Molecular simulation on the material/interfacial strength of the low-dielectric materials

In this paper, the material stiffness of amorphous/porous low-k material and interfacial strength between amorphous silica and low-k have been simulated by the molecular dynamics (MD) methods. Due to the low stiffness of the low-k material, the interfaces which include this material are critical for the most delamination and reliability issues around the IC back-end structure. MD simulation technique is applied to elucidate the crack/delamination mechanism at these critical interfaces. However, due to the amorphous nature of the low-k material (eg. SiOC:H), the atomic modeling technique of the amorphous/porous silica is first established. Through the experimental validation, the accuracy of this amorphous modeling technique is obtained, and the results show that this algorithm can represent the trend of the mechanical stiffness change due to different chemical composition of low-k material. A novel interfacial modeling technique, which models the status of chemical bonds at interface during the delamination loading, is developed. Afterward, the simulation of the mechanical strength of the amorphous silica/SiOC:H interface, is implemented. The simulation depicts that the existence of the strong Si-O covalent bond will significantly enhance the adhesive strength of the interface. Instead of the covalent bond at interface, the simulation results also reveal the multiple atomic scaled crack path within the material during the interfacial delamination. Hence, improving the material stiffness of the soft low-k material and preventing the pore at interface can increase the adhesive strength of the silica/low-k interfacial system.