Defect Analysis in Thermal Nanoimprint LithographyOverviewThermal NILFracture IssuesHot Pressing StepCooling StepRelease StepRevised ProcessesConclusionsQuestions?Defect Analysis in Thermal Nanoimprint LithographyYoshihiko Hirai, Satoshi Yoshida, and Nobuyuki TakagiJournal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, Vol. 21, No. 6, pp. 2765–2770, November 2003Presentation by Chris HannemannOverviewThermal nanoimprint lithography processStep-by-step FEA stress/strain simulationsExperiments/proposed process improvementsConclusionsThermal NILThermoplastic polymer heated above TgMold pressed and heldTemperature dropped below Tg to set polymerPolymer ‘released’ from moldFracture IssuesFracture defects occur during cooling (different thermal expansion rates) and mold releaseIncreased friction force in high aspect ratio features increases rate of fractureHot Pressing StepPolymer treated as rubber elastic bodyPolymer ‘stretched’ into cavity, though stress spreads easily due to fluidity of polymer above TgCooling StepStress and strain concentrations near corner of featureRelease StepPrincipal stress distribution during release stepFriction force pulls polymer upwardsRevised Processes Conventional Revised AdvancedConclusionsSimulations assert that stress concentrations near corner of the pattern are formed during the cooling process and from pressure applied below TgReleasing pressure below Tg and slowing the cooling process help mitigate fracture
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