Proceedings Article | 30 September 2009
KEYWORDS: Photomasks, Extreme ultraviolet lithography, Electron beam lithography, Extreme ultraviolet, Semiconducting wafers, Optical alignment, Inspection, Defect inspection, Metrology, Error analysis
Fabricating defect-free extreme ultraviolet lithography (EUVL) multi-layer (ML) mask blanks presents a big challenge in
EUVL technology. ML defect sources primarily come from substrate defects and ML deposition adders. Defect
reduction, therefore, needs to address many development aspects, such as substrate material, substrate polishing,
substrate cleaning, blank handling, and ML deposition. High investment cost and potential low blank yield can quickly
drive up EUVL cost of ownership. However, allowing a few defects on the ML blank can improve the blank yield
drastically. Utilizing such defect-blanks through defect mitigation schemes has been proposed. It includes directly
repairing small ML phase and amplitude defects, mask absorber pattern proximity repair, and using absorber pattern to
cover the ML defects. It includes directly repairing small ML phase and amplitude defects,1-2 repairing mask absorber
pattern to compensate the effect of an adjacent ML defect,3 and using absorber pattern to cover the ML defects.4 In each
case, the ML defects will first need to be identified and located during the ML blank defect inspection. To precisely
locate the ML defects on the blank, fiducial marks on the ML blank are needed for mask alignment and defect location
identification.
In this paper, we will present the details of the ML defect mitigation process flow, i.e., using absorber pattern to cover
the ML defects, and the corresponding experimental validation of this mitigation flow. We will also discuss the fiducial
marking scheme, its application in the defect mitigation flow, the error budget of ML defect mitigation, such as defect
position measurement error, fiducial mask position error, e-beam alignment errors, etc.
