Physical characterization of nanoimprinted polymer nanostructures using visible light angular scatterometry

Abstract

Visible light angular scatterometry is applied to characterize the geometry and physical properties of sub-100-nm-wide polymer gratings fabricated using nanoimprint lithography and electron beam lithography. Measurement sensitivities to small variations in linewidth and slope angle were evaluated theoretically, which suggests that TM polarized incident light offers improved sensitivity for the measurements of sub-45-nm critical dimensions ͑CDs͒. A variable angle scatterometer using a red laser is built, and measurement results of various polymethylmethacrylate ͑PMMA͒ gratings with sub-100-nm CDs reveals good accuracies and fit well to the scanning electron microscopy ͑SEM͒ measurements. In addition to geometry and dimension measurements, new functionality is implemented in the modeling to characterize polymer residue thickness, polymer flow dynamics, and evidence of stress in the nanoimprinted polymer gratings. Scatterometry is also applied to detect possible undercut line profiles resulting from electron beam lithography. The results promote using this low-cost and noninvasive technique to characterize polymer nanostructures as well as understand and control the underlying lithographic processes. © 2008 Society of Photo-Optical Instrumentation Engineers.

Scatterometry for in situ measurement of pattern reflow in nanoimprinted polymers

“…Recent studies have shown that measuring the shape evolution ͑reflow͒ of nanoimprinted lines during thermal annealing can provide important information about the levels of residual stress induced by NIL processing, the roles of polymer viscosity and rheology in creating those stresses, and their ultimate impact on the stability of patterns of different molecular masses. [1][2][3][4] In this work, we use optical scatterometry to provide in situ, nondestructive measurements of the reflow of thermal embossed NIL line gratings in polystyrene. In contrast with the more widely used pattern characterization techniques of cross-sectional scanning electron microscopy ͑SEM͒ and atomic force microscopy ͑AFM͒, which are time consuming, require sectioning of the sample ͑in the case of SEM͒, and typically require multiple samples quenched following annealing for different times to build up a complete picture of the reflow, scatterometry provides a continuous real-time annealing record from a single sample.…”

“…5 Scatterometry also provides a table-top alternative to line profiling by critical dimension small-angle x-ray scattering ͑CD-SAXS͒, 6 which requires an intense, synchrotron-based x-ray source. While scatterometry has previously been applied to the study of nanoimprinted polymers, 3,4,7 the current work is the first successful demonstration of its use for quantifying line profiles in situ during reflow and provides new insight into the profile evolution of gratings with high and low molecular masses.…”

Non-destructive multi-parameter investigation of nanoimprinted structures

“…For example, the surface can be measured in three dimensions using an atomic force microscope (AFM) [6] or a white light interferometer (WLI) [7]. Scatterometry [8] or diffractive tests [9] can be used to assess optical properties and make statements about shape fidelity. Each measurement technology has its advantages and disadvantages, which can complement the non-destructive evaluation of the NIL process.…”