FEM Analysis of Stress in the Structures under Bond Pad of Ultra Low-k Device

Abstract

  The mechanical integrity of wirebonds is sensitive to structures under the bond pads of ultra low-k dielectric devices. The authors calculated homogenized material properties of two basic wiring structures with three different wiring pitches in the device. Stress in the ULK layer under the bond pad was analyzed using 3D finite element method (FEM) models of ball bond, Al pad, dielectric film stacks and Si susbtrate with twelve different variations. The analyses results indicate that higher density of Cu wiring and via reduces stress in the ULK layer. The results also indicate that thicker FTEOS layer, thicker SiO₂ layer or thicker Al pad reduces stress in the ULK layer.