Grayscale Lithography

In addition to classic binary lithography, i.e. the generation of 2D structures in photoresist, Fraunhofer ENAS also has the option of 2.5D and 3D structuring. The generation of such 2.5D and 3D structures is achieved by means of grayscale lithography. By using low-contrast photoresists specially adapted for this purpose, different height levels can be generated by varying the dose. In this context, each variation in exposure intensity represents one gray level.

In this way, it is possible to create structures that are not possible with conventional lithography, which are of great interest to the industry. For example, lens arrays can be created without reflow processes, also pyramids, slanted gratings, pixel arrays and micro needles are possible.

There are basically two ways to generate grayscale structures, direct writing / maskless processes and processes with a mask. Both options are available at Fraunhofer ENAS.

Electron beam lithography offers the possibility to create flexible and maskless 2.5D and 3D grayscale structures. These can be used, for example, for the production of imprint masters for nano-imprint lithography.

A higher throughput is achieved by using i-line projection lithography. Special grayscale masks are used. Here, the transmission on the mask can be controlled via “pixelated sub-resolution structures”. The advantage is, that 2.5D and 3D exposures are also possible with existing i-line tools without the need of purchasing new equipment.