Full Paper

Nanoimprint Lithography and the Role of Viscoelasticity in the Generation of Residual Stress in Model Polystyrene Patterns†

  1. Yifu Ding,
  2. Hyun Wook Ro,
  3. Kyle J. Alvine,
  4. Brian C. Okerberg,
  5. Jing Zhou,
  6. Jack F. Douglas,
  7. Alamgir Karim,
  8. Christopher L. Soles*

Article first published online: 10 JUN 2008

DOI: 10.1002/adfm.200701402

Issue

Advanced Functional Materials

Advanced Functional Materials

Volume 18, Issue 12, pages 1854–1862, June 24, 2008

Additional Information

How to Cite

Ding, Y., Ro, H. W., Alvine, K. J., Okerberg, B. C., Zhou, J., Douglas, J. F., Karim, A. and Soles, C. L. (2008), Nanoimprint Lithography and the Role of Viscoelasticity in the Generation of Residual Stress in Model Polystyrene Patterns. Advanced Functional Materials, 18: 1854–1862. doi: 10.1002/adfm.200701402

Author Information

  1. Polymers Division, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899-8541 (USA)

*Polymers Division, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899-8541 (USA).

  1. †

    This work is partially funded by the NIST Office of Microelectronic Programs. K. J. Alvine and B. C. Okerberg acknowledge the support of the National Research Council NIST Postdoctoral Fellowship Program. We acknowledge the nanofabrication laboratory of the Center for Nanoscale Science and Technology (CNST) at NIST for providing facilities for the nanoimprint process. This work is an official contribution of the National Institute of Standards and Technology; not subject to copyright in the United States. Certain commercial materials and equipment are identified in this paper in order to specify adequately the experimental procedure. In no case does such identification imply recommendation by the National Institute of Standards and Technology nor does it imply that the material or equipment identified is necessarily the best available for this purpose. The error bars presented throughout this manuscript indicate the relative standard uncertainty of the measurement.

Publication History

  1. Issue published online: 18 JUN 2008
  2. Article first published online: 10 JUN 2008
  3. Manuscript Revised: 29 JAN 2008
  4. Manuscript Received: 30 NOV 2007

Funded by

  • NIST Office of Microelectronic Programs. K. J. Alvine
  • B. C. Okerberg
  • National Research Council NIST Postdoctoral Fellowship Program

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Keywords:

  • nanoimprint lithography;
  • patterning;
  • polystyrene;
  • viscoelasticity

Graphical Abstract

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Relaxation time map of various molecular mass polystyrene (PS) is used in thermal embossing nanoimprint lithography (NIL). With the proper selections of the imprinting temperature and time, process-induced stress can be controlled for a given PS. This effect can be directly measured by tracking the rate of the imprinted pattern leveling under thermal annealing.

Abstract

Understanding polymer deformation during the nanoimprinting process is key to achieving robust polymer nanostructures. Information regarding this process can be extracted from monitoring the decay of the imprinted polymer patterns during thermal annealing. In the present work, the effect of both the molar mass and the imprinting temperature on the pattern decay behavior during thermal annealing is investigated. Previously, it was found that the decay rate is fastest for a highly entangled polymer due to the elastic recovery caused by the residual stress created during the imprinting process. The present paper demonstrates that this residual stress level can be modified through control of the imprinting temperature. These results are contrasted with those for an unentangled polymer over a similar range of imprinting temperatures, where it is found that the pattern decay is controlled by simple Newtonian flow. In particular, the pattern decay is well described by surface-tension-driven viscous flow, and no imprinting-temperature effect is observed during thermal annealing. It is shown that the stability of the film against pattern decay can be optimized for moderately entangled polymer films. This effect is attributed to the competition between the effect of increased viscosity with increasing molar mass and increased residual stresses with entanglements. These observations provide guidance for the optimization of imprinting process in terms of selection of molar mass and processing temperatures.

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