Mechanism of Microstructure Evolution for the Cu/Ta/GaAs Structure after Thermal Annealing

Abstract

The diffusion behavior and microstructure evolution of Cu/Ta/GaAs multilayers after thermal annealing are investigated and the mechanism is proposed. A thin 30 nm tantalum layer was sputtered as a diffusion barrier to block Ga and As diffusion into the Cu layer. From the results of sheet resistance measurement, X-ray diffraction analysis, Auger electron spectroscopy and transmission electron microscopy, the Cu/Ta films on GaAs were found to be very stable up to 500 °C without Cu migration into GaAs. After annealing at 550 °C, the interfacial mixing of Ta with GaAs substrate occurred, resulting in the formation of TaAs2, and the diffusion of Ga through the Ta layer formed the Cu3Ga phase at the Cu/Ta interface. After annealing at 600 °C, the reaction of GaAs with Ta and Cu formed TaAs and Cu3Ga owing to Ga migration and interfacial instability.