This paper presents the extension of the well-established, rigorous, electromagnetic field solver waveguide for the efficient and fully rigorous simulation of patterned extreme ultraviolet (EUV) masks with multilayer defects. The new simulation method uses a rigorously computed multilayer defect data base in combination with on demand modeling of diffraction from absorber structures. Typical computation times are in the range of seconds to a few minutes. Selected simulation examples, including a defect printing exploration and a defect repair, demonstrate the functionality and the capability to perform fast, highly accurate, and flexible EUV multilayer defect computations.
This paper presents the extension of the well-established rigorous electromagnetic field (EMF) solver Waveguide for the efficient and fully rigorous simulation of patterned extreme ultraviolet (EUV) masks with multilayer defects using a rigorously computed multilayer defect data base combined with on demand computed absorber structures. Typical computation times are in the range of seconds up to a few minutes. The new simulation approach will be presented. Selected simulation examples and a defect repair example demonstrate the functionality and the capability to perform fast, highly accurate and flexible EUV multilayer defect computations.
Extreme ultraviolet (EUV) - lithography at a wavelength around 13.5 nm is considered as the most promising
successor of optical projection lithography. This paper reviews simulation models for EUV lithography. Resist
model parameters are calibrated with experimental data. The models are applied for the investigation of the
impact of mask multilayer defects on the lithographic process.
Rigorous simulation of light diffraction from optical and EUV masks predicts phase effects with an aberration like impact
on the imaging performance of lithographic projection systems. This paper demonstrates the application of advanced
modeling and optimization methods for the compensation of mask induced aberration effects. It is shown that
proper adjustment of the wavefront results in significant reduction of best focus differences between different features.
Different mask models have been compared: rigorous electromagnetic field (EMF) modeling, rigorous EMF
modeling with decomposition techniques and the thin mask approach (Kirchhoff approach) to simulate optical
diffraction from different mask patterns in projection systems for lithography. In addition, each rigorous model
was tested for two different formulations for partially coherent imaging: The Hopkins assumption and rigorous
simulation of mask diffraction orders for multiple illumination angles. The aim of this work is to closely approximate
results of the rigorous EMF method by the thin mask model enhanced with pupil filtering techniques. The
validity of this approach for different feature sizes, shapes and illumination conditions is investigated.
This paper employs rigorous electromagnetic field (EMF) solvers to investigate the printing behavior of EUV multilayer
defects. A compression model is applied to compute the defect induced deformation of the multilayer. A fully rigorous
Waveguide method is used to simulate the light diffraction from the defective EUV mask. This fully rigorous method
is compared with two other methods: A decomposition method combined with the Waveguide algorithm and a
hybrid method which computes the multilayer with an analytical method based on the Fresnel-formulas and the mask
absorber with a finite-difference time-domain (FDTD) algorithm. Cross sections and the critical dimensions (CD) of the
printed wafer features are evaluated by the application of a threshold model to the computed aerial images. The printability
of the multilayer defects and their impact on the CD of printed absorber features are investigated versus the defect
position, size and other parameters of the defect model. Finally, the influence of the mask absorber properties on the
defect-induced CD variation is investigated. It is shown that the printability of the defect depends on the absorber properties.
This paper discusses the modeling of reversible contrast enhancement layers (RCEL) for advanced optical lithography.
An efficient implementation of the Waveguide method is employed to investigate the process capability of RCEL and to
identify the most appropriate material and exposure parameters. It is demonstrated that the consideration of near field
diffraction effects and of bleaching dynamics is important to achieve correct results. A large refractive index of the resist
and the RCEL improves the achievable lithographic performance. It is shown that RCEL layers can be used to enhance
the performance of a NA=0.6 scanner to create a high contrast images with a pitch of 80nm.
This paper aims at identifying appropriate bottom anti-reflective coatings (BARCs) for double patterning techniques
such as Litho-Freeze-Litho-Etch (LFLE). A short introduction into the employed optimization methodology, including
variables, figures of merit, models and optimization algorithms is given. A study on the impact of a refractive index
modulation caused by the first lithographic step is presented. Several optimization surveys taking the index modulation
into account are set forth, and the results are discussed. In addition to optimization procedures aiming at optimizing one
litho step at a time, a co-optimization study for both litho steps is proposed. Finally, two multi-objective optimization
procedures that allow for a post-optimization exploration and selection of optimum solutions are presented. Numerous
solutions are discussed in terms of their anti-reflectance behavior and their manufacturing feasibility.
This paper uses advanced modeling techniques to explore interactions between the two lithography processes in a lithocure-
etch process and to qualify their impact on the final resist profiles and process performance. Specifically, wafer
topography effects due to different optical properties of involved photoresist materials, linewidth variations in the second
lithography step due to partial deprotection of imperfectly cured resist, and acid/quencher diffusion effects between
resist materials are investigated. The paper highlights the results of the simulation work package of the European MD3
project.
As the technology marches toward the 32-nm node and beyond in semiconductor manufacturing, double-patterning and double-exposure techniques are currently regarded as the potential candidates to produce lines and spaces and contact holes, respectively. We employ the Waveguide method, a rigorous electromagnetic field (EMF) solver, to investigate the impact of wafer topographies on two specific double-patterning techniques. At first, the topography effects induced by the first patterning on the second lithography process in a lithography-etch-lithography-etch process are demonstrated. A new methodology of the bottom antireflective coating optimization is proposed to reduce the impact of wafer topography on resist profiles. Additionally, an optical proximity correction (OPC) of the second lithography mask is demonstrated to compensate the wafer-topography-induced asymmetric deformations of line ends. Rigorous EMF simulations of lithographic exposures are also applied to investigate wafer-topography effects in a freezing process. The difference between the optical properties of the frozen (first) resist and the second resist potentially causes linewidth variations. Quantitative criteria for tolerable refractive index and extinction differences between the two resist materials are given. The described studies can be used for the optimizations of topographic waferstacks, the OPC of the second litho mask, and for the development of resist materials with appropriate optical properties.
This paper employs the Waveguide decomposition method as an efficient rigorous electromagnetic field (EMF) solver
to investigate three dimensional mask-induced imaging artifacts in EUV lithography. The major mask diffraction induced
imaging artifacts are first identified by applying the Zernike analysis of the mask nearfield spectrum of 2D
lines/spaces. Three dimensional mask features like 22nm semidense/dense contacts/posts, isolated elbows and line-ends
are then investigated in terms of lithographic results. After that, the 3D mask-induced imaging artifacts such as feature
orientation dependent best focus shift, process window asymmetries, and other aberration-like phenomena are explored
for the studied mask features. The simulation results can help lithographers to understand the reasons of EUV-specific
imaging artifacts and to devise illumination and feature dependent strategies for their compensation in the optical proximity
correction (OPC) for EUV masks. At last, an efficient approach using the Zernike analysis together with the
Waveguide decomposition technique is proposed to characterize the impact of mask properties for the future OPC process.
This article reviews standard and advanced modeling techniques in lithography simulation. Rigorous electromagnetic
field solvers such as the Waveguide Method and finite-difference
time-domain (FDTD) algorithms in combination with
vector imaging models predict the image formation inside the photoresist. Semi-empirical macroscopic and microscopic
models describe physical and chemical phenomena during the processing of resists. Various local and global optimization
techniques are applied to identify the best exposure and process parameters. Several examples demonstrate the application
of predictive simulation for the exploration of future lithography options and for the optimization of existing
technologies. This includes the consideration of mask material parameters in source/mask optimization, the evaluation
and comparison of different options for double exposure and double patterning techniques, and the investigation of
mask-induced imaging artifacts in EUV-lithography. Selected examples illustrate the application of lithography simulation
for the modeling of cost efficient alternative exposure techniques for special applications of micro- and nanotechnology.
As the technology marches towards the 32nm node and beyond in semiconductor manufacturing, double patterning and
double exposure techniques are currently regarded as the potential candidates to produce lines and spaces (L&S) and
contact holes (C/H), respectively. In this paper, the Waveguide method, a rigorous electromagnetic field (EMF) solver,
is employed to investigate the impact of wafer topographies on two specific double patterning techniques. At first, the
topography effects induced by the first patterning on the second lithography process in a lithography-etch-lithographyetch
(LELE) process are demonstrated. A new methodology of the bottom anti-reflective coating (BARC) optimization
is proposed to reduce the impact of wafer topography on resist profiles. Additionally, an optical proximity correction
(OPC) of the second lithography mask is demonstrated to compensate the wafer topography induced asymmetric
deformations of line ends. Rigorous EMF simulations of lithographic exposures are also applied to investigate wafer
topography effects in a freezing process. The difference between the optical properties of the frozen (first) resist and the
second resist potentially causes linewidth variations. Quantitative criteria for tolerable refractive index and extinction
differences between the two resist materials are given. The described studies can be used for the optimizations of
topographic waferstacks, the OPC of the second litho mask, and for the development of resist materials with appropriate
optical properties.
In this work, a framework for the assessment of different double exposure techniques is laid out. Both the simulation environment and the utilized models, derived from well-established resist models, are discussed. Numerous simulation results are evaluated to investigate strengths and weaknesses of different double exposure approaches. Non-linear superposition techniques are examined in respect of their process performance for both standard and sub 0.25 k1 values. In addition to a study of these effects in the scope of basic layouts, an application to interference-assisted lithography (IAL) is proposed and discussed.
A new and optimized electromagnetic field (EMF) solver based on the waveguide method with a decomposition
technique for rigorous optical and extreme ultraviolet (EUV) mask near field simulations is presented. The implemented
software algorithm enables full three dimensional (full 3D) mask simulations as well as three dimensional mask
simulations based on a parallelized decomposition technique (Q3D, "Q" stands for "quasi"). After a short introduction to
the waveguide method and to an optimized mask description, the basis of the decomposition technique and its
parallelization are presented. Subsequently the capabilities of the new electromagnetic field solver are demonstrated by
simulations of advanced optical and EUV imaging problems. Simulations of larger sized mask areas and of standard
sized defective EUV mask areas using the decomposition technique are shown. Finally, a further reduction of
computation time using parallelization is demonstrated.
KEYWORDS: Computer simulations, 3D image processing, Waveguides, Extreme ultraviolet, Near field, Photomasks, 3D modeling, Near field optics, Electromagnetism, EUV optics
A new and optimized waveguide based electromagnetic field solver with decomposition technique for rigorous optical
and extreme ultraviolet (EUV) mask near field simulations is presented. The model allows to perform full three
dimensional (full 3D) simulations as well as three dimensional simulations based on a decomposition technique (Q3D,
"Q" means "quasi"). After a short introduction of the waveguide method the decomposition technique is presented.
Subsequently the capabilities of the new electromagnetic field solver are demonstrated exemplarily based on state-of-the-art
optical and EUV systems. The simulation of larger mask areas and the fast simulation of standard sized mask areas is
shown. A comparison between the full 3D and the Q3D approach demonstrates the field of application of the
decomposition technique.
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