A compact laser-produced plasma x-ray source radiates 1 nm x rays with an average power of 24 W in 2π steradians. The x-ray conversion efficiency is 9% of the laser power delivered on target. The 300 W laser power is generated by a compact diode-pumped, solid-state Nd:YAG laser system. The point source x-ray radiation is collimated with a polycapillary optic to a parallel x-ray beam. The collimated plasma source (CPS) is used to demonstrate proximity x-ray lithography of 100 nm lines with a 16 μm gap between the mask and wafer. The CPS is optimized for integration with an x-ray stepper to provide a complete collimated plasma lithography exposure tool for the manufacture of high-speed GaAs devices.

Absolute intensities of spectra in a dense-plasma-focus (DPF) source have been recorded and analyzed. This DPF source has been identified as one of the more promising sources for X-ray lithography. The source, developed by Science Research Laboratory, Inc., is currently undergoing testing and further development at BAE Systems, Inc. The DPF operates at 60 Hz and produces an average output pulse of ~5 J of X rays into 4π steradians in a continuous operation mode. In all runs, there was an initial number of pulses, typically between 30 to 40, during which the X-ray output increased and the DPF appeared to be undergoing a conditioning process, and after which a "steady-state" mode was achieved where the average X-ray power was relatively constant. Each spectral run was exposed to ~600 J of output, as measured by the PIN. The X-ray spectral region between 0.8 and 3 keV was recorded on Kodak DEF film in a potassium acid phthalate (KAP) convex curved-crystal spectrograph. The source emits neon line radiation from Ne IX and Ne X ionization stages in the 900 to 1300 eV region, suitable for lithographic exposures of photoresist. Two helium-like neon lines contribute more than 50% of the total energy. From continuum shape, plasma temperatures were found to be approximately 170-200 eV. The absolute, integrated spectral outputs were verified to within 30% by comparison with measurements by a PIN detector and a radiachromic X-ray dosimeter.

X-ray spectra of Cu plasmas at the focus of a four-beam, solid-state diode-pumped laser have been recorded. This laser-plasma X-ray source is being developed for JMAR's lithography systems aimed at high- performance semiconductor integrated circuits. The unique simultaneous overlay of the four sub-nanosecond laser beams at 300 Hertz produces a bright, point-plasma X-ray source. PIN diode measurements of the X-ray output indicate that the conversion efficiency (ratio of X-ray emission energy into 2π steradians to incident laser energy) was approximately 9 percent with average X-ray power yields of greater than 10 Watts. Spectra were recorded on calibrated Kodak DEF film in a curved-crystal spectrograph. A KAP crystal (2d = 26.6 Angstroms) was used to disperse the 900 eV to 3000 eV spectral energies onto the film. Preliminary examination of the films indicated the existence of Cu and Cu XX ionization states. Additional spectra as a function of laser input power were also recorded to investigate potential changes in X-ray yields. These films are currently being analyzed. The analysis of the spectra provide absolute line and continuum intensities, and total X-ray output in the measured spectral range.

Thin film optical coatings are susceptible to damage by high intensity x rays. Time-resolved measurements of this damage are required to better understand the mechanism, so that more rugged coatings can be developed. In the present experiment, dark-field shadowgraphy was used to temporally map the x-ray damage across the surface of certain anti-reflecting (AR) coatings. Two beams from the NRL PHAROS III high power Nd:glass laser system were utilized to generate a point source of plasma x rays, which in turn was used to irradiate and damage the optical coatings. Thin, opaque filters, coupled with permanent magnets and pinholes, were used to shield the optical samples from ultraviolet and charged-particle damage, respectively. The absolute, time-integrated x-ray fluence was measured with a crystal spectrograph, and also was temporally resolved with an x-ray diode. The surface morphology of the damaged optical samples was examined after each shot visually, and later with a profilometer as well as with both scanning electron- and atomic-force microscopes. A measured threshold fluence for damage of 0.049±30% cal/cm2 agrees very well with a radiation-damage code prediction of 0.046 cal/cm2.

This paper describes a high-intensity, high pulse-repetition-rate picosecond-pulse excimer laser system and plasma x-ray source, which generates up to 3 W of average x-ray power, into 2(pi) steradians, in a spectral band from 10-16 angstrom. The XeCl excimer laser system output, at 308 nm, consists of a train of 16 pulses, each approximately 45 ps in duration and spaced by 2 ns. The energy of each pulse in the train is approximately 25 mJ, and the pulse-train repetition rate is 60 Hz. Each pulse in the train is focused to a spot of < 10 micrometers diameter on a metal tape target, resulting in an intensity of 1 X 1015 W cm-2. Spectral and spatial characteristics of the x-ray emission have been studied, and the laser energy to x-ray dose conversion efficiency has been measured in an experiment which simulates the x-ray lithography process. Lithographic efficiencies of 5.9% and 10.9% have been measured for copper and stainless steel targets, respectively.

Thin film coatings are susceptible to high intensity x-ray damage. The PHAROS III laser was utilized to generate a point source of x-ray emission used to determine the damage threshold of AR-coated space optics. Thin filters coupled with magnets were used to shield the specimens from thermal radiation and plasma debris. Grids supporting the thin filters could be patterned into the coatings. The surface morphology of damaged specimens has been examined with SEM and AFM microscopes to determine the nature of the damage in multilayer AR coatings. Microscopic techniques were used to measure the depths of coating damage and edge sharpness in the patterned region.

Large area, parallel beams of x-rays are potentially useful in many diffraction, imaging and other x-ray analysis applications. Diffraction, in typical experiments, uses only a small portion of the incident beam that is within a limited “rocking curve” of the crystal capable of diffracting, although the whole crystal may be illuminated by the incident beam. Signal intensity can be increased if the ”whole” crystal can be made to diffract simultaneously. Similarly for imaging, improved results also are possible if divergent beams are replaced with nearly parallel ones. Production of parallel beams of large areal extent has not been simple. Often this meant that the source had to be placed at great distances from the sample, reducing the incident intensity. Sometimes, asymmetric cuts of crystals can be used to increase beam cross-sectional areas.Production of parallel beams of large area! extent has not been simple. Often this meant that the source had to be placed at great distances from the sample, reducing the incident intensity. Sometimes, asymmetric cuts of crystals can be used to increase beam cross-sectional areas.

Capillary collimators have found a number of uses in fluorescence, diffraction and other x-ray fields. Most of these applications are realized with single, straight glass capillaries. Focussing of synchrotron x-radiation beams has been shown with tapered capillaries. In addition, numerous straight and bent capillaries, bundled into lens-like optics, offer experimenters many other possibilities for better use of the x-radiation from tubes, synchrotron radiation, and plasma sources or the x-ray intensity collected from samples.

We have measured the axial (z) and radial (x) distribution of the vacuum ultraviolet emission from excimer laser generated aluminum plasmas in vacuum and in 300 mTorr of argon. The ratio of the radiated line intensities (emission in a gas versus vacuum) on the z axis (i.e., x = 0) increased exponentially with distance from the target surface for plasmas generated in a 300 mTorr argon ambient. The absolute line intensities increased linearly with the argon pressure and approximately linearly with the ambient gas atomic cross section when other rare gases were substituted. The line intensity radial distribution was broader for plasmas in argon than in vacuum and the magnitude of the effect increased monotonically with z. The spectral data obtained from plasmas in a gas ambient are discussed in terms of the diffusion of plasma electrons in an ionized gas.

The observed low solubility of hydrophilic compounds in non-polar C02 can limit applications of supercritical-fluid technology in some high growth industries, such as biotechnology. Reverse micelle formation offers a means to overcome low solubility of hydrophilic compounds in carbon dioxide, yet commercially-available ionic surfactants exhibit relatively poor solubility in C02 at moderate pressures. Synthesis of amphiphiles containing functional groups which are known to interact favorably, in a thermodynamic sense, with carbon dioxide offers a potential solution to this problem. Our results with fluoroether-functional amphiphiles show this to be a valid premise. Apparently, there are several competing effects that determine the solubility of these materials in carbon dioxide: increasing molecular weight tends to drive the cloud-point curve to higher pressures, yet, addition of C02-philic fluoroether groups and branching of the C02-philic tails works to depress the cloud-point curve to lower pressures. Further, increasing the polarity of the polar head group induces the cloud-point curve to move to higher pressures. Finally, we have shown that fluoroether-functional amphiphiles permit extraction of thymol blue from aqueous solution into carbon dioxide.

The use of surfactants in nonpolar supercritical fluid (SCF) systems helps to increase solvating power of the SCF. Although C02 is the most widely used SCF, many commercially available surfactants generally exhibit poor solubility in this fluid. Our goal is to design and synthesize amphiphiles that are both functional and highly CO2-soluble, and evaluate the relationship between structure and solubility. The basis of the design involves the synthesis of molecules whose hydrophobic groups interact favorably, in a thermodynamic sense, with CO2 while the hydrophilic group(s) interacts with the chosen solute (water, polar molecules, metals). In this work, we will explore the relationship between structure and solubility of silicone-based amphiphiles in CO2 via high-pressure phase-behavior experiments. The phase-behavior results clearly indicate that the silicone-based amphiphiles exhibit high CO2 solubility at temperatures of 313 K and pressures below 40 MPa.

We report results from experiments performed to measure and characterize the intense K-shell radiation from aluminum x-pinch plasmas at peak driving currents ranging from 280 kA to 1.0 MA. Single pulse aluminum K-shell (predominantly line radiation at 1.6–2 keV) x-ray yields ranged from 7.6 J at 290 kA to 240 J at 1.0 MA. In the range from 280 to 470 kA, the yield scales with current to the power of 3.6, whereas nonoptimized K-shell yields at 800 kA and 1.0 MA indicate a power of about 3 or higher.

The dispersed emission in the vacuum ultraviolet (VUV) (1200–3000 Å) from the plasma generated by the interaction of a KrF excimer laser with an Al and a YBa2Cu3O7 target has been measured. Emission spectra were collected as a function of distance above the target surface and as a function of laser fluence. The qualitative features of the plasmas from the two different targets were similar. The character of the emission spectra changed from a pseudocontinuous emission at the target surface to discrete emission from singly, doubly ionized species as well as neutrals at distances greater than ∼1.5 mm. The spatial variation indicated two regions: a high-density sheath along the target where the core emission is close to blackbody; and beyond, a plasma with large opacity emitting a UV spectrum of intensity decreasing fast with distance. Estimates of the plasma temperature and density were between 2 and 4 eV and ∼1018/cm3, respectively.

Capillary optics appear to permit the fabrication of practical collimator systems for laser-driven x-ray point sources. With such collimators, the illumination of wafers can meet the tight requirements for lithographic patterning of sub-micron device structures. However, the use of x-radiation with photon energies between 800–1200 eV makes capillaries of conventional silica-based glass capillaries marginal due to their low reflectivity. The reflectivity of various materials were examined with the goal of finding alternate glasses, elements for doping glasses or surface coatings that may enhance these collimators for lithographic applications. Coating capillary surfaces with more reflective materials may be the most viable method for improving the radiation transport properties for capillary optics to be used in x-ray lithography.

Abstract : X-Ray spectra were collected from sodium imploded-wire emissions employing the 10 MA Saturn pulsed-power accelerator at the Sandia National Laboratories. The spectral profiles of the Na X and XI alpha resonance lines were determined with a high resolution KAP (002) spectrograph while a mica crystal spectrograph was used to acquire the entire sodium K-shell emission. The computer-processed time-integrated intensity data were interpreted by comparing with theoretically-predicted spectra. A static, collisional-radiative equilibrium model incorporating multifrequency radiation transport was used to compute the spectral intensities and line shapes. The comparison between observed and calculated opacity-broadened line profiles (especially Lyman alpha) indicates the presence of small emitting regions of high-density plasma which is also consistent with time-resolved, framing-camera X-ray pinhole images. Implications of these results for the Na-Ne photopumped x-ray laser are discussed.

An experimental verification of the theoretically predicted density enhancement of the dielectronic satellite spectra emitted by multiply charged lithiumlike ions in high-density plasmas is reported. These plasmas were created by the interaction of solid MgF2 and SiO2 targets with high-intensity, subpicosecond, ultraviolet laser radiation. Comparisons between the observed and theoretically predicted values for the intensity ratios between two different pairs of dielectronic satellite lines have enabled determinations of electron densities of the order of 10(23) cm-3 to be made in these high-density laser-produced plasmas.

Emission spectra from 1200 Å to 3500 Å have been measured for laser-generated plasmas produced by the focused output (1–4 J/cm2) of a Kr-F excimer laser onto solid targets of single and multicomponent materials (e.g., Al, Y2O3, BaO, Cu, and YBa2Cu3O7−δ). We have measured the spatial distribution and fluence dependence of the plasma emission. The emission spectra indicated that very large density gradients from the large opacity at the target surface were present. In general, the spectra were dominated by excited neutrals and singly and doubly ionized species. Plasma emission spectra from Al have been analyzed in more detail to derive plasma temperature and density. A plasma temperature of 2 eV and an electronic density of ~1018/cm3 at 2 J/cm2 was estimated from the relative line intensities. Spatial variation of the total vacuum ultraviolet emission provided evidence for laser absorption in the ablated material.