Studie van de impact van thermische gradiënten op de betrouwbaarheid van metalen gebruikt in de micro-elektronica

Abstract

The continuous scaling of microelectronic technologies has made back-end-of-line (BEOL) interconnect reliability increasingly sensitive to non-uniform thermal conditions. Reduced interconnect dimensions, high current densities, Joule heating, and nearby heat sources can generate pronounced temperature gradients along metal lines. Under such conditions, temperature is no longer merely a scalar parameter controlling diffusion kinetics: its spatial gradient introduces an additional driving force for atomic transport, known as thermomigration (TM). The resulting mass transport can interact with electromigration (EM) and stress migration (SM), thereby modifying void nucleation, void growth, and ultimately interconnect lifetime. This PhD investigates the impact of thermal gradients on the reliability of metal interconnects, with a particular focus on Cu interconnects. Experimental studies are combined with finite-element simulations and analytical modelling to quantify temperature distributions, thermally driven atomic transport, and the resulting reliability degradation. Dedicated test structures are used to investigate TM-induced void formation and growth under controlled non-uniform temperature fields. Analytical and numerical models are developed to describe TM-driven mass transport and to predict critical regions for void nucleation and growth. The interaction of TM with other driving forces, particularly EM and mechanically induced stress gradients, is also investigated to establish a more complete description of atomic flux under realistic operating conditions. The developed framework further enables lifetime estimation under combined electrical and thermal loading. The results demonstrate that sufficiently strong and non-uniform temperature distributions can significantly alter interconnect degradation and, under relevant conditions, make TM an important contributor to reliability failure. This work provides a physics-based framework for assessing interconnect reliability in the presence of thermal gradients and supports more accurate lifetime prediction for advanced microelectronic technologies.