Starting with the 45nm node, the minimum feature size on the mask has reached sub-wavelength dimension. In this
regime the electromagnetic field induced in the mask is significantly impacted by the mask topography. These so called
mask topography effects play an important role in the image formation process and need to be compensated for in the
optical proximity correction (OPC) model. Looking ahead to the 32nm process node, mask topography effects will
become even more pronounced. So, including these effects into the OPC model has become a must for advanced process
nodes. Modern OPC engines start to apply electromagnetic field (EMF) compensation techniques to take these effects
into account. Of course, due to the severe run time constrains for OPC models most EMF aware OPC models need to
rely on approximate methods. A reliable OPC verification process needs to include a fully rigorous treatment of the mask
topography effects with taking into account oblique light incidence and polarization of light. In this paper we investigate
the impact of rigorous mask topography simulation on the reliability of OPC verification and determine the influence of
EMF aware OPC models on OPC quality. We use lithography simulations on OPCed layout cells where we apply a fully
rigorous parallelized EMF solver to the mask model. Two different OPC models are used in this study; one based on the
conventional approach and another one using EMF compensation techniques. The results of the rigorous lithography
simulations are used to verify both OPC models. The impact of the EMF simulation on OPC verification quality is
illustrated by direct comparison with the corresponding Kirchhoff simulations for both OPC models.
A detailed defect printability analysis is reported for conditions that are fully representative for the world's first full field
EUV scanner, using 4X reticles, as obtained by simulation. For absorber type defects the historical rule of thumb
underestimates the printability. An opaque defect located in a space within a 40nm lines and space pattern can already
cause more than a 10% change in the space width from 80% of the space width onwards (>32nm at mask scale, >8 nm at
wafer scale) depending on its location. Absorber type clear defects start affecting line width in 40nm lines and spaces
from about twice the size of an opaque defect. Particles simulated as carbon cubes have a similar effect as absorber type
opaque defects provided that they are about 50% larger. Other possible particle materials are investigated as well. Local
carbon deposition, which may originate from SEM inspection, can cause a printing effect already at a thickness of only
2nm. Multilayer or substrate type defects require surface smoothing to less than about 2nm, as to keep the impact of so-called
phase defects under control. Experimental plans for comparison of simulations to exposures on the ASML Alpha
Demo Tool installed at IMEC are included.
Development of extended optical systems using liquid immersion for patterning enables numerical apertures > 1.2
lithography. Hyper numerical aperture (NA) lithography has to deal with extremely oblique incident light, mask
polarization, mask topography effects and large diffraction angle from mask feature with tight pitch. Simulation tools
predicting highly accurate results based on real experimental data are widely used in the industry and for lithography
process development. Predictability of Optical Proximity Correction (OPC) tools is strongly dependent on the amount
of physical effects taken into account. Therefore going below 45nm half pitch the correct description of the real mask
nature including the effects of mask topography, polarization and pellicle apodization is vital to the success of
immersion lithography.
In this paper we investigate the impact of pellicle apodization effects predicted by simulations for OPC. Significant
pellicle apodization induced CD differences including 1D and 2D OPC structures will be presented. The key emphasis
of this paper is to highlight the criticality of an integrated OPC solution including mask polarization, mask topography
and pellicle apodization effects for enabling immersion lithography moving beyond 45nm and 32nm nodes.
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