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Plasticity, Microstructure and the Thermal Dependence of Flow Stresses in Aluminum Thin Film Interconnects

Published online by Cambridge University Press:  22 February 2011

Ramnath Venkatraman
Ramnath Venkatraman*
Affiliation:
IBM Corporation, Microelectronics Division, 1710 North Street Endicott, NY 13760
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Abstract

A study was conducted towards fundamentally understanding the nature and magnitude of thermal stresses in aluminum thin films on silicon and correlating them with deformation mechanisms that serve to relax the stresses imposed by the thermal strain. A number of experiments and theoretical considerations are described in order to describe the sources of strengthening and stress relaxation in such films. It is shown that the flow stress of an aluminum film corresponds to the critical stress required to drive dislocation glide events. This mechanism entails an inverse flow stress dependence on the film thickness and grain size. A novel set of experiments in which the effects of strengthening due to finite film thickness and the grain size were separated and quantified is described. The variation of these strengthening components with temperature during heating and cooling were noted. Theoretical considerations of diffusional relaxation combined with the results of grazing incidence X-ray scattering (GIXS) experiments suggest that grain boundary diffusion is much less effective in limiting film flow stress than would be expected from the strain rate relation derived for a free-standing film. Line broadening observations in the GIXS experiments suggested large changes in dislocation density in the tested films during thermal cycling. The nature of these variations are qualitatively consistent with those of the film flow stress, suggesting that strain hardening could be an additional strengthening mechanism in Al films during thermal cycling.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 338: Symposium – Materials Reliability in Microelectronics IV , 1994 , 215
Copyright
Copyright © Materials Research Society 1994

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