Scratching of Patterned Composite Surfaces by Pad Asperities in Chemical-Mechanical Polishing

In chemical-mechanical polishing (CMP), as the rough polymer pad slides over patterned structures of metal interconnects and dielectrics the pad asperities themselves, though soft, may scratch the relatively hard layers. Generally, the fully-plastically deformed pad asperities with high interfacial friction are the sources of pad scratching. In this study, accordingly, scratching of Cu/dielectric line structures by soft asperities was investigated. First the scratching criteria and the scratch-regime maps previously constructed for monolithic layers were adapted for the patterned layers. Then sliding experiments were conducted on patterned Cu/dielectric layers of various linewidths using polymer pins loaded into the fully-plastically deformed state. Specifically, the role of the width of Cu and dielectric lines, in comparison with the contact diameter, was examined. The theoretical models predict that the scratch criteria for patterns with wide lines are the same as those for monolithic layers, whereas patterns with extremely narrow lines behave as composite layers with effective properties, which can be readily estimated by the rule-of-mixtures (ROM). Experimental results validate the scratch criteria based on contact mechanics.