Simulation of Granular Temperature of Abrasive Particles in the EKF-CMP System

Chemical mechanical planarization/polishing (CMP) is an important process in semiconductor manufacturing. This process integrates the chemical energy and physical energy to reduce the thickness and planarize the surface of wafer. In CMP process, the slurry is a key material to use its silica abrasive nanoparticles distributed on the polishing pad to cut the passivation layer of the wafer surface. In our previous researches, electro kinetic force (EKF) is applied to assist CMP process (EKF-CMP system) with great development potential. This study uses COMSOL Multiphysics analysis software with three modules, electric current, laminar flow and particle tracing, to simulate the dynamic behaviors of abrasive nanoparticles in the slurry under the influence of electro osmosis flow. The results show that the design with positive and negative staggered electrodes produces the convection flow pattern of abrasive particle in the slurry. The simulation result of particles' velocity field is in good agreement with the experimental result by Particle Image Velocimetry (PIV) method. To quantify the random motions of particles, this study defines the granular temperature as the specific fluctuation kinetic energy of particles. The granular temperature is introduced to be an index to measure the strength of particles fluctuation in the slurry. With the design of bidirectional electrode, the granular temperature increase in both Cu-Blanket film CMP and glass CMP systems. For Cu-Blanket film CMP system, EKF can improve 22.29% of material removal rate (MRR). While for glass CMP system, EKF can improve 9.52% of MRR. The Pearson correlation coefficient between granular temperature and MRR in Cu-Blanket film EKF-CMP and glass EKF-CMP systems are 0.94 and 0.91, respectively, so that the granular temperature can indicate the performance of material removal in EKF-CMP process appropriately. Appling the concept of granular temperature to investigate the particle behavior in CMP slurry is very innovative. The results of this study can be used as a reference for the essential design of the EKF-CMP system.