HIGH-TEMPERATURE STABILITY OF REFRACTORY-METAL VLSI GAAS-MESFETS

Commercially available, self-aligned VLSI GaAs MESFET's, with tungsten-based refractory-metal Schottky gates, nickel-based refractory-metal ohmic contacts, and aluminum interconnection metallization, have been thermally cycled and shown to be stable after 3 h at temperatures up to 500 degrees C. Both partially processed and fully processed wafers were found to be stable with no significant change occurring in either Schottky gate or ohmic contact properties. An increase in the channel resistance component of the series resistance is believed to be responsible for I-DS and g(m) degradation above 500 degrees C. The fact that commercially available, gold-free VLSI GaAs MESFET's are able to withstand such thermal cycles has very important consequences for monolithic optoelectronic integrated circuit (OEIC) fabrication because it means that it may now be Feasible to grow photonic device heterostructures epitaxially on MESFET VLSI wafers; process them into lasers, modulators, and/or detectors; and interconnect them with the electronics to produce VLSI-density OEIC's.