Images with a spatial resolution of 120-150 nm were obtained with 46.9 nm light from a compact capillarydischarge laser by use of the combination of a Sc-Si multilayer-coated Schwarzschild condenser and a freestanding imaging zone plate. The results are relevant to the development of compact extreme-ultraviolet laser-based imaging tools for nanoscience and nanotechnology. © 2005 Optical Society of America OCIS codes: 180.7460, 110.7440, 140.7240. Rapid progress in nanotechnology and nanoscience creates the need for new practical imaging tools capable of resolving nanometer-sized features. Shortwavelength light provides an opportunity to develop optical imaging systems with the highest resolution. The best resolution so far, 20 nm, has been obtained in imaging with soft-x-ray synchrotron radiation at 2.07 nm wavelength. 1 Submicrometer resolution was obtained with a soft-x-ray recombination laser, 2 and 75 nm resolution was reported with a low-repetitionrate (several pulses per day) laboratory-sized soft-xray laser.3 There is, however, a need for the development of more compact and practical nanometerresolution imaging systems. Toward this goal extreme-ultraviolet (EUV) light from high-order harmonic sources was used to demonstrate imaging systems with a resolution of better than 1 m, 4,5 and soft-x-ray imaging with laser-plasma-based sources has been investigated. [6][7][8] In this Letter we report what is to our knowledge the first demonstration of nanometer-scale imaging with a compact capillary-discharge pumped highrepetition-rate EUV laser. Spatial resolution of the 46.9 nm wavelength system is estimated to be 120-150 nm. This is to our knowledge the highest resolution achieved with a compact high-repetitionrate coherent EUV illumination source. The high average power ͑ϳ1 mW͒ and multihertz repetition rate of the Ne-like Ar capillary discharge laser source that we used 9,10 allowed us to perform real-time imaging, for which the image is continuously updated on the computer screen at the rate of the laser pulses.The imaging system is schematically illustrated in Fig. 1. It consists of a compact capillary-discharge 46.9 nm laser, a Sc-Si multilayer-coated reflective condenser, a zone-plate objective, and a CCD detector. The condenser, the imaged sample, and the objective were mounted onto motorized translation stages that were assembled inside a vacuum chamber connected to the EUV laser source with standard vacuum fittings. The illumination source is a compact capillary-discharge Ne-like Ar laser emitting at a wavelength of 46.9 nm with a pulse duration of ϳ1.2 ns. Its short wavelength, narrow spectral bandwidth, high photon fluence, and beam directionality make this source well suited for microscopy. The spectral bandwidth of the laser is ⌬ / Ͻ10 −4 . 9 The laser's output pulse energy and degree of spatial coherence depend on the capillary discharge length. For this experiment the laser was equipped with an 18 cm capillary discharge tube that provided an average pulse energy of ϳ0.1 mJ. This choice of cap...

The damage threshold and damage mechanism of extreme-ultraviolet Sc͞Si multilayer mirror coatings are investigated with focused nanosecond pulses at 46.9-nm radiation from a compact capillary-discharge laser. Damage threshold f luences of ϳ0.08 J͞cm 2 are measured for coatings deposited on both borosilicate glass and Si substrates. The use of scanning and transmission electron microscopy and small-angle x-ray diffraction techniques reveals the thermal nature of the damage mechanism. The results are relevant to the use of newly developed high-f lux extreme-ultraviolet sources in applications. However, the damage to these mirrors when exposed to high peak powers of EUV light has not been studied to our knowledge. This problem is now of particular relevance because the peak power and f luence of EUV sources have recently increased significantly (for example, the radiation f luence at the exit of a capillary-discharge Ne-like Ar laser operating at 46.9 nm can exceed 1 J͞cm 2 ) and is soon expected to achieve unprecedented values with the commissioning of EUV free-electron lasers. 2 -4 In this Letter we report results of the study of the optical damage mechanisms and the damage threshold for Sc͞Si EUV mirrors exposed to high-power EUV laser radiation. The study was conducted by focusing the output of a tabletop capillary-discharge Ne-like Ar laser emitting nanosecond duration pulses at a wavelength of 46.9 nm. The resulting damage to the multilayer coatings exposed to the EUV beam was analyzed with scanning electron microscopy (SEM), transmission electron microscopy (TEM), and small-angle x-ray diffraction (l 0.154 nm) techniques. Our results show that multilayer coatings on Si and borosilicate glass have similar damage threshold values of ϳ0.08 J͞cm 2 , compared with the 0.7 J͞cm 2 found necessary to damage a bare Si substrate. These values are similar to the thresholds found in Mo͞Si, W͞C, and W͞Si coatings measured at much shorter wavelengths. 6,7The Sc͞Si multilayers were deposited by dc magnetron sputtering at 3 mTorr of Ar pressure on superpolished borosilicate glass (surface roughness of s ϳ 0.4 nm) and on Si wafers (s ϳ 0.6 nm). The multilayers on borosilicate glass consisted of ten periods of Sc͞Si layers, each with a thickness of ϳ26.7 nm and a ratio of layer thickness of H͑Sc͒͞H͑Si͒ ϳ 0.7. A top 5-nm-thick Si protection layer capped the multilayers. The multilayer coatings deposited on Si consisted of 33 periods of Sc͞Si pairs with the same parameters as those deposited on borosilicate glass. In these structures the crystalline Sc layers were always separated from the amorphous Si layers by ϳ3 nm of amorphous ScSi interface layers formed by interdiffusion. The experimental setup used to irradiate the samples was described in Ref. 9. The laser emission was focused onto the target surface with a spherical R 10 cm Sc͞Si multilayer-coated mirror that was 2.5 cm in diameter and positioned at normal incidence. The ref lectivity of this particular mirror was measured to be ϳ30% at 46.9 nm. The capillarydischar...

Abstract:We report the demonstration of reflection mode imaging of 100 nm-scale features using 46.9 nm light from a compact capillary-discharge laser. Our imaging system employs a Sc/Si multilayer coated Schwarzschild condenser and a freestanding zone plate objective. The reported results advance the development of practical and readily available surface and nanostructure imaging tools based on the use of compact sources of extreme ultraviolet light.

We report high resolution imaging results obtained utilizing small-scale extreme ultraviolet laser sources. A compact capillary-discharge pumped Ne-like Ar laser emitting at a wavelength of 46.9 nm was used to demonstrate imaging with nanometer-scale resolution in transmission and reflection modes. We exploited the large photon fluence of this short wavelength laser to obtain high-resolution images with exposure times as short as 1 -10 seconds. Images with a spatial resolution better than 140 nm were obtained using the combination of a Sc/Si multilayer coated Schwarzschild condenser and free-standing objective zone plate. Preliminary results of imaging with a 13.9 nm extreme ultraviolet laser light are also discussed.

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