On the Sensitivity Improvement and Cross-correlation Methodology for Confocal EUV Mask Blank Defect Inspection Tool Fleet

摘要

A multibeam confocal inspection (MCI) beta-tool for mask blank defect detection has been developed and widely adopted at several organizations involved in the research and development of low-defect extreme ultraviolet (EUV) mask blanks. There are two important objectives of this tool development project: (1) ensuring that all printable multilayer and substrate defects are detectable at the half-pitch 45-nm technology node and beyond and (2) enabling a metrology standard for acceptance or rejection of mask blanks before further processing such as deposition and patterning. This paper documents the technical challenges and the latest best known methods developed to (1) improve the detection sensitivity of the current MCI tool before the next-generation tool arrives and (2) quantify the detection sensitivity differences and correlate the measurement results of the same mask blank from different MCI tools. Several options are discussed and found to be effective to increase sensitivity. Tool differences are discussed and a calibration standard based on a tool detection model and a confocal imaging model is proposed. This work will result in one of the key methodologies required to ensure the yield of EUV lithography.