bluuebunny/crossref_metadata_2025 huggingface dataset:
Progress Towards a 44-Å X-Ray Laser
Authors: MacGowan B. J. , Bourgade J. L. , Combis P. , Keane C. J. , London R. A. , Louis-Jacquet M. , Matthews D. L. , Maxon S. , Naccache D. , Rosen M. D. , Thiell G. , Whelan D. A.
Published: February 2023

Since 1984 when soft x-ray amplification was convincingly demonstrated at XUV wavelengths near 200 Å, much effort has gone into obtaining soft x-ray gain at shorter wavelengths. One motivation is the possibility of using a high brightness source of amplified spontaneous emission to perform holography of live biological specimens over short time scales.
Compact X-Ray Free-Electron Laser
Authors: Barletta W. , Atac M. , Bhowmik A. , Bobbs B. , Cline D. B. , Cover R. A. , Dixon F. P. , Gallardo J. , Kolonko J. , Pellegrini C. , Rakowsky G. , Wang X. , Westenskow G.
Published: February 2023

We present a design concept and simulation of the performance of a compact x-ray, free electron laser driven by ultra-high gradient rf-linacs. The accelerator design is based on recent advances in high gradient technology by a LLNL/SLAC/LBL collaboration† and on the development of bright, high current electron sources by BNL and LANL. The GeV electron beams generated with such accelerators can be converted to soft x-rays in the range from 2-10 nm by passage through short period, high field strength wigglers as are being designed at Rocketdyne. Linear light sources of this type can produce trains of picosecond (or shorter) pulses of extremely high spectral brilliance suitable for flash holography of biological specimens in vivo and for studies of fast chemical reactions.
Amplification in Na XI Hα, Mg XII Hα and Al XIII Hα Transitions
Authors: Kato Y. , Yamanaka M. , Daido H. , Tachi T. , Nishimura H. , Shiraga H. , Miura E. , Herman P. R. , Takabe H. , Jitsuno T. , Takagi M. , Nakai S. , Yamanaka C. , Key M. H. , Tallents G. J. , Rose S. J.
Published: February 2023

Observation of gain in Balmer-α (H α) transitions in Na XI, Mg XII and Al XIII is reported. Planer stripe targets were irradiated with intense, line-focused 351 nm laser light. Time evolution of the gain in Na XI Hα is also presented.
Population Inversion through Charge Exchange Process in Plasmas
Authors: Kato T. , Masai K. , Fujimoto T.
Published: February 2023

Population inversion due to charge exchange processes is investigated for helium-like ions in tokamaks by using a collisional radiative model. Dependence of charge exchange cross secions on the quantum numbers n, Z is estimated from the observed spectra.
Amplification and Gain Measurement of Extreme Ultraviolet Radiation (42.4Å, 45Å and 46Å) in He-like Al Laser Plasma
Authors: Muroo K , Tanaka Y , Kuroda H.
Published: February 2023

Concerning the extreme ultraviolet lasing in the laser-produced plasma, He -like Al scheme is atractive because the wavewlength of He-like 3-2 transitions are shorter than any other transition ever done, and very close to the water window. This scheme is expected to give a large population inversion caused by the rapid decaying of the n=2 level, and the great feed to the n=3 levels by the cascade radiative transitions and two electron transitions through the autoionized states.
Resistance of Short Pulses to Self-Focusing
Authors: Strickland D. , Corkum P.B.
Published: February 2023

Self-focusing arises in all materials, gases, liquids, solids or plasmas. Yet, it has been investigated only in the limit where the beam diameter is significantly less than the pulse length (cτ, where τ is the pulse duration). In this case, the beam is predicted to selffocus to moving singularities in the absence of other nonlinear effects. However, there is another extreme which is rarely, if ever, noted where the beam diameter is much larger than the pulse length and the pulse will disperse before any self-focusing can occur. Short pulse self-focusing is more related to the second extreme than the first.
Integration of the Schrödinger Equation on a Massively Parallel Processor
Authors: Parker Jonathan , Blodgett-Ford Sayoko , Clark Charles W.
Published: February 2023

The behavior of atoms in strong radiation fields depends critically upon the time evolution of the field. For example, it has been found1 that above-threshold ionization (ATI) spectra show radical changes as the duration of the exciting laser pulse decreases; there is also theoretical evidence2 for novel phenomena, such as population trapping, which occur only for relatively short pulses. In order to treat problems of this sort theoretically, one must employ methods that accommodate general time variation of the radiation field. The most direct such method is numerical integration of the time-dependent Schrödinger equation. This would be an entirely non-controversial approach if vast computational resources were not required to implement it in practice. To date there have been only a few reports3 of direct integration of the time-dependent Schrodinger equation for a three dimensional, one-electron atom in a radiation field.
Instrumentation for Generating Tunable VUV Radiation
Authors: Xiong Xiaoxiong , McIlrath Thomas J. , Westbrook Chris I.
Published: February 2023

In this paper, we discuss a simple system (one dye laser and one pumping laser) constructed for generating tunable vacuum ultraviolet (VUV) radiation suitable for high resolution spectroscopy. Our special considerations are focused on the capability of generating hydrogen lyman-α at 121.6 nm and helium two-photon excitation radiation at 120.3 nm, and on the capability of monitoring both the intensity and the wavelength of the generated VUV radiation for precision spectroscopy. Third-order sum-difference frequency mixing, ωVUV = 2ωUV - ωir, is used to generate the VUV radiation in rare gases of Kr, Xe, and Ar. The input UV frequency is tuned near, but not on, two-photon intermediate resonances (Kr: 4p - 5p) to enhance the nonlinear susceptibility χ(3), and to provide the tunability of the VUV radiation. Operating near, but not on, intermediate resonances allows an efficient, tunable system with only one tunable laser. The optimal phase matching condition is achieved by mixing two oppositely dispersive gases [1 - 5].
Spatial Distribution of High Order Harmonics Generated in the Tunneling Regime
Authors: Augst S. , Meyerhofer D. D. , Peatross J. , Moore C. I.
Published: February 2023

Production of laser harmonics occurs when a high-intensity laser interacts with a non-linear medium. At sufficiently high intensities any medium will show non-linear effects. We have observed high-order odd harmonic generation using a l-µm, 1-ps laser pulse at intensities between 1013 and 1016 W/cm2, and we have measured the spatial profiles of the harmonics. The existence of high order odd harmonics has previously been demonstrated1 in noble gases using intensities between 1013 and 1014 W/cm2.
Observation of Electromagnetically Induced Transparency
Authors: Imamoğlu A. , Boller K.-J. , Harris S. E.
Published: February 2023

We report the results of an experiment showing how an opaque atomic transition in neutral Sr may be rendered transparent to radiation at its resonance frequency. This is accomplished by applying an electromagnetic coupling field (Fig. 1) between the upper state 4d5d1D2 of the transition and another state 4d5p 1D2 of the atom. When the Rabi frequency of the coupling field exceeds the inhomogeneous width of the 5s5p1P1−4d5d1D2 transition, the medium becomes transparent on line center. In this work, we have changed the transmittance of neutral strontium from exp(−20) without a coupling laser to exp(−1) in the presence of a coupling laser, over a spectral range of 6 GHz (Fig. 2). The coupling laser that we have used is a single mode Littman dye laser with an intensity of 10 MW/ cm2 .
Future Directions of Laboratory X-ray Laser Research
Authors: Rosen Mordecai D.
Published: February 2023

Recently, gain-length products exceeding 8 have been achieved with the Ni-like (Ta and W),4d-4p x-ray laser scheme (MacGowan et. al. Phys. Rev. Lett. 65, 420 (1990)) with wavelengths just inside and just outside the water window, near the carbon K edge at 43.7 Å. This success, however, is tempered by the fact that it took two of the ten arms of Nova, the world's most powerful laser, to pump the exploding foils that served as the amplification medium. If applications of x-ray lasers are to become a reality, we must devote some thought and effort to schemes that can produce such short wavelength lasing using more user friendly and less costly facilities.
Direct Measurement of Nonequilibrium Electron Energy Distribution in Sub-Picosecond Laser-Heated Gold Films
Authors: Fann W. S. , Storz R. H. , Bokor J.
Published: February 2023

Electron heating in metals by ultrashort laser pulses has been under intensive investigations in recent years1,2. It is generally believed that in a very short time (< 1-2 fsec) after the optical excitation, the electrons equilibrate among themselves via the electron-electron interaction, and establish a thermal Fermi-Dirac distribution at an elevated temperature. The electron-phonon interaction operates on a longer timescale of several psec to equilibrate the electrons with the lattice phonons.1,2 During those several psec, the electrons are decoupled from lattice and it is possible to heat the electrons alone up to several thousand K. However no direct measurements of the electron energy distribution function in laser-heated metals have been reported so far. We have used ultraviolet photoemission spectroscopy to directly obtain the energy distribution function with 500 fsec time resolution. We confirm that on this time scale, the distribution is well described by a Fermi-Dirac function and we thus directly measure the time-dependence of the electron temperature.
Effects of Illumination Uniformity Improvement on X-ray Lasing Plasma
Authors: Kieffer J.C. , Nantel M. , Chaker M. , Pépin H. , Baldis H.A. , Dunn J. , Enright G.D. , Villeneuve D.M.
Published: February 2023

An accurate knowledge and an efficient control of the plasma conditions are required for the optimization of the gain to realize a small scale efficient X-ray laser1. We already observed that large scale density inhomogeneities were driven by laser nonuniform irradiation2. In the present work a novel focusing arrangement3, composed of a segmented wedge array (SWA) to overlap several line foci, was employed to produce a nearly uniform illumination. We use simultaneously spatially (2D) and time resolved diagnostic to see, in lasing plasmas, how critical is the irradiation nonuniformity, for various pumping schemes.
Laser-plasma sources for lithography
Authors: Forsyth James M.
Published: February 2023

The characteristics of laser-plasma sources for lithographic applications in different spectral ranges will be reviewed, and the performance potential will be summarized.
High Performance Multilayer X-Ray Optics
Authors: Stearns D. G.
Published: February 2023

Multilayer x-ray optics are becoming increasingly important in diverse applications such as x-ray projection lithography1, x-ray laser cavities2, x-ray microscopy3, astronomy4 and spectroscopy5. In this paper we focus on the current development of normal incidence reflective optics for the soft x-ray spectrum of ~45 - 130 Å. The ultimate goal is to develop a soft x-ray imaging system capable of high throughput and diffraction-limited performance over an appropriate image field.
Phase Matching for Large-Scale Frequency Upconversion in Plasma
Authors: Shkolnikov P. L. , Kaplan A. E. , Lago A.
Published: February 2023

We consider phase matching in generation of very short-wavelength coherent radiation by nonlinear frequency upconversion in plasma and suggest some ways to improve phase matching in high-order harmonic generation (HHG). We obtain the first to our knowledge simple analytical expressions for phase-matching factor in multiphoton mixing of an arbitrary order and demonstrate theoretically that high-order difference-frequency mixing in plasma could be, due to its potential for phase matching optimization, a more promising method of large-scale frequency upconversion than HHG.
Harmonic Frequency Generation and Chaos in Laser-Driven Molecular Vibrations
Authors: Zhang Chengyong , Katsouleas Tom , Joshi Chan
Published: February 2023

We investigate the onset of chaos in a system composed of an ionic molecule driven by a laser pulse whose frequency is nearly resonant with molecular vibrations. The continuous radiation spectrum generated by the molecule is shown to be of two different origins. For low intensity chirped lasers, the continuum is the result of a large number of discrete transitions between energy levels of the excited molecule. For unchirped and chirped lasers at higher intensities, the continuum is produced by chaotic motion of the molecule. This is evidenced by a sudden increase in the system’s dimensionality and the transition of the system’s largest Lyapunov exponent from negative to positive.
Measurement of Fast-Electron Energy Spectra in a 100 fs Laser-Produced Plasma
Authors: Rousse A. , Falliès F. , Geindre J. P. , Audebert P. , Gauthier J. C. , Mysyrowicz A. , Grillon G. , Chambaret J. P. , Antonetti A.
Published: February 2023

Fast electrons produced by the irradiation of plane-layered targets with 1 mJ, 100 fs, 2. 1016 W/cm2 CPM dye laser pulses at 10 Hz have been diagnosed by the Kα emission which they cause at various depths in the targets. The fast-electron energy spectrum and the absolute energy deposition have been deduced from a detailed comparison of the measured data with the results of a Monte-Carlo code calculating the Kα yield, target heating and ionization balance from various fast electron distributions.
Time Resolved Spectroscopy of Ultrashort Plasmas
Authors: Kieffer J. C. , Beaudoin Y. , Chaker M. , Côté C. Y. , Jiang Z. , Johnston T. W. , Matte J. P. , Pépin H. , Chien C. Y. , Coe S. , Mourou G. , Peyrusse O. , Mens A. , Verrecchia R. , Sauneuf R. , Schirmann D. , Dubau J.
Published: February 2023

X-ray diagnostics are employed to characterize a plasma produced by a
high contrast subpicosecond laser at intensities between
1016 W/cm2 and 1018 W/cm2.
The plasma dynamics and the basic processes which control the duration
of the X-ray pulse are quantitatively studied by means of polarization
spectroscopy and time resolved spectroscopy with a picosecond temporal
resolution. The experimental results are discussed with time dependent
calculations of the atomic physics coupled to kinetic Fokker-Planck
modelling.
Chirped Pulse Amplification in Cr:LiSrAlF6 to the Terawatt Level
Authors: Ditmire T. , Nguyen H. , Perry M. D.
Published: February 2023

We have developed a compact, flashlamp pumped Cr:LiSrAlF6 laser system capable of producing peak powers in excess of one terawatt. The chirped pulse amplification approach has been optimized for amplification of femtosecond pulses in Cr:LiSrAlF6. The system includes a Cr:LiSAF regenerative amplifier followed by a Cr:LiSAF power amplifier chain. The regenerative amplifier produces 12 mJ pulses at a 5 Hz repetition rate which are further amplified to 300 mJ at a 0.5 Hz repetition rate. Recompression results in a pulse energy of 150 mJ and pulse duration of under 135 fsec.
Intense Monochromatic Point X-Ray Source Produced by a Short-Pulse Laser and its Applications to Holographic Imaging
Authors: Schulz M. S. , Daido H. , Zeng G. M. , Nakatsuka M. , Kato Y. , Nakai S. , Turcu I. C. E. , Ross I. N. , Hening A.
Published: February 2023

A Young’s double slit experiment was carried out to investigate the coherence properties of a quasi-monochromatic point x-ray source in the water window spectral region. Plasma source sizes were determined by obtaining pinhole camera images. Emission spectra were recorded using a transmission grating spectrometer in conjunction with Kodak S101 x-ray film. In-line Gabor holograms of two fibers were obtained to demonstrate the viability of the laser plasma source as a suitable source for coherent imaging. Also discussed is the maximum achievable brightness of a monochromatic point x-ray source using a glass based laser system at the Institute of Laser Engineering, Osaka.
X-Ray Stimulated Electronic Raman Scattering in Non-Ionized Gases
Authors: Hudis E. , Shkolnikov P. L. , Kaplan A. E.
Published: February 2023

We theoretically demonstrate feasibility of resonantly-enchanced stimulated electronic Raman scattering of Se X-ray laser radiation in atomic He and Li, and estimate Stokes output.
Non-Specular X-ray Scattering from Multilayer Structures
Authors: Kortright Jeffrey B.
Published: February 2023

X-ray multilayer structures derive their utility primarily from the specular reflectance at the first order multilayer Bragg peak. Ideal x-ray multilayer structures would have composition modulation only along the direction of the sample normal (z direction) and would be homogeneous in the x-y plane. Ideal structures would thus exhibit only specular reflectance in the region of low scattering vector near the multilayer Bragg peaks. Structural inhomogeneities in the x-y plane within the multilayer (possibly arrising from the substrate) would give rise to diffuse non-specular scattered intensity in this region.
Source Issues Relevant to X-Ray Lithography
Authors: Nguyen Khanh , Attwood David
Published: February 2023

Synchrotrons and laser-produced plasmas (LPPs) are leading candidates for radiation sources for x-ray lithographic systems. Each has its own strengths and weaknesses. Synchrotrons offer higher flux and brightness but are large and expensive. Laser-produced plasmas sources may be cheaper and smaller but have low average power and non-directional output.
X-ray Production Efficiency at 130 Å from Laser-Produced Plasmas
Authors: Kauffman Robert L. , Phillion Donald W.
Published: February 2023

Laser-produced sources for soft x-ray projection lithography require high brightness in a narrow x-ray band in the region of high reflectivity for multilayer optics. Lasers will also probably be of only modest power matching near term laser technology development for high efficiency, high repetition rate lasers. Little experimental work has been done on characterizing x-ray emission below 300 eV at laser irradiations of a Joule or less. Experimental data will be needed over a large range of laser parameters including wavelength, intensity, and pulse width in order to assess the relative merits of any laser system proposed as a source for soft x-ray projection lithography.
Resist Characterization at Soft X-Ray Wavelengths
Authors: Kubiak G. D. , Kneedler E. M. , Berger K. W. , Bjorkholm J. E. , Mansfield W. M. , Windischmann H.
Published: February 2023

The characterization of resist materials for soft X-ray projection lithography (SXPL) in the 75-350 Å spectral region is an important issue, although it has received little attention to date. With the recent demonstration of diffraction-limited SXPL at 140 Å[1], the need to optimize resists at specific exposure wavelengths for future SXPL commercialization has become acute. Near 300 Å resist absorbance is so large that a single-layer resist strategy does not appear feasible, whereas near 80 Å it does. At intermediate wavelengths, for example where Mo/Si multilayer reflective coatings are efficient, it is not yet possible to determine whether a surface imaging or single-layer method is optimum. To estimate the maximum developed resist depth attainable at a given wavelength, the appropriate mass absorption coefficients may be used to calculate film absorbance. The accuracy of these estimates is questionable, however, especially at longer wavelengths where solid state effects can be pronounced. We have undertaken a study of single-layer resists in the spectral region relevant to SXPL and have characterized the sensitivity, contrast, and absolute absorbance of poly methylmethacrylate (PMMA), polysilane, and diazonapthoquinone/novolak resists. In addition, we have evaluated the lithographic performance of these materials at an exposure wavelength of 140 Å using an SXPL instrument illuminated by a laser plasma source (LPS) of high average power.
Soft X-ray reduction lithography using a reflection mask
Authors: Kinoshita H. , Kurihara K. , Mizota T. , Haga T. , Torii Y. , Takenaka H. , Ishii Y.
Published: February 2023

We have conducted the research work on X-ray projection lithography and have already demonstrated a 0.5 µm replicated pattern using a reflection mask. To obtain smaller features, we have designed a Schwarzschild typed demagnifying objective with a numerical aperture size of 0.1 and fabricated a Mo/B4C multilayer very precisely on its optics.
Where are We in the Development of Soft X-Ray Projection Lithography?
Authors: Freeman Richard R.
Published: February 2023

Since the first suggestion of doing projection lithography with soft x-rays was made by Hawryluk and Seppala, and Silvfast and Wood nearly 4 years ago, there has been a flood of activity on many of the basic principles and technologies. Foremost among these has been the development of high reflectivity coatings for mirrors that operate near 130 angstroms, the demonstration of diffraction-limited reduction imaging over a small field, and the design of high efficiency laser plasmas for compact illumination sources. Current work includes construction and repair of reflection masks, designs for large field cameras, and illuminators to couple them to the source, and development of advanced methods to measure and ultimately fabricate precision spherical and aspherical mirrors for large field cameras.
Issues Associated with the Design and Construction of an Imaging System for Soft X-ray Lithography
Authors: Zernike F.
Published: February 2023

Soft x ray projection lithography allows the printing of feature sizes of 1μm and smaller with reasonable depth of focus because the very short wavelength allows a small numerical aperture. Because attainable mirror reflectivities are low in this wavelength region, the number of mirrors has to be kept to a minimum. Here again the low numerical aperture helps. Compared to present deep UV (248nm.) systems, there are a number of clearcut differences that impact the design and the construction of such a system.
Practical Tolerancing and Performance Implications for XUV Projection Lithography Reduction Systems*
Authors: Viswanathan V. K.
Published: February 2023

The design aspects of candidate reflective optical systems for projection lithography using extreme-ultraviolet (XUV) exposure wavelengths from approximately 10 to 20 nm have been discussed by various authors.1-3 The very demanding requirements for XUV-projection systems include the ability to resolve 0.1-μm features over at least a 25 mm x 25 mm image field with less than 0.01-μm distortion while providing a minimum of 1-μm total depth of focus. Other practical considerations affecting system imaging capability include thermal distortion of the mirror surfaces due to absorption of a fraction of the incident radiation beam and alignment tolerances. We present our analyses of the magnitude of these latter two effects on two types of reflective projection optical designs. We use the usual criteria for manufacturing and alignment errors4 and Zernike polynomials5 to represent the thermal and other distortions induced by the incident flux. We find that concentric, symmetric two-mirror systems2 are significantly less sensitive to thermal and alignment errors than off-axis, four-mirror systems.
Precision bending of substrate for high perfomance x-ray optics
Authors: Allred D.D. , Shi Y. , Berrondo M. , Perkins R.T. , Yuan F. , Knight L.V. , Reyes-Mena A.
Published: February 2023

We have investigated producing aspheric mirrors for x rays with order-of-magnitude improvements in surface finish, figure, and lightness for x-ray mirror blanks.
Multilayer Mirror Technology
Authors: Stearns D. G. , Rosen R. S. , Vernon S. P.
Published: February 2023

Recent advances in multilayer (ML) fabrication and characterization have brought this technology to the verge of satisfying the severe requirements posed by soft x-ray projection lithography (SXPL). To enable a viable production SXPL system, the ML coatings must simultaneously demonstrate (1) high normal incidence reflectivity in the range of 65-70% at λ=130Å, (2) ML period errors of less than 0.5% over the optical surface to maintain diffraction- limited imaging and (3) long term stability under realistic operating conditions. In addition, it is possible that certain optical designs will require laterally graded coatings with similar tolerances for the ML period errors. This set of stringent requirements can only be achieved via a thorough understanding and control of the ML deposition process, ML structure and properties.
Multilayer Performance for Soft X-ray Schwarzchild Optics
Authors: Gutman Georgy , Parker Kevin , Wood James L. , Watts Richard
Published: February 2023

One of the most important requirements for soft x-ray optics is high normal incidence reflectivity. But to ensure a high throughput optical system, Schwarzchild objectives in particular, it is not only necessary to fabricate multilayer coatings with the highest possible reflectivity but to achieve the designed d-spacing uniformity/grading and match the d-spacings of the concave and convex mirrors. The latter is especially important for high throughput multi-mirror lithography optical schemes.[1]
Multilayer Damage and Repair Issues in Soft-X-Ray Projection Lithography
Authors: Gaines D. P. , Spitzer R. C. , Ceglio N. M.
Published: February 2023

Current soft x-ray projection lithography (SXPL) system designs require multilayer coated optics to operate at levels approaching predicted maximums for near normal incidence reflectivity. Effects that (potentially) degrade multilayer performance in the SXPL environment are discussed. Appropriate repair strategies are suggested, and preliminary results are presented.
Silicide Layer Growth Rates in Mo/Si Multilayers
Authors: Rosen R. S. , Stearns D. G. , Viliardos M. A. , Kassner M. E. , Vernon S. P. , Cheng Y.
Published: February 2023

Mo/Si multilayers (ML's) are attractive for x-ray optics due to the relatively high associated reflectivity. However, the reflectivity is known to decrease with the formation of diffuse interlayer regions resulting from interdiffusion at the Mo-Si interfaces [1-2]. Most of the previous studies have reported interdiffusion coefficients [1-4] and effective activation energies [2-4] over a range of temperature assuming that the interdiffusion coefficient is invariant with annealing time. Recent results by the authors [2] have suggested that there may be an initial "surge" contraction (~ 0.1- 0.2 nm) of the ML structure. Therefore, it is the objective of this study to perform a series of annealing treatments of Mo/Si ML's at relatively low temperatures to determine the Mo-Si interdiffusion kinetics as a function of time.
Soft-X-ray Projection Lithography Experiments using Schwarzschild Imaging Optics
Authors: Tichenor D. A. , Kubiak G. D. , Malinowski M. E. , Stulen R. H. , Haney S. J. , Berger K. W. , Brown L. A. , Sweatt W. C. , Bjorkholm J. E. , Freeman R. R. , Himel M. D. , MacDowell A. A. , Tennant D. M. , Wood O. R. , Bokor J. , Jewell T. E. , Mansfield W. M. , Waskiewicz W. K. , White D. L. , Windt D. L.
Published: February 2023

Projection imaging experiments are described. A Schwarzschild objective is illuminated with 14-nm radiation using an ellipsoidal condenser and a laser plasma source.
Large-Area, High-Resolution Pattern Replication using a Two- Aspherical-Mirror System
Authors: Kinoshita Hiroo , Kurihara Kenji , Mizota Tutomu , Haga Tuneyuki
Published: February 2023

The ability to replicate 0.1 μm patterns using multilayer reduction optics has already been demonstrated1),. However, if we are to exploit this technology for practical lithography of VLSI devices, the problems of large exposure area and high throughput must be solved.
Mask Technologies for Soft X-ray Projection Lithography at 13nm
Authors: Tennant D.M. , MacDowell A.A. , Mulgrew P.P. , Pastalan J.Z. , Waskiewicz W.K. , Windt D.L. , Wood O.R.
Published: February 2023

Imaging systems using soft X-ray reflective optics can be configured with either a transmission [1] or reflection mask [2] to print onto resist coated wafers. Transmission masks are well suited for high contrast and high resolution imaging. However, thin membranes are needed for such masks which can be fragile and sensitive to heating effects. Ultimately it is therefore desirable to take advantage of the robust nature of a thick reflecting mask. Practical reflective masks intended for use at λ=13 nm require Mo/Si multilayer reflective coatings with minimum features sizes from 2.0 to 0.1 μm in order to demonstrate a 0.1 μm printing capability with systems designed mask to wafer reduction from 20X to 1X, respectively. In this work we compared a variety of technologies for patterning transmissive and reflective masks containing features on this size scale. Transmissive masks which are reported consist of patterned absorbers on silicon membranes with features as small as 0.1 μm. Reflective masks patterned using various methods including; absorbing layers formed on top of multilayer reflectors; reflective coating removal by reactive ion etching (RIE); and ion damage of multilayer regions by ion implantation are also reviewed [2]. With a view to the future,we have begun to assess these reflective masks in a number of areas. Of principal interest are the reflectance contrast; resolution; process complexity; and repairability.
Reflection Mask Repair for Soft-X-Ray Projection Lithography
Authors: Hawryluk A. M. , Gaines David P. , Stewart Diane
Published: February 2023

Soft-x-ray projection lithography (SXPL) will use a reflective mask consisting of an x-ray multilayer mirror, patterned with a thin (~50-100 nm) layer of gold. Pattern repair techniques that do not degrade the multilayer mirror reflectivity must be developed if SXPL is to become an acceptable choice for lithography. Mask repair results from both clear and opaque mask repair experiments are discussed and analyzed.
Future Lithographic Requirements
Authors: Carruthers John R.
Published: February 2023

The future manufacture of IC's beyond 2000 will require pattern transfer systems of considerable complexity and cost. Critical dimensions below 150 nm must be controlled in three dimensions without interference from proximity effects and with an overlay/alignment capability that approaches 50 nm (3 sigma) from layer to layer over larger field sizes of 25 to 30 mm on a side. The metrology to develop and control these systems also needs to be developed with precision approaching atomic dimensions. The implications of these requirements on continuing the scaling treadmill approach for ULSI development are discussed.
Application of Lithography Simulation to Projection X-Ray
Authors: Neureuther A.R.
Published: February 2023

Simulators and materials modeling approaches from optical projection
printing provide an advantageous starting point in addressing
technology issues in the emerging field of projection x-ray
lithography. A brief overview will be given of relevant imaging,
resist characterization, resist exposure, resist dissolution, pattern
transfer, and electromagnetic scattering programs available from
Berkeley. The overview will also highlight important observations
drawn from simulation and modeling which are helping optical
projection printing at todays 0.35 um feature sizes. Key issues in
projection x-ray lithography imaging, materials, and masks where these
Technology CAD tools are making an impact will then be discussed.
Limits of Ultra Violet Lithography
Authors: Pease R. Fabian
Published: February 2023

Any new technology must offer significant improvement over an entrenched technology to become adopted. Here we describe where ultra-violet lithography might evolve to in ten years time the earliest possible time for soft x-ray lithography to be ready for manufacture.
Condenser Optics for Soft X-ray Projection Lithography
Authors: Vernon Steve , Sommargren Gary , Seppala Lynn , Gaines David
Published: February 2023

Condenser optics has been designed, fabricated and coated for use in a "front-end" test bed facility at LLNL. Details of condenser design and coating processes will be discussed.
X-ray characterization of a three-element condenser system for soft x-ray projection lithography
Authors: Gaines D.P. , Sommargren G.L. , Vernon S.P.
Published: February 2023

A three-element condenser system has been designed and fabricated for use in a soft x-ray projection lithography facility at Lawrence Livermore National Laboratory. The design uses Kohler illumination to transport x-rays generated by a laser-produced plasma onto an x-ray reflection mask. The condenser optics are coated with molybdenum silicon multilayers to provide peak reflectance at an operating wavelength of approximately 13.0 nm.
Surface Finish Requirements for SXPL Optics
Authors: Windt D. L. , Waskiewicz W. K. , Griffith J. , Bjorkholm J. E.
Published: February 2023

In order for soft X-ray projection lithography to become a viable
candidate for the mass production of integrated circuits having
0.1-μm design rules, it will be necessary to satisfy an array
of technical performance requirements. Among these requirements is
system throughput (i.e. wafers/hour.) For SXPL exposure tools
operating at 14 nm using multilayer X-ray mirrors, the system
throughput depends sensitively on the peak reflectance of the
multilayers. The peak reflectance, in turn, can be deleteriously
affected by the surface finish of the mirror substrates. That is, the
roughness of the substrate can propagate through the multilayer during
growth, resulting in reduced reflectance. Therefore, it is imperative
to use X-ray mirror substrates with low surface roughness.
Substrate Recovery of Mo-Si Multilayer Coated Optics
Authors: Stearns D. G. , Baker S. L.
Published: February 2023

Multilayer coated optics in a soft x-ray projection lithography system are subject to environmental effects that can degrade their performance such as corrosion, contamination and excessive radiation exposure. When the damage is limited to the multilayer coatings it is cost effective to recycle the optics by removing the damaged coatings and recoating the substrates. The main challenge is to develop a substrate recovery process that completely removes the coating without compromising the figure and surface finish requirements of the original substrate. Typical requirements for the precision imaging optics are a surface finish of less than 1 Å root-mean-square (RMS) and peak-to-valley figure error of less than 10 Å.
Development and Characterization of a 10x Schwarzschild System for Soft-X-Ray Projection Lithography
Authors: Tichenor D. A. , Kubiak G. D. , Malinowski M. E. , Stulen R. H. , Haney S. J. , Berger K. W. , Nissen R. P. , Schmitt R. L. , Wilkerson G. A. , Brown L. A. , Spence P. A. , Jin P. S. , Sweatt W. C. , Chow W. W. , Bjorkholm J. E. , Freeman R. R. , Himel M. D. , MacDowell A. A. , Tennant D. M. , Wood O. R. , Waskiewicz W. K. , White D. L. , Windt D. L. , Jewell T. E.
Published: February 2023

Multilayer-coated Schwarzschild imaging objectives have been used to demonstrate high-resolution soft-x-ray imaging.1-2 In our previous work3 a 20x reduction Schwarzschild imaging objective served a useful tool for studying the mounting and alignment of soft-xray optical elements and the quality and alignment of the condensing optics. However, the field of view, 25 μm by 50 μm, is much too small for a practical lithography tool. We have optimized and fabricated a new Schwarzschild system to achieve a 0.4 mm diameter field of view using 0.1 μm design rules. The increased field of view, although not large enough for a practical lithography tool, approximates the ring width in practical ring-field designs. This objective also covers enough area on the wafer to perform device fabrication experiments. This paper describes the development and characterization of the imaging system and the supporting illumination system.
Soft X-ray Projection Imaging using 32:1 Schwarzschild Optics
Authors: Nagata Hiroshi , Ohtani Masayuki , Murakami Katsuhiko , Oshino Tetsuya , Maejima Yukihiko , Tanaka Toshihiko , Watanabe Takeo , Yamashita Yoshio , Atoda Nobufusi
Published: February 2023

X-ray projection lithography is expected as a candidate for VLSI production in the near future. To get a resolution of 0.1μm and wide exposure area simultaneously, reduction systems with aspherical mirrors are required1,2), but the machining precision required to fabricate aspherical surfaces has not been achieved. Thus reduction systems with spherical airrors3-5) are preferable in current study of mounting and alignment of optical elements and resist process.
Optic Fabrication and Metrology for Soft X-Ray Projection Lithography
Authors: Himel Marc D.
Published: February 2023

One of the many technology areas that lie on the critical-path to the success of soft X-ray projection lithography (SXPL) is the fabrication and metrology of aspheric mirrors. I will review the progress of our collaboration with a number of companies to determine if the mirror fabrication and metrology technologies can be developed so that SXPL can meet the early next century demand for 0.1 μm design rule devices. The figure and finish tolerances for these mirrors are well beyond the current state-of-the-art for aspheres and even beyond industry's capability to fabricate spheres. To achieve the desired imaging capability will require mirrors with subnanometer figure errors over the full spatial frequency bandwidth, from 10 nm to 250 mm. Although exact full bandwidth tolerances have not been determined, we have estimated that the nanoscale rms roughness (as measured over a bandwidth of 10 nm to 1.0 μm) must be less than 0.1 - 0.2 nm so that high reflectivity multilayers can be attained. Specifications for the figure errors of a 5X reduction system being developed by GCA/Tropel range from 1.0 to 3.0 nm PV (depending on the mirror) for a 36 term Zernike polynomial fit. Although we have not yet estimated the specification for spatial frequencies between 1.0 μm and 25 mm, there is evidence that they could have a significant effect on imaging performance at X-ray wavelengths near 14 nm.1
Surface Metrology of Soft X-Ray Optics
Authors: Vorburger T. , McWaid T. , Fu J. , Evans C.J. , Estler W.T. , Parks R.E.
Published: February 2023

The reflectivity and scattering of mirrors used for x-ray optics at a wavelength of 13.6 nm depend on spatial wavelengths of the surface topography ranging from atomic dimensions to the full aperture of the mirror. Accordingly, we are developing measurement and calibration approaches that will span over 8 orders of magnitude of spatial wavelength from 1 nm to 150 mm. As shown in Fig. 1, the array of profiling techniques in our laboratory includes scanning tunneling microscopy, atomic force microscopy, stylus profiling, and phase measuring interferometry for both finish and figure. In addition, a calibrated stylus instrument produces measurements of surface finish profile with good resolution and accuracy. Thus, NIST is developing the capability to provide continuous power spectral information over the full bandwidth. The overlapping spatial wavelength regimes of the various approaches enable us to test any methods divergence between them.
Point Diffraction Interferometry at Soft X-ray Wavelengths
Authors: Sommargren Gary E. , Hostetler Ralph
Published: February 2023

To achieve the image performance necessary for soft x-ray projection lithography, interferometric testing at the design wavelength is required to accurately characterize the wavefront of the imaging system. The wavefront depends not only on the surface figure of the individual optics and on their relative alignment, but also on aperture dependent phase shifts induced by the resonant multilayer coatings on the optical surfaces. This paper describes the design and lithographic fabrication of an array of point diffraction interferometers on a Si3N4 membrane that has been over-coated with a spatially graded absorbing film to provide fringe contrast control. Experimental results using a visible light analogue (larger pinholes and different absorption gradient) will be presented.
Beamline Design for at Wavelength Interferometry
Authors: Jackson K. , Beguiristain R. , Koike M. , Attwood D. , Sommargren G.
Published: February 2023

A facility for research associated with the pursuit of extreme ultraviolet (EUV) and soft x-ray (SXR) projection lithography is proposed. The facility would be based on unique opportunities for research in science, and technology due to the availability of high-brightness, partially coherent radiation at wavelengths extending from 140 Å to 40 A from an undulator at the Advanced Light Source (ALS). The large flux of radiation from the undulator poses serious problems for the optical components in the beamline. A major aspect of the research proposed herein is to develop a facility which permits the detailed characterization of complex, high-numerical-aperture multilayer coated optical surfaces with regard to their deviation from ideal as-prescribed shapes.
The New Reflectometry Facility at the National Institute of Standards and Technology
Authors: Tarrio C. , Watts R. N. , Lucatorto T. B. , Haass M. , Calcott T. A. , Jia J.
Published: February 2023

The National Institute of Standards and Technology (NIST), as part of its soft x-ray metrology program, is constructing a new reflectometry beamline designed to improve our XUV measurement service. The new facility, intended primarily to characterize soft x-ray multilayer optics and to measure the optical properties of materials, consists of a newly commissioned varied line-spaced grating monochromator and a new reflectometry chamber currently under construction. The monochromator is designed to cover the 3.5 – 40 nm region of the spectrum with high throughput, a resolving power of 100 to 2000, and a spot size of 0.5 mm x 0.5 mm. In addition, the reflectometer is designed to measure the specular and non-specular reflectivities of optics up to 35 cm in diameter at any orientation with respect to the incoming x-ray beam. In this talk, we describe the optical properties and the performance of the new monochromator and discuss the capabilities of a hybrid reflectometer consisting of the newly commissioned monochromator and the existing reflectometer chamber already in use at NIST.
FEL Sources For Soft X-Ray Projection Lithography On The Duke 1 GeV Storage Ring
Authors: Johnson Lewis E. , Madey John M. J.
Published: February 2023

The Free Electron Laser has been proposed as a source to extend projection lithography to even greater resolution[1]. The envisioned high power, coherence and wavelength tunabality of these sources make the FEL a welcome radiation source to overcome some of the limitation with optics and resist technology that plague the current sources. The narrow line width imposed by the FEL should generate a steeper step in resist. Moreover, the higher power should allow us to explore regions in the resist once currently of reach.
Solid State Laser Driver for Projection X-ray Lithography
Authors: Hackel Lloyd A. , Dane C. Brent , Hermann Mark R. , Zapata Luis E.
Published: February 2023

The design of a diode pumped solid state laser for use as an x-ray driver is described. The laser will deliver 400 mJ per pulse in a 5ns to 8ns pulselength at a 1000 Hz pulse repetition rate. The laser architecture is a master oscillator/power amplifier. A microchannel cooling technique developed at LLNL is used to allow the diodes to operate at the high repetition rate. The oscillator amplifier concept has been demonstrated in a Nd:glass system. Progress to date and experimental results will be presented. The laser will deliver 400 mJ per pulse in a 5ns to 8ns pulselength at a 1000 Hz pulse repetition rate. The laser architecture is a master oscillator/power amplifier. A microchannel cooling technique developed at LLNL is used to allow the diodes to operate at the high repetition rate. The oscillator amplifier concept has been demonstrated in a Nd:glass system. Progress to date and experimental results will be presented.
Soft X-Ray Generation by a Table-Top High-Repetitive Glass Laser
Authors: Aritome H. , Haramura K. , Sekiguchi H. , Hara H. , Mochizuki T.
Published: February 2023

Soft x-rays generated from a laser produced plasma are of interest as a source for an x-ray microscope and also for x-ray lithography. In this paper, the x-ray generation from a recently developed, table-top high repetitive, high energy moving glass slab laser1) is demonstrated. The laser system can be operated at 5 Hz with laser pulse energy of 6 J. The size of the system is expected to be 3.4 m × 1.2 m × 1.3 m except for the power supply and the cooling unit.
Picosecond Measurement of Hot Carrier Luminescence in In0.53Ga0.47As
Authors: Kash Kathleen , Shah Jagdeep
Published: February 2023

Time resolved optical measurements provide considerable information about carrier energy loss processes in semiconductors by measuring the time evolution of the carrier distribution function. Picosecond luminescence spectra using a streak camera or a Kerr shutter [1-3] and subpicosecond excite and probe absorption experiments [4,5] have been reported in GaAs. A comparable study in the smaller bandgap ternary and quaternary semiconductors would be of considerable interest from both the physics and the device viewpoint, but has not yet been reported.
Picosecond dephasing and energy relaxation of excitons in semiconductors
Authors: Masumoto Yasuaki
Published: February 2023

Picosecond relaxation processes of excitons, including dephasing processes, are systematically studied in CuCl, CdSe and GaAs/AlAs MQW (multi-quantum well structures) by observing time-resolved induced absorption, luminescence and non-degenerate four-wave mixing. By studying the transient induced absorption from the exciton (polariton) state to the excitonic molecule state, time-resolved energy distribution of excitons in CuCl is determined (Fig.1).1) Another technique, i.e. time-resolved luminescence measurement, is applied to excitons in CdSe and GaAs/AlAs MQW (Figs.2 and 3).2,3) By analyzing the above-mentioned experiments the distribution of excitons in the two-dimensional energy-time coordinates is successfully determined. Thus, energy relaxation processes of excitons are clearly visualized. Prior to energy relaxation, coherently generated excitons are considered to be dephased. Phase relaxation of excitons in CuCl is directly measured for the first time in the picosecond time domain by means of time-resolved non-degenerate four-wave mixing (Fig.4).4) These new techniques will be demonstrated and the dephasing as well as energy relaxation mechanism of excitons and excitonic polaritons will be discussed. In the above experiments characteristics of a picosecond tunable optical parametric oscillator pumped by a mode-locked Nd3+:YAG laser as well as a picosecond tunable dye laser synchronously pumped by a mode-locked ion laser are complementarily utilized.
Stimulated VUV Radiation from HD Excited by a Picosecond ArF* Laser
Authors: Luk T. S. , Egger H. , Muller W. , Pummer H. , Rhodes C. K.
Published: February 2023

Picosecond rare gas halogen lasers are well suited for wavelength up-and-down conversion by nonlinear processes. With the clear advantage of the high peak power, which minimizes the photoionization loss through the reduction of the pulse duration, multiphoton excitation has proved to be an efficient method of generating stimulated emission1 in the vacuum ultraviolet (VUV) region. Furthermore, with use of the optical Stark2 shift, the number of available excitation channels can be increased, and, consequently, a large number of intense line sources should be available. In this experiment, strong stimulated emission has been observed in the 110 - 150 nm region on both the C → X and B → X transitions from HD excited by a two-quantum process.