Evolution of the Cu-Al Alloy/ SiO2 Interfaces during Bias Temperature Stressing

Abstract

Alloys of copper with small amounts of aluminum have recently been investigated as the interconnect metal directly on or as the low resistivity diffusion barrier/adhesion promoter between copper and In the present work the electrical stability of the metal-oxide-semiconductor (MOS) capacitors of such alloys on thermal oxide on p-silicon was investigated. MOS samples preannealed at 250°C and subjected to bias temperature stressing (BTS) at 200 and 250°C under an electrical field of 1.5 or 2 MV/cm showed stable C-V behavior with no observed shifts along the voltage axis. However, an observed decrease in the by about 4-5% was associated with the higher BTS temperature or the field. Such changes were not observed if the preanneal was performed at 300°C instead of 250°C. Our X-ray photoelectron spectroscopy (XPS) analyses of the metal/ interface suggest that the observed instabilities in samples preannealed at 250°C (not observed in those preannealed at 300°C) are related to the interface interactions between Al (in the alloy) and The higher temperature preanneal or higher BTS conditions led to stabilization of this interface leading to stable MOS behavior as is also supported by the results of the measurements which is also presented and discussed in this work. © 2001 The Electrochemical Society. All rights reserved.