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Photomask LER Inspection and Metrology System Based on the Enhanced Knife-Edge Interferometry
Abstract
With the goal of creating a new photomask inspection system, this research represents the design flow for the enhanced knife-edge interferometry (EKEI)-based photomask inspection system.
In this study, the market and the background of the photomask were firstly investigated. After the investigation, the chart for the state of the art for the current photomask inspection system was created. By analyzing the current inspection method, the research motivation was proposed. To reach the goal of research motivation, five objectives were created to guide the route for further research. During the time achieving these objectives, the knife-edge interferometry (KEI)-based system was firstly introduced for edge inspection. The diffraction theory was carefully derived from wave optics and geometrical optics, respectively. After that, the KEI system was implemented for edge corrosion measurement. Next, we proposed the EKEI method for higher resolution and sensitivity requirements for photomask inspection. Compared with the conventional KEI system, the EKEI system improves its sensitivity and resolution 10 times. Then the EKEI-based photomask inspection system was prototyped and utilized for photomask inspection. The final prototype can inspect the pattern, defect, and LER from the photomask in a high-speed, low-cost manner. In the simulation part, the geometrical-based optics model was developed for LER-introduced knife edge diffraction simulation. We found and characterized the negative correlation between the LER value and the similarity from the EKEI system. Moreover, the photomask with certain LER was designed for the experiment. Different LER values were applied to the pattern to validate the simulation result. The experiment results show the same trend as the simulation results. At last, the research discussed the limitations and the future works for that system. As a result, by following the anticipated objectives, we successfully invented an enhanced knife edge interferometry-based photomask inspection system for photomask pattern dimension, defect, and LER characterization. A geomatical-based optic model was invented and shows good agreement with experiment results.
Citation
Wang, Zhikun (2022). Photomask LER Inspection and Metrology System Based on the Enhanced Knife-Edge Interferometry. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /198665.