The positive photoresist mr P 22G was developed for greyscale lithography in ultra-thick resist films. The resist enables film thicknesses of 115–140 µm in a single coating step, with double coating up to 200 µm. Due to its low residual absorption after exposure, greyscale patterns up to ~180 µm deep can be produced with a stable operational greyscale working range of ~140 µm.

Exposure wavelengths of 330–420 nm are suitable. Direct write lithography (DWL) is recommended for greyscale patterning. Nearly pixel-free greyscale masks (e.g. HEBS glass based) can also be used.

The 2.5D master structures produced in this way are transferred to materials for permanent use, e.g. by thermal moulding with PDMS and subsequent UV moulding into OrmoComp® or OrmoClear®FX or metallisation, electroplating and replication into OrmoComp® or other suitable materials.

Main applications of the >100 µm deep greyscale master structures are in micro-optics, particularly in free-form optical structures such as lenses, prisms and mirrors for beam shaping and steering. In microfluidics, masters for deep and very deep patterns could also be produced for ‘organ on a chip’ or ‘tumour on a chip’ systems – for drug testing without animal testing.

As part of the OPTIMAL project (https://www.optimal-project.eu/), hierarchical structures were produced in ma-P 22G, i.e. µm and nm scale features were combined in one resist film which, after pattern transfer, could e.g. be used in aviation, with properties for drag reduction and de-icing on the same surface (presented e.g. here: https://mne2025.exordo.com/programme/presentation/194).

In general, mr P 22G enables the fabrication of very deep greyscale patterns using standard-lithography-equipment (laser/LED direct writing, or mask aligner if necessary). Users can thus produce designs themselves and adapt them flexibly – independently of specialised suppliers of resist masters.

Patterning examples with Direct write lithography (DWL 66⁺, 405 nm laser):

(Patterning and pictures by courtesy of Heidelberg Instruments Mikrotechnik GmbH)

Pattern transfer example: 

Pattern transfer from a 130 μm high mr-P 22G pattern (a), fabricated at Heidelberg Instruments) by thermal moulding with PDMS, (b) followed by UV moulding with OrmoClear®FX (c)

Hierarchical patterns:

Confocal laser microscope pictures a hierarchical wave structure: 85 µm deep, 280 µm wide by DWL and 400 nm deep, 1 µm wide by LIL on its surface (right: upper ~ 8 µm)

Hierarchical wave structure: 85 µm deep, 280 µm wide (by DWL) and 400 nm deep, 1 µm wide (by laser interference lithography) on its surface (right: upper ~ 8 µm)