Abstract
We describe a simple bilayer photoresist that is particularly well suited for laser lithography at an exposure wavelength of 405 nm on glass substrates, which are often used for the fabrication of binary diffractive optics and computer-generated holograms. The resist consists of a poly-dimethyl glutarimide (PMGI) bottom layer that is used as an antireflection coating between a glass substrate and a positive or negative photoresist. The optical properties of the PMGI layer at 405 nm result in excellent suppression of reflections into the photoresist and good process latitude.
Highlights
Optical systems somtimes require components that are made with photolithography on glass substrates
A binary amplitude hologram can be converted into a binary phase hologram by etching the area of the glass substrate that is not covered by the chromium mask using a reactive ion etching (RIE) process followed by removal of the chromium layer
We revisit this fabrication process for computer-generated holograms (CGHs) and describe an alternative process that is simpler than the established chromium-onglass process, performs better with high numerical aperture (NA) photolithography tools, and offers greater process flexibility
Summary
Optical systems somtimes require components that are made with photolithography on glass substrates. Photomasks for projection or contact lithography are perhaps the most prominent examples. Photomasks are a specialized form of optical elements known as diffractive optics or computer-generated holograms (CGHs), which are fabricated using lithographic patterning technologies. The hologram is fabricated by patterning a chromium layer on a glass substrate.[3,4,5,6,7,8] The result is a binary amplitude hologram with transparent and opaque fringes. A binary amplitude hologram can be converted into a binary phase hologram by etching the area of the glass substrate that is not covered by the chromium mask using a reactive ion etching (RIE) process followed by removal of the chromium layer. We revisit this fabrication process for CGHs and describe an alternative process that is simpler than the established chromium-onglass process, performs better with high numerical aperture (NA) photolithography tools, and offers greater process flexibility
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