Improved Stability of Pd/Ti Contacts to p-Type SiC Under Continuous DC and Pulsed DC Current Stress

The enhanced stability of Pd/Ti contacts to p-type SiC under high-current-density continuous direct-current (DC) stressing is investigated and compared with previous work on Ti/Al contacts. Additionally, differing failure modes were observed for the Pd/Ti contacts under continuous DC and pulsed DC stress. The improved stability of the Pd/Ti contacts is demonstrated through a 29% increase in the applied continuous DC current required to cause electrical failure during a 1 h test compared with the Ti/Al contacts. The metallization scheme includes a TiW barrier and a thick electroplated Au overlayer. While severe intermixing and voiding in the ohmic contact layer caused the Pd/Ti contacts to fail under continuous DC stress, electromigration of the Au overlayer degraded the contacts under pulsed DC stress. The temperature of the surface of the contacts was reduced from over 649A degrees C for contacts that failed under continuous DC current to between 316A degrees C and 371A degrees C for pulsed DC current. The difference in temperature and failure modes of the continuous and pulsed DC stressed contacts indicates different failure mechanisms.