Relation between Local Composition, Chemical Environment and Phase Shift Behavior in Cr-Based Oxycarbonitride Thin Films
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Relation between Local Composition, Chemical Environment and Phase Shift Behavior in Cr-Based Oxycarbonitride Thin Films J.R. Smith*, P.C.J. Graat+, D.A. Bonnell*, R.H. French† *Dept. of Materials Science and Engineering University of Pennsylvania, MSE + Max Planck Institute of Metals Research, Stuttgart, Germany † E.I. DuPont de Nemours, Inc. ABSTRACT: The latest deep ultra-violet (DUV) photomask technology requires macroscopic properties such as optical transmission, reflectance, and chemical reactivity to be precisely controlled. Therefore, a fundamental understanding of the relationship between atomic bonding and nanometer scale property variation is required. Thin films of Cr-OC-N are compositionally graded to produce specific attenuation and phase shift of optical radiation. A combination of techniques was used to relate the local atomic bonding to macroscopic properties. Sputtered neutral mass spectroscopy was used to resolve local composition, and variable angle spectroscopic ellipsometry was used to determine local optical properties (on nm scale) that are then related to local composition. Core level shifts in X-ray photoelectron spectroscopy characterize changes in the Cr environment associated with changes in composition. A model is suggested in which bonding at the atomic level is controlled within different 10-100 nm sized regions which can be combined to produce arbitrary optical properties. INTRODUCTION The minimum feature size in state of the art integrated circuitry steadily decreases with time. Techniques of lithographic production need to evolve to meet this demand. The most conceptually simple method is to decrease the wavelength of the incident radiation used in patterning. In recent years, patterning wavelength has decreased with feature size from 488 nm, 365 nm, 248 nm to 157 nm. In traditional binary image mask lithography, incident wavelength limits minimum feature size due to diffraction broadening. Phase-shifting photolithography effectively combats this problem. Phase shifting photomasks allow the possibility of “sub-resolution” lithography - 157 nm radiation can be used to print features as small as 80 nm with phase shifting photomasks. Optical lithography might also prove useful in new fabrication schemes, for example in conjunction with self assembly in the patterning of organic materials. This process requires substantial wavelength flexibility. Solutions for phase shifting/wave guide technology developed for traditional optical lithography will facilitate engineering on the nanometer scale. Controlling phase shift and transmission at a variety of wavelengths is currently done empirically. Understanding the fundamental relationship between bonding and optical properties in phase shifting photomask films would yield a strategy for developing new masks for emerging nanofabrication needs. This is the goal of the present work using a combination of XPS, EELS, SNMS and ellipsometric results on production-grade CrOCN phase-shifting photomask films designed for 180° phase shift and 5-10% tr
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