Experimental study of numerical optimization for 3-D microstructuring using DMD-based grayscale lithography

Xiaoxu Ma, Yoshiki Kato, Floris Van Kempen, Yoshikazu Hirai*, Toshiyuki Tsuchiya, Fred Van Keulen, Osamu Tabata

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

18 Citations (Scopus)


Digital micromirror device (DMD)-based grayscale lithography is a promising tool for 3-D photolithography of thick photoresists, because this technique provides a patterning solution for free-form 3-D microstructures. Among the numerous process parameters in DMD-based grayscale lithography, the exposure dose pattern corresponding to the grayscale mask pattern, the focal position in the photoresist, and the development time most strongly influence the final profile of the 3-D microstructure. However, finding the best combination of the three process parameters is a difficult and time-consuming task. In this paper, we propose a process optimization method for DMD-based grayscale lithography that is based on the 3-D photolithography simulation and sensitivity analysis. This optimization tool provides not only automatic process optimization for all three process parameters, i.e., the exposure dose pattern, the focal position, and the development time, but also a solution to improve fabrication accuracy for critical features by adopting a variable weight factor. Through a series of experiments, using a 20-μm-thick positive photoresist, the validity and effectiveness of the proposed optimization method and the improvement of the fabrication accuracy were successfully demonstrated. [2015-0055]

Original languageEnglish
Article number7151788
Pages (from-to)1856-1867
JournalIEEE Journal of Microelectromechanical Systems
Issue number6
Publication statusPublished - 2015


  • 3-D microstructuring
  • 3-D photolithography
  • digital micromirror device (DMD)-based grayscale lithography
  • fast marching method
  • lithography simulation
  • optimization
  • thick photoresist


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