Using photo-activated localization microscopy (PALM) for imaging fluorophore-doped photoresists

Photoresists play a key role in the photolithographic process being necessary to print the structure layout of dies of microchips. Following Moore’s law leads to ever smaller assemblies reaching the single-digit nanometer range. Typical methods for quality assurance are scatterometry and atomic force microscopy facing challenges and disadvantages. Since overcoming the Abbe limit via superresolution techniques fluorescence microscopy can be another approach. This article describes the measurement analyses done with PALM/STORM on lithographical produced samples of positive resist doped with Atto 565. Lines with 200 nm thickness and equal spacing were studied. Thereby, ThunderSTORM provided better results than QuickPALM for data analysis. For the first experiment, using a permanently switched on 405 nm laser beam with low intensity shows the best resolution results. A rotating lambda half-wave plate in the second experiment leads to a slight increase of data quality. Further studies combining these two approaches will be carried out.