## 3 Results  
The characteristics of the 193-nm DUV microscope system are demonstrated by a comparison with commercial equipment used for optical surface inspection. For this, the aspherical stitching interferometer (ASI) based on Fizeau interference was used for the observation of surface figure, and the coherence correlation interferometer (CCI) based on white-light interferometer was used for the observation of surface roughness. The location of the defects (here, we consider the region where the fabricated alphabet patterns exist as defects) can be determined by measuring the surface figure of the sample using the ASI-Q (QED technology) instrument. As shown in Figure 4a, the red square indicates the area where the fabricated alphabet patterns are formed. Despite enlarging the image, it is still not possible to identify the patterns, because the lateral resolution of the ASI-Q is several \(\upmu\)m at best. It is applied to quickly determine the position of the defects before the detailed imaging of the defects using the 193-nm DUV microscope system. Figure 4b shows the 3D image of several alphabet patterns observed inside a region measured using a CCI-optics (Taylor Hobson) instrument. Compared with Figure 4a, the enhanced image with high-resolution alphabet patterns is shown in a narrow area (0.825 mm \(\times\) 0.825 mm). However, it is not sufficient to distinguish the pattern shapes, because it does not reach a spatial resolution high enough to recognize the shape of the alphabet pattern, when we consider the CCI with the lateral resolution of 0.76 \(\upmu\)m.  
Figure 5a shows the fabricated sample on the stage. The 4-inch sample is fixed on the sample stage and the bright spot (denoted by the red circle) presents the area where the patterns exist. Figure 5b  
Figure 4: Surface images of the alphabet patterns observed using ASI-Q and CCI-optics. (**a**) Surface image of 4-inch sample as shown in Figure 3 using ASI-Q. (**b**) Detailed 3D image of alphabet patterns on the sample using CCI-optics. Figure 3: Sample design for the evaluation of the spatial resolution of the 193-nm DUV microscope system. shows the SEM images of the patterns. The SEM images were used to verify that the fabricated patterns were in good agreement with the designed patterns. Patterns with an average line width of 400 nm were used. Pattern imaging was carried out by two sequential processes using two objective lenses. First was wide-field imaging (field of view (FOV) = 625 \(\upmu\)m \(\times\) 467 \(\upmu\)m) using an objective lens with NA 0.28 and second was detailed imaging (FOV = 135 \(\upmu\)m \(\times\) 100 \(\upmu\)m) using an objective lens with NA 0.50. Figure 5c shows the pattern images of two cases, which clearly distinguish alphabet patterns with a line width of 400 nm. The spatial resolution of the 193-nm DUV microscope imaging system was evaluated by analyzing the imaging results of the alphabet and 1D grating patterns. Figure 6a shows the DUV microscope image of alphabet patterns obtained with an NA 0.5 objective lens. In this condition, the pixel size was 100 nm. In this figure, the red bar is marked to investigate the spatial resolution of the pattern quantitatively. As a result, the spatial resolution at this position was estimated to be 235 nm by using the knife-edge method [21,22], as shown in Figure 6b. The normalized intensities of 10% and 90% with respect to the background intensity occur at 240 and 475 nm, respectively; thus, the spatial resolution is 235 nm when the intensity varies from 10% to 90%. This can be directly applied to detect defects and cracks on large-area optical components. Figure 6c shows the DUV microscope image of the 1D grating structure with a periodicity of 450 nm. The periodicity of 450 nm of the 1D grating structure and a line width of 225 nm are identified by analyzing this image. As shown in Figure 6d, the spatial resolution is confirmed to be 225 nm, when we consider the full width at half-maximum with respect to a certain single peak intensity distribution in the line profiles.