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24 March 2006 Verification of the system of defect inspection on patterned wafers using sub-200nm wavelength light
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Bright-field inspection is still strongly required for 45 nm semiconductor device processes to detect several kinds of defects on patterned wafers. We have been carrying out verification of our defect inspection system using sub-200nm wavelength light. As part of the verification work, we evaluated the system's inspection imaging characteristics by using a pilot POC tool and by simulations. The image evaluation system used has a sub-200 nm wavelength light source. Two kinds of magnifications, 100x or 250x, can be selected. Test wafers with the same patterns and programmed defects were used. Simultaneously, UV (365 nm) images were taken by an inspection tool. The results of the reflectivity simulations suggest that the average reflectance at 198 nm is basically the same as that for present inspection wavelengths. A three dimensional electromagnetic simulator was used to evaluate the images of patterns and programmed defects described above. Image contrasts for Line and Spaces were also calculated. It is confirmed from both the experimental and simulation results that (1) sub-200 nm images are superior to UV images in contrast, and that (2) the image contrast improves with increasing magnification because of a reduction in pixel size. Further, a quantitative defect detection procedure was taken to identify programmed defects. Several sizes of extrusion defects were evaluated. Examination of the differential images under the three optical conditions showed that sub-200 nm light and 250x were most desirable, followed by sub-200 nm light and 100x. Sub-200 nm provided an enough pixel grey level difference value to detect extrusion defects down to 50 nm.
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Tetsuo Takahashi, Yoko Miyazaki, Toshihiko Tanaka, Tsuneo Terasawa, and Naoya Takeuchi "Verification of the system of defect inspection on patterned wafers using sub-200nm wavelength light", Proc. SPIE 6152, Metrology, Inspection, and Process Control for Microlithography XX, 615226 (24 March 2006);

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