Dr. Saptaparna Das Profile

Dr. Saptaparna Das

Sr. Optical Engineer at Cymer LLC

SPIE Involvement:

Author

Area of Expertise:

ultrafast spectroscopy in condensed phase and interfaces , characterization of organic and inorganic/hybrid photovoltaics , photo-lithography , optical properties of nanomaterials , triplet photophysics

Sr. Optical Engineer, Cymer An ASML Company June 2016 – present
- Designing and performing experiments to analysis the optics lifetime for 193 nm light sources
- Designing and developing optical assemblies for 193 nm light sources
- Analyzing the damage for 193 nm optics and developing a new optics damage tester tool.

Postdoctoral Researcher, at University of Pennsylvania Aug 2015-May 2016
- Built a new 2D Electronic and 2D Infrared Spectrometer.
- Performed ultrafast multidimensional dynamics of artificial photosynthetic systems and donor-acceptor type molecules.
- Performed theoretical calculations to estimate electronic and vibrational transitions of various optically-active chromophores.

Graduate Research Assistant, University of Southern California, Advisor: Prof. Stephen Bradforth 2009-2015
- Performed transient absorption measurements to understand the physical reason behind a good/bad device performance of a polymer based organic photovoltaic and hybrid nano-structured photovoltaics.
- Performed time-resolved measurements to optimize the coupling required between two tetracenes to enhance the singlet fission yield in an isolated dimer molecule in the solution.
- Characterized the dynamics behind the generation of intramolecular charge transfer states in mimics of photosynthetic complexes.

Proceedings Article | 16 November 2018 Paper

Accelerated testing of high fluence protective coated optics

Saptaparna Das, John Melchior, Eric Mason

Proceedings Volume 10805, 1080526 (2018) https://doi.org/10.1117/12.2500240

KEYWORDS: Optical coatings, Fluorine, Crystals, Photons, Absorption, Surface finishing, Thin film coatings, Excimer lasers, Statistical analysis

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Excimer lasers are the commonly used light sources for photo-lithography industries; one challenge is to minimize the production interruption by providing a reliable source of DUV (193 nm) photons. This requires CaF₂ optics with high transmission and optical uniformity at 193 nm over a long lifetime. However, CaF₂ crystal can possess defects due to mis-orientation and dislocations in the sub-grain boundaries, which can act as an absorption or scattering center leading to transmission loss and thermal stress induced birefringence in the CaF₂ crystal. In addition, the CaF₂ surface can suffer from different mechanical stress due to cleaning and finishing processes leading to formation of surface imperfections/fractures known as sub-surface damage. This sub-surface damage layer is prone to damage under high fluence 193 nm exposure and can lead to fluorine escape from the CaF₂ lattice. Protective coatings for CaF₂ optics have been developed to prevent surface fluorine depletion from 193 nm exposure. However, these protective coatings can also develop defects due to imperfections in the coating fabrication process and/or photochemical reaction initiated by 193 nm photons in presence of traces of oxygen, water vapor or carbon dioxide. Therefore, to provide uninterrupted 193 nm photons a robust protective coating is required to extend the lifetime of CaF₂ optics. Generally, field learnings for high fluence protective coating can require from 6 months to a year of normal operation and thus validation of protective coatings based on field data alone can hinder the adoption of improved technology. To expedite this selection process, an accelerated 193 nm exposure setup was built to test high fluence protective coatings from different suppliers at various elevated fluences for a short period of time (~2-3 weeks). This setup was successful in screening the best high fluence protective coating under highly accelerated 193 nm exposure. Additionally, based on the relative performance of the protective coatings under accelerated conditions and use case in-laser fluence conditions, the lifetime for the high fluence protective coatings were estimated for the use case scenario.

Proceedings Article | 21 March 2018 Paper

DUV light source sustainability achievements and next steps

Yzzer Roman, Ted Cacouris, Kumar Raja Guvindan Raju, Dinesh Kanawade, Walt Gillespie, Siqi Luo, Eric Mason, David Manley, Saptaparna Das

Proceedings Volume 10587, 1058716 (2018) https://doi.org/10.1117/12.2299387

KEYWORDS: Light sources, Neon, Deep ultraviolet, Carbon, Metals, Semiconducting wafers, Helium, Semiconductors, Nitrogen

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Proceedings Article | 20 August 2015 Presentation + Paper

Absolute polaron yield of donor-acceptor P3HT:fullerene bulk heterojunction composites

Saptaparna Das, Alia Latif, William Thornbury, Barry Thompson, Stephen Bradforth

Proceedings Volume 9549, 95490N (2015) https://doi.org/10.1117/12.2189531

KEYWORDS: Polarons, Polymers, Absorption, Chromophores, Doping, Interfaces, Excitons, Polymer thin films, Composites, Diffusion

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