Backside copper metallization of GaAs MESFET's using Ta and TaN as diffusion barrier

Abstract

Backside copper metallization of GaAs MESFET's ( Metal Semiconductor Field Effect Transistor) using Ta and TaN as the diffusion barrier layers was studied. A thin diffusion barrier Ta(40nm) or TaN(40nm) was sputtered on the GaAs substrate as the diffusion barrier for copper metallization. Material reactions of these films with GaAs substrate at different annealing temperatures were characterized by X-ray diffraction, Auger electron spectroscopy and transmission electron microscopy. Copper and diffusion barrier layer films were very stable up to 500 degrees C. At higher temperatures, Ta atoms started to react with GaAs substrate to form TaAs and TaAs, and Cu atoms started to penetrate into the GaAs substrate. The backside of the GaAs MESFET's was metallized using these Cu/Ta and Cu/TaN films. After 300 degrees C 2 hr annealing, the MESFET's showed very little change in the device characteristics. The experimental results show that both Ta and TaN are good diffusion barriers for backside copper metallization in GaAs devices.