Contact Metallization and Packaging Technology Development for SiC Bipolar Junction Transistors, PiN Diodes, and Schottky Diodes Designed for Long-Term Operations at 350 degree C

摘要

This report describes the development of composite ohmic contact and packaging technologies for the wideband gap semiconductor silicon carbide (SiC) with demonstrations of these technologies using 4H-SiC JFETs (junction field effect transistors). The goal of this effort is protection against oxidation/inter-diffusion and stable operation in air at 350 degrees C for up to 10,000 hr. Ta-Si and Ru-Ta barrier layers have been developed and tested for composite contacts that consist of the ohmic contact layer (e.g., Ni2Si), the barrier layer, an adhesion layer such as Pt and a gold cap layer that is suitable for wire bonding. Reliability and failure analysis studies have been conducted for chip metallizations for die attachment and for large area wire bonding to substrate metals, die metals and die metals over SiO2. 1800V/5A 4H-SiC JEFETs have been designed and fabricated using the Ta-Si and Ru-Ta barrier layers in the composite ohmic contacts. The devices were characterized at 300 C and used in the design of a 2W, 270-28V dc-dc converter. With Vgate = -33V, the JFETs were able to block 600V with J.