4 August 1993 Linewidth determination using simulated annealing
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Using etched quartz as a phase shifter for i-line phase shift masks requires an etched depth of 385 nm referenced from the quartz surface. Recent work shows a direct relationship of focus offset as a function of the phase angle as it deviates from 180 degree(s). Knowing the etched depth and phase in transmission becomes critical to the production and verification of these masks. A method of interferometrically evaluating a phase shift mask is proposed. The method calculates the phase shift from the surface profile imaging system. Results show that errors of less than 5% are obtained for features as small as 1/6th of the optical resolution of the system and less than 2% for features as small as 1/2 of the resolution. When noise is included in the modeling, errors of 5% are obtained for S/N of 10 and less than 2% for S/N of 100.
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Katherine Creath, Katherine Creath, Shiyu Zhang, Shiyu Zhang, "Linewidth determination using simulated annealing", Proc. SPIE 1926, Integrated Circuit Metrology, Inspection, and Process Control VII, (4 August 1993); doi: 10.1117/12.149021; https://doi.org/10.1117/12.149021

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