Sub 100-nm defect classification and analysis on extreme ultraviolet (EUV) mask blanks and substrates

Abstract

The most critical challenges in EUVL include the manufacturing of defect-free EUVL substrates, blanks, and masks. Developing capability in the areas of sub-100nm defect metrology, characterization, and analysis provides the key path for defect root-cause analysis in the defects elimination roadmap. We have demonstrated successful application of integrated surface analytical techniques, including AES (Auger Electron Spectroscopy), EDX (Electron Dispersion X-ray Spectrometry), SEM, and AFM to review, analyze, and characterize defects on EUVL multilayer blanks and substrates, following the optical defect inspection process by the Lasertec M1350, which does defect scanning, mapping, image review, and fiducial marking. Small defects, 40nm wide and 10nm tall, have been analyzed in morphology as well as in composition. In order to overcome the electron beam charging problem on the substrate materials during analysis, we applied marking and metal film coating on the LTEM substrates and acquired composition data. Defect metrology data serve as finger prints of the EUV blank fabrication process. We have discovered that the majority of the multilayer defects today are embedded bumps, pinholes, and organic materials that originated from the LTEM substrates. Composition data of the defects also suggested that process chemicals and human handling of process are the culprit of these defects. Therefore defect reduction efforts should be focused on the processes or procedures which take place from the glass finishing process to the very first layers of silicon molybdenum deposition.