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Inorganic photoresist

№14 Department of photochemical phenomena in semiconductors
   Ivan Indutnyy

Areas of Application: Optical and laser lithography, holography, production of diffractive optics (diffraction gratings, Fresnel lenses and arrays of lenses, etc.), nano-optical devices (subwavelength gratings, with grating period up to 100 nm, photonic crystals),  master-discs  and rainbow holograms.

 Proposed inorganic photoresist based on thin films of chalcogenide glasses deposited onto substrate by thermal vacuum evaporation. It is known, that chemical properties of such layers can be changed by light or electron-beam irradiation. Using proprietary etching solutions we can obtain positive or negative resist effect: rate of irradiated resist dissolution essentially higher or lower, than non-irradiated one.
    The effects of lightsensitivity of chalcogenide thin films and chalcogenide-Ag structures were discovered in V.E. Lashkaryov Institute of Semiconductor Physics (ISP) NAS of Ukraine. Investigating mechanism of photostimulated transformations in such layers made it possible to elaborate thin-film photosensitive media with the number of unique characteristics.
Also worked out are some technologies of these photosensitive layers (inorganic resists) application in photolithography, for information storage, in diffractive optics (diffraction gratings, Fresnel lenses and arrays of lenses), for direct mastering of optical discs and so on. Such resists are very promising for interferential pattern registration and relief-phase holograms formation.

Main technical features of these inorganic resist:
Resolution capability     -         intrinsic resolution of chalcogenide layers – 1nm
Spectral sensitivity         -          UV, visible, IR, electron, ion beam
Sensitivity for recording of :
    1) holographic optical elements and contact photolithography   - 5 – 50 cm²/J
    2) laser lithography                                                                -  300 cm²/J  
Method of deposition                         -                                      vacuum deposition
Postexposure treatment:
Chalcogenide layers                           -                                         wet etching
Chalcogenide-Ag  structure               -                                        wet and dry etching

Chalcogenide photoresist also characterized by thermal stability (up to 400^oC), absence of shrinkage under post-exposure processing, high mechanical strength and chemical durability and can be used on both planar and non-planar substrates. Furthermore the use of inorganic chalcogenide photoresists will be advantageous for the technological processes, because chalcogenide films can be deposited very homogeneously and inorganic photoresists can be applied with the same technological processes as functional layers in ICs. Additionally, such photoresists possess a very high refractive index, ranging from 2.3 to 3.0 and even higher, they are stable, do not need any thermal treatment and are transparent in the infrared from 600 nm up to 12-15 μm. These properties allowed to apply chalcogenide photoresists in fabrication of effective diffraction gratings, IR microlens arrays, microlenses for optical fibers together with two- and three-dimensional photonic crystals.
The technology is patented, tested, available for demonstration. Prototype samples of  diffraction gratings (with spatial frequency from 600 up to 6000 mm -1), masters of rainbow holograms and optical disks are made and  tested.
Prototype sample of  diffraction grating.