"HighFive" grayscale lithography for greater flexibility in the production of freeform micro-optics

The faster and easier production of free-form micro-optics in larger quantities - that is the goal of "HighFive", a series of highly dynamic grayscale lithography systems. In close cooperation with industry, the next generation system "HighFive-C" was developed at Fraunhofer IOF.

"HighFive" allows the mass production of micro-optical, microfluidic as well as micromechanical components and integrated structures and realizes a dynamic workflow. For this purpose, the system combines grayscale lithography with a digital photomask and a nanometer-precise positioning system.

Among other applications, the components produced with the "HighFive" system are used in special lighting systems for the automotive industry, in lightweight sensor systems, in customized room lighting units, as well as in "lab on a chip" systems or in integrated miniaturized optical systems such as virtual reality (VR) or augmented reality (AR) glasses.

How "HighFive" works

In grayscale lithography, a high-power UV LED illuminates a digital microdisplay. The pattern that is then generated on the display is projected onto a wafer glazed with gray-tone photoresist, resulting in the formation of gradual surface structures of up to 100 μm PV.

The "HighFive" line steppers at Fraunhofer IOF can pattern substrates up to 300 mm (12 inches) and are prepared for wafers up to 450 mm (18 inches). Increasing the size of wafer substrates and the number of optical chips per wafer leads to a reduction in manufacturing costs and thus favors mass production.

More flexibility and higher throughput than conventional lithography processes

In contrast to other photolithographic processes, such as laser beam lithography or electron beam lithography, "HighFive" is characterized by high flexibility and high throughput.

This is made possible by adjusting the z dimension, which is not taken into account within classical lithography, where binary structures are primarily used. The gradients in the illumination pattern thus lead to an arbitrary surface structure in the applied photoresist on the wafer. Gradual adjustment of the magnification allows the processing time and resolution to be tuned to individual application areas.

This makes the "HighFive" grayscale lithography system an extremely flexible process that enables the generation of gradual surface profiles and high-precision microstructures, thus creating individual solutions for refractive and diffractive optical structures.

Researchers at Fraunhofer IOF are now focusing on further development of the "HighFive" system, including increasing the resolution below 600 nm, processing highly curved substrates by introducing additional degrees of freedom, and shortening the process time by applying advanced writing strategies.