David Scott Torres

Mass-limited, debris-free laser-plasma EUV source

Abstract The development of a laser-plasma EUV line emission source based on frozen water droplet targets which is essentially debris-free and capable of continuous, high-repetition-rate (>1 kHz) operation is described. Created by modest (

Characterization of a laser plasma water droplet EUV source

We have configured a new type of target for laser plasma x-ray generation. This target consists of an in-vacuum flowing stream of liquid water droplets. We have successfully produced plasmas using this target, and have measured its extreme ultraviolet (EUV) emission spectrum. Bright lines from Li-like and He-like oxygen dominate in the plasma radiation in this region. Most importantly, not target debris related effects were observed for this type of target. A nearby Mo/Si multilayer EUV mirror suffered no reflectivity reduction at 13 nm after exposure to 105 laser shots on target. This observation constitutes a major breakthrough in the utilization of laser plasma radiation for practical applications, in particular, for EUV projection lithography of advanced microelectronic circuits. The simplicity and versatility of a continuously-fed target with naturally smooth surface and no associated debris problems meshes strongly with the critical engineering required for envisioned production line EUV projection lithography installations. Additionally, through the use of water based solutions as targets, it should be possible to tailor the EUV emission spectrum to match the source requirements for other potential applications, such as the x-ray microscopy.

X-ray microscopy and imaging of Escherichia coli, LPS and DNA.

Ultrastructural examination by transmission and scanning electron microscopy involves a series of specialized preparation steps which may introduce artefacts in the micrographs. X‐ray microscopy can take instant images of speci‐mens but is mostly restricted to a few synchrotron X‐ray sources. We have utilized a bench‐top nanosecond laser‐plasma to produce a single‐shot source of nanosecond X‐rays tuned for maximum contrast with carbon‐rich material. To examine the ultrastructure by absorption profiles, we utilized a laser‐produced plasma generated by a single‐shot laser (1.06 μm wavelength, 5 × 1012 W cm−2 intensity) focused on to a silicon target as an X‐ray source for high‐resolution X‐ray microscopy. This approach eliminates the specimen preparation steps. Whole hydrated cells of Escherichia coli and purified preparations of lipopolysaccharide (LPS) and chromosomal DNA (cDNA) were streaked onto poly(methyl methacrylate) (PMMA)‐coated grids (resist). This resist was exposed to X‐rays under vacuum at a distance of 2.5 cm from the target disc. The silicon plasma produced by a 10‐ns burst of laser energy (at 20 J) radiates strong emission lines in the region of 300 eV. The X‐rays penetrate the sample and their absorption profile is transferred on to the resist where PMMA acts as a negative to generate an image. By atomic force microscopy imaging of this photoresist we have visualized layers around cells of E. coli, darker areas inside the cell probably corresponding to cDNA, and preliminary images of LPS and DNA molecules. This technique has resolution at the 100 Å level, produces images similar to the space‐filling models of macromolecules and may be of great value in the study of the ultrastructure of hydrated live biological specimens.

Ultrastructural imaging and molecular modeling of live bacteria using soft x-ray contact microscopy with nanoseconds laser-plasma radiation

X-ray images of the various live bacteria, such as Staphylococcus and Streptococcus, and micromolecule such as chromosomal DNA from Escherichis coli, and Lipopolysacchride from Burkholderia cepacia, are obtained with soft x-ray contact microscopy. A compact tabletop type glass laser system is used to produce x-rays from Al, Si, and Au targets. The PMMA photoresists are used to record x-ray images. An AFM (atomic force microscope) is used to reproduce the x-ray images from the developed photoresists. The performance of the 50nm spatial resolutions are achieved and images are able to be discussed on the biological view.

Biological X-Ray Microscopy with a Compact Laser System

We describe progress being made in an x-ray imaging technology that provides high-resolution single frame x-ray images of in-vitro specimens captured in a time sufficiently short that radiation damage mechanisms to the structure are not recorded. Several different biology and medical research groups find this type of microscopy particularly well-suited to the detailed analysis of sub-cellular features, and to the study of live organisms subjected to various forms of external stimuli. This technology utilizes bright x-ray sources produced by compact pulse laser systems. The incorporation of advanced x-ray optical and electron-optical systems will lead to the development of a compact, real-time x-ray microscope, having a broad range of applications.

A Debrisless Laser-Plasma Source for EUV and XUV Generation

Interest in debris-free sources of short-wavelength EUV radiation has risen in recent years due primarily to anticipated needs in the area of projection lithography, where smaller feature sizes and increased production rates are targeted for the near-future in the semiconductor industry. Consequently, laser-plasmas have come to the forefront as attractive source candidates for such lithography systems. As compact, modular, and highrep-rate sources, laser-plasmas have already demonstrated the required minimum efficiency[1,2]. The water-droplet laser-plasma source[3] offers the additional advantages of low-cost (~

Debris-free laser plasma source using ice droplets

10−6/shot), continuous, debris-free operation that future lithography systems require. Broadband emission from solid-target laser-plasmas created from high-Z materials, which can lead to off-band heating by absorption of the primary collection optics[3], is another problem that is circumvented with the narrow-band droplet laser-plasma. In addition, solute-doped droplet targets are promising candidates for generating debris-free XUV radiation having, in general, the same advantages as the water droplet EUV source.

Collimators for laser plasma x-ray sources

We describe the development of a laser-plasma source based on frozen water droplet targets which is essentially debris- free and capable of continuous, high-repetition-rate (> 1 kHz) operation. Created by modest (< 1 J) laser energies, this source produces copious emission at 13 nm and 11.6 nm, the preferred wavelengths for EUV projection lithography, with negligible target operation costs. Extension of this source to other wavelengths is considered.

Nanosecond-resolved biological x-ray microscopy with a compact laser system

Several novel approaches to collimating x-rays have been proposed in the last few years. Although some show promise as collimators for point x-ray sources, little work has so far been done on their integration with laser plasmas. Here we discuss their potential and possible applications.

Application of X-ray micrography and imaging to study the effect of gentamicin on Pseudomonas aeruginosa.

Nanosecond flash x-ray microscopy of living biological specimens is demonstrated with subcellular spatial resolution. Single shot images, produced by a compact laser- plasma x-ray source optimized for maximum image contrast, are captured before radiation processes can affect the specimen.