Dr. Scott Mansfield Profile

Dr. Scott Mansfield

at GLOBALFOUNDRIES Inc

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Author

Publications (3)

SPIE Journal Paper | 31 July 2018

Subresolution assist features impact and implementation in extreme ultraviolet lithography for next-generation beyond 7-nm node

Vivian Wei Guo, Fan Jiang, Alexander Tritchkov, Srividya Jayaram, Scott Mansfield, Larry Zhuang, Yuyang Sun, Xima Zhang, Todd Bailey, James Word

JM3, Vol. 18, Issue 01, 011003, (July 2018) https://doi.org/10.1117/12.10.1117/1.JMM.18.1.011003

KEYWORDS: SRAF, Photomasks, Metals, Extreme ultraviolet lithography, Personal protective equipment, Photovoltaics, Extreme ultraviolet, Image quality, Source mask optimization, Lithography

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The next-generation beyond 7-nm node potentially requires the implementation of subresolution assist features (SRAF) with extreme ultraviolet (EUV) lithography. This paper aims at providing a clear SRAF strategy for the next-generation beyond 7-nm node designs through a series of experiments. Various factors are considered, including stochastic effects, three-dimensional (3-D) mask effects, through-slit effects, aberrations, and pixelated source mask optimization (SMO) sources. We consider process variability bands with a variety of process conditions, including focus/dose/mask bias changes and also the normalized image log-slope/image log-slope as our objective functions, to determine what the best SRAF solution is for a set of test patterns. Inverse lithography technology is implemented to optimize both the main feature (MF) mask and SRAF placement, in particular, asymmetric SRAF placement to balance the 3-D mask effects. SRAF can potentially mitigate image shift through-focus, i.e., nontelecentricity, caused by EUV 3-D shadowing effect. This shadowing effect is pattern-dependent and contributes to the overlay variation. As we approach the next-generation beyond 7-nm node, this image shift can be more significant relative to the overlay budget, hence, we further investigate the impact of SRAF placement to the image shift. Moreover, the center of focus shift due to the large 3-D mask absorber thickness can be potentially mitigated by SRAF implementation. The common process window is significantly impacted by both the center of focus shift and the individual depth of focus and is evaluated using both metal and contact layer test cases. We study the source impact to SRAF insertion by experimenting with both a symmetric source (standard source) and an asymmetric source (SMO source). Finally, we understand the importance of using full flare map and full through-slit model (including aberration variation through-slit) in the MF correction. Furthermore, we evaluate the need of using full models in SRAF insertion. This is a necessary step to determine the strategy of SRAF implementation for the next-generation beyond 7-nm node.

Proceedings Article | 19 March 2018 Paper

SRAF requirements, relevance, and impact on EUV lithography for next-generation beyond 7nm node

Vivian Wei Guo, Fan Jiang, Alexander Tritchkov, Srividya Jayaram, Scott Mansfield, Larry Zhuang, Yuyang Sun, Xima Zhang, Todd Bailey

Proceedings Volume 10583, 105830N (2018) https://doi.org/10.1117/12.2297410

KEYWORDS: SRAF, Photomasks, Extreme ultraviolet lithography, Image quality, Source mask optimization, Optical proximity correction

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The next generation beyond 7nm node potentially requires the implementation of Sub-Resolution Assist Features (SRAF) with EUV lithography. This paper aims at providing a clear SRAF strategy for the next generation beyond 7nm node designs through a series of experiments. Various factors are considered, including: stochastic effects, 3D mask effects, through-slit effects, aberrations, and pixelated SMO sources.

EUV has 13.5nm as its wavelength, which is much smaller than the wavelength used in ArF lithography, and this gives very different imaging challenges compared to the ArF case. Due to the small wavelength and numerical aperture (NA) of the current EUV tools, depth of focus is not as significant of a concern as in DUV. Instead, EUV lithography is severely challenged by stochastic effects, which are directly linked to the slope of the intensity curve. DUV SRAF has been shown to be a powerful tool for improving NILS/ILS, as well as DOF, and here we explore how that translates into EUV imaging. In this paper, we consider Process Variability (PV) Bands with a variety of process conditions including focus/dose/mask bias changes and also the NILS/ILS as our objective functions, to determine what the best SRAF solution is for a set of test patterns. We have full investigations on both symmetric SRAF and asymmetric SRAF.

SRAF can potentially mitigate image shift through focus, i.e. non-telecentricity, caused by EUV 3D shadowing effect. This shadowing effect is pattern dependent and contributes to the overlay variation. As we approach the next generation beyond 7nm node, this image shift can be more significant relative to the overlay budget, hence we further investigate the impact of SRAF placement to the image shift. Moreover, the Center of Focus shift due to the large 3D mask absorber thickness can be potentially mitigated by SRAF implementation. The common process window is significantly impacted by both the center of focus shift and the individual depth of focus. We study the change by adding SRAF using both a symmetric source (standard source) and an asymmetric source (SMO source). Once SRAF is inserted for the test patterns, the common process window is plotted to compare the solutions with and without SRAF.

Finally, we understand the importance of using full flare map and full through slit model (including aberration variation through slit) in the main feature correction, but in this paper, we will further evaluate the need of using full models in SRAF insertion. This is a necessary step to determine the strategy of SRAF implementation for the next generation beyond 7nm node.

Proceedings Article | 19 March 2018 Presentation + Paper

A comparison of different methods of characterizing EUV photoresist shrinkage

Ramya Viswanathan, Scott Mansfield, Wenxin Li, Shuhai Fan, Roger Cornell, Hongxin Zhang

Proceedings Volume 10583, 105830Z (2018) https://doi.org/10.1117/12.2297695

KEYWORDS: Metrology, Etching, Photoresist materials, Scanning electron microscopy, Optical proximity correction, Extreme ultraviolet lithography, Critical dimension metrology, Deep ultraviolet, Extreme ultraviolet, Data modeling

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