As design rules shrink, there is an increase in the complexity. OPC/RET have been facilitating unprecedented yield at k1
factors, they increase the mask complexity and production cost, and can introduce yield-detracting errors. Currently OPC
modeling techniques are based on extensive CD-SEM measurements which are limited to one dimensional structures or
specific shape structures e.g. contact holes. As a result the measured information is not representing the whole spatial 2D
change in the process. Therefore the most common errors are found in the OPC design itself and in the resulting
patterning robustness across the process window. A new methodology for OPC model creation and verification is to
extract contours from complex test structures which beside the CD values contain further information about e.g. various
In this work we use 2D contour profiles extracted automatically by the CD-SEM over varying focus and exposure
conditions. We will show that the measurement sensitivity and uncertainty of that algorithm through the whole process
window fulfills the requirements of the ITRS with respect to CD-SEM metrology tools. This will be done on various test
structures normally being used for OPC model generation and OPC stability monitoring. Furthermore a study on
systematic influences on the quality of the extracted contours has been started. This study includes the evaluation of
various parameters which are considered as possible contributors to the uncertainty of the edge contour extraction. As
one of the parameters we identified the pixel size of the SEM images. Furthermore, a new metric for calculating
repeatability and reproducibility determination for 2D contour extraction algorithms will be presented. By applying this
contour extraction based methodology to different CD-SEM tool generations the influence of SEM beam resolution to
the quality of the contours will be evaluated.
Modular OPC modeling, describing mask, optics, resist and etch processes separately is an approach to keep efforts for
OPC manageable. By exchanging single modules of a modular OPC model, a fast response to process changes during
process development is possible. At the same time efforts can be reduced, since only single modular process steps have
to be re-characterized as input for OPC modeling as the process is adjusted and optimized. Commercially available OPC
tools for full chip processing typically make use of semi-empirical models. The goal of our work is to investigate to what
extent these OPC tools can be applied for modeling of single process steps as separate modules. For an advanced gate
level process we analyze the modeling accuracy over different process conditions (focus and dose) when combining
models for each process step - optics, resist and etch - for differing single processes to a model describing the total
Optical & process model are used in conjunction with Mentors Calibre OPC tool to predict the behavior of a lithography process. Resist models rely exclusively on empirical measurement data, while optical models are calibrated based on the users knowledge of tool settings, but also fitting unknown parameters to empirical measurements. The final OPC model is a combination of optical & process behaviors prediction which includes resist & other process influence to meet the ever increasing demand of advanced lithography technology nodes like 90nm & below on model accuracy. Reliance of optical model creation on empirical measurement data is undoubtedly raising suspicion of how well the derived diffraction model is able to provide an accurate description of how light energy is distributed inside the resist. Various work & effort had been conducted in the past to cover defocus phenomenal on final model outcome & methodology introduced on better prediction from defocus to achieve better simulation quality, investigation has been carried out to study in further detail of existing strategy of resist & optical decoupling methodology in this work.
Optical lithography simulation plays a decisive role in the development of technology for the manufacturing process of semiconductor devices. Its role in reticle inspection has only recently gained more attention. Filters determining which defects need repair and which ones can be ignored help set up the filter classes in inspection systems. These calculations are performed offline. In an effort to increase the accuracy of inspection it would be desirable to place the decision level as close to the actual process as possible. Therefore, an inspection system based on aerial images is a step in this direction. In addition, an optical simulator calculates from the aerial image the resist image. To do so very fast resist image models are needed (see figure 7). Quick models so far were restricted by accuracy and speed. In this paper a new very fast model will be presented that allows calculation of large areas suitable for inspection purposes. Finally a 'virtual inspection' system will be presented pinpointing at weak spots in the layout. In an effort to calculate larger areas of the resist in less time we had to take completely new approaches. They led us to analytical descriptions of the image transfer into the resist. Within these descriptions we begin in this first paper to investigate an approach based on the propagation of a top aerial image into the resist. The aerial image may come from calculations, as in the present article, or as well from measurements. The purpose of this article is to demonstrate the performance of the Fast Resist Model with respect to accuracy and time consumption. The limits of the current model are equally described.
The applicability and accuracy of newly developed analytical models for resist process effects are investigated. These models combine a stationary level set formulation with a lumped parameter model. They allow to propagate the 3D photoresist profile given the 3D aerial image distribution. The first model, based on the vertical propagation algorithm (VPM), takes into account the 2D intensity distribution inside the resist, including the absorption. The second model incorporates the scaled defocus algorithm (SCDF), which describes the 3D intensity of the resist, taking into account the defocus values. In this paper we investigate the applicability for any geometry, for process window determination and the accuracy by taking reference to the fully fledged simulator SOLID-C. The suggested methods allow to calculate 3D resist profile in a fast way thereby enabling the prediction of large areas.
Proc. SPIE. 4345, Advances in Resist Technology and Processing XVIII
KEYWORDS: Lithography, Standards development, Data modeling, Promethium, Photoresist materials, Photoresist processing, Diffusion, Inspection, Process modeling, Picture Archiving and Communication System
The use of experimental development rate information is used to demonstrate various deficiencies in the dissolution rate equations commonly employed in commercial lithography simulation programs. An improved version of the Notch dissolution rate equation, incorporating one new parameter, is proposed, which addresses the observed deficiencies. Simulation work comparing the new equation to the standard Notch model reveals significant differences in process window and exposure margin, yet negligible changes in feature profile and iso-dense bias at best focus and exposure.