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We have developed a method for producing alignment marks on a wafer using exposed photoresist. Alignment to the exposed pattern is possible without having to develop out the pattern, provided that there is enough contrast between the exposed and unexposed areas. The exposed pattern was easily found for alignment using the He–Ne laser alignment system in our stepper. Although the contrast between the exposed and unexposed resist was rather faint to the human eye, the contrast was greatly improved using a commercially available contrast enhancement layer, so this method can be used in contact lithography where multiple mask levels must be exposed prior to development. The ability to align to the exposed pattern prior to development is especially useful in stepper-based lithography. For example, wafers may be aligned using the stepper for multiple mask exposures or for multilevel resist schemes prior to pattern development. In addition, very thick resist can be exposed using multiple exposures and changing the depth of focus. © 1999 American Vacuum Society.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures (Volume:17 , Issue: 3 )
Date of Publication: May 1999