Talbot Lithography

The "Talbot Lithography" project is developing a flexible basic technology for the production of complex, periodic microstructured elements. In particular, the technological approach enables the production of gratings with profile depths that cannot be achieved with comparable methods.

As a central element of a spectrometer, diffractive gratings are of great importance, especially as spectroscopy is gaining in importance as a qualitative and quantitative method of investigation in many areas of industry and science (bio-med, agri-food, chemistry, ...) for the optimisation of production processes.

Currently used grating production technologies (mechanical splitting & interference lithography) have limitations with regard to the writing times and homogeneity of the structure or the achievable structure diversity. Both limitations can be reduced with Talbot lithography.

In the underlying Talbot effect, an amplitude grating is illuminated with a spatially coherent wave; a characteristic intensity distribution appears behind the grating (see Figure 1). This contains planes which correspond to a self-image of the illuminated grating and are used to expose a photoresist.

To produce diffractive gratings, for example, several slightly offset exposures with different exposure times are applied to the photoresist. The blaze grating structure shown in Figure 2, for example, can be realised using this principle. The offset can be realised by moving the substrate during the exposure, or alternatively the position of the writing spot can also be controlled via the direction of incidence of the illuminating wave.

When using cross grids instead of line grids, a 2D grid of writing spots is available in the writing plane, which can be used to generate 2D grids with virtually any structure using substrate movement. This opens up prospects for new periodic, microstructured elements for optical devices.