26 June 2003 Characterizing illumination angular uniformity with phase-shifting masks
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A phase shifting mask pattern consisting of a linear phase grating is introduced as a potential tool to measure or monitor illumination angular distribution and uniformity in optical projection printing. An implementation as simple as four phase steps serves to steer the illumination into and out of the pupil at an angle determined by the period of the grating. The total intensity captured within the pupil is recorded in resist, allowing for a fast analysis of the illuminator’s fill of the pupil. The advantage over existing techniques lies in the fact that the analysis of the source has been transferred to the design of the mask pattern. A cursory inspection of a single dose-matrix wafer with a low magnification optical microscope readily displays signs of source irregularity. If signs of irregularity exist, the capability exists for the user to complete a more in-depth analysis of the source intensity distribution. Illumination pupil-fill is easily monitored across the field, tool-to-tool, or over time, or can be compared to the intended design. Due to mask simplicity, this technique is especially useful for monitoring quadrupole or quasar illuminators. Mask requirements are discussed, concluding that with an average grating period of 2μm and tolerance of up to 40nm layer to layer overlay error, fabrication appears feasible.
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Gregory McIntyre, Gregory McIntyre, Andrew R. Neureuther, Andrew R. Neureuther, } "Characterizing illumination angular uniformity with phase-shifting masks", Proc. SPIE 5040, Optical Microlithography XVI, (26 June 2003); doi: 10.1117/12.485438; https://doi.org/10.1117/12.485438

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