*Correspondence: heather.patrick@nist.gov Alternative Lithographic Technologies, F.M. Schellenberg, Ed., Proc. SPIE 7271, in press (2009). In situ measurement of annealing-induced line shape evolution in nanoimprinted polymers using scatterometry Heather J. Patrick, 1,2,* Thomas A. Germer, 1 Yifu Ding, 3 Hyun Wook Ro, 1 Lee J. Richter, 1 and Christopher L. Soles 1 1 National Institute of Standards and Technology, Gaithersburg, MD 20899 USA 2 KT Consulting, Inc., Antioch, CA 94509 USA 3 Department of Mechanical Engineering, University of Colorado, Boulder, CO 80309 USA ABSTRACT Thermal embossing nanoimprint lithography (NIL) is an area of continuing interest because it allows direct patterning of nanoscale structures into a wide variety of functional polymer materials. Measuring the shape evolution of nanoimprinted lines during thermal annealing can provide insights into mechanisms of polymer stability and the dynamics of polymer flow. Recently, we have used optical scatterometry to extract the profile of nanoimprinted lines in low- and high-molecular mass polymer gratings during annealing of the gratings at the glass transition temperature. The data are obtained in situ using a spectroscopic ellipsometer and analyzed using a rigorous-coupled-wave scatterometry model. The results obtained from scatterometry are in very good agreement with those measured ex situ by atomic force microscopy and specular x-ray reflectivity, revealing very different decay mechanisms for gratings in low- and high-molecular mass polymers. The role of the se- lection of grating model in determining the uncertainties the grating line profile extracted from scatterometry is also discussed. Keywords: nanoimprint, optical critical dimension, polymers, scatterometry, spectroscopic ellipsometry, stress, rheology 1. INTRODUCTION Nanoimprint lithography (NIL), in which features on a pre-patterned mold are transferred directly into a polymer material, is a rapidly maturing alternative to optical techniques for nanoscale patterning of semiconductors. One method, thermal embossing NIL, can also be used to directly pattern functional polymers, e.g., those that have semiconducting, piezoelectric, or insulating properties. Understanding the stability and decay mechanisms of these as-imprinted struc- tures is crucial to the development of thermal embossing NIL. Prior studies have shown that measuring the shape evolu- tion (reflow) of nanoimprinted lines during thermal annealing can provide important information about the stability of patterns of different molecular masses, the expected impact of mold release temperature on pattern shapes, and the roles of residual stresses and polymer viscosity on pattern stability. 1,2,3,4 Recently, we have been investigating the use of scatterometry to provide in situ, non-destructive measurements of line gratings in nanoimprinted polymers during annealing. 5 In contrast with pattern characterization through cross- section scanning electron microscopy (SEM) or atomic force microscopy (AFM), which are time consuming, require sectioning of the sample (in the case of SEM), and typically require multiple samples annealed for different times to build up a complete picture of the annealing response, scatterometry provides a real-time annealing record from a single sample and, with appropriate model development, can be used to extract line parameters and shape of the lines at any point during the anneal. We will review recent results from scatterometry analysis of gratings measured in situ by spec- troscopic ellipsometry during annealing and show that line parameters obtained from scatterometry are in very good agreement with values obtained using AFM and specular x-ray reflectivity (SXR). Finally, we present results obtained by using three different scatterometry line profile models to analyze a subset of the spectroscopic ellipsometry data, as part of an effort to quantify uncertainties in the line profiles obtained from scatterometry.