Simultaneous Formation of Ni/Ti/Al/Ag Ohmic Contacts to both p- and n-type for 4H-SiC RSD

Abstract

Semiconductor pulsed power switch SiC RSD (reversely switched dynistor) has difficulty in the preparation of its ohmic contact due to the nature of the material itself and the structure of alternating P+ and N+ regions at the anode. In order to solve the problem, an ohmic contact scheme considering both p-type and n-type semiconductors is proposed in this paper, and the effects of some process conditions on the ohmic contact during the manufacture are discussed, too. The ohmic contact characteristics can be evaluated by the contact resistance ρc which is measured by C-TLM method. Experimental results show that the ohmic contact of both p-type and n-type can be formed when the metal is Ni/Ti/Al/Ag (80/30/80/500 nm). The corresponding annealing condition is RTA at 1050°C in N2 atmosphere for 5 minutes. SiO2 protection before high temperature annealing can reduce ρc, while dry-wet oxidation before metal deposition has little improvement in ohmic contacts. The relationships between RMS and ρc are summarized in the end that neither too smooth nor too rough surface is good for the ohmic contacts.