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As critical dimensions become smaller, a greater demand is being placed on existing i-line lithographic capability to support 0.35 micrometers technology. One method that is gaining wider acceptance is the use of a top side anti reflective coating (TARC). The effect of the TARC is to reduce the interference effects occurring in the film stack so that critical dimension (CD) variation as a result of topography is minimized. Unfortunately, the TARC provides no improvement with other lithographic responses that define the process window of a resist. Another approach is to use a contrast enhancement material (CEM). It is well known that a CEM can improve the depth of focus and resolution of a given resist system, and it is suspected that it may also possess some of the interference reduction properties of conventional TARCs. The purpose of this work is to investigate how effective the CEM acts as a TARC, and to determine any additional lithographic improvements which will increase the overall 0.35 micrometers process window. Process optimization of the CEM and TARC revealed that similar processing schemes could be used for both materials, but that it was necessary to remove the CEM (w/ a water rinse) prior to post exposure bake (PEB). The bulk photospeed swing ratio of the SPR3000 alone, was compared to SPR3000/Aquatar and SPR3000/CEM. Results showed that the Aquatar reduced the Eo swing ratio by 75%, while the CEM reduced the Eo swing ratio by about 55%. Similar improvements were seen with 0.35 micrometers CD swing ratio data. Exposure latitude and focus latitude (0.35 micrometers lines/spaces) data was generated using the same resist/enhancement schemes mentioned above at thicknesses corresponding to an Emax and Emin. Results of the lithography at each thickness were overlaid to determine the process window. Results showed the Aquatar and CEM processes to provide improved 0.35 micrometers windows, and that using a contrast enhancement material as a TARC is another alternative which can be used to increase the capability of commercially available i-line resists.
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