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15 March 2006 Advanced exposure and focus control by proximity profile signature matching
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As the advanced IC device process shrinks to below sub-micron dimensions (90 nm, 65 nm and beyond), the process window (Depth of Focus, DOF) decreases to as low as < 0.2 μm. The impact of defocus on final CD results cannot be ignored any more or be compensated by adjusting exposure energy without side effect because the optical behavior of focus is totally different from that of exposure energy. We have developed an advanced control system to detect and correct for variations in both focus and exposure energy. A library of focus exposure matrix (FEM) models is first set up with pattern profiles of different pitches. The inline photoresist profiles of features of various pitches are then fitted to the database in the FEM models. The exposure and focus with which those features have been processed can be estimated. This approach utilizes information of both resist profile and proximity through focus behaviors and therefore gives more accurate extrapolation of defocus than using profile or proximity alone. The approach can also be used to distinguish process drifts caused by exposure and focus from those caused by other process parameters such as PEB temperature, developing parameters and illumination.
© (2006) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Wenzhan Zhou, Alex See, and Jin Yu "Advanced exposure and focus control by proximity profile signature matching", Proc. SPIE 6155, Data Analysis and Modeling for Process Control III, 61550H (15 March 2006);

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