[Show abstract][Hide abstract] ABSTRACT: Coherent extreme ultraviolet beams from tabletop high harmonic generation offer several revolutionary capabilities for observing nanoscale systems on their intrinsic length and time scales. By launching and monitoring hypersonic acoustic waves in such systems, we characterize the mechanical properties of sub-10nm layers and find that the material densities remain close to their bulk values while their elastic properties are significantly modified. Moreover, within the same measurement, by following the heat dissipation dynamics from 30-750nm-wide nanowires, we uncover a new thermal transport regime in which closely-spaced nanoscale heat sources can surprisingly cool more efficiently than widely-spaced heat sources of the same size.
SPIE Metrology, Inspection, and Process Control for Microlithography XXIX, San Jose, CA; 02/2016
[Show abstract][Hide abstract] ABSTRACT: Analytical probes capable of mapping molecular composition at the nanoscale are of critical importance to materials research, biology and medicine. Mass spectral imaging makes it possible to visualize the spatial organization of multiple molecular components at a sample's surface. However, it is challenging for mass spectral imaging to map molecular composition in three dimensions (3D) with submicron resolution. Here we describe a mass spectral imaging method that exploits the high 3D localization of absorbed extreme ultraviolet laser light and its fundamentally distinct interaction with matter to determine molecular composition from a volume as small as 50 zl in a single laser shot. Molecular imaging with a lateral resolution of 75 nm and a depth resolution of 20 nm is demonstrated. These results open opportunities to visualize chemical composition and chemical changes in 3D at the nanoscale.
[Show abstract][Hide abstract] ABSTRACT: Understanding thermal transport from nanoscale heat sources is
important for a fundamental description of energy flow in materials,
as well as for many technological applications including thermal
management in nanoelectronics and optoelectronics, thermoelectric
devices, nanoenhanced photovoltaics, and nanoparticle-mediated
thermal therapies. Thermal transport at the nanoscale is fundamentally
different from that at the macroscale and is determined by the
distribution of carrier mean free paths and energy dispersion in
a material, the length scales of the heat sources, and the distance
over which heat is transported. Past work has shown that Fourier’s
law for heat conduction dramatically overpredicts the rate of heat
dissipation from heat sources with dimensions smaller than the
mean free path of the dominant heat-carrying phonons. In this work,
we uncover a new regime of nanoscale thermal transport that dominates
when the separation between nanoscale heat sources is small
comparedwith the dominant phononmean free paths. Surprisingly,
the interaction of phonons originating from neighboring heat
sources enables more efficient diffusive-like heat dissipation, even
from nanoscale heat sources much smaller than the dominant phonon
mean free paths. This finding suggests that thermal management
in nanoscale systems including integrated circuits might not
be as challenging as previously projected. Finally, we demonstrate
a unique capability to extract differential conductivity as a function
of phonon mean free path in materials, allowing the first (to our
knowledge) experimental validation of predictions from the recently
developed first-principles calculations.
Proceedings of the National Academy of Sciences 03/2015; 112(16). DOI:10.1073/pnas.1503449112 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The authors are expanding the capabilities of the SHARP microscope by implementing complementary imaging modes. SHARP (the SEMATECH High-NA Actinic Reticle Review Project) is an actinic, synchrotron-based microscope dedicated to extreme ultraviolet photomask research. SHARP's programmable Fourier synthesis illuminator and its use of Fresnel zoneplate lenses as imaging optics provide a versatile framework, facilitating the implementation of diverse modes beyond conventional imaging. In addition to SHARP's set of standard zoneplates, we have created more than 100 zoneplates for complementary imaging modes, all designed to extract additional information from photomasks, to improve navigation, and to enhance defect detection. More than 50 new zoneplates are installed in the tool; the remaining lenses are currently in production. We discuss the design and fabrication of zoneplates for complementary imaging modes and present image data, obtained using Zernike phase contrast and different implementations of differential interference contrast (DIC). First results show that Zernike phase contrast can significantly increase the signal from phase defects in SHARP image data, thus improving the sensitivity of the microscope. DIC is effective on a variety of features, including phase defects and intensity speckle from substrate and multilayer roughness. The additional imaging modes are now available to users of the SHARP microscope. (C) The Authors.
Journal of Micro/ Nanolithography, MEMS, and MOEMS 02/2015; 14(1):013507. DOI:10.1117/1.JMM.14.1.013507 · 1.43 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper, we present an experimental verification of Zernike phase contrast enhanced EUV multilayer (ML) blank defect detection using the SHARP EUV microscope. A programmed defect as small as 0.35 nm in height is detected at focus with signal to noise ratio (SNR) up to 8. Also, a direct comparison of the through-focus image behavior between bright field and Zernike phase contrast for ML defects ranging from 40 nm to 75 nm in width on the substrate is presented. Results show the advantages of using the Zernike phase contrast method even for defects with both phase and absorption components including a native defect. The impact of pupil apodization combined with Zernike phase contrast is also demonstrated, showing improved SNR is due to the stronger reduction of roughness dependent noise than defect signal, confirming our previous simulation results. Finally we directly compare Zernike phase contrast, dark field and bright field microscopes.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate image plane holographic microscopy in the soft X-ray (SXR) spectral region, combining the coherent output from a 46.9-nm wavelength table-top SXR laser and two Fresnel zone plates. Phase and amplitude maps of the object are simultaneously obtained from holograms created at the image plane by the superposition of a reference and object beam originating from the zero and first diffraction order of the zone plates. We have used the microscope to record holograms of nanometer-scale periodic Si elbow patterns with 30% absorption contrast at the laser wavelength. The measured phase shift of 2.3 rad accurately predicts the Si dense line step height of 100 nm. The scheme is scalable to shorter wavelengths and allows for simultaneous high spatial and temporal resolution.
[Show abstract][Hide abstract] ABSTRACT: Beamline 2.1 (XM-2) is a transmission soft X-ray microscope in sector 2 of the Advanced Light Source at Lawrence Berkeley National Laboratory. XM-2 was designed, built and is now operated by the National Center for X-ray Tomography as a National Institutes of Health Biomedical Technology Research Resource. XM-2 is equipped with a cryogenic rotation stage to enable tomographic data collection from cryo-preserved cells, including large mammalian cells. During data collection the specimen is illuminated with `water window' X-rays (284–543 eV). Illuminating photons are attenuated an order of magnitude more strongly by biomolecules than by water. Consequently, differences in molecular composition generate quantitative contrast in images of the specimen. Soft X-ray tomography is an information-rich three-dimensional imaging method that can be applied either as a standalone technique or as a component modality in correlative imaging studies.
[Show abstract][Hide abstract] ABSTRACT: X-ray microscopy is powerful in that it can probe large volumes of material at high spatial resolution with exquisite chemical, electronic and bond orientation contrast1, 2, 3, 4, 5. The development of diffraction-based methods such as ptychography has, in principle, removed the resolution limit imposed by the characteristics of the X-ray optics6, 7, 8, 9, 10. Here, using soft X-ray ptychography, we demonstrate the highest-resolution X-ray microscopy ever achieved by imaging 5 nm structures. We quantify the performance of our microscope and apply the method to the study of delithiation in a nanoplate of LiFePO4, a material of broad interest in electrochemical energy storage11, 12. We calculate chemical component distributions using the full complex refractive index and demonstrate enhanced contrast, which elucidates a strong correlation between structural defects and chemical phase propagation. The ability to visualize the coupling of the kinetics of a phase transformation with the mechanical consequences is critical to designing materials with ultimate durability.
[Show abstract][Hide abstract] ABSTRACT: A self-contained electro-optical module for scanning extreme ultraviolet (EUV) reflection microscopy at 13.5 nm wavelength has been developed. The system has been designed to work with stand-alone commercially available EUV high harmonic generation (HHG) sources through the implementation of narrowband harmonic selecting multilayers and off-axis elliptical short focal length zoneplates. The module has been successfully integrated into an EUV mask scanning microscope achieving diffraction limited imaging performance (84 nm point spread function).
[Show abstract][Hide abstract] ABSTRACT: Energy efficient nanomagnetic logic (NML) computing architectures propagate
and process binary information by relying on dipolar field coupling to reorient
closely-spaced nanoscale magnets. Signal propagation in nanomagnet chains of
various sizes, shapes, and magnetic orientations has been previously
characterized by static magnetic imaging experiments with low-speed adiabatic
operation; however the mechanisms which determine the final state and their
reproducibility over millions of cycles in high-speed operation (sub-ns time
scale) have yet to be experimentally investigated. Monitoring NML operation at
its ultimate intrinsic speed reveals features undetectable by conventional
static imaging including individual nanomagnetic switching events and
systematic error nucleation during signal propagation. Here, we present a new
study of NML operation in a high speed regime at fast repetition rates. We
perform direct imaging of digital signal propagation in permalloy nanomagnet
chains with varying degrees of shape-engineered biaxial anisotropy using
full-field magnetic soft x-ray transmission microscopy after applying single
nanosecond magnetic field pulses. Further, we use time-resolved magnetic
photo-emission electron microscopy to evaluate the sub-nanosecond dipolar
coupling signal propagation dynamics in optimized chains with 100 ps time
resolution as they are cycled with nanosecond field pulses at a rate of 3 MHz.
An intrinsic switching time of 100 ps per magnet is observed. These
experiments, and accompanying macro-spin and micromagnetic simulations, reveal
the underlying physics of NML architectures repetitively operated on nanosecond
timescales and identify relevant engineering parameters to optimize performance
[Show abstract][Hide abstract] ABSTRACT: Gray-scale e-beam lithography has been performed to match the EUV and e-beam aerial image log slope for studying shot noise fundamentals in the two mechanisms through line-edge roughness (LER) measurements for 50 nm lines and spaces patterned on a leading chemically amplified EUV resist. The measured e-beam exposure latitude decreased from 0.4 with binary patterning to 0.28 with gray-scale e-beam exposure designed to match the EUV incident image profile, closely matching the EUV exposure latitude of 0.26. Calculations of absorption statistics with EUV and e-beam suggest that the shot noise with e-beam patterning is expected to be 10% larger than the shot noise with EUV patterning. However, despite the matched image gradients and close to identical absorbed quanta predictions, the e-beam patterned LER is 2.5× larger than the EUV patterned LER.
[Show abstract][Hide abstract] ABSTRACT: The SEMATECH High Numerical Aperture Actinic Reticle Review Project (SHARP) is a synchrotron-based extreme ultraviolet (EUV) microscope dedicated to photomask research. SHARP has been operational and serving users since June, 2013, and in eight months, SHARP has recorded over 71,000 high-resolution images. Exposure times are 5 to 8 seconds, and 8 or more through-focus series can be collected per hour at positions spanning the entire mask surface. SHARP’s lossless coherence-control illuminator and variable numerical aperture (NA) enable researchers to emulate the imaging properties of both current and future EUV lithography tools. SHARP’s performance continues to improve over time due to tool learning and upgraded capabilities, described here. Within a centered, 3-μm square image region, we demonstrate an illumination power stability above 99%, and an average uniformity of 98.4%. Demonstrations of through-focus imaging with various illumination coherence settings highlight the capabilities of SHARP.
[Show abstract][Hide abstract] ABSTRACT: Nanomagnetic logic is an energy efficient computing architecture that relies
on the dipole field coupling of neighboring magnets to transmit and process
binary information. In this architecture, nanomagnet chains act as local
interconnects. To assess the merits of this technology, the speed and
reliability of magnetic signal transmission along these chains must be
experimentally determined. In this work, time-resolved pump-probe x-ray
photo-emission electron microscopy is used to observe magnetic signal
transmission along a chain of nanomagnets. We resolve successive error-free
switching events in a single nanomagnet chain at speeds on the order of 100 ps
per nanomagnet, consistent with predictions based on micromagnetic modeling.
Errors which disrupt transmission are also observed. We discuss the nature of
these errors, and approaches for achieving reliable operation.
[Show abstract][Hide abstract] ABSTRACT: A table top nanofabrication system which combines the classic Talbot imaging effect and a compact table top soft-x ray laser is described in this paper. Periodic nanostructures on millimeter square are fabricated using this robust, simple and defect tolerant fabrication method. Talbot lithography allows for a complete coherent extreme ultraviolet lithography process in a compact table top system. Double exposure allowed for the reduction of the feature sizes.
Proceedings of SPIE - The International Society for Optical Engineering 02/2014; DOI:10.1117/12.2041688 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present a single-shot Fourier transform holography setup with ~100nm spatial resolution and 1 ns temporal resolution using a tabletop extreme ultraviolet (EUV) laser. Flash images allowed for the imaging of nano-pillars oscillating at MHz frequencies that will enable the evaluation of mechanical properties of nanoscale mechanical oscillators.
Proceedings of SPIE - The International Society for Optical Engineering 02/2014; DOI:10.1117/12.2041698 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We recorded the fast oscillation of sub-micron cantilevers using time-resolved extreme ultraviolet (EUV) Fourier transform holography. A tabletop capillary discharge EUV laser with a wavelength of 46.9 nm provided a large flux of coherent illumination that was split using a Fresnel zone plate to generate the object and the reference beams. The reference wave was produced by the first order focus while a central opening in the zone plate provided a direct illumination of the cantilevers. Single-shot holograms allowed for the composition of a movie featuring the fast oscillation. Three-dimensional displacements of the object were determined as well by numerical back-propagation, or "refocusing" of the electromagnetic fields during the reconstruction of a single hologram.
[Show abstract][Hide abstract] ABSTRACT: Despite achieving 15-nm half pitch, the progress in extreme ultraviolet chemically amplified resist has arguably decelerated in recent years. We show that this deceleration is consistent with approaching stochastic limits both in photon counts and material parameters.Contact hole printing is a crucial application for extreme ultraviolet lithography and is particularly challenged by resist sensitivity due to inherent inefficiencies in darkfield contact printing. Checkerboard strong phase shift masks have the potential to alleviate this problem through a 4× increase in optical efficiency. The feasibility of this method is demonstrated using the SEMATECH-Berkeley Microfield Exposure Tool pseudo phase shift mask configuration and preliminary results are provided on the fabrication of an etched multilayer checkerboard phase shift mask.
Journal of Photopolymer Science and Technology 01/2014; 27(6):725-730. DOI:10.2494/photopolymer.27.725 · 1.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Progress in the ultimate performance of extreme ultraviolet resist has arguably decelerated in recent years suggesting an approach to stochastic limits both in photon counts and material parameters. Here we report on the performance of a variety of leading extreme ultraviolet resist both with and without chemical amplification. The measured performance is compared to stochastic modeling results using the Multivariate Poisson Propagation Model. The results show that the best materials are indeed nearing modeled performance limits.
Journal of Photopolymer Science and Technology 01/2014; 27(6):747-750. DOI:10.2494/photopolymer.27.747 · 1.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: New approach to full-field soft x-ray holographic microscopy is being developed based on the principle of self-interferencce incoherent digital holography, with simple optical configurations and higher efficiencies. Theorectial and preliminary experimental results will be presented.
Digital Holography and Three-Dimensional Imaging; 01/2014
[Show abstract][Hide abstract] ABSTRACT: Diffractive optical elements such as Fresnel zoneplate lenses have many uses at extreme ultraviolet (EUV), particularly in short focal length, high-resolution applications. However, the diffraction efficiency of a pure absorption zoneplate is limited to about 10%, and it suffers additional loss through the membrane support material. To this end, the authors explored the possibility of silicon nitride (Si3N4) as a EUV phase shifting material. At an etched depth of 244 nm, they measured a diffraction efficiency of 18% in the first order and 18% in the zero order, which compares favorably to an amplitude grating of 10% and 25%, respectively. The measured efficiency as a function of etch depth matches the scalar theory quite well using a measured EUV index of refraction 0.9790 + 0.0066i at the wavelength of 13.5 nm. To further increase the efficiency, zoneplates were made freestanding, with the support membrane completely removed, and a 15% absolute efficiency was obtained. Vector electromagnetic calculations showed that at normal incidence, these optics produce excellent wavefront and efficiency for outer zones of 50 nm or larger. Zoneplates of narrower zones or those illuminated obliquely can suffer larger wavefront errors and low efficiency and would require careful design optimization. In the work, the authors also demonstrated a technique to package zoneplates and associated apertures for high precision insertion and removal from a EUV instrument. This technique has yielded alignment accuracy from a few microns to few 10s microns, depending on the exact design.
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 11/2013; 31(6):06F606-06F606-5. DOI:10.1116/1.4826695 · 1.46 Impact Factor