Thermal characteristics of submicron vias studied by scanning Joule expansion microscopy

Thermal characteristics of submicron vias strongly impact reliability of mu ltilevel VLSI interconnects. The magnitude and spatial distribution of the temperature rise around a via are important to accurately estimate intercon nect lifetime under electromigration (EM), which is temperature dependent. Localized temperature rise can cause stress gradients inside the via struct ures and can also lead to thermal failures under high current stress condit ions, such as electrostatic discharge (ESD) events, This letter reports the first use of a novel thermometry technique, scanning Joule expansion micro scopy; to study the steady state and dynamic thermal behavior of small geom etry,ias under sinusoidal and pulsed current stress. Measurement of the spa tial distribution of temperature rise around a submicron via is reported wi th sub-0.1 mu m resolution, along with other thermal characteristics includ ing the thermal time constant.