Particle Scale Modeling Of Material Removal And Surface Roughness In Chemical Mechanical Polishing PDF Download

ABSTRACT: Chemical mechanical polishing (CMP) is widely used in the microelectronics industry to achieve planarization and patterning of metal and dielectric layers for microelectronic device manufacturing. Rapid advances in the microelectronics industry demand a decrease in the sizes of the devices, resulting in the requirement of a very thin layer of material removal with atomically flat and clean surface finish by CMP. Furthermore, new materials, such as copper and polymeric dielectrics, are introduced to build faster microprocessors, which are more vulnerable to defect formation and also demand more complicated chemistries. These trends necessitate improved control of the CMP that can be achieved by studying the slurry chemical and particulate properties to gain better fundamental understanding on the process. In this study, the impacts of slurry particle size distribution and stability on pad-particle-surface interactions during polishing are investigated. One of the main problems in CMP is the scratch or pit formation as a result of the presence of larger size particles in the slurries. Therefore, in this investigation, impacts of hard and soft (transient) agglomerates on polishing performance are quantified in terms of the material removal rate and the quality of the surface finish. It is shown that the presence of both types of agglomerates must be avoided in CMP slurries and robust stabilization schemes are needed to prevent the transient agglomerate formation. To stabilize the CMP slurries at extreme pH and ionic strength environments, under applied shear and normal forces, repulsive force barriers provided by the self-assembled surfactant structures at the solid/liquid interface are utilized. A major finding of this work is that slurry stabilization has to be achieved by controlling not only the particle-particle interactions, but also the pad-particle-substrate interactions. Perfect lubrication of surfaces by surfactants prevented polishing. Thus, effective slurry formulations are developed by studying the frictional forces, which are representative of the particle-substrate interactions, while achieving stability by introducing adequate interparticle repulsion. Finally, optimal slurry particulate properties are examined by analyzing the material removal mechanisms for silica-silica polishing. Based on the reported findings, a slurry design criterion is developed to achieve optimal polishing performance.