Modeling stress and stressmigration in microelectronics interconnects

Yaping Luo, Purdue University

Abstract

This thesis is motivated by reliability problems related to thermal stresses in electronic Cu/low-K Interconnects. The interconnect failures are aggravated by reduction in feature size on the device to tens of nanometer as is currently the case. The aggressive downscaling has caused mainly two types of failures. The first is due to stress concentration, which is responsible for thin film cracking and delamination; and the other failure mechanism is stressmigration and electromigration. The goal of the proposed thesis research is to develop analytical descriptions for modeling the reliability of Cu/low-k interconnects. The thesis begins with a study of thermal stresses in multi-layer thin films. The thermal stresses in multiple layer thin films are obtained based on beam theory through an approach that is proven to yield more accurate analytical results comparing to previously developed solutions in literature. To further examine the stress concentration, the singular stress analysis is carried out for multi-material wedges including layered structures, and the nature of stress singularities is extensively investigated. To relate the singular stress field to failures in microelectronic interconnect structures, a numerical procedure for calculating stress intensity factors was developed to calculate the stress intensity factors. Another significant interconnect failure mechanism, stressmigration, is also analyzed in the thesis. Stressmigration is a complex physical phenomenon caused by diffusion at both grain boundary and in the lattice. A novel analytical description which is different from other approaches existing in literature is developed in the present study. The existing treatments in the literature are based on the definition of a chemical potential while the current approach utilizes the first law of thermodynamics. The developed procedure is applied to model the motion of an elliptical void in stressed grain taking into account both surface diffusion and lattice diffusion.

Degree

Ph.D.

Advisors

Subbarayan, Purdue University.

Subject Area

Mechanical engineering

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