Grayscale Lithography

Creating 3D Topographies on the microscale

Grayscale lithography is used to create three-dimensional micro- and nanostructures with height gra­dients, enabling the fabrication of textured surfaces with micro- and nanotopographies.

In laser lithography, the CAD virtual landscape is mapped to the system’s gray values where each value corresponds to an exposure intensity level. During exposure, the laser intensity is modulated pixel by pixel, thereby precisely controlling the exposure depth. Up to 1000 exposure gray levels are accessible in a single exposure step, offering highest vertical resolution without critical alignments. The resulting exposed substrate is processed by methods such as reactive ion etching or electroplating to create a 3D topography. The exposure concept is scaleable up to a substrate size of 1.4  x 1.4 m. Challenging issues posed by Grayscale lithography such as stitching effects or non-linearities are solved by advanced techniques such as multi-pass-exposures and optimized gray value distributions, respectively.

A key application area of Grayscale lithography are micro-optical elements such as Fresnel lenses and blazed gratings, micro­lenses and microlens arrays, all of which are key components in modern-day micro-optics. Grayscale lithography is also used in the creation of MEMS, MOEMS, microfluidics, and textured surfaces. Grayscale lithography packages are available in several performance levels from Standard to Professional. Our Grayscale “specialists” are the systems in the DWL series.

Grayscale thermal scanning probe lithography (t-SPL) with the NanoFrazor Explore and Scholar systems uses ultra-sharp heated silicon tips to pattern high-re­solution 3D structures directly by evaporating thermally sensitive resist. The structures can be transferred into almost any other materials by standard methods. The technique requires no wet development and causes no damage to the substrate. Lateral resolution of below 25 nm is routinely achieved. Closed-loop lithography enables a vertical resolution of less than 1 nm. Applications of t-SPM include nanophotonics, for example computer generated holograms, 3-D multimode waveguides, or grating couplers. Other applications include nanofluidic devices, components for electron optics such as 3D-phase plates, and any other area that requires 3D nanostructured surfaces.

Grayscale Microstructures

 

Blazed Gratings

A diffraction grating optimized for efficiency at a particular wavelength and diffraction order shows an example of a typical Micro Optics application. Both the angle of the sawtooth-like profile and the groove spacing are tuned to match the specific application requirements. Blazed gratings are key components of many optical instruments, such as monochromators and spectrometers used in sensors, communication systems and other tools.
Courtesy of IGI

Diffusers and reflectors

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

Compound micro- and nanostructures

“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.

Fresnel lenses

Fresnel micro-lenses are still a crucial component in today’s micro-optics and opto-electronics. Originally invented to reduce mass and volume of lenses used in lighthouses, Fresnel micro-lenses manufactured by grayscale direct-write lithography are used in mobile devices, enabling ultra-light and compact powerful cameras that fit in our pockets.
Courtesy of HIMT

Grayscale Nanostructures

 

Photonic molecule

Twin Gaussian profiles with varying distance ∆x written in PPA and etched into SiO2, to be stacked in distributed Bragg reflector. Cross-sections show Gaussian profiles for different ∆x, which controls the coupling strength between the cavities and the resulting photonic molecule. Precise Gaussian profile is patterned using the NanoFrazor and the closed-loop lithography approach.
Courtesy of Armin Knoll at IBM Zurich

Brownian motors-based nanoparticle sorting device

Nanofluidic ratchets fabricated with single-nanometer accuracy by NanoFrazor patterning. A nanofluidic device with a precisely engineered 3D topography harnesses Brownian motion to separate particles with down to 1nm size difference by guiding them in opposite directions.
Courtesy of IBM Research, Publications in Science and PRL 2018

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