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Title: Control and signal processing for lithography
Authors: CHEN MING
Keywords: Lithography, Critical Dimension, wafer warpage, real-time control, resist thickness, optimal feed-forward control
Issue Date: 26-Sep-2008
Citation: CHEN MING (2008-09-26). Control and signal processing for lithography. ScholarBank@NUS Repository.
Abstract: This thesis investigates the application of advanced control and signal processing methods to improve lithography performances.Wafer warpage can result in spatial variation in critical dimension (CD). A real-time temperature control method was proposed for post-exposure bake. It was demonstrated experimentally that real-time control of bake plate temperature to give nonuniform temperature distribution across warped wafer can reduce CD variation.Resist thickness is nonuniform after spin coating. Resist thickness was monitored with a spectrometer during post-apply bake, and controlled by manipulating the heating power of bake plate in real-time. Experimental results showed that both thickness nonuniformity and CD nonuniformity were reduced.A multizone feed-forward controller was proposed to reject the disturbance caused by placement of a cold wafer on the bake plate. The optimal feed-forward signals can be obtained by solving a linear programming problem. Experimental results showed that the disturbance would be reduced to less than 0.1Deg C.
Appears in Collections:Ph.D Theses (Open)

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