Etch-free additive lithographic fabrication methods for reflective and transmissive micro-optics

Qiang Fu, Hadi Amata, Wolfgang Heidrich
Optics Express 2021

Figure 1. Additive lithographic fabrication pipeline. (a) Iterative pattern transfer for additive multi-level DOE fabrication. The discarded RIE step in conventional lithography fabrication is replaced by additive sputter deposition and lift-off to form the desired 3D structures. (b) An optional nanoimprint step enables the replication of the multi-level structures from the hard stamp to the product wafer via a soft stamp, and imprinting onto UV curable optical adhesives on the substrate.

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Abstract

With the widespread application of micro-optics in a large range of areas, versatile high quality fabrication methods for diffractive optical elements (DOEs) have always been desired by both the research community and by industry. Traditionally, multi-level DOEs are fabricated by a repetitive combination of photolithography and reactive-ion etching (RIE). The optical phase accuracy and micro-surface quality are severely affected by various etching artifacts, e.g., RIE lag, aspect ratio dependent etching rates, and etching artifacts in the RIE steps. Here we propose an alternative way to fabricate DOEs by additively growing multi-level microstructures onto the substrate. Depth accuracy, surface roughness, uniformity and smoothness are easily controlled to high accuracy by a combination of deposition and lift-off, rather than etching. Uniform depths can be realized for both micrometer and millimeter scale features that are simultaneously present in the designs. The grown media can either be used directly as a reflective DOE, or as a master stamp for nanoimprinting refractive designs. We demonstrate the effectiveness of the fabrication methods with representative reflective and transmissive DOEs for imaging and display applications.



Animation of the fabrication workflow

Presentation at OptiFAB 2021

Our presentation entitled "Additive lithographic fabrication of a Tilt-Gaussian-Vortex mask for focal plane wavefront sensing" was presented at SPIE OptiFAB 2021. Please watch the pre-recorded presentation video in the SPIE digital library.

Papers

OE paper [Fu2021EtchFree.pdf (3.55MB)]
Link [Optics Express]

SPIE paper [Fu2021Additive.pdf (1.0MB)]
link [SPIE OptiFAB 2021]

Citation

  @article{Fu2021EtchFree,
  title={Etch-free additive lithographic fabrication methods for reflective and transmissive micro-optics},
  author={Fu, Qiang and Amata, Hadi and Heidrich, Wolfgang},
  journal={Optics Express},
  volume={29},
  number={22},
  pages={36886--36899},
  year={2021},
  publisher={Optical Society of America}
  }

  @inproceedings{Fu2021Additive,
  title={Additive lithographic fabrication of a {Tilt-Gaussian-Vortex} mask for focal plane wavefront sensing},
  author={Fu, Qiang and Amata, Hadi and Gerard, Benjamin and and Marois Christian and Heidrich, Wolfgang},
  booktitle={OptiFAB 2021},
  volume={11889},
  pages={1188911:1--9},
  year={2021},
  organization={International Society for Optics and Photonics}
  }