Elastodynamic Characterization of Imprinted Nanolines
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0924-Z08-31
ELASTODYNAMIC CHARACTERIZATION OF IMPRINTED NANOLINES Ward L. Johnson1, Colm M. Flannery1, Sudook A, Kim1, Roy Geiss1, Paul R. Heyliger2, Chris L. Soles3, Walter Hu4, and Stella W. Pang4 1 Materials Reliability Division, National Institute of Standards and Technology, Boulder, CO, 80305 2 Department of Civil Engineering, Colorado State University, Fort Collins, CO, 80523 3 Polymers Division, National Institute of Standards and Technology, Gaithersburg, MD, 20899 4 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI, 48109
ABSTRACT The advancement of imprint lithography as a method for fabricating nanostructures is impeded by a lack of effective tools for characterizing mechanical properties and geometry at the nanoscale. This paper describes progress in establishing methods for determining elastic moduli and cross sectional dimensions of imprinted nanolines from Brillouin light scattering (BLS) measurements using finite-element (FE) and Farnell-Adler models for the vibrational modes. An array of parallel nanoimprinted lines of polymethyl methacrylate (PMMA) with widths of ~65 nm and heights of ~140 nm served as a model specimen. Several acoustic modes were observed with BLS in the low-gigahertz frequency range, and the forms of the vibrational displacements were identified through correlation with calculations using measured bulk-PMMA moduli and density as input. The acoustic modes include several flexural, Rayleigh-like, and Sezawa-like modes. Fitting of Farnell-Adler calculations to the measured dispersion curves was explored as a means of extracting elastic moduli and nanoline dimensions from the data. Some of the values obtained from this inversion analysis were unrealistic, which suggests that geometric approximations in the model introduce significant systematic errors. In forward calculations, the frequencies determined with the FE method were found to more closely match experimental values, which suggests that this method may be more accurate for inversion analysis. Initial estimates of uncertainties in the FE calculations support this conclusion.
INTRODUCTION Nanoimprint lithography (NIL) has emerged as a leading candidate for relatively lowcost nanoscale patterning of materials. It has attracted particular attention as a method for fabricating patterned polymers with length scales beyond the fundamental limits of conventional photolithography used for integrated circuits. However, numerous technical obstacles must be overcome before NIL reaches the point of broad industrial implementation [1]. These obstacles primarily are associated with the mechanical behavior of imprinted material during stamping, cooling, and removal from the mold. To successfully model and optimize these processes, one must have information on the mechanical properties of the material, which generally is unattainable from conventional techniques because of the length scales involved. Direct
measurements of the elastic moduli of imprinted polymeric nanostructures are especia
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