Daniel Thomae

Flexible mask illumination setup for serial multipatterning in Talbot lithography

A flexible illumination system for Talbot lithography is presented, in which the Talbot mask is illuminated by discrete but variable incidence angles. Changing the illumination angle stepwise in combination with different exposure doses for different angles offers the possibility to generate periodic continuous surface relief structures. To demonstrate the capability of this approach, two exemplary micro-optical structures were manufactured. The first example is a blazed grating with a stepsize of 1.5 μm. The second element is a specific beam splitter with parabolic-shaped grating grooves. The quality of the manufacturing process is evaluated on the basis of the optical performance of the resulting micro-optical elements.

Talbot-carpets of periodic and quasi-periodic close-packed 2D mask structures calculated by a modified chirp-z-algorithm

In this contribution we simulate theoretically the resulting 3D Talbot-carpets of different initial close-packed 2D mask structures. Especially, we investigate the transition from regular periodic to quasi-periodic tessellations. For the pure periodic mask structure a hexagonally tessellation was selected. The calculated field distribution adjacent to the mask still shows a lateral six-fold symmetry but also a rather complex characteristics in the propagation direction. In particular, the appearance and the repetition of self-imaging planes deviate significantly from the classical Talbot-effect. For the quasi-periodic tessellation a Penrose tapestry based on rhombus pairs was chosen. A pronounced lateral fivefold symmetry becomes visible in the field distribution. In the propagation direction dominant planes with increased intensity are observed clearly, but, instead of a simple periodicity, a complex behavior becomes obvious. The numerical algorithm used in our simulations is based on a modified angular spectrum method, in which Bluesteins fast Fourier (FFT) algorithm is applied. This approach allows to decouple the sampling points in the real space and in the spatial frequency domain so that both parameter can be chosen independently. The introduced fast and flexible algorithm requires a minimized number of numerical steps and a minimal computation time, but still offers high accuracy.

Influence of oblique illumination on perfect Talbot imaging and nearly perfect self-imaging for gratings beyond five diffraction orders

The Talbot self-imaging effect of amplitude gratings is afflicted with aberrations that distort the self-image. This occurs especially if the grating period p is only a few times larger than the illumination wavelength λ. For example, for lithographic applications of the Talbot effect these aberrations lower the lateral writing resolution and should be minimized. Noponen found, however, some discrete ratios of p/λ in the interval of 2.0<p/λ<3 that are aberration-free. We generalize the definition of the Talbot distance to include oblique illumination and show how Noponens discrete ratios can be shifted by it. In the second part, we look at ratios of p/λ larger than 3, so that there are more than five diffraction orders behind the grating. For this region we present a method to find ratios of p/λ with at least minimal aberrations and present some self-image examples that are of interest for lithographic purposes up to the range of p/λ≈12.

Tailored Microoptical and Sub-Wavelength Structures

Diffractive optical elements (DOEs) are of enormous importance for applications in spectroscopic and imaging systems. We demonstrate that modified Talbot-Lithography is a fast and flexible technology for the mastering of micro-optical components, especially to manufacture high efficient spectroscopic diffractive gratings with an extended profile depth. The characteristics of DOEs also open up new opportunities for their integration in variable elastomeric optical components. We present theoretical investigations of the mechanical deformation of an initial Blazed-like diffractive grating and its impact on the optical diffraction efficiency.