High-resolution actinic imaging and phase metrology of 193 nm CPLTM reticles

The recent introduction of chromeless-phase lithography (CPL) has provided lithographers with a powerful wavefront engineering tool for patterning at k1 values below 0.3. Reliable image formation at such extreme k1 requires a wellcharacterized CPL photomask. However, the limitations of available optical inspection tools have made the test and measurement of CPL photomasks a difficult task. In this paper, we describe preliminary imaging and phase metrology results on a leading-edge CPL reticle using an high-resolution 193-nm microscope. This microscope features a solidstate 5-kHz repetition rate, 193.4 nm actinic light source in conjunction with high-numerical-aperture (0.75 NA) optics to provide 200X magnification, 150-nm Rayleigh resolution and 35-nm pixel size over a 30-micron image field. A recently-developed phase metrology architecture facilitates optical path difference (OPD) measurements of isolated or dense features on a sub-200-nm spatial scale. We discuss the phase measurement process and present images and corresponding OPD measurements of line and contact structures on an ArF CPL reticle that is designed mainly for the 65 nm technology node. We compare these OPD measurements with predictions based on surface nano-profilometer (SNP) step-height measurements of the same feature regions.