Dr. Prasad Dasari Profile

Dr. Prasad Dasari

Principal Scientist

SPIE Involvement:

Author

Publications (24)

SPIE Journal Paper | 25 October 2016

Measuring self-aligned quadruple patterning pitch walking with scatterometry-based metrology utilizing virtual reference

Taher Kagalwala, Alok Vaid, Sridhar Mahendrakar, Michael Lenahan, Fang Fang, Paul Isbester, Michael Shifrin, Yoav Etzioni, Aron Cepler, Naren Yellai, Prasad Dasari, Cornel Bozdog

JM3, Vol. 15, Issue 04, 044004, (October 2016) https://doi.org/10.1117/12.10.1117/1.JMM.15.4.044004

KEYWORDS: Semiconducting wafers, Metrology, Optical lithography, Scatterometry, Critical dimension metrology, Finite element methods, Scatter measurement, Diffractive optical elements, Transmission electron microscopy, Reactive ion etching

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Proceedings Article | 24 March 2016 Paper

Paper

Scatterometry-based metrology for SAQP pitch walking using virtual reference

Taher Kagalwala, Alok Vaid, Sridhar Mahendrakar, Michael Lenahan, Fang Fang, Paul Isbester, Michael Shifrin, Yoav Etzioni, Aron Cepler, Naren Yellai, Prasad Dasari, Cornel Bozdog

Proceedings Volume 9778, 97781W (2016) https://doi.org/10.1117/12.2228329

KEYWORDS: Transmission electron microscopy, Metrology, Optical lithography, Scatterometry, Reactive ion etching, Etching, Semiconducting wafers, Diffractive optical elements, Critical dimension metrology, Scatter measurement

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Proceedings Article | 24 March 2016 Paper

Paper

Hybrid enabled thin film metrology using XPS and optical

Alok Vaid, Givantha Iddawela, Sridhar Mahendrakar, Michael Lenahan, Mainul Hossain, Padraig Timoney, Abner Bello, Cornel Bozdog, Heath Pois, Wei Ti Lee, Mark Klare, Michael Kwan, Byung Cheol Kang, Paul Isbester, Matthew Sendelbach, Naren Yellai, Prasad Dasari, Tom Larson

Proceedings Volume 9778, 97780M (2016) https://doi.org/10.1117/12.2220299

KEYWORDS: Metrology, Thin films, X-rays, X-ray optics, Semiconducting wafers, Wafer-level optics, Process control, Ellipsometry, Diffractive optical elements, Deposition processes, Optical testing, Dielectrics, Optical properties

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Proceedings Article | 19 March 2015 Paper

Paper

Comprehensive BEOL control using scatterometry and APC

Padraig Timoney, Jamie Tsai, Sudhir Baral, Laertis Economikos, Alok Vaid, Haibo Lu, Byungcheol Kang, Paul Isbester, Prasad Dasari, Roy Kort, Naren Yellai

Proceedings Volume 9424, 94241G (2015) https://doi.org/10.1117/12.2087320

KEYWORDS: Copper, Chemical mechanical planarization, Scatterometry, Metrology, Semiconducting wafers, Resistance, Reactive ion etching, Etching, 3D modeling, Back end of line

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Copper interconnects have been adopted in advanced semiconductor manufacturing due to benefits of reduced RC delay, cross talk and power consumption. With each technology node, interconnects reduce in size resulting in increased line resistivity, a critical metric in determining the device performance. Reactive Ion Etching (RIE) and Copper Chemical Mechanical Polishing (Cu CMP) are two of the key back end of the line (BEOL) processes that affect the interconnect performance. Due to variations from incoming processes and the inherent variability induced by these processes, dielectric trench depth and resulting copper line height variations that can potentially result from these processes have direct impact to RC delay.

Traditional inline metrology methods used are time consuming and do not provide the needed wafer level metrics. In addition, measurement of remaining dielectric thickness on solid pads is not a good representative of the actual device structures and has been inaccurate for process due to dishing of the copper pads. Efficient control of BEOL processes requires measurement of metal line thickness and other critical profile parameters from which resistance can be extracted. In order to relate BEOL process steps and understand their interactions, it is necessary to have a directly comparable measurement methodology on a similar measurement structure.

Over the past several years, scatterometry has been proven as the only metrology method to provide the full profile information of the Cu lines. Scatterometry is a diffraction based optical measurement technique using Rigorous Coupled Wave Analysis (RCWA), where light diffracted from a periodic structure is used to characterize the details of profile. Unique algorithms, such as Holistic Metrology can be used to make the scatterometry development process faster.

In this paper, we will present how scatterometry can be used to measure copper line height on 3D structures and how feed forward from RIE can be applied for control of Cu CMP process for 20nm technology node. The importance of incoming trench depth variations is demonstrated for CMP polish time control in order to stabilize the copper line height. Validation data is presented for different scatterometry models including accuracy, repeatability and DoE tracking. Electrical resistance is shown to correlate to the copper trench profile measured by scatterometry. The paper will demonstrate the capability for reducing copper line height variation and the correlation of the reducing trench height variation to improved stabilization of electrical resistance.

Proceedings Article | 10 April 2013 Paper

Paper

Scatterometry evaluation of focus-dose effects of EUV structures

Prasad Dasari, Oleg Kritsun, Jie Li, Catherine Volkman, Jiangtao Hu, Zhuan Liu

Proceedings Volume 8681, 86810T (2013) https://doi.org/10.1117/12.2012120

KEYWORDS: Critical dimension metrology, Scatterometry, Extreme ultraviolet lithography, Extreme ultraviolet, Semiconducting wafers, Metrology, Scanners, 3D modeling, Scanning electron microscopy, Ellipsometry

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Proceedings Article | 10 April 2013 Paper

Paper

Evaluating scatterometry 3D capabilities for EUV

Jie Li, Oleg Kritsun, Prasad Dasari, Catherine Volkman, Tom Wallow, Jiangtao Hu

Proceedings Volume 8681, 86810S (2013) https://doi.org/10.1117/12.2011675

KEYWORDS: Semiconducting wafers, Scatterometry, Metrology, Extreme ultraviolet, Critical dimension metrology, Extreme ultraviolet lithography, 3D metrology, Neodymium, Spectroscopic ellipsometry, Lithography

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Proceedings Article | 5 April 2012 Paper

Paper

Faster diffraction-based overlay measurements with smaller targets using 3D gratings

Jie Li, Oleg Kritsun, Yongdong Liu, Prasad Dasari, Catherine Volkman, Jiangtao Hu

Proceedings Volume 8324, 83241I (2012) https://doi.org/10.1117/12.916747

KEYWORDS: Semiconducting wafers, Overlay metrology, 3D acquisition, 3D metrology, Finite element methods, Diffraction gratings, Time metrology, Spectroscopy, Reflectance spectroscopy, 3D modeling

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Proceedings Article | 5 April 2012 Paper

Paper

Scatterometry metrology challenges of EUV

Prasad Dasari, Jie Li, Jiangtao Hu, Zhuan Liu, Oleg Kritsun, Catherine Volkman

Proceedings Volume 8324, 83240M (2012) https://doi.org/10.1117/12.916006

KEYWORDS: Scatterometry, Extreme ultraviolet lithography, Critical dimension metrology, Extreme ultraviolet, Metrology, Semiconducting wafers, Double patterning technology, Cadmium, Optical lithography, Ellipsometry

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Proceedings Article | 20 April 2011 Paper

Paper

Metrology characterization of spacer double patterning by scatterometry

Prasad Dasari, Jie Li, Jiangtao Hu, Zhuan Liu, Oleg Kritsun, Catherine Volkman

Proceedings Volume 7971, 797111 (2011) https://doi.org/10.1117/12.879900

KEYWORDS: Scatterometry, Critical dimension metrology, Semiconducting wafers, Metrology, Double patterning technology, Etching, Process control, Scatter measurement, Reflectometry, Scanning electron microscopy

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Proceedings Article | 20 April 2011 Paper

Paper

Advancements of diffraction-based overlay metrology for double patterning

Jie Li, Oleg Kritsun, Yongdong Liu, Prasad Dasari, Ulrich Weher, Catherine Volkman, Martin Mazur, Jiangtao Hu

Proceedings Volume 7971, 79711Y (2011) https://doi.org/10.1117/12.879552

KEYWORDS: Overlay metrology, Double patterning technology, Reflectance spectroscopy, Detection and tracking algorithms, Time metrology, Semiconducting wafers, Diffraction, Diffraction gratings, Spectroscopy, Reflectometry

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SPIE Journal Paper | 1 October 2010

Scatterometry characterization of spacer double patterning structures

Prasad Dasari, Jiangtao Hu, Zhuan Liu, Asher Tan, Oleg Kritsun, Catherine Volkman, Christopher Bencher

JM3, Vol. 9, Issue 04, 041309, (October 2010) https://doi.org/10.1117/12.10.1117/1.3531999

KEYWORDS: Scatterometry, Critical dimension metrology, Double patterning technology, Semiconducting wafers, Etching, Reflectance spectroscopy, Metrology, Spectroscopy, Reflectometry, Lithography

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Proceedings Article | 2 April 2010 Paper

Paper

Scatterometry characterization of spacer double patterning structures

Prasad Dasari, Jiangtao Hu, Zhuan Liu, Asher Tan, Oleg Kritsun, Catherine Volkman, Chris Bencher

Proceedings Volume 7638, 76381J (2010) https://doi.org/10.1117/12.848518

KEYWORDS: Scatterometry, Critical dimension metrology, Double patterning technology, Semiconducting wafers, Etching, Metrology, Overlay metrology, Scatter measurement, Spectroscopy, Ellipsometry

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Proceedings Article | 2 April 2010 Paper

Paper

Advanced diffraction-based overlay for double patterning

Jie Li, Yongdong Liu, Prasad Dasari, Jiangtao Hu, Nigel Smith, Oleg Kritsun, Catherine Volkman

Proceedings Volume 7638, 76382C (2010) https://doi.org/10.1117/12.848516

KEYWORDS: Overlay metrology, Double patterning technology, Spectroscopic ellipsometry, Semiconducting wafers, Time metrology, Optical components, Metrology, Diffraction, Integrated circuits, Critical dimension metrology

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Proceedings Article | 2 April 2010 Paper

Paper

A comparison of advanced overlay technologies

Prasad Dasari, Nigel Smith, Gary Goelzer, Zhuan Liu, Jie Li, Asher Tan, Chin Hwee Koh

Proceedings Volume 7638, 76381P (2010) https://doi.org/10.1117/12.848189

KEYWORDS: Overlay metrology, Semiconducting wafers, Scatterometry, Error analysis, Data modeling, Reflectometry, Process control, Spectroscopy, Diffraction gratings, Carbon

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Proceedings Article | 24 March 2009 Paper

Paper

Diffraction-based overlay metrology for double patterning technologies

Prasad Dasari, Rahul Korlahalli, Jie Li, Nigel Smith, Oleg Kritsun, Cathy Volkman

Proceedings Volume 7272, 727212 (2009) https://doi.org/10.1117/12.816590

KEYWORDS: Overlay metrology, Double patterning technology, Optical lithography, Data modeling, Metrology, Semiconducting wafers, Scatterometry, Spectroscopy, Lithography, Etching

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Proceedings Article | 23 March 2009 Paper

Paper

Simultaneous overlay and CD measurement for double patterning: scatterometry and RCWA approach

Jie Li, Zhuan Liu, Silvio Rabello, Prasad Dasari, Oleg Kritsun, Catherine Volkman, Jungchul Park, Lovejeet Singh

Proceedings Volume 7272, 727207 (2009) https://doi.org/10.1117/12.814706

KEYWORDS: Overlay metrology, Critical dimension metrology, Semiconducting wafers, Scatterometry, Double patterning technology, Error analysis, Reflectivity, Metrology, Cadmium, Diffraction gratings

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Proceedings Article | 26 March 2008 Paper

Paper

Diffraction based overlay metrology for alpha-carbon applications

Chandra Saru Saravanan, Asher Tan, Prasad Dasari, Gary Goelzer, Nigel Smith, Seouk-Hoon Woo, Jang Ho Shin, Hyun Jae Kang, Ho Chul Kim

Proceedings Volume 6922, 69222W (2008) https://doi.org/10.1117/12.775811

KEYWORDS: Semiconducting wafers, Overlay metrology, Diffraction, Scatterometry, Spectroscopy, Diffraction gratings, Photomasks, Silicon, Reflectivity, Optical alignment

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Proceedings Article | 22 March 2008 Paper

Paper

Evaluating diffraction based overlay metrology for double patterning technologies

Chandra Saru Saravanan, Yongdong Liu, Prasad Dasari, Oleg Kritsun, Catherine Volkman, Alden Acheta, Bruno La Fontaine

Proceedings Volume 6922, 69220C (2008) https://doi.org/10.1117/12.774736

KEYWORDS: Overlay metrology, Double patterning technology, Silicon, Scatterometry, Optical lithography, Diffraction, Spectroscopy, Critical dimension metrology, Photoresist materials, Metrology

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Proceedings Article | 22 March 2008 Paper

Paper

Overlay metrology tool calibration using blossom

Lewis Binns, Nigel Smith, Prasad Dasari

Proceedings Volume 6922, 69220M (2008) https://doi.org/10.1117/12.773277

KEYWORDS: Overlay metrology, Calibration, Metrology, Reticles, Semiconducting wafers, Image processing, Reflectivity, Signal to noise ratio, Diagnostics, Radar

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As overlay budgets continue to shrink, there is an increasing need to more fully characterize the tools used to measure overlay. In a previous paper, it was shown how a single-layer Blossom overlay target could be utilized to measure aberrations across the field of view of an overlay tool in an efficient and low-cost manner. In this paper, we build upon this method, and discuss the results obtained, and experiences gained in applying this method to a fleet of currently operational overlay tools. In particular, the post-processing of the raw calibration data is discussed in detail, and a number of different approaches are considered. The quadrant-based and full-field based methods described previously are compared, along with a half-field method. In each case we examine a number of features, including the trade off between ease of use (including the total number of measurements required) versus sensitivity / potential signal to noise ratio. We also examine how some techniques are desensitized to specific types of tool or mark aberration, and suggest how to combine these with non-desensitized methods to quickly identify these anomalies. There are two distinct applications of these tool calibration methods. Firstly, they can be used as part of the tool build and qualification process, to provide absolute metrics of imaging quality. Secondly, they can be of significant assistance in diagnosing tool or metrology issues or providing preventative maintenance diagnostics, as (as shown previously) under normal operation the results show very high consistency, even compared to aggressive overlay requirements. Previous work assumed that the errors in calibration, from reticle creation through to the metrology itself, would be Gaussian in nature; in this paper we challenge that assumption, and examine a specific scenario that would lead to very non-Gaussian behavior. In the tool build / qualification application, most scenarios lead to a systematic trend being superimposed over Gaussian-distributed measurements; these cases are relatively simple to treat. However, in the tool diagnosis application, typical behavior will be very non- Gaussian in nature, for example individual outlier measurements, or exhibiting bimodal or other probability distributions. In such cases, we examine the effect that this has on the analysis, and show that such anomalous behaviors can occur "under the radar" of analyses that assume Gaussian behavior. Perhaps more interestingly, the detection / identification of non-Gaussian behavior (as opposed to the parameters of a best fit Gaussian probability density function) can be a useful tool in quickly isolating specific metrology problems. We also show that deviation of a single tool, relative to the tool fleet, is a more sensitive indicator of potential issues.

Proceedings Article | 17 March 2008 Paper

Paper

Multi-patterning overlay control

C. Ausschnitt, P. Dasari

Proceedings Volume 6924, 692448 (2008) https://doi.org/10.1117/12.772865

KEYWORDS: Overlay metrology, Double patterning technology, Error analysis, Metals, Optical alignment, Optical lithography, Lithography, Photomasks, Metrology, Image processing

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Proceedings Article | 5 April 2007 Paper

Paper

Blossom overlay metrology implementation

C. Ausschnitt, W. Chu, D. Kolor, J. Morillo, J. Morningstar, W. Muth, C. Thomison, R. Yerdon, L. Binns, P. Dasari, H. Fink, N. Smith, G. Ananew

Proceedings Volume 6518, 65180G (2007) https://doi.org/10.1117/12.712669

KEYWORDS: Overlay metrology, Metrology, Photomasks, Imaging systems, Semiconducting wafers, Lithography, Manufacturing, Imaging metrology, Scanning electron microscopy, Optical lithography

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Proceedings Article | 5 April 2007 Paper

Paper

Overlay metrology tool calibration

L. Binns, P. Dasari, N. Smith, G. Ananew, H. Fink, C. Ausschnitt, J. Morningstar, C. Thomison, R. Yerdon

Proceedings Volume 6518, 65180I (2007) https://doi.org/10.1117/12.712769

KEYWORDS: Calibration, Overlay metrology, Semiconducting wafers, Metrology, Photomasks, Standards development, Lithography, Manufacturing, Optics manufacturing, Optical calibration

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In a previous publication, we introduced Blossom, a multi-layer overlay mark (Ausschnitt, et al. 2006, [1]). Through further testing carried out since that publication, Blossom has been shown to meet the requirements on current design rules (Ausschnitt, et al. 2007, [2]), while giving some unique benefits. However, as future design rules shrink, efforts must be made now to ensure the extensibility of the Blossom technology. Previous work has shown that the precision component of Total Measurement Uncertainty (TMU) can be reduced by using extra redundancy in the target design, to achieve performance beyond that of a conventional box-in-box measurement. However, improvements that single contributor to TMU would not be sufficient for future design rules; therefore we have also to consider the Tool Induced Shift (TIS) variability and tool to tool matching contributions to TMU. In this paper, we introduce a calibration artifact, based on the Blossom technology. The calibration artifact is both compact, and produced by standard lithography process, so it can be placed in a production scribe line if required, reducing the need for special sets of calibration wafers compared to other possible calibration methodologies. Calibration is currently with respect to the exposure tool / process / mask, which is arguably more pertinent to good yield, and less expensive, than calibration to an external standard; externally calibrated artifacts would be straightforward to manufacture if needed. By using this artifact, we can map out remaining optical distortions within an overlay tool, to a precision significantly better than the operational tool precision, in a way that directly relates to overlay performance. The effect of process-induced mark uncertainties on calibration can be reduced by performing measurements on a large number of targets; by taking multiple measurements of each target we can also use the artifact to evaluate the current levels of process induced mark uncertainty. The former result leads to an improvement method for TIS and matching capability. We describe the artifact and its usage, and present results from a group of operational overlay tools. We show how the use of this information also provides further insight into the layout optimizations discussed previously (Binns et al. 2006 [3]). It provides the current limits of measurement precision and mark fidelity with respect to target redundancy, enabling us to use a predictive cost-benefit term in the optimization. Finally, examining the bulk behaviour of a fleet of overlay tools, allows us to examine how future mark layouts can also contribute to minimizing TMU rather than just precision.

Proceedings Article | 10 May 2005 Paper

Paper

Metal etcher qualification using angular scatterometry

Igor Jekauc, Jasen Moffitt, Sushil Shakya, Elizabeth Donohue, Prasad Dasari, Christopher Raymond, Mike Littau

Proceedings Volume 5752, (2005) https://doi.org/10.1117/12.598828

KEYWORDS: Semiconducting wafers, Etching, Metals, Scatterometry, Polymers, Profilometers, Scanning electron microscopy, Critical dimension metrology, Metrology, Tin

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Proceedings Article | 10 May 2005 Paper

Paper

Lithography tool qualification using angular scatterometry

Mike Littau, Christopher Raymond, Prasad Dasari, Jasen Moffitt, Sushil Shakya

Proceedings Volume 5752, (2005) https://doi.org/10.1117/12.600413

KEYWORDS: Lithography, Scatterometry, Semiconducting wafers, Metrology, Optical lithography, Model-based design, Scanners, Process control, Photoresist materials, Diffraction gratings

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Showing 5 of 24 publications

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