High temperature packaging of silicon carbide devices.

摘要

To address the need for high temperature packaging of silicon carbide (SiC) devices for power electronics applications, this dissertation describes a high temperature metallization scheme that is capable of operating reliably at 400°C in air. To achieve this goal, this study has examined the metallization processes for an ohmic contact, substrate metallization, wire-bond interconnects, and die-attach techniques to fully utilize the advantages of SiC devices.; Tungsten carbide (WC) ohmic contacts fabricated on 6H-SiC are described and were evaluated in this study. This contact was protected against oxidation and metal-interdiffusion using Pt as a diffusion/oxidation barrier. A gold cap layer was deposited for the purpose of wirebonding to the device. WC showed a good ohmic contact to n-type SiC with a specific contact resistance of 1.09 x 10-5 O-cm2.; The long term reliability of electroless nickel plated aluminum nitride (AIN) and silicon nitride (Si3N4) substrates was studied. After 150 hours of exposure to 300°C, nickel failed as a barrier layer over copper. However, tungsten carbide shows promise as a diffusion barrier for copper metallization on Si3N4 substrates. The metallization stack Si3N4/Cu/WC/Ti/Pt/Ti/Au was analyzed "as-deposited" and after annealing. The stack remained stable for 100 hours at 400°C in air.; A new bonding technique, transient liquid phase (TLP) bonding, is proposed and demonstrated for two binary alloy systems, Ag-In, and Au-In. A nearly void-free joint was achieved for SiC chips bonded to Si3 N 4 AMB substrates. There was no indication of bonding degradation at the interface after annealing at 400°C for 100 hours in air. The results of die shear and die pull testing before and after annealing at 400°C for 100 hours exceeded the minimums specified by MIL standards.; Eight (8) and 15 mil Al wires were bonded to nickel bonding pads on standard DBC AIN and Si3N4 substrates. Three mil gold wires were bonded to Au pads on gold-plated AIN and Si3N4 substrates. One mil Au wires were bonded to Au sputtered SiC die Ball shear testing (destructive) and ball bond pull testing was performed. The average shear strength was 65 grams and destructive pull test failures were mid span or ball neck breaks.