Lord Rayleigh's well-known equations for resolution and depth of focus indicate that resolution is better improved by reducing the wavelength of light rather than by increasing the numerical aperture (NA) of the projection optics, particularly when NA is approaching its physical limit of 1.0 in air (or vacuum). Vector aerial image simulations of diffraction-limited Deep Ultraviolet (DUV) and Extreme Ultraviolet (EUV) lithographic systems verify this simple view, even though Rayleigh's constants in Microlithography are not constant because of a variety of image enhancement techniques that attempt to compensate for the shortcomings of the aerial image when it is pushed to the limit. The aerial image is not the whole story, however. The competition between DUV and EUV systems will be decided more by economic and technological factors such as risk, time and cost of development and cost of ownership. These in turn depend on cost, availability and quality of light sources, refracting materials, photoresists and reticles.

The continuing trend towards higher integration density of microelectronic circuits requires steadily decreasing feature sizes. The SIA roadmap defines the technologies needed to meet this challenges. One of the fundamental requirements for lithography with a resolution of 100 nm and below is the development of new high-performance optical designs for projection lenses.

In this paper, a comparison of two different solutions for the illuminator is presented. The systems are intended to comply with the illumination requirements, but have different advantages and drawbacks. The examples represent solutions based on conical reflection and on a fly's-eye integrator. A comparison is given and the potentials of the different solutions are outlined.

In this paper, the metrology and fabrication concepts at Carl Zeiss will be reviewed. The present status in the fabrication of specific EUVL mirrors will be reported as well.

The precise alignment of Extreme Ultra-Violet Lithography (EUVL) imaging system is necessary in order to achieve diffraction-limited performance. Interferometric testing at the exposure wavelength is needed to ensure proper alignment and to achieve an acceptable final wavefront. We have built a prototype at-wavelength interferometer at the NewSUBARU facility. This interferometer is a phase-shifting point diffraction interferometer (PS/PDI) testing specially constructed Schwarzschild optics. Preliminary experiments using visible light were performed in order to learn this PS/PDI. The Schwarzschild optics were aligned using visible wavefront measurements with the interferometer. The precision of the visible measurements was evaluated. Experiments using EUV radiation have been started.

High performance reflective coatings for EUVL projection systems can be produced by using e-beam evaporation in combination with ion beam smoothening of the interfaces. Using this technique, we recently demonstrated a near normal incidence reflectivity of 69.5%. Another, equally important part of the optimization of the coating process is the lateral control of the thickness of the layers, that is the d-spacing of the coating. In this paper we demonstrate the ability to obtain a uniformity of the d-spacing of the coating of better than +/- 0.05% over a 6' area, both on flat and concave surfaces (uniformity specified in terms of wavelength of maximum reflectance). All reflectance measurements have been carried out at the PTB facilities at the electron storage rings BESSY I and BESSY II in Berlin.

Mo/S multilayer mirrors have been exposed to intense monochromatic EUV radiation in order to investigate a possible deterioration of the mirror reflectance under different vacuum conditions. Power densities up to 3 mW/mm² were applied at the PB undulator beamline at BESSY II, applying a hydrocarbon enriched vacuum. The mirror reflectance has been monitored in situ during several hours of exposure. Vacuum pressures of 3 X 10^-8 mbar (without hydrocarbons) and 10^-7 mbar (with hydrocarbons) at EUV intensities of 3 mW/mm², respectively 0.2 mW/mm² have been applied. The reflectance of the mirrors decreased when exposed to EUV radiation in hydrocarbon enriched vacuum, while no loss in reflectance was observed when no hydrocarbons were added to the vacuum. Ozone-cleaning experiments, using UV produced ozone from air at atmospheric pressure, were performed and show that Mo/S mirrors do not suffer from prolonged exposure to ozone.

High-accuracy characterization of optical components has been one of the main services of the PTB radiometry laboratory at BESSY I. Now, after the shut down of BESSY I with the end of 1999, PTB is operating two new beamlines suitable for EUV reflectometry at their new laboratory at BESSY II. As at BESSY I, synchrotron radiation from a bending magnet is used for reflectometry but additionally a beamline at an undulator covering the same spectral range from 50 eV to 1800 eV can be used for special applications where, e.g., high radiant power or very high spectral purity is needed. In this paper, the characteristics of the beamlines are presented. We present the results of the beamline characterization on photon flux, spectral resolution, spectral purity and beam stability with special respect to the EUV photon energy range. During the phase of simultaneous operation of BESSY I and II in 1999, a direct comparison was done for reflectance measurements at high equality Mo/Si EUV mirrors. The results showed perfect agreement: (68.98 +/- 0.17)% at BESSY I and (69.10 +/- 0.24)% at BESSY II. The wavelength scale was calibrated using the absorption resonances of Ar, Kr, and Xe whose energies are known with a relative uncertainty of about 10^-4. The measured peak positions agreed within this uncertainty.

A method of designing multilayers with broadband wavelength responses for use as coatings in EUV optics at normal incidence is presented int his paper. The method is based on the well-known Fresnel equations and recursive calculation combined with a defined merit function, with random variation of the thickness of each layer. This allows the design of multilayers for specific requirements. The method was used to design Mo/Si multilayers with broadband wavelength responses for the EUV region, 18 - 20 nm. Such mirrors were made by magnetron sputtering in 99.99% pure argon. The deposition rates, after calibration, were 0.12 nms^-1 for molybdenum and 0.07 nms^-1 for silicon. The broadband multilayers were deposited on 30 mm diameter K9 glass substrates with rms surface roughnesses less than 0.8 nm.

A laser-generated water plasma source has been built, operating around-the-clock. We characterized this source looking at several aspects that are important for a possible EUV source to be used in a next-generation lithographic tool. We characterized the source spectrally, measured the size of the source, the angular dependence of the EUV emission and the temporal dependence of the EUV pulses. We also investigated the level of debris produced by the source and the contamination of EUV optics by the water plasma. Finally, this laser-generated water plasma has been successfully used in a shearing interferometer, in which the imaging equality of EUV optics can be assessed accurately at-wavelength.

We discuss the results of the studies of Z-pinch sources for photolithographic applications developed by Lambda Physik. We also report the results of fundamental investigations pursued by Fraunhofer-Institut fuer Lasertechnik. Friedrich- Schiller Universitat Jena, Max-Born Institut Berlin, and Gustav August Universitat Gottingen. The later efforts are supported by German government and steered by the industrial consortium led by Lambda Physik.

The EUV light source is a critical factor for the success of Extreme Ultraviolet Lithography (EULV), ASML, FOM and Philips Research have developed a portable set of diagnostics for the characterization of candidate EUV sources, called Flying Circus. The set of diagnostics is used to perform the following measurements: Absolute EUV power measurements, pulse-to-pulse intensity fluctuations, plasma size and shape, size/shape/positional stability, spectral distribution of radiation and stability, timing jitter and contamination by the source. These measurements are to be performed on-site, at the laboratories of the different source developers. The design as well as the first calibration measurements performed by the Flying Circus on the FOM Xe double gas jet source and on the PLEX z-pinch source will be discussed.

A compact debris shutter for use with a laser produced plasma source is designed for installation to our EUV interferometer. The shutter is for operation under vacuum based on a gyroscope design for space satellites. It is of a hollow cylinder shape of 20 cm diameter enabling to stop debris of the plasma source traveling at a speed below 260 m/s at a spinning speed of 6000 rpm.

Here we report the general layout of the beamline and concentrate our attention on the characteristics of the optical elements as well as on the optical performances (monochromator's resolving powers and efficiencies, flux and spot dimensions) of the beamline.

The diffraction gratings are widely used to monochromatize and even focus the soft X-ray radiation produced by the high brilliance third generation synchrotron radiation sources. Nevertheless, the final performance of an instrument that uses a diffraction grating is sensitive to any figure error and to any undesired groove density variation along the surface of the grating itself. Therefore, typical requirements are 0.1 - 0.2 arcsec (even less) on the residual slope errors (after proper shape subtraction), while the groove density is required to be constant along the surface with a percentage error below 0.1%. Vice-versa, sometimes groove density variation is required along the surface to correct spherical aberrations or to change the focal properties of a grating. Since the gratings, in the soft X-ray region, work in grazing incidence mode, the ideal instrument to measure it is a mono-dimensional profilometer. At ELETTRA, the Italian third generation synchrotron radiation source, we have an in house modified version of the Long Trace Profiler.

Since synchrotron radiation (SR) has several excellent properties such as high brilliance, broad continuous energy spectrum and small divergence, we can obtain x-ray images with high contrast and high spatial resolution by using of SR. In 2D imaging using SR, air gap method is very effective to reduce the scatter contamination. However, to use air gap method, the geometrical effect of finite source size of SR must be considered because spatial resolution of image is degraded by air gap. For 2D x-ray imaging with SR, x-ray mammography was chosen to examine the effect of air gap method. We theoretically discussed the optimization of air gap distance suing effective scatter point source model proposed by Muntz, and executed experiment with a newly manufactured monochromator with asymmetrical reflection and an imaging plate.

An aspheric wave-front recording system was designed to produce a holographic grating for use in a standard soft X- ray flat field spectrograph interchangeable with a mechanically ruled varied-line-spacing (VLS) grating. The grating grooves recorded with the designed aspheric wave- front recording system were processed to form a laminar groove profile by means of reactive ion etching. Measurements done with synchrotron radiation and a laboratory X-ray source are reported for this laminar-type grating and a commercial grating replicated from a mechanically ruled VLS grating that was specifically designed and fabricated for the standard soft X-ray flat- field spectrography. The laminar-type holographic grating is found to have an absolute first-order efficiency of approximately 10% for wavelengths of approximately 4.5 - 12 nm. It is also shown that the holographic grating is effective in suppressing the higher orders and stray-light level for soft X-ray of 4.36 nm (C-K) and has a comparable spectral resolution to the replica VLS grating.

The effect of elevated temperature on the structural stability of Mo/Si, Mo₂C/Si and Mo/Mo₂C/Si/Mo₂C (d_Mo2C equals 0.6 nm) multilayers was investigated. The multilayers deposited by dc magnetron sputtering are annealed at temperatures ranging from 200 degree(s)C to 700 degree(s)C. The multilayer mirrors were designed for normal incidence reflectivity at about 13 nm wavelength. X-ray scattering, transmission electron microscopy and atomic force microscopy were used for characterization of the multilayer structures. The results are correlated to the measured normal incidence reflectivity using synchrotron radiation. We achieved maximal normal incidence reflectivities of 61.8% at 13.0 nm wavelength for Mo₂C/Si and 59.9% at 13.3 nm for Mo/Si multilayers having Mo₂C diffusion barriers. While the reflectivity of Mo/Si multilayers decreased considerably after annealing above 300 degree(s)C the Mo₂C/Si multilayers showed a superior thermal stability up to 600 degree(s)C.

The XM-1 is a soft x-ray full-field microscope that uses zone plates for the condenser and objective lenses. One of the main features of XM-1 is the high spatial resolution, which is made possible by the fine features of the objective zone plate. At present, the microscope uses a zone plate with an outer zone width of 25 nm. Several test patterns containing periodic lines and spaces were fabricated to measure the resolution of the microscope. Experimental data shows that the microscope can resolved 25 nm features. As simulations indicate that good contrast can be observed with even smaller features, test patterns with finer features are being fabricated to actually determine the resolution limit of the microscope.

The XM-1 soft x-ray microscope utilizes bending-magnet radiation from the Advanced Light Source in Berkeley, CA. This radiation is collected by a `large' (9 mm diameter) fresnel condenser zone plate which projects light through a pinhole and illuminates the sample. The radiation transmitted through the sample is then focused and magnified by a high-precision objective micro zone plate and recorded by a soft x-ray CCD camera. Our condenser zone plate and pinhole combination serves ad our adjustable monochromator for selecting the desired photon energy, giving us a (lambda) /(Delta) (lambda) of 700. This moderate spectral resolution allows for spectroscopic imaging with XM-1, including samples of magnetic materials with contrast provided by magnetic circular dichroism. Our user-friendly software programs allow for frequent utilization of complex image processing techniques.