Impact of 40nm BEOL Film Stack on Cu Wire Bond Wire Pull Performance

Abstract

Cu wire bond has been widely adopted instead of Au as the choice of wire-bond material mainly for high electrical performance and lower cost. However, Cu wire-bond means greater bond stress than Au wire-bond to the under layer BEOL film stacks, particularly for low K or ultra low K dielectric materials used in advanced nodes for better BEOL RC delay performance. In this work, we used Cu wire pull failure rate as an index to study and optimize the BEOL film stack. In addition, we also studied the Cu wire-bond conditions on the wire-pull performance to find the optimized bond condition. Robust process condition with improved Cu wire-pull performance has been achieved that can meet the 40nm Cu wire-bond requirements. The improved BEOL film stacks and process has passed all the process and product qualifications and implemented as the baseline process for SMIC's 40nm-node high volume production.