Thermal Stability of Sputtered Tungsten Carbide as Diffusion Barrier for Copper Metallization

Abstract

This work investigated the thermal stability of tungsten carbide films deposited by a sputtering process with a WC target as diffusion barrier layer between Cu and Si. The as-deposited film has a nanocrystalline structure and a low electrical resistivity of around 227 μΩ cm. Film characterization reveals that the film was able to preserve the integrity of the Cu (500 Å)/n-Si structure without formation of up to a 600°C annealing for 30 min. In addition, diode leakage current measurements on the same contact structure, but with a substrate did not show deterioration of electrical characteristics up to a 550°C annealing. As the thickness of the barrier was reduced to 150 Å, the film retained the integrity of diodes up to 500°C without increasing the diode leakage current. The failure of film after high temperature annealing is attributed to the Cu diffusion into the Si substrate through grain boundaries or local defects of the barrier layer, in which some local defects may arise from the formation of © 2001 The Electrochemical Society. All rights reserved.