F. Cerrina

Fabrication of ultralow-loss Si/SiO 2 waveguides by roughness reduction

We demonstrate 0.8-dB/cm transmission loss for a single-mode, strip Si/SiO(2) waveguide with submicrometer cross-sectional dimensions. We compare the conventional waveguide-fabrication method with two smoothing technologies that we have developed, oxidation smoothing and anisotropic etching. We observe significant reduction of sidewall roughness with our smoothing technologies, which directly results in reduced scattering losses. The rapid increase in the scattering losses as the waveguide dimension is miniaturized, as seen in conventionally fabricated waveguides, is effectively suppressed in the waveguides made with our smoothing technologies. In the oxidation smoothing case, the loss is reduced from 32 dB/cm for the conventional fabrication method to 0.8 dB/cm for the single-mode waveguide width of 0.5 microm . This is to our knowledge the smallest reported loss for a high-index-difference system such as a Si/SiO(2) strip waveguide.

SHADOW: A synchrotron radiation ray tracing program☆

Abstract We present the new ray-tracing program SHADOW. The program was written specifically for the XUV optics range, but is now completely general. Its capabilites are discussed in terms of the physical basis on which the program is built, with particular emphasis on the synchrotron radiation applications.

NANOMETER FOCUSING OF HARD X RAYS BY PHASE ZONE PLATES

Focusing of 8 keV x rays to a spot size of 150 and 90 nm full width at half maximum have been demonstrated at the first- and third-order foci, respectively, of a phase zone plate (PZP). The PZP has a numerical aperture of 1.5 mrad and focusing efficiency of 13% for 8 keV x rays. A flux density gain of 121 000 was obtained at the first-order focus. In this article, the fabrication of the PZP and its experimental characterization are presented and some special applications are discussed.

Sub-50 nm period patterns with EUV interference lithography

We have used transmission diffraction gratings in an interferometric setup to pattern one-and two-dimensional periodic patterns with periods near 50 nm. The diffraction gratings were written with e-beam lithography. The exposures were made at 13.4 nm wavelength with undulator radiation, which provides spatially coherent radiation. This technique offered a multiplication of pattern frequency by a factor of 2 and √2 in the one-and two-dimensional cases, respectively. Interference lithography with gratings offers a number of advantages, including achromaticity and insensitivity to misalignment. The demonstrated structures include line/space patterns with 45 nm period and a square array of holes with 56 nm period.

SHADOW: A synchrotron radiation and X-ray optics simulation tool

Abstract We announce the release of SHADOW 2.0 - the computer ray-tracing program widely used in the synchrotron radiation community. We discuss new physical models and system extensions recently introduced. The physical models added are capillaries and Kumakhov lenses, general compound mirrors, and transmission crystals. We have extended the base of operating systems available to SHADOW users, overhauled the UNIX graphics, and written a MENU mode for UNIX. We also discuss new physical models in progress - a shaped absorber, segmented mirrors, and extensions to higher orders in the polynomial calculations.

Exposure of 38 nm period grating patterns with extreme ultraviolet interferometric lithography

Extreme ultraviolet (EUV, λ=13 nm) lithography is considered to be the most likely technology to follow ultraviolet (optical) lithography. One of the challenging aspects is the development of suitable resist materials and processes. This development requires the ability to produce high-resolution patterns. Until now, this ability has been severely limited by the lack of sources and imaging systems. We report printing of 38 nm period grating patterns by interferometric lithography technique with EUV light. A Lloyd’s Mirror interferometer was used, reflecting part of an incident beam with a mirror at grazing incidence and letting it interfere with the direct beam at the wafer plane. High-density fringes (38 nm pitch) were easily produced. Monochromatized light of 13 nm wavelength from an undulator in an electron storage ring provided the necessary temporal and spatial coherence along with sufficient intensity flux. This simple technique can be extended to sub-10 nm resolution.

Hard x-ray phase zone plate fabricated by lithographic techniques

A Fresnel phase zone plate with an unprecedented focusing efficiency of 33% was fabricated using an x‐ray lithographic technique and was tested using synchrotron x rays. Contributions by the zeroth‐order x ray to the focus were minimal. Spatial resolution in the micrometer range was achieved. The measured spot size was dominated by geometric demagnification of the source. It should be possible to obtain submicrometer resolution by aperturing the source. Experimental results of focusing efficiency measurements, intensity distribution at the focal plane, and spatial resolution tests are reported.

Resist line edge roughness and aerial image contrast

We report the results of an experimental study of the correlations between line edge roughness (LER) and aerial image contrast for different lithographies in identical processing conditions. The characterization has been performed using atomic force microscopy carbon nanotube tips to image the top and bottom of trenches with very high resolution. Experimental results generally support that higher aerial image contrast leads to lower line edge roughness, but differences exist among the lithographies and resists. Top surface roughness results show similar trends with LER. Higher aerial image modulation also yields higher resist sidewall angle.

SHADOW: New developments

Abstract We describe the new extensions that we have implemented in our synchrotron radiation ray tracing code, SHADOW. The most important are the new wiggler source, the extension of 100 keV of the optical constant database, the novel power density calculations capabilities and the inclusion of the full crystal and multilayer optics cases. Current work and future prospects will also be discussed.

Talbot lithography: Self-imaging of complex structures

The authors present a self-imaging lithographic technique, capable of patterning large area periodic structures of arbitrary content with nanoscale resolution. They start from the original concept of Talbot imaging of binary gratings—and introduce the generalized Talbot imaging (GTI) where periodic structures of arbitrary shape and content form high-definition self-images. This effect can be used to create the complex, periodic patterns needed in the many lithographic fabrication steps of modern semiconductor devices. Since the process is diffraction limited, the achievable resolution depends only on the wavelength, mask patterning, and degree of coherence of the source. Their approach removes all the complex extreme ultraviolet (EUV) reflective masks and optics, replacing them with nanopatterned transmission masks and makes the whole process simple and cost effective. They have successfully verified the GTI concept using first a He–Ne laser, and then demonstrated its potential as a nanolithography method using a compact table-top soft x-ray (EUV) 46.9nm laser source. These sources provide the high degree of coherence needed by diffraction-based imaging and are extendable to shorter wavelengths. They have recorded EUV GTI images up to the sixth Talbot plane, with consistent high quality good results, clearly demonstrating the ability of the GTI method to record high-resolution patterns at large distances.The authors present a self-imaging lithographic technique, capable of patterning large area periodic structures of arbitrary content with nanoscale resolution. They start from the original concept of Talbot imaging of binary gratings—and introduce the generalized Talbot imaging (GTI) where periodic structures of arbitrary shape and content form high-definition self-images. This effect can be used to create the complex, periodic patterns needed in the many lithographic fabrication steps of modern semiconductor devices. Since the process is diffraction limited, the achievable resolution depends only on the wavelength, mask patterning, and degree of coherence of the source. Their approach removes all the complex extreme ultraviolet (EUV) reflective masks and optics, replacing them with nanopatterned transmission masks and makes the whole process simple and cost effective. They have successfully verified the GTI concept using first a He–Ne laser, and then demonstrated its potential as a nanolithography method...