Aleksey Maryasov

Defect Inspection with an EUV Microscope

An actinic EUV microscope for defect detection on mask blanks for operation in dark field using table top discharge produced plasma (DPP) source has been developed. Several test structures (pits and bumps) and natural defects on multilayer mirrors were characterized with an atomic force microscope (AFM) and then investigated by our Schwarzschild Objective (SO) based EUV microscope. Possible defect detection limits with large field of view (FOV) and moderate magnification will be discussed in terms of required source photon flux and detection camera performance.

EUV Dark‐Field Microscopy for Defect Inspection

An actinic EUV microscope for defect detection on mask blanks for operation in dark field using a table‐top discharge‐produced plasma source has been developed. Several test structures (pits and bumps) on multilayer mirrors were investigated by our Schwarzschild objective‐based EUV microscope at 13.5‐nm wavelength and then characterized with an atomic force microscope. Possible defect‐detection limits with large field of view and moderate magnification are discussed in terms of required irradiation dose and system performance.

EUV actinic mask blank defect inspection: results and status of concept realization

One of the most challenging requirements for the next generation EUV lithography is an extremely low amount of critically sized defects on mask blanks. Fast and reliable inspection of mask blanks is still a challenge. Here we present the current status of the development of our actinic Schwarzschild objective based microscope operating in dark field with EUV discharge produced plasma source. For characterization of the microscope performance, several programmed defect structures - artificial pits and bumps were created on top of multilayer mirror (ML) surfaces and investigated both with EUV microscope and atomic force microscope (AFM). Defect size sensitivity of actinic inspection in dark field mode without resolving the defects is under study. The dependency between defect shape, size and position in relation to the ML surface and its scattering signal will be discussed. Furthermore, first results of a defect mapping algorithm are presented.

Analysis of distinct scattering of extreme ultraviolet phase and amplitude multilayer defects with an actinic dark-field microscope

The authors report on experimental and simulative scattering analyses of phase and amplitude defects found in extreme ultraviolet multilayer mirrors, such as mask blanks for EUV lithography. The goal of the analyses is to develop a novel mask blank inspection procedure using one single inspection tool that allows to determine whether a defect is a surface type (amplitude) defect, or a buried type (phase) defect. The experiments were carried out with an actinic dark-field reflection microscope. Programmed defects of both types were fabricated, using different nanostructuring techniques. Analytical and rigorous scattering simulations were carried out to predict and support the experimental results.

Actinic EUV-mask metrology: tools, concepts, components

There is a strong demand for standalone actinic tools for mask blank and mask metrology. We expect to deliver contributions to key issues for the infrastructure tools such as actinic reflectometer, actinic defect inspection and components like high brightness sources together with our partners. With our EUV-reflectometer EUV-MBR we are ready to fulfill HVM requirements in accurate and sensitive spectral metrology. Migrating from mask blanks to masks is supported with integrated fiducial mark detection and small spot sizes of down to < 0.03 mm2. Hence, the EUV-MBR is able to detect minimal variations on mask blank and can support process monitoring for our partners in European EXEPT project. For actinic blank inspection a proof of concept experiment based on an EUV microscope at BASCs EUV-Lamp allows for comparing actinic signatures with AFM scans. Results allow for extrapolation to sub 30 nm sensitivity and fast full blank scan. For LPP sources we demonstrated a new concept utilizing a laser, with parameters optimized for high brightness EUV generation and a new regenerative target concept for high position stability, gain, repetition rate operation and efficiency in the first proof of concept experiment. Up to 350 W/(mm2 sr) from < 20 μm source size have been demonstrated.

Numerical modeling of influence telescope segment placement at aperture and its quality on focusing radiated field

The feasibility of using scalar diffraction theory for calculation of different telescope aperture segments influence and their surface quality represented by phase inhomogeneity on radiated field focusing quality is analyzed. An algorithm and a program for numerical calculation that are free from optical system axis symmetry and also constraint type kr>>1 is developed and described. The values of phase inhomogeneity determine the requirements for quality high aperture and/or segmented mirrors, that in general case have not axis symmetry. The influence level of factor of segment placement and its quality on resultant focusing is the metrics of Strehl ratio. Decrease of influence value of phase inhomogeneity at move off segments from axis (in case of axial symmetry) is determined, and than some increase observed at coming near the aperture edge. The developed method makes it possible to get amplitude and phase distribution for real surface and at arbitrary distances from the telescope mirror. It affords a basis for further research on image correction received from distant stars by using calculated spread function of optical system and also is very promising for resolution increasing.

Quantum Efficiency Determination of a Novel CMOS Design for Fast Imaging Applications in the Extreme Ultraviolet

We present quantum efficiency (QE) and quantum yield (QY) measurements of novel deep optical stack etching extreme-ultraviolet complementary metal-oxide-semiconductor photodiodes of different sizes and derive future potentials. QE values between 24% and 50% at 13.5 nm were achieved. Variations in QE and QY measurement results were analyzed.

Estimation of quality of 3D holographic images by means of stereogrammetry

The method for estimation quality and adequacy of reconstructed holographic 3D images by means of stereogrammetry and digital image processing is proposed. The quality as a subjective parameter is considered and analyzed with the most often used criteria, which can be applied to reconstructed 3D scene or object. The method of stereogrammetry with its application for holographic images is considered and expressions for definition of methods accuracy are derived for ideal and non-ideal stereopairs. The measuring accuracy of surface of holographic image estimated to be less then 25 μm which is far below of the human eye resolution, and hence stereogrammetry method can be employed for quality estimation in 3D holographic simulators.