Technical Activities

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"Technical Activities 2004" - Table of Contents

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Electron and Optical Physics Division
The strategy for meeting this goal is to improve measurement science and to develop the measurements and standards needed by emerging science and technology-intensive industries.

GOAL: To support
emerging electronic,
optical, and nanoscale
technologies.

Strategic Focus Areas:

   

First

Nanoscale Electronics and Magnetics - to develop techniques for fabricating nanostructures and measuring their electronic and magnetic properties.

Second   

Extreme Ultraviolet Radiation Metrology - the development of metrology for extreme-ultraviolet (EUV) optics, the maintenance of national primary standards for radiometry in the EUV and adjoining spectral regions, and the operation of national user facilities for EUV science and applications.

Third

Coherent Matter-Wave and Quantum Information Processing Metrology - the development of ultracold atom technology, in particular the use of coherent matter waves in sensors, atom interferometers, and quantum information processing devices.

Extreme Ultraviolet Radiation Metrology

the development of metrology for extreme-ultraviolet (EUV) optics, the maintenance of national primary standards for radiometry in the EUV and adjoining spectral regions, and the operation of national user facilities for EUV science and applications.

INTENDED OUTCOME AND BACKGROUND

The intended outcomes of this program are: maintenance and continuous improvement of the national primary measurement standards for extreme ultraviolet radiation (EUV: wavelengths between 4 nm and 250 nm, i.e., from soft x rays to vacuum ultraviolet), development of techniques for fabricating and characterizing EUV optical systems, and the development of a synchrotron-based, national primary standard for source-based optical radiometry.

The Division has longstanding responsibility for the national primary radiometric standards in the EUV region of the spectrum. EUV radiation is an important tool for determining the electronic structure of materials, diagnosing plasmas, measuring dynamics of the upper atmosphere, and probing the structure and dynamics of astrophysical objects.

One of the top candidates for next-generation semiconductor manufacturing technology is an EUV micropatterning tool, since operation at this short a wavelength (13 nm vs. 193 nm for present, production ultraviolet lithography) enables diffraction-limited imaging of features with smaller critical dimensions. We are working actively with the semiconductor industry to develop new metrology and testing capabilities as needs arise in their effort to commercialize this next-generation lithography.

The Division’s key tool for EUV metrologyis the NIST Synchrotron Ultraviolet Radiation Facility (SURF III). SURF III, the successor to the world’s first dedicated source of synchrotron radiation, is a low-energy (<400 MeV), high beam-current (up to 1 A), perfectly circular electron storage ring. Its operational characteristics are ideal for EUV metrology. It does not produce the hard x-ray radiation of higher energy sources, and it can be operated over a wide range of beam energies to match the spectral response of systems of interest. As a calculable source of radiation from the far infrared through EUV spectral regions, SURF is also used as a primary standard for source-based radiometry throughout the optical spectrum.

Accomplishments

  • Characterization of Damaged EUV Condenser Optics

      Figure 6

    Figure 6. Measured EUV reflectivity over surface of a condenser optic, and an SEM image of a small region showing the striations associated with the erosion of the multilayers.

    EUV lithography is a candidate process for producing the next generation of semiconductor devices, with feature sizes that are 50 nm or less. One of the outstanding issues that must be solved in order for EUV lithography to proceed to commercialization is the durability of condenser optics, which collect and direct the radiation from its source. EUV radiation is produced by high-temperature plasmas generated by electrical discharges or high-intensity lasers. These plasmas emit not only EUV radiation, but also broadband radiation, electrons, and ions. This hostile environment can damage the condenser optics and reduce its lifetime, which must be months long for EUV lithography to be commercially viable.

    In collaboration with SEMATECH we have analyzed one such condenser element, which had operated for three months in the Engineering Test Stand at Sandia National Laboratories. This condenser had a Mo/Si multilayer reflective coating, and it was used to collect the radiation from a laser-produced Xe plasma. After exposure to the plasma, the optic was covered by a visible array of erosion-associated striations. The origin of these stripes was a mystery.

    As shown in Fig. 6, the reflectivity of the optic was measured at the NIST/DARPA EUV facility, while the surface composition and structure were measured using the Electron Physics Group’s SEM, AUGER, and AFM facilities. This combination of tools allowed an understanding of the optic’s EUV reflectivity in terms of the nanoscale compositional and structural properties of the surface.

    The measurements showed that the low-reflectance stripes were due to periodic stripes of increased roughness, and that each stripe corresponded to one additional Mo/Si bilayer of the multilayer coating being removed.


    CONTACT: Dr. Shannon Hill
    (301) 975-4283
    shannon.hill@nist.gov


  • Long-Term Endurance Testing of EUV Projection Optics

    The lithography tool that exposes the wafers in the patterning process is called a stepper. It consists of a radiation source and its condenser optics to illuminate the patterning mask, projection optics to image the mask onto a resist-coated wafer, and a mechanical device that aligns the wafer to the mask. Although the system is operated under vacuum, there is still a significant amount of water and hydrocarbons present. These materials interact with the EUV and cause the performance of the optics in the system to degrade. The effect is significant, and it is a critical factor in determining the operational lifetime of a stepper.

    NIST recently commissioned a beamline on SURF III dedicated to longterm exposure studies of EUV multilayer projection optics. It contains a spherical, 75 mm diameter, Mo/Si multilayer focusing mirror. This images the EUV beam onto a sample optic with a spot size of approximately 0.6 mm × 0.8 mm (FWHM). The sample chamber is separated from the mirror chamber with a removable, 0.3 µm thick beryllium foil. It filters out long-wavelength radiation and allows a differential vacuum between the sample chamber and SURF. This permits exposure of the sample optics to EUV radiation in the presence of larger partial pressures of water and other species, to simulate the environments present in EUV steppers.


    CONTACT: Dr. Charles S. Tarrio
    (301) 975-3737
    charles.tarrio@nist.gov


  • Nanoscale Chemical Imaging

      Figure 7

    Figure 7. Simulated reconstruction of a polymer sample, as imaged by transmission electron microscopy. Length of bar in lower right is 1 µm.


    We are developing state-of-the-art measurement techniques and algorithms to acquire three-dimensional, chemically resolved images of nanoscale samples, using transmission electron microscopy. We seek an enhanced, fundamental understanding of the probe-sample interactions relevant to electron microscopy, including incoherent and coherent scattering, electron energy loss spectroscopy, and x-ray generation and propagation. In this joint project, we use instrumentation to acquire data in the Chemical Science and Technology Laboratory and investigate reconstruction algorithms to form the images with the Information Technology Laboratory.

    Earlier work led to reconstructions of integrated circuit interconnects using an x-ray microscope, as well as to the detailed observation of M x-ray absorption edges in tantalum and tungsten. More recently, the possibility of performing reconstructions on polymer samples up to 8 µm in size using a scanning transmission electron microscope has been demonstrated in simulation. The total size is noteworthy because nearly all tomographic reconstructions use smaller samples to avoid the multiple-scattering regime. Here it is shown that multiple scattering can be accounted for mathematically, and reconstructions may be performed, even in the presence of a few scattering events. A simulated reconstruction appears in Fig. 7.


    CONTACT: Dr. Zachary H. Levine
    (301) 975-5453
    zachary.levine@nist.gov


  • Absolute Radiometry at SURF III

      Figure 8

    Figure 8. Monochromator during alignment.


    The SURF III facility recently became the source of the most accurate ultraviolet lamp calibrations in the world.

    The SURF upgrade in the mid-1990s was motivated by the need to improve our source calibration capabilities in the ultraviolet spectral region. To accomplish this, the magnet system had to be improved, which in SURF’s case meant replacement of the coils, the steel used in the back legs, the power supply, and the control system.

    Recently these immense improvements were put to the test during a Consultative Committee for Photometry and Radiometry (CCPR) key comparison between several national measurement institutes, piloted by the German Physikalisch-Technische Bundesanstalt (PTB). This comparison focused on the calibration of specially prepared deuterium lamps in the spectral range from 200 nm to 350 nm.

    NIST was the sole laboratory to employ synchrotron radiation in the calibration process, leading to the smallest uncertainties among all participating laboratories. The uncertainty achieved at SURF was 0.5 % (coverage factor k = 1) for the entire spectral range.

    For this comparison, a detection system, consisting of a monochromator, a diffusing device, and a photodetector, was calibrated against SURF, utilizing the calculability of synchrotron radiation in conjunction with our accurate monitoring of its operational parameters. Figure 8 shows a monochromator during alignment. Once the system was calibrated, it could be used to determine the spectral irradiance of a lamp.


    CONTACT: Dr. Uwe Arp
    (301) 975-3233
    uwe.arp@nist.gov


First strategic focus   |   Second strategic focus   |   Third strategic focus

"Technical Activities 2004" - Table of Contents