KrF photolithography is difficult to attain usable process window for sub-100nm patterning due to the limitation from both the illumination and resist chemistry. For sub-0.15um FLASH process, sub-100nm trench, which is the smallest critical dimension to be resolved, becomes a real challenge to use conventional KrF lithography. REAPS (Resolution Enhance Assisted by Physical Shrinkage) process, utilizing the physical reaction catalyzed by the temperature in the patterned resist, is originally developed to enhance the resolution for contact hole in DRAM process. Instead of direct printing desirable feature using KrF process, REAPS treats the printed pattern by coating a water-soluble polymer upon patterned resist. This applying polymer layer provides a physical drive force to iso-tropically deform the resist patterns through controlled thermal process. Although REAPS process is an effective resolution enhancement technology to extend KrF lithography capability to even smaller dimension, its shrinkage performance and process window heavily depend on accurately temperature control of hot plate. To overcome the drawbacks of high temperature sensitivity of pattern shrinkage and achieve stable process control ability, a study on appropriate temperature setting and multi-step REAPS was carried out, and our results illustrate REAPS is applicable to isolated trench process and a sub-lOOnm trench can be achieved by this approach.
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