DIFFUSION BARRIER STUDIES FOR Cu.

Abstract

Diffusion barriers to the migration of Cu were investigated with the intent of using Cu in place of Al for the wiring of VLSI chips. Bilayers of Cu with Ta, W, Zr, V, Ti-W, TiN and Si//3 N//4 were tested by annealing at temperatures from 250 to 750 degree C. Rutherford backscattering and Auger electron spectroscopy were used to analyze the annealed samples, while the resistivity was monitored to evaluate the interdiffusion and the consequent degradation of the conductivity of the films. Ta, TiN and Si//3 N//4 are found to be excellent diffusion barriers for annealing around 600 degree C for several hours. The electrical conductivity of the bilayers formed with these materials and with V remained close to that for bulk Cu. Ta does outdiffuse through the Cu to the surface with an activation energy of 1. 1 eV. The concentration of Ta in the bulk Cu is very low, while a Ta-rich layer was observed within 5 nm of the surface.