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

Abstract

ABSTRACT The recent introduction of chromeless-phase lithography (CPL) has provided lithographers with a powerful wavefrontengineering tool for patterning at k 1 values below 0.3. Reliable image formation at such extreme k 1 requires a well-characterized CPL photomask. However, the limitations of available optical inspection tools have made the test andmeasurement of CPL photomasks a difficult task. In this paper, we describe preliminary imaging and phase metrologyresults on a leading-edge CPL reticle using an high-resolution 193-nm microscope. This microscope features a solid-state 5-kHz repetition rate, 193.4 nm actinic light source in conjunction with high-numerical-aperture (0.75 NA) optics toprovide 200X magnification, 150-nm Rayleigh resolution and 35-nm pixel size over a 30-micron image field. Arecently-developed phase metrology architecture facilitates optical path difference (OPD) measurements of isolated ordense features on a sub-200-nm spatial scale. We discuss the phase measurement process and present images andcorresponding OPD measurements of line and contact structures on an ArF CPL reticle that is designed mainly for the 65nm technology node. We compare these OPD measurements with predictions based on surface nano-profilometer (SNP)step-height measurements of the same feature regions.Keywords : phase metrology, CPL, actinic, ArF, photomask, phase shift mask