Enabling laboratory EUV research with a compact exposure tool

Abstract

In this work we present the capabilities of the designed and realized extreme ultraviolet laboratory exposure tool (EUV-LET) which has been developed at the RWTH-Aachen, Chair for the Technology of Optical Systems (TOS), in cooperation with the Fraunhofer Institute for Laser Technology (ILT) and Bruker ASC GmbH. Main purpose of this laboratory setup is the direct application in research facilities and companies with small batch production, where the fabrication of high resolution periodic arrays over large areas is required. The setup can also be utilized for resist characterization and evaluation of its pre-and post-exposure processing. The tool utilizes a partially coherent discharge produced plasma (DPP) source and minimizes the number of other critical components to a transmission grating, the photoresist coated wafer and the positioning system for wafer and grating and utilizes the Talbot lithography approach. To identify the limits of this approach first each component is analyzed and optimized separately and relations between these components are identified. The EUV source has been optimized to achieve the best values for spatial and temporal coherence. Phase-shifting and amplitude transmission gratings have been fabricated and exposed. Several commercially available electron beam resists and one EUV resist have been characterized by open frame exposures to determine their contrast under EUV radiation. Cold development procedure has been performed to further increase the resist contrast. By analyzing the exposure results it can be demonstrated that only a 1:1 copy of the mask structure can be fully resolved by the utilization of amplitude masks. The utilized phase-shift masks offer higher 1 st order diffraction efficiency and allow a demagnification of the mask structure in the achromatic Talbot plane.

Improving the resolution and throughput of achromatic Talbot lithography

“…This maximum distance is particularly important for partially coherent sources, as for example for plasma-based radiation sources, where l c is only a few micrometers long. 30 In the case of synchrotron sources, spatial coherence is large, on the order of several thereby the patterned area decreases with increasing distance from the grating and vanishes at a distance:…”

Sub-micrometer structuring of surfaces with deep UV lasers

“…Basically, however, this effect is based on the so called Talbot effect, which states that behind the mask with periodic transmission profile there is series of image planes in which the intensity profile of the mask is repeated. Recently, this method was implemented at EUV wavelengths for sub-30 nm structuring, demonstrating its applicability for radiation sources of limited spatial coherence and broad spectral bandwidth 21,22 .This method becomes especially powerful with the use of phase shift masks, that are able to suppress the 0 th diffraction order and redirect most of the applied energy to the ±1 st diffraction orders, providing efficiencies up to 90% 23 .…”

Development of an ultra-compact inline transmission grating spectrograph for extreme ultraviolet wavelengths

“…The transmission gratings have been initially developed as phase-shifting transmission masks for EUV interference lithography [13][14][15] and consist of a structured polymer on top of a silicon nitride membrane with a thickness of 45 nm. The lithographic process of the Talbot lithography requires transmission gratings with a low intensity into the 0 th diffraction order and a high diffraction efficiency into the 1 st diffraction orders, which is also beneficial for the use in EUV-TGS.…”