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Ultrafast Radiation Detection by Modulation of an Optical Probe Beam

Description: We describe a new class of radiation sensor that utilizes optical interferometry to measure radiation-induced changes in the optical refractive index of a semiconductor sensor medium. Radiation absorption in the sensor material produces a transient, non-equilibrium, electron-hole pair distribution that locally modifies the complex, optical refractive index of the sensor medium. Changes in the real (imaginary) part of the local refractive index produce a differential phase shift (absorption) of an optical probe used to interrogate the sensor material. In contrast to conventional radiation detectors where signal levels are proportional to the incident energy, signal levels in these optical sensors are proportional to the incident radiation energy flux. This allows for reduction of the sensor form factor with no degradation in detection sensitivity. Furthermore, since the radiation induced, non-equilibrium electron-hole pair distribution is effectively measured ''in place'' there is no requirement to spatially separate and collect the generated charges; consequently, the sensor risetime is of the order of the hot-electron thermalization time {le} 10 fs and the duration of the index perturbation is determined by the carrier recombination time which is of order {approx} 600 fs in, direct-bandgap semiconductors, with a high density of recombination defects; consequently, the optical sensors can be engineered with sub-ps temporal response. A series of detectors were designed, and incorporated into Mach Zehnder and Fabry-Perot interferometer-based detection systems: proof of concept, lower detection sensitivity, Mach-Zehnder detectors were characterized at beamline 6.3 at SSRL; three generations of high sensitivity single element and imaging Fabry-Perot detectors were measured at the LLNL Europa facility. Our results indicate that this technology can be used to provide x-ray detectors and x-ray imaging systems with single x-ray sensitivity and S/N {approx} 30 at x-ray energies {approx} 10 keV.
Date: February 22, 2006
Creator: Vernon, S P & Lowry, M E
Partner: UNT Libraries Government Documents Department

Recovery of EUVL substrates

Description: Mo/Si multilayers, were removed from superpolished zerodur and fused silica substrates with a dry etching process that, under suitable processing conditions, produces negligible change in either the substrate surface figure or surface roughness. Full recovery of the initial normal incidence extreme ultra-violet (EUV) reflectance response has been demonstrated on reprocessed substrates.
Date: January 19, 1995
Creator: Vernon, S.P. & Baker, S.L.
Partner: UNT Libraries Government Documents Department

Preliminary investigation of an additive approach to the fabrication of precision aspheres

Description: We report progress in the aspherization of precision optical substrates via deposition of graded period Mo/Si multilayer coatings using a masking technique. These preliminary results show good agreement between the measured and desired thickness profiles over 85% of the sample, however, thickness deviations of up to 7 % are observed in the central area. The errors are attributed to misalignments of the mask relative to the substrate during deposition.
Date: May 24, 1996
Creator: Weber, F.W.; Montcalm, C.; Vernon, S.P. & Kania, D.R.
Partner: UNT Libraries Government Documents Department

Multilayer coatings for the EUVL front-end test bed

Description: Good illumination uniformity at the mask and wafer planes, and high wafer thoroughput in the EUVL front-end test bed facility at LLNL require graded period multilayer (ML) coatings on several of the optics. The ML deposition was accomplished using a newly developed deposition technique which avoids the use of {open_quotes}uniformity masks{close_quotes} to define the spatial dependence of the ML period variation. The capabilities of the process in providing the specified ML coatings are discussed for both EUVL condenser and imaging systems.
Date: January 19, 1995
Creator: Vernon, S. P.; Carey, M. J.; Gaines, D. P. & Weber, F. J.
Partner: UNT Libraries Government Documents Department

Coating strategy for enhancing illumination uniformity in a lithographic condenser

Description: A three-element Koehler condenser system has been fabricated, characterized, and integrated into an EUV lithographic system. The multilayer coatings deposited on the optics were designed to provide optimal radiation transport efficiency and illumination uniformity. Extensive EUV characterization measurements performed on the individual optics and follow-on system measurements indicated that the condenser was operating close to design goals. Multilayer d-spacings were within 0.05 nm of specifications, and reflectances were approximately 60%. Illumination uniformity was better than {plus_minus}10%. The broadband transport efficiency was 11%.
Date: January 26, 1995
Creator: Gaines, D.P.; Vernon, S.P.; Sommargren, G.E. & Kania, D.R.
Partner: UNT Libraries Government Documents Department

X-ray characterization of a four-bounce projection system

Description: A four-bounce two-element projection system designed to achieve 0.14 {mu}m resolution over a 1.2 {times} 5 mm{sup 2} ring field has been fabricated. The radiation transport properties of both the individual multilayer-coated optics and the assembled system has been measured. The individual mirror measurements demonstrated that the coatings were within 0.03 nm of d-spacing specifications; however, the mirrors exhibited significant scatter which reduced reflectance below the design specification of 60%. The peak radiation transport efficiency of the assembled projector was 7% at 13.2 nm. To the best of the authors` knowledge, this represented the first measurement of the radiation transport efficiency of a multi-element optical system for EUV lithography. Experiments performed at LLNL`s front-end test bed facility were consistent with the measured transport efficiency.
Date: January 19, 1995
Creator: Gaines, D.P.; Vernon, S.P.; Sommargren, G.E. & Fuchs, D.
Partner: UNT Libraries Government Documents Department

RadTracker: Optical Imaging of High Energy Radiation Tracks

Description: This project examined the possibility of extending the recently demonstrated radoptic detection approach to gamma imaging. Model simulations of the light scattering process predicted that expected signal levels were small and likely below the detection limit of large area, room-temperature detectors. A series of experiments using pulsed x-ray excitation, modulated gamma excitation and optical pump-probe methods confirmed those theoretical predictions. At present the technique does not appear to provide a viable approach to volumetric radiation detection; however, in principal, orders of magnitude improvement in the SNR can result by using designer materials to concentrate and localize the radiation-absorption induced charge, simultaneously confining the optical mode to increase 'fill' factor and overlap of the probe beam with the affected regions, and employing high speed gated imaging detectors to measure the scattered signal.
Date: March 2, 2007
Creator: Vernon, S P; Lowry, M E; Comaskey, B J; Heebner, J E; Kallman, J S & Richards, J B
Partner: UNT Libraries Government Documents Department

Magnetic force microscopy of single-domain cobalt dots patterned using interference lithography

Description: We have fabricated arrays of Co dots of diameters 100 and 70 nm using interference lithography. Density of these arrays is 7.2x10{sup 9}/in{sup 2}. Magnetic force microscopy indicate that the Co dots are single domain with moments that can be controlled to point either in-plane or out-of-plane. Interference lithography is a process that is easily scaled to large areas and is potentially capable of high throughput. Large, uniform arrays of single-domain structures are potentially useful for high-density, low-noise data storage.
Date: March 20, 1996
Creator: Fernandez, A.; Bedrossian, P.J.; Baker, S.L.; Vernon, S.P. & Kania, D.R.
Partner: UNT Libraries Government Documents Department

Large GMR values of sputtered Co/Cu multilayer structures with Co-Cu buffer layers

Description: We demonstrate large giant magnetoresistance (GMR) values of Co/Cu multilayers (MLs) sputtered on combined Co18{angstrom}/Cu48{angstrom} buffer layer. GMR values at room temperature reach 62% at the first antiferromagnetically (AF) coupling peak and 33% at the 2nd AF coupled peak, which are very close to those found in Co/Cu MLs sputtered on a Fe buffer layer. The large GMR effect is attributed to the superior superlattice structure of these samples, as evidenced by the x-ray reflectivity data as well as the TEM micrographs. In particular, the role of thin Co initial layer deposited beneath the Cu buffer layer on improved ML structure has been clarified from cross-sectional micrographs of high-resolution TEM.
Date: February 29, 1996
Creator: Huai, Y.; Vernon, S.P.; Stearns, D.G.; Cerjan, C. & Kania, D.R.
Partner: UNT Libraries Government Documents Department

Electrical and Optical Gain Lever Effects in InGaAs Double Quantum Well Diode Lasers

Description: In multisection laser diodes, the amplitude or frequency modulation (AM or FM) efficiency can be improved using the gain lever effect. To study gain lever, InGaAs double quantum well (DQW) edge emitting lasers have been fabricated with integrated passive waveguides and dual sections providing a range of split ratios from 1:1 to 9:1. Both the electrical and the optical gain lever have been examined. An electrical gain lever with greater than 7 dB enhancement of AM efficiency was achieved within the range of appropriate DC biasing currents, but this gain dropped rapidly outside this range. We observed a 4 dB gain in the optical AM efficiency under non-ideal biasing conditions. This value agreed with the measured gain for the electrical AM efficiency under similar conditions. We also examined the gain lever effect under large signal modulation for digital logic switching applications. To get a useful gain lever for optical gain quenched logic, a long control section is needed to preserve the gain lever strength and a long interaction length between the input optical signal and the lasing field of the diode must be provided. The gain lever parameter space has been fully characterized and validated against numerical simulations of a semi-3D hybrid beam propagation method (BPM) model for the coupled electron-photon rate equation. We find that the optical gain lever can be treated using the electrical injection model, once the absorption in the sample is known.
Date: January 3, 2007
Creator: Pocha, M D; Goddard, L L; Bond, T C; Nikolic, R J; Vernon, S P; Kallman, J S et al.
Partner: UNT Libraries Government Documents Department

Reticle blanks for extreme ultraviolet lithography: Ion beam sputter deposition of low defect density Mo/Si multilayers

Description: We report on growth of low defect density Mo/Si multilayer (ML) coatings. The coatings were grown in a deposition system designed for EUVL reticle blank fabrication. Complete, 81 layer, high reflectance Mo/Si ML coatings were deposited on 150 mm dia (100) oriented Si wafer substrates using ion beam sputter deposition. Added defects, measured by optical scattering, correspond to defect densities of 2x10{sup -2}/cm{sup 2}. This represents a reduction in defect density of Mo/Si ML coatings by a factor of 10{sup 5}.
Date: June 24, 1996
Creator: Vernon, S.P.; Kania, D.R.; Kearney, P.A.; Levesque, R.A.; Hayes, A.V.; Druz, B. et al.
Partner: UNT Libraries Government Documents Department

Surface characterization of optics for EUV lithography

Description: The surface topography of optics fabricated for Extreme Ultraviolet Lithography has been measured using a combination of phase-measuring interferometry and atomic force microscopy. Power Spectral Densities were computed over spatial frequencies extending from 2.0{times}10{sup {minus}8} nm{sup {minus}1} to 7.7{times}10{sup {minus}2} nm{sup {minus}1}. Roughness values for frequencies greater than 1.0{times}10{sup {minus}6} were 0.64 nm rms for a spherical optic and 0.95 nm rms for an aspheric optic. These values are significantly larger than 0.088 nm rms, which as obtained using a spherical optic representative of current limits in surface polishing technology. 9 refs., 4 figs.
Date: May 28, 1996
Creator: Gaines, D.P.; Sweeney, D.W.; DeLong, K.W.; Vernon, S.P.; Baker, S.L.; Tichenor, D.A. et al.
Partner: UNT Libraries Government Documents Department

Quartz substrates for EUVL reticles

Description: A EUVL reticle blank was fabricated on a specially polished quartz blank. The stress-induced distortion of the multilayer coating was unacceptably large. The distortion can be effectively eliminated by coating the backside of the reticle blank with an identical coating. This strategy has the potential to eliminate multilayer induced stress distortion for the reticle blank in a manner which is compatible with the existing reticle fabrication infrastructure.
Date: February 10, 1995
Creator: Kania, D.R.; Weber, F.J.; Vernon, S.P.; Hawryluk, A.; Baker, S.L.; Golub, A.M. et al.
Partner: UNT Libraries Government Documents Department

High average power laser for EUV lithography

Description: We have demonstrated the operation of a high average power, all solid state laser and target system for EUV lithography. The laser operates at 1.06 {mu}m with a pulse repetition rate of 200 Hz. Each pulse contains up to 400 mJ of energy and is less than 10 ns in duration. The ELTV conversion efficiency measured with the laser is independent of the laser repetition rate. Operating at 200 Hz, the laser has been used for lithography using a 3 bounce Kohler illuminator.
Date: January 19, 1995
Creator: Kania, D.R.; Gaines, D.P.; Hermann, M.; Honig, J.; Hostetler, R.; Levesque, R. et al.
Partner: UNT Libraries Government Documents Department

Precision optical aspheres for extreme ultraviolet lithography

Description: We have demonstrated significant advances in the production of aspheric optics for extreme ultraviolet lithography. An optic has been fabricated with an aspheric departure of 1.5 {mu}m, a figure error of 0.7 nm rms and a nanoroughness of 0.25 nm rms. Further improvements are required in the figure and nanoroughness to reach high throughput and near diffraction limited performance in an EUVL system. 8 refs., 2 figs.
Date: May 1, 1996
Creator: Kania, D.R.; Gaines, D.P.; Sweeney, D.S.; Sommargren, G.E.; La Fontaine, B.; Vernon, S.P. et al.
Partner: UNT Libraries Government Documents Department

Masks for extreme ultraviolet lithography

Description: In extreme ultraviolet lithography (EUVL), the technology specific requirements on the mask are a direct consequence of the utilization of radiation in the spectral region between 10 and 15 nm. At these wavelengths, all condensed materials are highly absorbing and efficient radiation transport mandates the use of all-reflective optical systems. Reflectivity is achieved with resonant, wavelength-matched multilayer (ML) coatings on all of the optical surfaces - including the mask. The EUV mask has a unique architecture - it consists of a substrate with a highly reflective ML coating (the mask blank) that is subsequently over-coated with a patterned absorber layer (the mask). Particulate contamination on the EUVL mask surface, errors in absorber definition and defects in the ML coating all have the potential to print in the lithographic process. While highly developed technologies exist for repair of the absorber layer, no viable strategy for the repair of ML coating defects has been identified. In this paper the state-of-the-art in ML deposition technology, optical inspection of EUVL mask blank defects and candidate absorber patterning approaches are reviewed.
Date: September 1, 1998
Creator: Cardinale, G; Goldsmith, J; Kearney, P A; Larson, C; Moore, C E; Prisbrey, S et al.
Partner: UNT Libraries Government Documents Department

X-ray bang-time and fusion reaction history at ~ps resolution using RadOptic detection

Description: We report recent progress in the development of RadOptic detectors, radiation to optical converters, that rely upon x-ray absorption induced modulation of the optical refractive index of a semiconductor sensor medium to amplitude modulate an optical probe beam. The sensor temporal response is determined by the dynamics of the electron-hole pair creation and subsequent relaxation in the sensor medium. Response times of a few ps have been demonstrated in a series of experiments conducted at the LLNL Jupiter Laser Facility. This technology will enable x-ray bang-time and fusion burn-history measurements with {approx} ps resolution.
Date: May 1, 2012
Creator: Vernon, S. P.; Lowry, M. E.; Baker, K. L.; Bennett, C. V.; Celeste, J. R.; Cerjan, C. et al.
Partner: UNT Libraries Government Documents Department

Thermal stability of Mo/Si multilayers

Description: The thermal stability of Mo/Si multilayers for x-ray mirror applications was investigated by annealing studies at relatively low temperatures for various times. The as-deposited and annealed multilayers were examined using conventional small and large angle x-ray diffraction, normal incidence x-ray reflectance measurements using a synchrotron source, selected area electron diffraction, and high-resolution electron microscopy. The as-deposited structure consists of pure layers of crystalline Mo and amorphous Si separated by thin regions of amorphous Mo-Si. At temperatures between 200--400{degrees}C, the amorphous Mo-Si interlayers grow and hexagonal MoSi{sub 2} forms by a thermally activated process(es), and the bilayer spacing and x-ray reflectivity decrease. A determination of the effective activation energy of the process(es) suggests long-term stability at the mirror operating temperature, although additional low temperature testing is warranted. 11 refs., 5 figs., 2 tabs.
Date: July 1, 1991
Creator: Rosen, R.S.; Stearns, D.G. (Lawrence Livermore National Lab., CA (United States)); Viliardos, M.A.; Kassner, M.E. (Oregon State Univ., Corvallis, OR (United States). Dept. of Mechanical Engineering) & Vernon, S.P. (Vernon Applied Physics, Torrance, CA (United States))
Partner: UNT Libraries Government Documents Department