The introduction of double and triple patterning tightened the Overlay current nodes’ specifications across the industry to levels of 5nm and 3nm respectively. Overlay error is a combination of Intra-field and field-to-field errors. The Intra-field error includes several systematic signatures, such as overlay magnitude differences between X and Y axes, field center vs edge and more. The recent developments in scanner technology improved the intra-field Overlay to high orders. In this work we have quantified the state-of-the-art residual overlay errors and applied the RegC® (registration/overlay control) process, a new solution of deep sub-nanometer pattern shift, to further improve the overlay process control, in addition to the current lithography’s state-of-the-art capabilities. As a result we managed to reduce the baseline overlay error by more than one nanometer and reduced systematic intrafield non-uniformities, by removing the 3 sigma difference between X and Y to zero. The combination of intra-field control by RegC® with high order correction per exposure (CPE) by the scanner provides a new era of overlay control required for the 2x and 1x multiple patterning processes.
Mask Manufacturers are continuously asked to supply reticles with reduced CD (Critical Dimension) specification, such as CD Uniformity and Mean to target. To meet this on-going trend the industry is in a quest for higher resolution metrology tools, which in-turn drives the use of SEM metrology into standard mask manufacturing process. As dimensions of integrated circuit features reduce, the negative effects of roughness of the features, and/or of components such as photo-resist and ancillary structures used to produce the features, become more pronounced since there is not necessarily a corresponding reduction of roughness with dimension reduction. As a result of the increased problems, metrics that quantify roughness of specific sections of an integrated circuit have been developed; for example, line edge roughness (LER) measures the roughness of a linear edge.
This paper concentrates on one specific area of the Mask Metrology, being measurement of the different Roughness metrics of the reticle features such as lines and contacts, using a new SEM metrology tool, the Applied Materials RETicleSEM. We describe the comprehensive Roughness Analysis Algorithm package that performs precise measurements of the different Roughness metrics including Fourier analysis, auto-correlation function and correlation length. This package can be used to isolate and characterize the roughness of specific wavelength ranges that may be of interest for mask manufacturing process and/or mask quality control considerations. We conclude with sample results of Roughness Analysis on real SEM images of Reticle lines. The influence of CD roughness on the precision of measurements is considered. The proof that long-wave roughness can be one from the sources of flyers during CD measurements is presented.
Downscaling of semiconductor fabrication technology nodes brought forth a need to reassess the accuracy of 3D metrology. Accuracy is defined relative to a reference tool measurement. The authors have studied the accuracy of 3D SEM measurement results for various feature geometries and materials, matching the results to Monte Carlo simulations. Analysis of the SEM images based on an analytical model was performed. Careful analysis of the matching curves for 3D algorithm results and reference data (geometric parameters of the feature) reviled an appropriate behavior of algorithm in the vicinity of the nominal process window, and for sufficiently small feature rounding (production node). We performed matching of 3D CD SEM measurement to reference geometry data using Monte Carlo simulation. We analyzed the accuracy of measurement for a wide range of the feature geometry parameters (height, sidewall angle, top and bottom rounding). The simple physical model for corner rounding estimation is considered. We perform the model waveform analysis of the feature rounding influence on the height measurements. Serving as a process-monitoring tool, the algorithm performance was found in agreement with the required tolerance typical of the nominal process window ± 10%. Serving on extreme R&D, where rounding further away from the nominal window ± 10% is counted significant, there lie observable deviations in accuracy of height and sidewall angle measurement. These are explained through extreme corner rounding effects.
The rapid shrink of device dimensions requires not only excellent 1D CD precision, but also characterization of corner rounding and line end shape. To meet this on-going trend the industry is in a quest for higher resolution metrology tools, which in-turn drives the use of SEM metrology as more crucial. The industry challenge is to reduce corner rounding and area loss. The metrology challenge, is to be able to measure accurately and precisely these characters, in order to be able to control your process. In our study we will introduce the development of a new algorithm for general shape analysis. The purpose of this algorithm is to allow effective control of the correspondence of the feature’s shape to the design geometry. The disadvantage of the standard CD SEM metric such as contact area was discussed widely in the literature but new metrics were not discussed yet. We consider the following issues and challenges related to the development of a generic algorithm for general shape 2D analysis.
First stage of this algorithm is a generic segmentation of the two dimensional features. It should be robust to noise, as well as brightness and contrast changes. Output of this phase will be the contour representing the bottom of the feature. The second stage is the obtaining of new CD metrics for these contours, especially for contours corresponding to contacts with OPC structures. We consider the corner rounding as an example of such new metric. The same techniques can be elaborated for a large range of 2D structures with different levels of complexity. The obtaining of new metrics can be useful as handles for advanced process control (i.e. what to measure on the 2D feature with complex shape such as contact with OPC structures). We consider in this paper the application of the developed metrics for reticle contact with OPC structure monitoring problem that simulates a high level of complexity.
Proc. SPIE. 5446, Photomask and Next-Generation Lithography Mask Technology XI
KEYWORDS: Reticles, Metrology, Image segmentation, Image processing, Feature extraction, Scanning electron microscopy, Photomasks, Optical proximity correction, Algorithm development, OLE for process control
The rapid shrink of device dimensions requires reduced feature size on reticles and hence, improved CD uniformity and CD measurement precision in order to achieve tight process control. To meet this on-going trend the industry is in a quest for higher resolution metrology tools, which in-turn drives the use of SEM metrology into standard mask and manufacturing process. This paper concentrates on one specific area of Mask Metrology, being measurement of 2D (Two Dimensional) features such as contacts with sub resolution features -0 using a new SEM metrology tool, the Applied Materials' RETicleSEM. We consider the basic requirements for performing 2D measurements on a reticle as well as the algorithmic development to generalize a solution for these requirements. We consider three main requirements from such algorithm: a) It should be generic and deal with general shape features; b) It should provide new geometric metrics - such as contact area and corner roundness; c) It should measure new geometric patterns such as OPC (Optical Proximity Corrections) features and small CDs. We discuss the following issues/challenges related to the development of a generic algorithm for general shape 2D analysis: a) Limitations of the standard approach for Contacts qualification based on the Area loss measurement (Area based). b) A generic segmentation of the feature. It should be robust to noise, as well as brightness and contrast changes. c) The complexity of two dimensional general shape features metrology, especially OPC measurements. Limitations of the standard CD SEM metrology based on metrics describing simple geometric shapes such as ellipses and lines. The obtaining of new metrics can be useful as handles for advanced process control (i.e. what to measure on the 2D feature with complex shape such as contact with OPC structures).
SEM Metrology becomes the standard metrology for the mask industry, as the precision and accuracy requirements tighten continuously. At the same time, analysis of general shape features becomes an important task in wafer metrology. In this paper we consider the basic requirements and suggested implementations for performing 2D metrology on reticles and wafers, [i.e. measurements of OPC (Optical Proximity Correction) structures, End of Lines, Dual Damascene and Corner Rounding]. The authors consider the following challenges related to the development of a generic algorithm for general shape 2D analysis: (1) A generic segmentation of the feature. It should be robust to noise, as well as brightness and contrast changes. (2) The complexity of two dimensional general shape features metrology. Standard CD SEM metrology is based on metrics describing simple geometric shapes such as ellipses and lines). (3) Obtaining such metrics that can be used as handles for process control (i.e. what to measure on the 2D feature). In the first part of the paper we describe a novel algorithm for segmentation and geometric analysis of general shape features based on a Smoothing Spline and the methods of differential geometry. Next, we consider the numerical methods implemented for shape analysis of noisy contours. In the second part of the paper the performance of our methods on synthetic contours of circular arc with different noise levels is demonstrated. We conclude with sample results of several suggested metrics measured on real SEM images of reticles and wafers.