As the design rule of wafer has been shrinking, the patterns on the mask also need to be getting smaller and even
smaller for some sub-resolution assist features, which makes mask inspection process need a high resolution (HR)
inspection systems. For this HR mask inspection, most mask inspector makers adopt a TDI(Time Delay & Integration)
sensor to enhance acquired image quality with the acceptable scan speed, thus, to minimize the inspection cost.
However, even TDI sensor may not get a sufficient gray level of pattern image for the most advanced mask patterns.
Furthermore, it might generate some false defects depending on the pattern shape and scan direction (in combination
with pattern direction). We manufactured two programmed defect masks (PDM); one is a ArF EPSM and another is a
EUV mask. By inspecting these masks with perpendicular scan directions, respectively, we evaluated the correlation
between scan direction and defect size/shape experimentally. We found that the inspection with the parallel direction to
pattern direction can increase the inspectability for the patterns and the defect sensitivity since this helps to enhance
signal to noise ratio from the TDI sensor. Our analysis can increase sensitivity of TDI sensor effectively without any
additional hardware modification.