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230ARTICLE IN PRESSC.-S. <strong>Lin</strong> et al. / Materials Science in Semiconductor Processing 10 (2007) 227–234smoothness of the image and sharpness of thepattern edge, the best exposure processing time canbe found. If the test substrates are over or underexposed, the image will not be sharp enough. Thisshows that the image has bright and dark pixelsmixed inside and the summation of the low graylevelpixels will be larger, also the percentage ratiowill be higher for the selected area. On the otherhand, the number of high gray-level pixels for theselected area of the test substrate as well as thepercentage ratio will be smaller. A properly exposedsubstrate shows a sharp image better than those ofthe over or under exposed images.Fig. 4 shows images grabbed in real time by thehigh-speed imaging system. From the images, it iseasy to find that the longer the development time theclearer the image of the photoresist pattern. Thecontrast of the exposed portion is higher than that ofthe un-exposed portion for the selected area. However,when the optimum developing time passes, thedevelopment fluid begins to etch the entire photoresist,which destroys the exposed and unexposedportions and causes the contrast to degrade. Hence,as the optimum development comes, the substrate istaken out from the development fluid and preparedto do the next manufacturing process.Fig. 5 consists of histograms which show a singlepeak that occurs when the developing time is notlong enough. The exposed and unexposed areas arenot clear, hence the contrast of the image is notobserved. After a little while, the pattern of theexposed area shows up, and the histogram willchange from single peak to double peaks. The moretime the passes, the better the image contrast with asmaller percentage ratio of low gray-level pixels andlarger high gray-level pixels [6].Fig. 4. The 640 480 image after development for different time periods (A) 1.8 s, (B) 6.3 s, (C) 10.7 s, (D) 16.9 s, (E) 21.7 s, (F) 26.2 s,(G) 30.8 s, (H) 35.9 s, (I) 40.2 s, (J) 45.5 s, (K) 50.4 s, and (L) 55.9 s.
ARTICLE IN PRESSC.-S. <strong>Lin</strong> et al. / Materials Science in Semiconductor Processing 10 (2007) 227–234 2311500The histogram for 1.8 seconds development process1500The histogram for 30.8 seconds development processpixels1000500pixels10005000050100 150 200 250gray scale0050 100 150 200 250gray scalepixels1500100050000The histogram for a 6.3 seconds development process50 100 150 200 250gray scalepixels120010008006004002000The histogram for 35.9 seconds development process0 50 100 150 200 250gray scalepixels1200100080060040020000The histogram for 10.7 seconds development process50 100 150 200 250gray scalepixels120010008006004002000The histogram for 40.2 seconds development process0 50 100 150 200 250gray scalepixels120010008006004002000The histogram for 16.9 seconds development process0 50 100 150 200 250gray scalepixels150010005000The histogram for 45.5 seconds development process0 50 100 150 200 250gray scale1500The histogram for 21.7 seconds development process1500The histogram for 50.4 seconds development processpixels1000500pixels100050000 50 100 150 200 250gray scale00 50 100 150 200 250gray scale1500The histogram for 26.2 seconds development process1500The histogram for 55.9 seconds development processpixles1000500pixles100050000 50 100 150 200 250gray scale00 50 100 150 200 250gray scaleFig. 5. The histogram of images for development times (A) 1.8 s, (B) 6.3 s, (C) 10.7 s, (D) 16.9 s, (E) 21.7 s, (F) 26.2 s, (G) 30.8 s, (H) 35.9 s,(I) 40.2 s, (J) 45.5 s, (K) 50.4 s, and (L) 55.9 s.
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