Precise optical constant determination in the soft X-ray, EUV, and VUV spectral range

Optical constants of materials are essential for predicting and interpreting optical responses, which is crucial when designing new optical components. Although accurate databases of optical constants are available for some regions of the electromagnetic spectrum, for the vacuum ultraviolet VUV , the extreme ultraviolet EUV , and soft X ray spectral ranges, the available optical data suffer inconsistencies, and their determination is particularly challenging. Here, we present a selected example of ruthenium Ru for the determination of optical constants from the VUV to the soft X ray spectral range using reflectivity measurements performed with synchrotron radiation. The subtleties of reflectivity measurements are discussed for a large wavelength range, from 0.7 to 200 nanometer

Evaluation of Ta-Co alloys as novel high-k extreme ultraviolet mask absorber

Background: A plausible approach for mitigating the mask 3-D (M3D) effects observed in extreme ultraviolet (EUV) lithography is to replace the existing mask absorber with alternative materials. Absorbers with a high EUV extinction coefficient k allow for lower best focus variation (BFV) through pitch and reduced telecentricity errors (TCEs).Aim: We aim to evaluate Ta-Co alloys as potential high-k mask absorbers from material suitability and imaging standpoints.Approach: We study the film morphology, surface composition, and stability of Ta-Co alloys in mask cleaning solutions and a hydrogen environment as present in the EUV scanner to assess the material suitability from an experimental aspect. Optical constants for three selected compositions, viz., TaCo, Ta2Co, and TaCo3, were determined from EUV angle-dependent reflectivity measurements. Next, utilizing rigorous simulation software, the imaging performance of Ta-Co alloys is evaluated and compared with the reference absorber. The recommended absorber thickness for Ta-Co alloy absorbers is based upon normalized image log slope (NILS) enhancement, threshold to size, and balancing of diffraction order amplitudes. A 10 nm line and space pattern with a pitch of 20 nm and 14 nm square contact holes with a pitch of 28 nm are used for the simulation study using high numerical aperture 0.55 EUV lithography process settings. The primary imaging metrics for through pitch evaluation include NILS, TCE, and BFV.Results: The Ta-Co alloys exhibit a higher EUV extinction coefficient k compared with the currently used Ta-based absorber. TaCo and Ta2Co demonstrate smooth surfaces and are stable in a hydrogen environment and in mask-cleaning solutions.Conclusion: Ta-Co alloys allow for a reduction in M3D effects at a lower absorber thickness compared with a 60 nm Ta-based reference absorber

Characterization of Ru4-xTax (x = 1,2,3) alloy as material candidate for EUV low-n mask

Ru4-xTax (x = 1,2,3) alloys are studied as absorber candidates for EUV low-n mask. We report the morphology, surface roughness as well as the chemical composition of the as-deposited alloy films for better theoretical model building of the EUVL absorber stack. Their refractive indices are reconstructed by optimizing measured EUV reflectivity data for the purpose of enabling rigorous EUVL imaging calculations in the future work. The stabilities (both physical and chemical) of these absorber candidates are verified which contribute to a long lifetime of the mask in its working environment. This includes the resistance assessments of the thin films against high temperature up to 500 °C, different mask cleaning solutions and hydrogen environment which is present in EUV scanners. Etching of RuTa is explored using halogen-based reactive ion etch technique. A low etch rate is obtained with a moderate etch selectivity to Ru, which is the capping layer of multilayer mirror on a EUVL mask

Pancreatic surgery outcomes: multicentre prospective snapshot study in 67 countries

Background: Pancreatic surgery remains associated with high morbidity rates. Although postoperative mortality appears to have improved with specialization, the outcomes reported in the literature reflect the activity of highly specialized centres. The aim of this study was to evaluate the outcomes following pancreatic surgery worldwide.Methods: This was an international, prospective, multicentre, cross-sectional snapshot study of consecutive patients undergoing pancreatic operations worldwide in a 3-month interval in 2021. The primary outcome was postoperative mortality within 90 days of surgery. Multivariable logistic regression was used to explore relationships with Human Development Index (HDI) and other parameters.Results: A total of 4223 patients from 67 countries were analysed. A complication of any severity was detected in 68.7 percent of patients (2901 of 4223). Major complication rates (Clavien-Dindo grade at least IIIa) were 24, 18, and 27 percent, and mortality rates were 10, 5, and 5 per cent in low-to-middle-, high-, and very high-HDI countries respectively. The 90-day postoperative mortality rate was 5.4 per cent (229 of 4223) overall, but was significantly higher in the low-to-middle-HDI group (adjusted OR 2.88, 95 per cent c.i. 1.80 to 4.48). The overall failure-to-rescue rate was 21 percent; however, it was 41 per cent in low-to-middle-compared with 19 per cent in very high-HDI countries.Conclusion: Excess mortality in low-to-middle-HDI countries could be attributable to failure to rescue of patients from severe complications. The authors call for a collaborative response from international and regional associations of pancreatic surgeons to address management related to death from postoperative complications to tackle the global disparities in the outcomes of pancreatic surgery (NCT04652271; ISRCTN95140761)