Computational analysis and chemical mechanical polishing for manufacturing of optical components

• Main Author: Nguyen, Nhu Y
• Other Authors: Zhong Zhaowei
• Format: Theses and Dissertations
• Language: English
• Published: 2017
• Subjects: DRNTU::Engineering::Mechanical engineering::Assistive technology
• Online Access: http://hdl.handle.net/10356/69489
• Institution: Nanyang Technological University

High precision optical components are required for modern life and future. To achieve component’s surfaces with high quality, chemical mechanical polishing (CMP) is required. It is a unique method to obtain the global uniformity planarization across the surface without scratches. In the polishing of optical components, a new approach has been applied, including two phases: phase one is using the fixed abrasive pad with abrasive-free slurry and phase two is using the soft pad (the fabric cloth pad) with colloidal silica slurry. This process has created a better uniformity surface with lower surface roughness. The non-uniformity of substrates after polishing is one of the most interesting things in current trends in research. One of the reasons for the non-uniformity is a pad wear profile. Researching on the pad wear profile by improving the pad conditioning process creates a better pad surface, and through that the substrates is polished with better uniformity. Another reason for the non-uniformity is the distribution of abrasive particles in the interface between the wafer and pad surfaces under effects of the pad and wafer rotations. In this research, an analytical model was established by combining of the kinematic motions and the contact time to investigate the pad wear non-uniformity. The results have indicated that the cutting path density and the contact time at positions near the pad center are more than that near the pad edge. It is a good agreement with experiments. New shapes of the pad and the conditioner have been developed to create a better pad wear profile. The pad after conditioning is convex and more uniform. In addition, a new computational fluid dynamic model was built. It was a combination of multiphase and discrete phase modelling to investigate the abrasive particles behaviour and the slurry distribution in the interface. The total numbers of particles in the gap were quantified to characterize their mechanical effects under different operating parameters. The simulation results have shown that the particles are non-uniformly distributed below the wafer and provided a deeper insight understanding of the material removal of the CMP mechanism. From the understanding above, a new idea has been developed to explain the mechanism of the CMP processes.