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Shear Stress Analyses in Chemical Mechanical Planarization with Cu/Porous Low-k Structure

In current LSI devices, porous low-k films are adopted as interlayer dielectrics (ILDs). However, the extremely low Young's moduli of these films result in defects such as delamination, which are sometimes induced during chemical mechanical planarization (CMP). The main cause of delamination is thought to be shear stress induced by CMP downward pressure. In this study, we demonstrated that finite element method (FEM) results could be used to predict dangerous stress fields during CMP. It was revealed that shear stress concentrated on the ILD boundary with a large modulus difference. Moreover, stresses at dense lines were always lower than those at isolated lines. Furthermore, shear stress was sensitive to frictional force. The effect of a plasma-damaged layer on shear stress was quite limited. Consequently, these considerations provide a useful suggestion for future work on Cu/porous low-k-film fabrication as well as on the CMP of LSI devices.