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Laser photolithography & UV exposure :
Greyscale, microlens and grating
In lithography, we use to call “greyscale applications” those, which refer to partial polymerization of the overall photoresist thickness.
To do so, it is necessary to modulate the dose (which results in the power density by the resin for the duration of the exposure). Naturally, the thicker the layer, the more the contrast and the number of levels will be visible
However, the quality of the final function produced will depend on the capacity to discriminate different greyscale levels in a linear manner (micro-lens or blazed gratings) or on the contrary in an abrupt way (index or phase contrast function, Fresnel lens). It is therefore essential that the technology used is compatible with the writing in thick layers as well as thin layers and that the number of grey scale levels (number of possible dose) is not limited.
The technology developed by Kloé with its Dilase equipment is thus perfectly adapted. Indeed, it associates large depth of the focus (compatibility with the writing of thick layers with the same rendering as in thin layers without modifying the focusing distance), the vector write mode and the modulation in real time of the writing speed and the emission power of the laser. Consequently, the number of grey levels is unlimited, varies in a controlled and continuous manner in photoresist thicknesses ranging from a few nanometres a hundred of microns.