Extreme Ultraviolet Coherent Diffractive Imaging Reflectometry: High-Fidelity, High-Resolution, Quantitative Characterization of Nanostructures

The development and integration of next-generation semiconductor and quantum devices is approaching a significant metrology hurdle. These devices often rely on intricately designed 3D multilayer structures, with layer thicknesses of only a few nanometers. The composition of these structures, while critical to their overall function, is extremely difficult to measure non-destructively. Thus, there is an open need for non-destructive, 3D imaging techniques applicable to general samples. This thesis addresses this challenge in a novel way by combining two techniques. First, extreme ultraviolet (EUV) light can determine composition, layer thicknesses, and interface quality by measuring the reflectivity as a function of incidence angle (aka reflectometry). Traditionally, the spatial resolution of EUVR is limited by the spot size on the sample, typically &gt;1 &micro;m, and the magnitude-reflectance alone is often insufficient to fully characterize a sample. We combine EUVR with a coherent diffractive imaging technique called ptychography, which provides a quantitative measurement of the amplitude and phase reflectivity of nanostructures with a resolution not limited by the illumination size or optic quality. In doing so, this thesis demonstrates a unique, non-destructive, 3D sample-characterization technique whose resolution approaches the diffraction limit. We call the technique EUV CDI reflectometry (EUV CDIR). The first chapter describes an experiment that allowed us to develop the theory and techniques necessary for grazing-incidence ptychographic imaging. The second chapter describes an initial demonstration of the technique on a semiconductor test sample, and benchmarks it against other metrologies, such as transmission electron microscopy (TEM) and atomic force microscopy (AFM). The next three chapters describe almost-complete demonstrations of techniques that, together, can increase the achievable throughput by 100x or more. This capability has already gained significant interest from industry, and the final chapter outlines some of our work with several collaborators to characterize a wide variety of samples related to industry and materials science.</p

Quantitative Chemically-Specific Coherent Diffractive Imaging of Buried Interfaces using a Tabletop EUV Nanoscope

Characterizing buried layers and interfaces is critical for a host of applications in nanoscience and nano-manufacturing. Here we demonstrate non-invasive, non-destructive imaging of buried interfaces using a tabletop, extreme ultraviolet (EUV), coherent diffractive imaging (CDI) nanoscope. Copper nanostructures inlaid in SiO2 are coated with 100 nm of aluminum, which is opaque to visible light and thick enough that neither optical microscopy nor atomic force microscopy can image the buried interfaces. Short wavelength (29 nm) high harmonic light can penetrate the aluminum layer, yielding high-contrast images of the buried structures. Moreover, differences in the absolute reflectivity of the interfaces before and after coating reveal the formation of interstitial diffusion and oxidation layers at the Al-Cu and Al-SiO2 boundaries. Finally, we show that EUV CDI provides a unique capability for quantitative, chemically-specific imaging of buried structures, and the material evolution that occurs at these buried interfaces, compared with all other approaches.Comment: 12 pages, 8 figure

Coherent Fourier scatterometry using orbital angular momentum beams for defect detection

Defect inspection on lithographic substrates, masks, reticles, and wafers is an important quality assurance process in semiconductor manufacturing. Coherent Fourier scatterometry (CFS) using laser beams with a Gaussian spatial profile is the standard workhorse routinely used as an in-line inspection tool to achieve high throughput. As the semiconductor industry advances toward shrinking critical dimensions in high volume manufacturing using extreme ultraviolet lithography, new techniques that enable high-sensitivity, high-throughput, and in-line inspection are critically needed. Here we introduce a set of novel defect inspection techniques based on bright-field CFS using coherent beams that carry orbital angular momentum (OAM). One of these techniques, the differential OAM CFS, is particularly unique because it does not rely on referencing to a pre-established database in the case of regularly patterned structures with reflection symmetry. The differential OAM CFS exploits OAM beams with opposite wavefront or phase helicity to provide contrast in the presence of detects. We numerically investigated the performance of these techniques on both amplitude and phase defects and demonstrated their superior advantages&mdash;up to an order of magnitude higher in signal-to-noise ratio&mdash;over the conventional Gaussian beam CFS. These new techniques will enable increased sensitivity and robustness for in-line nanoscale defect inspection and the concept could also benefit x-ray scattering and scatterometry in general. &nbsp;</p

Temporal and spectral multiplexing for EUV multibeam ptychography with a high harmonic light source

We demonstrate temporally multiplexed multibeam ptychography implemented for the first time in the EUV, by using a high harmonic based light source. This allows for simultaneous imaging of different sample areas, or of the same area at different times or incidence angles. Furthermore, we show that this technique is compatible with wavelength multiplexing for multibeam spectroscopic imaging, taking full advantage of the temporal and spectral characteristics of high harmonic light sources. This technique enables increased data throughput using a simple experimental implementation and with high photon efficiency. &nbsp;</p

Tabletop EUV Coherent Diffractive Imaging and Small Angle Scattering of Colloidal Crystals

We demonstrate full-field quantitative ptychographic imaging using tabletop high harmonics to visualize the extended structure of silica close-packed nanosphere multilayers with <20nm spatial resolution, and also extract small-angle EUV Bragg scattering order/disorder correlations

Tabletop EUV Coherent Diffractive Imaging and Small Angle Scattering of Colloidal Crystals

We demonstrate full-field quantitative ptychographic imaging using tabletop high harmonics to visualize the extended structure of silica close-packed nanosphere multilayers with <20nm spatial resolution, and also extract small-angle EUV Bragg scattering order/disorder correlations

Supplementary document for Nonlinear post-compression in multi-pass cells in the mid-IR region using bulk materials - 6030486.pdf

Tables for material information, explanation of code details, alternative representations of dat

Supplementary document for High-fidelity ptychographic imaging of highly periodic structures enabled by vortex high harmonic beams - 6603827.pdf

supplementary documen