AFM Study of Forces Between Polyurethane Pads and Ceria Nanoparticles

INTRODUCTION Interactions of the ceria particles with polyurethane surfaces are of great interest for polishing processes used in modern semiconductor industry. Specifically, ceria abrasive nanoparticles and polyurethane polishing pads are now broadly used in the process called Chemical-Mechanical Planarization/Polishing (CMP) [1,2,3]. To optimize the process of CMP, various chemicals, abrasives, polishing pads, etc. have been investigated [4,5,6,7,8]. However, due to the large number of parameters that can influence the CMP process, the optimization of CMP by experimental means has been difficult to do. Modeling the CMP process, see, e.g., refs.[9,10] can help to rationalize the CMP optimization. To increase the predictive effectiveness of the models, one needs to know the interaction between the pads and the abrasive particles. The technique that is capable of measuring such information is atomic force microscopy (AFM), see, e.g., [11]. To measure the forces between the ceria particles and the pads with the AFM, we attached the ceria particles to the AFM tip with epoxy. Attachment of large balls to the AFM tip has been reported before, see, e.g., [12], as well as functionalizing the tip surface with various molecules. Here we report the first successful attachment of nanosize (~50-100nm) particles to the AFM tip and the direct measurements of forces using such tips. Specifically, we report study of adhesion and long-range force between nanosize ceria particles and three different polyurethane polishing pads.