For many critical lithography applications the main contributor to wafer intra-field CD variation is the reticle CD
variation. Current practice is that the input data needed to correct the effect of the reticle on the wafer CD is gathered
using wafer exposures and SEM or scatterometry analysis. This approach consumes valuable scanner time and adds
wafer costs. In this work we evaluate the potential for Intra-Field CD non-uniformity (CDU) correction based on aerial
image reticle measurements for a complex 2D structure, including peripheral structures. The application selected is a
45nm rotated brick wall structure (active area DRAM). A total of 10 line / space structures (both horizontal and vertical)
through pitch represent the periphery. Mask qualification has been performed using the newly developed Zeiss WLCD32
metrology tool, which measures wafer level CD on masks using aerial imaging technology. Excellent correlation is
shown between intra-field wafer data and WLCD32 data. Furthermore, a comparison is made between the correction
potential of ASML DoseMapper recipes based on wafer data and on WLCD32 mask data, indicating that the potential
CDU improvement via both approaches is similar. Exposures with the resulting dose recipes have been used to confirm
this predicted correction potential in a realistic setting.
The semiconductor industry has adopted water-based immersion technology as the mainstream high-end litho enabler
for 5x-nm and 4x-nm devices. Exposure systems with a maximum lens NA of 1.35 have been used in volume
production since 2007, and today achieve production levels of more than 3400 exposed wafers per day. Meanwhile
production of memory devices is moving to 3x-nm and to enable 38-nm printing with single exposure, a 2nd generation
1.35-NA immersion system (XT:1950Hi) is being used. Further optical extensions towards 32-nm and below are
supported by a 3rd generation immersion tool (NXT:1950i).
This paper reviews the maturity of immersion technology by analyzing productivity, robust control of imaging, overlay
and defectivity performance using the mainstream ArF immersion production systems. We will present the latest results
and improvements on robust CD control of mainstream 4x-nm memory applications. Overlay performance, including
on-product overlay control is discussed. Immersion defect performance is optimized for several resist processes and
further reduced to ensure high yield chip production even when exposing more than 15 immersion layers.
Finite element wall stress simulations on patient-specific models of abdominal aortic aneurysm (AAA) may provide a better rupture risk predictor than the currently used maximum transverse diameter. Calcifications in the wall of AAA lead to a higher maximum wall stress and thus may lead to an elevated rupture risk. The reported material properties for calcifications and the material properties actually used for simulations show great variation. Previous studies have focused on simplified modelling of the calcification shapes within a realistic aneurysm shape. In this study we use an accurate representation of the calcification geometry and a simplified model for the AAA. The objective of this approach is to investigate the influence of the calcification geometry, the material properties and the modelling approach for the computed peak wall stress. For four realistic calcification shapes from standard clinical CT images of AAA, we performed simulations with three distinct modelling approaches, at five distinct elasticity settings. The results show how peak wall stress is sensitive to the material properties of the calcifications. For relatively elastic calcifications, the results from the different modelling approaches agree. Also, for relatively elastic calcifications the computed wall stress in the tissue surrounding the calcifications shows to be insensitive to the exact calcification geometry. For stiffer calcifications the different modelling approaches and the different geometries lead to significantly different results. We conclude that an important challenge for future research is accurately estimating the material properties and the rupture potential of the AAA wall including calcifications.
In recent years, simulations of the blood flow and the wall mechanics in the vascular system with patient-specific boundary conditions by using computational fluid dynamics (CFD) and computational solid mechanics (CSM) have gained significant interest. A common goal of such simulations is to help predict the development of vascular diseases over time. However, the validity of such simulations and therefore the validity of the predictions are often questioned by physicians. The aim of the research reported in this paper is to validate CFD simulations performed on patient-specific models of abdominal aorta aneurysms (AAAs) using patient-specific blood velocity inflow profiles. Patient-specific AAA geometries were derived from images originating from Computed Tomography (CT) or Magnetic Resonance (MR) imaging. Patient-specific flow profiles were measured with Phase-Contrast MR imaging (Quantitative flow, Qflow). Such profiles, determined at the inflow site of the AAA, were used as inflow boundary condition for CFD simulations. Qflow images that were taken on a number of planes along the AAA were used for the validation of the simulation results. To compare the measured with the simulated flow we have generated synthetic Qflow images from the simulated velocities on cut-planes positioned and oriented according to the planes of the validation images. The comparison of the real with the simulated flow profiles was performed visually and by quantitatively comparing flow values on cross sections of the AAA in the measured and the synthetic Qflow images. In a preliminary study on two patients we found a reasonable agreement between the measured and the simulated flow profiles.
Finite element method based patient-specific wall stress in
abdominal aortic aneurysm (AAA) may provide a more accurate rupture
risk predictor than the currently used maximum transverse diameter.
In this study, we have investigated the sensitivity of the wall
stress in AAA with respect to geometrical variations. We have
acquired MR and CT images for four patients with AAA. Three
individual users have delineated the AAA vessel wall contours on the
image slices. These contours were used to generate synthetic feature images for a deformable model based segmentation method. We investigated the reproducibility and the influence of the user variability on the wall stress. For sufficiently smooth models of the AAA wall, the peak wall stress is reproducible for three out of the four AAA geometries. The 0.99 percentiles of the wall stress show
excellent reproducibility for all four AAAs. The variations induced by user variability are larger than the errors caused by the segmentation variability. The influence of the user variability appears to be similar for MR and CT. We conclude that the peak wall stress in AAA is sensitive to small geometrical variations. To increase reproducibility it appears to be best not to allow too much geometrical detail in the simulations. This could be achieved either by using a sufficiently smooth geometry representation or by using a more robust statistical parameter derived from the wall stress distribution.