I. C. E. Turcu

X‐ray emission from plasmas generated by an XeCl laser picosecond pulse train

Tenfold enhancement of keV x‐ray emission is observed from plasmas generated by an XeCl laser picosecond pulse train as compared to previous results obtained using a 25 ns KrF laser pulse. When a picosecond pulse train of only 165 mJ total energy is used to generate a plasma, the conversion efficiency to x rays at hν≊0.85 keV is 2.4%.

Plasma x‐ray source for lithography generated by a ≊30 J, 30 ns KrF laser

A plasma x‐ray source for lithography is generated by focusing ≊30 J, 30 ns KrF laser pulses onto Cu targets at irradiances up to 2×1014 W/cm2. Energy conversion efficiency from 249 nm laser light to x rays at 1.0 keV≤hν≤1.4 keV is measured as a function of target irradiance and the maximum efficiency is ≊2.5%. The full width half‐maximum duration of the plasma x‐ray pulse is ≊5 ns which corresponds to a peak power x‐ray conversion efficiency ≊7.5%.

Efficient keV x-ray emission from plasmas generated with 4 ps KrF excimer laser pulses

A high x‐ray conversion efficiency is observed from plasmas produced with 4 ps pulses at 249 nm using commercial KrF lasers. Copper plasmas convert 11% of laser energy into hν∼1.2 keV photons, carbon plasmas 6.8% into ‘‘water window’’ photons (0.28 keV<hν<0.53 keV) and aluminum plasmas 0.4% into hν∼1.6 keV photons.

Spatial coherence of a repetitive laser‐plasma point x‐ray source in the water window spectral region

We propose and demonstrate a coherent laser‐plasma point x‐ray source in the water window spectral region operating at a repetition rate of up to 100 Hz. The emission from the 10‐μm‐diameter source is filtered to generate monochromatic radiation at a 3.37 nm wavelength. Soft x‐ray fringes of the Young’s interference experiment were obtained with a visibility of 0.62±0.1 with a slit pair of 10.5 μm separation at a distance of 31.7 cm from the source. The source can be used to take either a hologram or transmission scanning x‐ray micrograph within a reasonable exposure time of several minutes.

Laser‐plasma x‐ray generation using an injection‐mode‐locked XeCl excimer laser

A discharge‐excited XeCl excimer laser equipped with unstable resonator optics was injection locked to a low‐power picosecond pulse train resulting in an efficient high‐power output consisting of a train of ∼150‐ps pulses separated by ∼2 ns and lasting for the duration of the excimer gain. The laser had a total energy of approximately 250 mJ and when focused to an irradiance of ∼5×1013 W cm−2 on metal targets produced keV x rays with a conversion efficiency of ≊2.5%.

Short-pulse, extreme-ultraviolet continuum emission from a table-top laser plasma light source

We have observed extreme-ultraviolet (XUV) “line-free” continuum emission from laser plasmas of high atomic number elements using targets irradiated with 248 nm laser pulses of 7 ps duration at a power density of ∼1013 W/cm2. Using both dispersive spectroscopy and streak camera detection, the spectral and temporal evolution of XUV continuum emission for several target atomic numbers has been measured on a time scale with an upper limit of several hundred picoseconds limited by amplified spontaneous emission.

X-ray lithography with efficient picosecond KrF laser-plasma source at 1nm wavelength

Abstract Exposure times for X-ray lithography using excimer laser-plasma sources, are reduced by an order of magnitude when the 20ns KrF laser pulses are modulated with trains of 150 ps pulses using a novel excimer-dye laser system.

Spatial coherence measurements and x-ray holographic imaging using a laser-generated plasma x-ray source in the water window spectral region

The properties of a coherent x‐ray point source in the water window spectral region generated using a small commercially available KrF laser system focused onto a Mylar (essentially carbon) target have been measured. By operating the source in a low‐pressure (approximately 20 Torr) nitrogen environment, the degree of monochromaticity was improved due to the nitrogen acting as an x‐ray filter and relatively enhancing the radiation at a wavelength of 3.37 nm (C vi 1s‐2p). X‐ray pinhole camera images show a minimum source size of 12 μm. A Young’s double slit coherence measurement gave fringe visibilities of approximately 62% for a slit separation of 10.5 μm at a distance of 31.7 cm from the source. To demonstrate the viability of the laser plasma as a source for coherent imaging applications a Gabor (in‐line) hologram of two carbon fibers, of different sizes, was produced. The exposure time and the repetition rate was 2 min and 10 Hz, respectively.

Novel route for the production of X-ray masks from a range of organometallic films

Abstract The majority of commercial photomasks and X-ray masks produced at present are manufactured by a multi-step process which involves the use of etching. This route imposes a limitation on the resolution that can be achieved. We describe here a new approach which utilises a recently synthesised range of organometallic compounds designed to undergo direct conversion to metal under the influence of electron beam irradiation. This opens up the prospect of a novel route for the production of both X-ray masks and EUV masks in essentially a single processing step. The attainable resolution is better than 300nm, since the process involves the direct deposition of metal atoms under the influence of a focused electron beam. The method is very versatile in that a whole range of metals and metal alloys can be deposited, e.g. gold, platinum and palladium and their corresponding alloys. We describe here the production of a gold X-ray mask, which was used in conjunction with a compact laser plasma source.

1 nm x-ray lithography using novel mask fabrication technique

High-resolution commercial photomasks and x-ray masks are at present manufactured by a multistep process which involves the use of etching. This route imposes a limitation on the resolution that can be achieved. We describe here a new approach to the fabrication of x-ray masks involving the use of organometallic compounds which undergo direct conversion to metal under the influence of electron beam irradiation. This approach permits fabrication of both x-ray masks and extreme ultraviolet masks in essentially a single processing step. The attainable resolution is unaffected by any limitation incurred by etching processes and is dependent only on such factors as electron scattering and electron beam diameter. We describe here the production of a gold x-ray mask, which was used in conjunction with a compact laser plasma source to demonstrate the lithographic process.