W. Chao

Commissioning an EUV mask microscope for lithography generations reaching 8 nm

The SEMATECH High-NA Actinic Reticle review Project (SHARP) is a synchrotron-based, EUV-wavelength microscope, dedicated to photomask imaging, now being commissioned at Lawrence Berkeley National Laboratory. In terms of throughput, resolution, coherence control, stability and ease of use, SHARP represents a significant advance over its predecessor, the SEMATECH Berkeley Actinic Inspection Tool (AIT), which was decommissioned in September 2012. SHARP utilizes several advanced technologies to achieve its design goals: including the first Fouriersynthesis illuminator on a zoneplate microscope, EUV MEMS mirrors, and high-efficiency freestanding zoneplate lenses with numerical aperture values up to 0.625 (4×). In its first week of operation, SHARP demonstrated approximately 150 times higher light throughput than AIT and a spatial resolution down to 55-nm half-pitch with 0.42 4×NA (i.e. the smallest feature size on our test mask.) This paper describes the current status of the tool commissioning and the performance metrics available at this early stage.

Biological soft X-ray tomography on beamline 2.1 at the Advanced Light Source

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 (284-543u2005eV). 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.

Characterization of extreme ultraviolet laser ablation mass spectrometry for actinide trace analysis and nanoscale isotopic imaging

We demonstrate a new technique for trace analysis that has nanometer scale resolution imaging capability: Extreme Ultraviolet Time-of-Flight Laser Ablation Mass Spectrometry (EUV TOF). We describe the characterization of this technique and discuss its advantages. Using the well-standardized NIST 61x glasses, the results show the EUV TOF spectra contain well defined signatures of U, Th, and their oxides, with far fewer spectral interferences than observed in Time-of-Flight Secondary Ion Mass Spectrometry (SIMS TOF). We demonstrate that the ratio of U and Th ions to the oxide ion signatures is adjustable with EUV laser pulse energy. Sample utilization efficiency (SUE) which measures the ratio of detected ions to atoms in the ablated volume was used as a measure of trace analysis sensitivity of EUV TOF. For U and Th, SUE is 0.014% and 0.017%, respectively, which is comparable to SIMS TOF in the same mass range. In imaging mode EUV TOF is capable to map variations in composition with a lateral resolution of 80 nm. Such high lateral resolution enabled mapping of the isotope distribution of 238U and 235U in closely spaced micron-size uranium oxide particles from isotope standard materials. Trace elemental sensitivity and nanometer spatial resolution gives EUV TOF great potential to dramatically improve the state-of-the-art laser ablation/ionization mass spectrometry and elemental spectro-microscopy for applications such as geochemical, forensic and environmental analysis.

Image Plane Holographic Microscopy With a Table-Top Soft X-Ray Laser

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.

Inspection 13.2 nm table-top full-field microscope

We present results on a table-top microscope that uses an EUV stepper geometry to capture full-field images with a halfpitch spatial resolution of 55 nm. This microscope uses a 13.2 nm wavelength table-top laser for illumination and acquires images of reflective masks with exposures of 20 seconds. These experiments open the path to the realization of high resolution table-top imaging systems for actinic defect characterization.

Broader view on extreme ultraviolet masks: adding complementary imaging modes to the SHARP microscope

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.

Time Resolved Holography Scheme Using a Table Top Soft X-Ray Laser

We demonstrate a versatile table-top holography setup capable of acquiring single-shot soft X-ray holograms with a 10–90 % knife edge spatial resolution of 170±26 nm and 1 ns temporal resolution. A Fresnel zone plate is used to create the reference wave as well as to illuminate the sample in a Fourier transform holography scheme. A 100 μm in diameter central opening in the zone plate allows the incident beam to pass through and directly illuminate the object. A pinhole is located in the sample mask allowing the first order from the zone plate to pass while blocking the higher orders. This setup can be used to enhance edges for conventional single-shot soft X-ray holography imaging.

Movies At The Nanoscale Using Extreme Ultraviolet Laser Light

We report on the first demonstration of stop-motion imaging with ~50 nm spatial resolution using an extreme ultraviolet laser. Images of an AFM tip resonating at ~270 kHz were acquired with 1 ns temporal resolution.

High resolution full-field imaging of nanostructures using compact extreme ultraviolet lasers

Recent advances in the development of high peak brightness table-top extreme ultraviolet (EUV) and soft x-ray (SRX) lasers have opened new opportunities for the demonstration of compact full-field EUV/SXR microscopes capable of capturing images with short exposures down to a single laser shot. We demonstrate the practical application of table-top zone plate EUV microscopes that can image nanostructures with a spatial resolution of 54 nm and below and exposure times as short as 1.2 ns, the duration of a single laser shot.

EUV extendibility research at Berkeley Lab

Extreme ultraviolet (EUV) Lithography remains the preferred technology to replace DUV immersion lithography in high volume production at the 7-nm node and beyond. With numerous 0.33 numerical aperture (NA) tools in the field, EUV has proven itself as technically extremely capable, yet availability remains a gating item for the insertion of EUV into high volume production. With 0.33-NA so close to production, the research and development activity in EUV has now in large part shifted over to high NA (≥ 0.5). High NA EUV significantly stresses several current challenges and gives rise to fundamentally new challenges. The most significant new challenge arises from angular bandwidth limitations of the mask multilayer requiring the use of anamorphic optics [1] or new multilayer material systems. The most significant extended challenge revolves around stochastics in photoresist materials and exposure processes. To address these challenges, a new suite of tools has and is being developed at Berkeley Lab including a variable NA mask imaging microscope [2] and a 0.5-NA microfield exposure tool [3–5]. These tools build on to existing facilities at Berkeley including a 0.3-NA microfield exposure tool [6] and an EUV reflectometer/scatterometer [7].