Electromigration for advanced Cu interconnect and the challenges with reduced pitch bumps

Abstract

Cu Column bump has seen growing adoption in both high-end and low-cost mobile devices as well as in consumer, computing and networking devices. Higher input/output (I/O) density and very fine pitch requirements are driving very small feature sizes such as small bump on a narrow pad or bump on lead (BOL), while higher performance requirements are driving increased current densities, thus making electromigration (EM) performance a real and serious concern. As the fine pitch and bump sizes decrease (in both mass reflow and thermo compression bonding processes) and the current density through the bump increases, EM reliability is becoming an alarming issue across the industry. High current density in Cu column bump combined with Joule heating may easily cause an early EM failure in field applications. Many researchers [1-3, 11-13] have published copper column EM data with a number of studies and EM variables, but no data has been published for robust BOL/bump design rules for high temperature and high current conditions which is indigent in high performance packages. This project has been initiated to resolve EM challenges in the industry by identifying the BOL/ bump design with regards to the temperature/current conditions so a robust design rule/process window can be established for next generation packages.