Researchers at AMO GmbH and the Chair of Electronic Devices at RWTH Aachen University have implemented a novel class of pinholes to increase the spatial uniformity of laser beams and demonstrated their efficiency in improving the quality of laser interference lithography gratings.
Laser interference lithography is a cost-effective nanofabrication technique widely used in semiconductor manufacturing and photonics. It relies on the interference of multiple laser beams to create a periodic pattern on a photoresist, which can then be transferred to a substrate to create precise nanostructures or photonic devices. Interference lithography provides high-resolution patterning capabilities and is essential for various applications in advanced optics, electronics and nanotechnology.
The precision of this technique, however, is limited by the uniformity of the laser beam itself. In fact, the intensity of the laser beam follows a Gaussian profile so that the exposure dose in the resist varies with a maximum at the center of the interference pattern and a falloff in both the x and y directions. As a result, the feature dimensions in the exposed resist also vary from the center to the edges of the exposed substrate. A team of researchers from AMO GmbH and the Chair of Electronic Devices at RWTH Aachen University has now experimentally demonstrated an effective approach to counteract this effect.
The approach follows the theoretical proposal of Hariharan and co-workers to modify a Gaussian beam by adding an annular transparent phase mask to a standard circular pinhole. The element modifies the shape of the Gaussian beam and results in a significant increase in full width at half maximum (FWHM) intensity. In addition, the phase mask helps eliminate optical noise such as speckles, making it ideal for applications where a speckles-free uniform beam shape is critical, such as in holography or interferometry systems.
Giovanna Capraro and co-workers have carefully studied the design parameters of such Hariharan pinholes. In addition, they performed an experimental proof of concept by implementing the Hariharan pinholes in a laser interference lithography setup and comparing their performance with conventional pinholes. The use of Hariharan pinholes resulted in a 26% increase in the uniformity of the fabricated structures, demonstrating the potential of the approach. The results have been reported in Advanced Photonic Research.
This research has been funded by the European Union’s Horizon 2020 research and innovation program under the Marie-Skłodowska-Curie grant agreement no. 813159 (GREAT) and by the German Federal Ministry for Economic Affairs and Climate Action under grant agreement no. 49MF210208 (PESOS).
Capraro, G., Lipkin, M., Möller, M., Bolten, J. and Lemme, M.C.
Phase Mask Pinholes as Spatial Filters for Laser Interference Lithography.
Adv. Photonics Res. 2300225 (2023).