Properties of Silicon Carbide
Fully indexed with over 1000 references to published and unpublished sources, this book draws together the expert knowledge of numerous researchers from around the world to completely characterize the SiC system.
TABLE OF CONTENTS Properties of Silicon Carbide
Chapter 9: SiC Devices and Ohmic Contacts
9.1 Ohmic Contacts to SiC
G.L. Harris, G. Kelner and M. Shur
November 1993
A INTRODUCTION
Low resistance, reliable, temperature-stable ohmic contacts are a prerequisite for the commercialization of SiC device technology. Still, these contacts are not yet satisfactory for a variety of reasons: the annealing temperature is too high, the contacts penetrate too deep, they deteriorate when devices operate at elevated temperature, and the contact resistance is quite high. The problem of stable contacts to SiC may be resolved by using refractory metals. Refractory metals can be used to form both carbides and silicides. Silicides appear to provide a stable resistance if carbides are not present [1]. Contact systems based on such metals as nickel, chromium, titanium, cobalt and tungsten have been demonstrated for n-type SiC. Most contact systems for p-type SiC are Al-based and this imposes a limitation on the operating temperature of SiC devices with p-type contacts.
B OHMIC CONTACTS
Recently, Kelner and co-workers [2] obtained a specific ohmic contact resistance of 3.5 x 10 -6 ? cm -2 with a carrier concentration of 4 x 10 18 cm -3 to 6H-SiC. The contacts were resistively evaporated nickel that was rapidly thermally annealed at 1000 C, for 30 s, in a forming gas atmosphere. Crofton et al [3] recently reported a contact resistance as low as 10 -5 ? cm 2 to p-type SiC. Another problem to be solved is the fabrication of low resistivity Au or Al overlays for device interconnects.
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