Extreme ultraviolet (EUV) photons expose photoresists by complex interactions starting with photoionization that create primary electrons (∼80 eV), followed by ionization steps that create secondary electrons (10 to 60 eV). Ultimately, these lower energy electrons interact with specific molecules in the resist that cause the chemical reactions which are responsible for changes in solubility. The mechanisms by which these electrons interact with resist components are key to optimizing the performance of EUV resists. A resist exposure chamber was built to probe the behavior of electrons within photoresists. Resists were exposed under electron beam and then developed; ellipsometry was used to identify the dependence of electron penetration depth and number of reactions on dose and energy. Additionally, our group has updated a robust software that uses a first principles-based Monte Carlo model called low-energy electron scattering in solids (LESiS) to track secondary electron production, penetration depth, and reaction mechanisms within materials-defined environments. LESiS was used to model the thickness loss experiments to validate its performance with respect to simulated electron penetration depths to inform future modeling work.
Since completely defect-free masks will be hard to achieve, it is essential to have a good understanding of the printability of the native extreme ultraviolet (EUV) mask defects. In this work, we performed a systematic study of native mask defects to understand the defect printability they cause. The multilayer growth over native substrate mask blank defects was correlated to the multilayer growth over regular-shaped defects having similar profiles in terms of their width and height. To model the multilayer growth over the defects, a multilayer growth model based on a level-set technique was used that took into account the tool deposition conditions of the Veeco Nexus ion beam deposition tool. Further, the printability of the characterized native defects was studied at the SEMATECH-Berkeley Actinic Inspection Tool (AIT), an EUV mask-imaging microscope at Lawrence Berkeley National Laboratory. Printability of the modeled regular-shaped defects, which were propagated up the multilayer stack using level-set growth model, was studied using defect printability simulations implementing the waveguide algorithm. Good comparison was observed between AIT and the simulation results, thus demonstrating that multilayer growth over a defect is primarily a function of a defect’s width and height, irrespective of its shape.
EUV photons expose photoresists by complex interactions starting with photoionization that create primary electrons (~80 eV), followed by ionization steps that create secondary electrons (10-60 eV). Ultimately, these lower energy electrons interact with specific molecules in the resist that cause the chemical reactions which are responsible for changes in solubility. The mechanisms by which these electrons interact with resist components are key to optimizing the performance of EUV resists. An electron exposure chamber was built to probe the behavior of electrons within photoresists. Upon exposure and development of a photoresist to an electron gun, ellipsometry was used to identify the dependence of electron penetration depth and number of reactions on dose and energy. Additionally, our group has updated a robust software that uses first-principles based Monte Carlo model called “LESiS”, to track secondary electron production, penetration depth, and reaction mechanisms within materials-defined environments. LESiS was used to model the thickness loss experiments to validate its performance with respect to simulated electron penetration depths to inform future modeling work.
KEYWORDS: Photomasks, Extreme ultraviolet, Multilayers, Chemical species, Extreme ultraviolet lithography, Inspection, Monte Carlo methods, Computer simulations, Waveguides, Transmission electron microscopy
The availability of defect-free masks is considered to be a critical issue for enabling extreme ultraviolet lithography (EUVL) as the next generation technology. Since completely defect-free masks will be hard to achieve, it is essential to have a good understanding of the printability of the native EUV mask defects. In this work, we performed a systematic study of native mask defects to understand the defect printability caused by them. The multilayer growth over native substrate mask blank defects was correlated to the multilayer growth over regular-shaped defects having similar profiles in terms of their width and height. To model the multilayer growth over the defects, a novel level-set multilayer growth model was used that took into account the tool deposition conditions of the Veeco Nexus ion beam deposition tool. The same tool was used for performing the actual deposition of the multilayer stack over the characterized native defects, thus ensuring a fair comparison between the actual multilayer growth over native defects, and modeled multilayer growth over regular-shaped defects. Further, the printability of the characterized native defects was studied with the SEMATECH-Berkeley Actinic Inspection Tool (AIT), an EUV mask-imaging microscope at Lawrence Berkeley National Laboratory (LBNL). Printability of the modeled regular-shaped defects, which were propagated up the multilayer stack using level-set growth model was studied using defect printability simulations implementing the waveguide algorithm. Good comparison was observed between AIT and the simulation results, thus demonstrating that multilayer growth over a defect is primarily a function of a defect’s width and height, irrespective of its shape. This would allow us to predict printability of the arbitrarily-shaped native EUV mask defects in a systematic and robust manner.
KEYWORDS: Finite-difference time-domain method, Photomasks, Chemical species, Transmission electron microscopy, Multilayers, Extreme ultraviolet lithography, Extreme ultraviolet, Monte Carlo methods, Atomic force microscopy, Inspection
Availability of defect-free masks is considered to be a critical issue for enabling extreme
ultraviolet lithography (EUVL) as the next generation technology. Since completely defect-free
masks will be hard to achieve, it is essential to have a good understanding of the defect
printability as well as the fundamental aspects of a defect that result in the defects being printed.
In this work, the native mask blank defects were characterized using atomic force microscopy
(AFM) and cross-section transmission electron microscopy (TEM), and the defect printability of
the characterized native mask defects was evaluated using finite-difference time-domain (FDTD)
simulations. The simulation results were compared with the through-focus aerial images obtained
at the SEMATECH Actinic Inspection Tool (AIT) at Lawrence Berkeley National Lab (LBNL)
for the characterized defects. There was a reasonable agreement between the through-focus
FDTD simulation results and the AIT results. To model the Mo/Si multilayer growth over the
native defects, which served as the input for the FDTD simulations, a level-set technique was
used to predict the evolution of the multilayer disruption over the defect. Unlike other models
that assume a constant flux of atoms (of materials to be deposited) coming from a single
direction, this model took into account the direction and incident fluxes of the materials to be
deposited, as well as the rotation of the mask substrate, to accurately simulate the actual
deposition conditions. The modeled multilayer growth was compared with the cross-section
TEM images, and a good agreement was observed between them.
Extreme ultraviolet (EUV) lithography is the leading contender for adoption as the next generation
lithography technique. One of the critical challenges in this technology is producing defect-free masks.
Particles generated in the fabrication process often deposit on the mask blank and result in phase and
amplitude defects. Hence, it is important to study the transport, behavior and generation of particles in the
ion deposition tool used for mask blank deposition. We show results on detecting particles from ultrahigh
vacuum (UHV) valves by using optical counters and condensation particle counters. The particles were
also trapped using impactor plates and analyzed with Energy-dispersive x-ray spectroscopy (EDX) for
elemental composition.
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