Analysis of various blur effects on mask CD distortion
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Implementation of high resolution E-beam tools is an attractive candidate for next generation lithography. To understand the forward scattering blur and proximity in 100kV E-beam tool, we studied E-beam acceleration voltage effects on dose sensitivity and iso-dense CD bias. We measured and analyzed the dose sensitivity (nm/%dose) near the design CD using various local density patterns. Proximity effects due to backscattering were much larger in 100keV exposure and caused the degraded dose sensitivity. We made a simple model and analyzed each contribution from a resist process, forward scattering and backscattering. We concluded that backscattering was the major reason of decreasing ILS(Image Log Slope) and the difference of forward scattering blur between 50 and 100 keV was negligible. Backscattering contribution compared to that of forward scattering was two times larger in the 100keV exposure, which can make accurate CD control difficult.