Nanoscale bondability between Cu-Al intermetallic compound for Cu wirebonding

In this paper, the interfacial nanoscale bondability between copper (Cu) and Aluminum (Al) intermetallic compound (IMC) for Cu wirebonding has been carefully investigated. Preliminary results demonstrated that IMC cracks from the edge of bonding interface and spreads into the center area. This is the cause of open fail. The IMC between Cu and Al was initially generated in the form of CuAl₂, and gradually increased the content of Cu and turned into CuAl when the working temperature was increased. The final stage of IMC growth is Cu₉Al₄ and the aluminum pad will be vanished as the result of Cu diffusivity. Nanoscale atomic modulus and rupture strength are predicted by using molecular dynamics (MD) simulations. Atomic-level tensile stress and tensile strain are predicted to examine the IMC bonding strength along the bonding interface. Temperature and tensile speed are two major factors on determining the bonding strength. Material in high temperature has greater kinetic energy and has better formability. Higher pulling speed in tensile test would results in material easier fracture. Interfacial fracture is different in different tensile speed as well as the working temperature. Nano-indentation tests demonstrate an excellent agreement with the MD simulation. A series of comprehensive s studies are conducted in the present research.