Key parameters influencing Cu-Sn interfacial void formation

Abstract

Recent trends in 3D integration and dimensional scaling technologies have attracted interest in micro-connects as a novel method for interconnection. Micro-connects, including small volume interconnects (or microbumps) and Solid Liquid Interdiffusion (SLID) bonds for Micro- or Nanoelectromechanical Systems (MEMS and NEMS) are functionally far superior compared with traditional large volume interconnects and enable novel integration techniques for the miniaturisation and diversification of complex integrated systems. As micro-connects have smaller volumes than traditional forms of interconnects, they become more susceptible to microstructural defects. Such defects can lead to the catastrophic and costly failures within complex integrated systems. This study of Cu-Sn micro-connects has resulted from the publishing of several papers on the reliability reduction with interfacial voiding cited as the root cause. Interfacial voids (often referred to as Kirkendall voids) form in micro-connects fabricated using electroplated Cu in contact with the low melting point metal Sn. A variety of Cu electroplating chemistries and current densities were used to assess the void formation characteristics and the resulting IMC growth rates. The variety of parameters is designed to assess the impacts on void formation. This data will enable electronic integration developers to better understand the reliability impacts and for manufactures to understand key parameters associated with void formation.