• Ph.D. (expected in Jan 2015) in Physics, specialized in innovative tabletop coherent EUV/X-ray imaging, for fast, widefield and high resolution (down to 22 nm) nano-imaging applications including metrology/defect • Demonstrated achievement with 9 publications and 1 pending patent; Spearheaded the full life cycle of challenging projects, including strategic planning, modeling/simulating, designing, hardware purchasing & machining, system constructing, data acquisition & processing software development, and reporting • 6 years’ hands-on lab experience of designing/constructing complex optical/imaging systems, and operating various lasers (DPSS/femtosecond); Familiar with opto-mechanics, eletro-optics, polarization, stages, detectors • Proficient in using/testing/programming CMOS/CCD sensors; Experienced in building a modular EUV/X-ray camera; Hobbyist of commercial DSLR and Kinect 3D motion sensing cameras • Proficient in optical system modeling & beam propagation simulation; Knowledge of ZEMAX modeling/design • Experienced in lithography (photo- or e-beam) and other clean room fabrication; Other hardware skills: machining, electronics, gas/vacuum, temperature control, analytical instruments (SEM/AFM, optical microscope, XRD, ellipsometer/profilometer/interferometer), laser characterization (spectrum, mode, wavefront, pointing stability) • Solid knowledge of general physics/optics, lasers, nonlinear optics, spectroscopy, diffraction/scatterometry • Proficient in test/data acquisition automating, UI design with LabVIEW and procedure development • 5 years’ image processing (filtering, remapping, masking, HDR combining) & data analysis experience with C++/MatLab/Python, and high performance computing/large data sets processing with parallel/GPU computing • Collaborated with Intel and Samsung to promote technology transfer of laboratory diffractive nano-imaging for industry metrology/defect inspection applications; Familiar with semiconductor industry
Publications (6)
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A new technology transforms mask inspection images through focus into 3D lithography images in resist. This enables early detection and ranking of hotspots, and distinguishes mask-induced and process-induced hotspots. The results can be used in several ways including: 1) feed back to OPC teams to improve process window; 2) feed forward to the litho team for scanner adjustment; and, 3) feed forward to wafer inspection in the form of care areas to reduce time to result for wafer-based process window discovery.
We demonstrate hyperspectral coherent imaging in the EUV spectral region for the first time, without the need for hardware-based wavelength separation. This new scheme of spectromicroscopy is the most efficient use of EUV photons for imaging because there is no energy loss from mirrors or monochromatizing optics. An EUV spectral comb from a tabletop high-harmonic source, centered at a wavelength of 30nm, illuminates the sample and the scattered light is collected on a pixel-array detector. Using a lensless imaging technique known as ptychographical information multiplexing, we simultaneously retrieve images of the spectral response of the sample at each individual harmonic. We show that the retrieved spectral amplitude and phase agrees with theoretical predictions. This work demonstrates the power of coherent EUV beams for rapid material identification with nanometer-scale resolution.
Coherent diffraction imaging (CDI) has matured into a versatile phase-contrast microscopy technique capable of producing diffraction limited images without the need for high precision focusing elements. CDI has been most appropriately applied in the EUV/X-ray region of the spectrum where imaging optics are both difficult to produce and inefficient. By satisfying basic geometric constraints (such as Nyquist sampling of scattered intensities) diffraction imaging techniques essentially replace any imaging elements with sophisticated computer algorithms. We demonstrate the utility of our CDI-based, phase-contrast EUV microscope by quantitatively imaging objects in both transmission and reflection. Patterned feature depth is obtained in transmission using keyhole coherent diffraction imaging (KCDI) and feature height is quantitatively extracted in the first general, table-top reflection mode CDI microscope.
Recent breakthroughs in high harmonic generation have extended the reach of bright tabletop coherent light sources
from a previous limit of ≈100 eV in the extreme ultraviolet (EUV) all the way beyond 1 keV in the soft X-ray region.
Due to its intrinsically short pulse duration and spatial coherence, this light source can be used to probe the fastest
physical processes at the femtosecond timescale, with nanometer-scale spatial resolution using a technique called
coherent diffractive imaging (CDI). CDI is an aberration-free technique that replaces image-forming optics with a
computer phase retrieval algorithm, which recovers the phase of a measured diffraction amplitude. This technique
typically requires the sample of interest to be isolated; however, it is possible to loosen this constraint by imposing
isolation on the illumination. Here we extend previous tabletop results, in which we demonstrated the ability to image a
test object with 22 nm resolution using 13 nm light [3], to imaging of more complex samples using the keyhole CDI
technique adapted to our source. We have recently demonstrated the ability to image extended objects in a transmission
geometry with ≈100 nm resolution. Finally, we have taken preliminary CDI measurements of extended nanosystems in
reflection geometry. We expect that this capability will soon allow us to image dynamic processes in nanosystems at the
femtosecond and nanometer scale.
Coherent diffractive imaging (CDI) using EUV/X-rays has proven to be a powerful microscopy method for imaging nanoscale objects. In traditional CDI, the oversampling condition limits its applicability to small, isolated objects. A new technique called keyhole CDI was demonstrated on a synchrotron X-ray source to circumvent this limitation. Here we demonstrate the first keyhole CDI result with a tabletop extreme ultraviolet (EUV) source. The EUV source is based on high harmonic generation (HHG), and our modified form of keyhole CDI uses a highly reflective curved EUV mirror instead of a lossy Fresnel zone plate, offering a ~10x increase in photon throughput of the imaging system, and a more uniform illumination on the sample. In addition, we have demonstrated a record 22 nm resolution using our tabletop CDI setup, and also the successful extension to reflection mode for a periodic sample. Combining these results with keyhole CDI will open the path to the realization of a compact EUV microscope for imaging general non-isolated and non-periodic samples, in both transmission and reflection mode.
We implement coherent diffractive imaging (CDI) using a phase-matched high-harmonic generation (HHG) source
at 13 nm, demonstrating reconstructed images with a record 22 nm resolution for any tabletop, light-based
microscope. We also demonstrate the first reflection-mode CDI using a compact extreme ultraviolet (EUV)
source, achieving ≈100 nm resolution. A clear path towards even higher spatial resolution reflection-mode
tabletop imaging using apertured-illumination schemes will be discussed.
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