Grayscale Lithography

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Creating Topographies on the Microscale

Grayscale lithography is used for the creation of 2.5D micro- and nanostructures with varying height gradients, enabling the fabrication of surfaces with complex topographies.

In direct write laser lithography, the CAD virtual landscape is mapped to the system’s gray values where each value corresponds to an exposure intensity level. During the exposure this laser intensity is modulated on a pixel-by-pixel level, thereby controlling the exposure depth for each individual pixel. Up to 1,000 gray levels are accessible in a single exposure step, offering the highest vertical resolution without critical alignments. The resulting exposure is then processed by methods such as RIE or electroplating to create the 2.5D topography. The grayscale exposure concept is also scalable, with systems capable of patterning substrates up to 800 mm x 800 mm in size. Common challenging issues, such as stitching effects and non-linearities, are solved with advanced patterning techniques such as multi-pass exposures and optimized gray value distributions.

A key application area for grayscale lithography is the creation of micro-optical elements such as Fresnel lenses, blazed gratings micro-lenses and micro-lens arrays, all of which are key components in modern day micro-optics. Grayscale lithography can also be used in the creation of MEMS, MOEMS, microfluidic devices, and textured surfaces.

Heidelberg Instruments offers numerous grayscale packages, depending on the required performance level for the application.

Grayscale patterning is also possible using thermal scanning probe lithography with our NanoFrazor® systems. The NanoFrazor® Explore and NanoFrazor® Scholar use an ultra-sharp heated silicon tip to pattern high resolution 2 and 2.5D structures by sublimating a thermal sensitive resist. The structures can then be transferred into almost any other material by standard methods. This technique of lithography requires no wet development and causes no damage to the substrate. Lateral resolutions of below 25 nm are routinely achieved with these systems. Additionally, the closed-loop lithography method enables a vertical resolution of less than 1 nm. Application areas for the NanoFrazor® systems include CGH’s, 3D multimode waveguides, and grating couplers, 3D phase plates, and many other areas that require 2.5D nanostructured surfaces.

Related images

SEM image of a Multi level diffractive flat lens (MDL), maximum strucure height: 2 µm Reference: M. Meem, S. Banerji, A, Majumder, C. Pies, T. Oberbiermann, B. Sensale-Rodriguez & R. Menon, “Large-area, high-NA multi-level diffractive lens via inverse design,” Optica 7(3) 252-253 (2020)
SEM image of a Multi level diffractive flat lens (MDL), maximum strucure height: 2 µm Reference: M. Meem, S. Banerji, A, Majumder, C. Pies, T. Oberbiermann, B. Sensale-Rodriguez & R. Menon, “Large-area, high-NA multi-level diffractive lens via inverse design,” Optica 7(3) 252-253 (2020)
Confocal microscope image of a Multi level diffractive flat lens (MDL), strucure height: 2 µm Reference: M. Meem, S. Banerji, A, Majumder, C. Pies, T. Oberbiermann, B. Sensale-Rodriguez & R. Menon, “Large-area, high-NA multi-level diffractive lens via inverse design,” Optica 7(3) 252-253 (2020)
Confocal microscope image of a Multi level diffractive flat lens (MDL), strucure height: 2 µm Reference: M. Meem, S. Banerji, A, Majumder, C. Pies, T. Oberbiermann, B. Sensale-Rodriguez & R. Menon, “Large-area, high-NA multi-level diffractive lens via inverse design,” Optica 7(3) 252-253 (2020)
A fresnel lenses is a volume- and mass-reduced type of micro-optic
Micrograph showing the image of a fresnel lens (diameter 506 µm, height 10 µm).
Confocal microscope image of a convex fresnel lens.
Confocal microscope image of a convex fresnel lens (diameter 506 µm, height 10 µm).
Confocal microscope image of a micro lens array in a honeycomb arrangement.
Confocal microscope image of a micro lens array in a honeycomb arrangement (hexagon radius 10 µm, height 2.7 µm).
Confocal microscope image of a pyramid (pitch 47 µm, height 5.8 µm).
Confocal microscope image of a pyramid (pitch 47 µm, height 5.8 µm).
Confocal microscope image of the central part of a concave fresnel lens.
Confocal microscope image of the central part of a concave fresnel lens (diameter of the central part: 120 µm, height 11 µm).
SEM image of a fabricated Fresnel axicon, a conical lens. The resist thickness is 100 µm, the depth of the structure approximately 70 µm, the width of each fresnel ring is 79 µm. (Courtesy of Heidelberg Instruments)
SEM image of a fabricated Fresnel axicon, a conical lens. The resist thickness is 100 µm, the depth of the structure approximately 70 µm, the width of each fresnel ring is 79 µm. (Courtesy of Heidelberg Instruments)
SEM image of microfabricated fish relief structures using grayscale lithography via DWL 66+. The structures were exposed with Write Mode III and CI-over 10 stitching reduction. The maximum height is 63 µm. (Courtesy of Heidelberg Instruments)
SEM image of microfabricated fish relief structures using grayscale lithography via DWL 66+. The structures were exposed with Write Mode III and CI-over 10 stitching reduction. The maximum height is 63 µm. (Courtesy of Heidelberg Instruments)
Retro-reflector structure was patterned using DWL66+. 2.5D micro-structures designed to control reflection or diffusion of light are used in light sources and illumination, like backlight units in LCD displays. (Courtesy of karmic.ch)
Retro-reflector structure was patterned using DWL66+. 2.5D micro-structures designed to control reflection or diffusion of light are used in light sources and illumination, like backlight units in LCD displays. (Courtesy of karmic.ch)
“Moth eye” compound microlenses array replicated with nanoimprint technology shows DLW66+ capabilities for 2.5D patterning. Texturing surfaces using grayscale lithography can control and modify their hydrophobicity, friction, haptics, and adhesion. (Courtesy of ShenZhen Nahum-Eli Optical Technology Inc.)
“Moth eye” compound microlenses array replicated with nanoimprint technology shows DLW66+ capabilities for 2.5D patterning. Texturing surfaces using grayscale lithography can control and modify their hydrophobicity, friction, haptics, and adhesion. (Courtesy of ShenZhen Nahum-Eli Optical Technology Inc.)
SEM micrograph of a pyramid array obtained by grayscale lithography.
SEM micrograph of a pyramid array obtained by grayscale lithography.
With Heidelberg Instruments Grayscale lithography enables complex structures like this Fresnel Vortex Axicon.
Heidelberg Instruments Grayscale Lithography enables this Fresnel Vortex Axicon with angles from 22° to 45° with a height of 10 µm.
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Suitable Systems

DWL 66+ – a laser lithography tool for R&D in microelectronics, MEMS, microfluidics and more with Grayscale exposure mode

DWL 66+

  • Direct Write Laser Lithography System

Our most versatile system for research and prototyping with variable resolution and wide selection of options.

DWL 2000 GS and DWL 4000 GS industrial-level grayscale lithography for masks and wafers for IC, MEMS, micro-optic, and more

DWL 2000 GS / DWL 4000 GS

  • Direct Write Laser Lithography System

The most advanced industrial grayscale lithography tool on the market.

NanoFrazor Scholar – the academic nanofabrication tool for nanopatterning of quantum devices, grayscale photonics and more

NanoFrazor® Scholar

  • Thermal Scanning Probe Lithography System

Table-top thermal scanning probe lithography system with in-situ AFM imaging, compact and compatible with glovebox.

NanoFrazor Explore – Thermal Scanning Probe lithography with direct laser sublimation and grayscale patterning capability

NanoFrazor® Explore

  • Thermal Scanning Probe Lithography System

Thermal scanning probe lithography tool with a direct laser sublimation and grayscale modules, excellent alternative to e-beam lithography tools.

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