmic behavior after annealing at 1050 °C for both n- and p-type SiC implanted with nitrogen and aluminum at the levels of the order of 1019 and 1021 cm-3, respectively. Tanimoto et al.[4] and Kiritani et al. [5] also reported simultaneous formation for Ni-based contacts such as Ni and Al/Ni to SiC heavily doped with N (>1020 cm-3) after annealing at 1000°C. NiAl-based materia
Data Loading...
