Microstructure and Stress Analyses of Copper Films Deposited on Biased Substrates by Microwave Plasma-Assisted Sputtering

Abstract

ABSTRACTPure copper films have been deposited on <100> Si substrates either at the floating potential or biased to various dc voltages ranging from 0 to - 125 V. Argon ions from the discharge produced in a distributed electron cyclotron resonance microwave plasma reactor were used for sputtering of a copper target biased to various dc voltages. For sputter deposition, the Si substrates placed on a water-cooled substrate holder were maintained at ambient temperature. The argon pressure was 0.13 Pa and the dc target voltage was fixed at - 600 V. The deposition rate of films was investigated as a function of the substrate bias voltage. The crystallographic structure of films and size of copper crystallites were determined by x-ray diffraction analyses. The surface morphology of films was examined by atomic force microscopy. The electrical resistivity of films was deduced from the thickness and sheet resistance of films determined by profilometry and four point probe measurements, respectively. The magnitude of residual stresses in copper films was calculated from the radius of curvature of Cu/Si samples deduced from profilometry measurements. The evolution of the microstructure, surface morphology and electrical resistivity of films as well as the magnitude of residual stresses developed in these films were studied as functions of the substrate bias voltage. These major characteristics of films were found to be dependent on the energy of argon ions impinging on the surface of films grown on biased substrates. The effect of the ion energy on the physical features of films is analyzed and discussed in this paper.