AIMER™: full reticle area, scanner-effective EUV mapping reflectometry

Abstract

EUV-Lithography is preparing for high volume manufacturing. For actinic qualification of components for EUVL like mask blanks, masks, pellicles or optics, spectral resolved metrology (e.g. reflectometry) is frequently applied. With the EUV-AIME effective inband mapping reflectometry we demonstrated a proprietary new concept for full area qualification of mask blanks or masks. While spectral reflectance measurements provide unweighted information on peak reflectance (Rmax), central wavelength of the reflection curves (CWL50) and bandwidth (FWHM), AIMER combines those to an effective figure of merit “as effectively seen by the EUVL scanner”. Short measurement times are achieved because a single acquisition measures about 25*15 mm2 in less than 5 seconds. A full (152 mm)2 reticle map is acquired in less than one hour, including sample load and unload. AIMER provides intrinsic spatial resolution of (20μm)2, delivering sensitivity to larger defects or allowing for finding marks or small metrology pads on structured EUV masks. When compared to the typical 1 mm2 spot measured in the spectral mode, AIMER excels in higher number of photons collected and such lower shot noise limits in reproducibility.