FEM study of deformation and stresses in copper wire bonds on Cu lowK structures during processing

Copper low-k structures are industry´s choice to meet new requirements in terms of lower trace resistance, lower electrical losses, higher current densities and higher speeds in the back end of line interconnects of ICs. However, the reliability of such structures is a primary concern. In this study, the influence of the material properties of both dielectric layer and metal layer on the stresses in the bond pad structure is discussed. We consider a simplified bond pad structure with a blanket dielectric layer below a single damascene Cu in oxide layer. The pressure from the deforming bond on the bond pad is used as loading. A tolerance analysis points out that the Poisson ratio of the dielectric layer has the largest impact on both von Mises and maximal principal stress in the dielectric layer, while the influence of the stiffness of the dielectric layer on the stresses in the dielectric layer is limited. The stresses in the metal layer are mainly determined by the Young´s modulus of both dielectric layer and metal layer. Comparing the value of the maximal principal stress in the metal layer to the ultimate tensile strength reveals that these critical values can be reached during the bonding process, leading to deformation of the bond pad.