Modeling and characterization of abrasive-free copper chemical mechanical planarization process

Abstract

The fundamental aspects of abrasive-free copper Chemical Mechanical Planarization (CMP) process have been investigated in this study. Firstly, the mechanism of material removal (wear mechanism) has been studied by performing qualitative analysis of the polished wafer surface using AFM, SEM and EDX. The surface analysis shows that chemical wear (corrosive wear) is the dominant wear mechanism in abrasive-free copper CMP process while other possible mechanical wear mechanisms are fatigue wear, particle adhesion and abrasion wear. However, the increase of slurry flow rate and relative velocity and the decrease of pressure give the dominance of corrosive wear in material removal mechanisms, and vice versa. Secondly, the process has been characterized to understand the effect of pressure, relative velocity and slurry flow rate on Material Removal Rate (MRR) and With-in Wafer Non-Uniformity (WIWNU). Experimental results show the non-prestonian effect of pressure on MRR. Besides, the synergistic effect of relative velocity and pressure on MRR has been investigated from the interfacial contact condition (between wafer and pad) view point, and a process has been developed using the recipe of the early stage of a??Mixed Contact Modea??. Finally, a MRR model for abrasive-free copper CMP process has been developed based on the assumption of periodic distribution of pad asperities, elastic contact between pad and wafer surface and corrosive wear theory. This model takes into account the non-prestonian phenomenon of MRR, and predicts the theoretical MRR that closely fits with experimental results. In addition, the effect of velocity, chemical reactivity of slurry, pad surface geometry and material property of pad and wafer on MRR can be explained by the MRR model.