Extreme ultraviolet lithography (EUVL) sources emit a broad spectrum of wavelengths ranging from EUV to DUV and
beyond. If the deep ultraviolet (DUV) reaches the wafer it will affect imaging performance by exposing the photoresist.
Hence it is critical to determine the amount of DUV out of band (OoB) present in a EUVL tool, as well as its effect on
the printed features on the wafer.
In this study we investigate the effect of DUV OoB in EUVL. A model is developed in order to be able to quantify the
DUV/EUV ratio at wafer level and all the required input parameters are estimated in the range from 140 to 400nm, as
well as for the EUV at 13.5nm. The transmission of the optical system was estimated based on the optical design and
reflectivity measurements of the mirrors. The mask reflectivity for multilayer (ML) and absorber was measured at
wavelengths down to 140 nm and for EUV. The sensitivity to EUV and DUV for a variety of resist platforms was
measured at 13.5 nm, 157 nm, 193 nm, 248 nm and 365 nm. The source spectra were also measured. By using these
inputs, it was possible to estimate the DUV/EUV ratio for two different ASML tool configurations, the EUV Alpha
Demo Tool and the NXE:3100. Both NXE:3100 with LPP (laser produced plasma) source and Alpha Demo Tool with
DPP (discharge produced plasma) source show less than 1% DUV/EUV ratio in resist.
The modeling predictions were compared to experimental results. A methodology is introduced to measure the
DUV/EUV ratio at wafer level in situ. With this aim, an aluminum coated mask was fabricated and its reflectivity was
qualified in both EUV and DUV wavelength range. By comparing the dose to clear exposures of a reflective blank and
of the aluminum mask, it is possible to quantify the DUV/EUV ratio. The experimental results are in order of magnitude
agreement with modeling predictions. The proposed experimental approach can be used to benchmark the DUV
sensitivity of different resist platforms and may be used to monitor DUV OoB.
ArF lithography technology requires minimization of optical losses due to scattering and absorption. Consequently, it is necessary to optimize the coating process of metal fluorides. The properties of metal fluoride thin films are mainly affected by the deposition methods, their parameters (temperature and deposition rate) and the vacuum conditions. A substrate temperature of more than 300°C is a condition for high density and low water content of metal fluorides.
Therefore, a substrate temperature of 150°C results in inhomogeneous films with high water content. Until now, the best results were achieved by boat evaporation. This paper will demonstrate that most of the common metal fluorides like MgF2, AlF3, and even LaF3 can be deposited by electron beam evaporation. In comparison to other deposition methods, the prepared thin films have the lowest absorption in the VUV spectral range. Furthermore, metal fluoride thin films were prepared by ion assistance. It will be demonstrated, that they have less water content, high packing density, and low absorption in the VUV spectral range. In this study, single layers of LaF3 and AlF3 and antireflection coatings were prepared by electron beam evaporation with and without
ion-assistance. The mechanical, structural, and optical properties were examined and discussed.
The latest generation of 193nm immersion lithography optics, with a numerical aperture (NA) of 1.35 and ultra pure water as
immersion fluid serves the 45nm node on the ITRS roadmap. The potential solutions for the next step, the 32nm node, as
presented in December 2007 by the ITRS are: 193nm double patterning / exposure, 193nm with 2nd generation fluid and
EUVL. The performance of such next generation lithography optics is increasingly driven by the coating performance. For
193nm the performance of the antireflection and high reflection coatings is driven by the increasing NA, which requires the
control of polarisation effects and transmission uniformity over light incidence angles. For EUV only high reflection coatings
are needed and the NA is comparatively small. But the performance is limited by higher absorption and lower refractive
index contrasts of the applicable coating materials at 13.5nm with respect to 193nm. In this talk we discuss and compare the
different requirements and challenges in coating material, design, process, lifetime and accuracy for next generation
The key technologies for modern production processes with enhanced spatial resolution, require high performance DUV- excimer laser optics with enhanced optical properties. Major challenges imposed onto the requested new generation of optical elements are concentrated on lowest absorption and scattering as well as stability against highest pulse number throughput. These targets are the driving force within the German Joint Research Project 'OPUS II', which is dedicated to the development of high quality optical components for the DUV spectral range. As a major contribution to these investigations, sets of reflecting stacks with four different numbers of layer pairs of LaF3/MgF2 were produced by 6 partners of the consortium and characterized in respect to their optical performance and structural properties. The characterization includes spectrophotometric measurements from the VUV up tot eh mid RI range. calorimetric absorption measurements at 193 nm, and a comparative study in total scatter behavior at 193 nm, which was performed by three laboratories within the project. Also, besides the intrinsic stress and the surface topography of the layers, the non-linear absorption behavior of selected samples have been determined. The results are presented and discussed with respect to possible applications.