In the past, the successful application of PLD for X-ray multilayer synthesis has already been demonstrated for C-spacer systems. Recently, the method has also been tested for Mo/Si layer stacks. A UHV-coating machine has been used to prepare X-ray mirrors on 4 in. substrates. The ablation of both Mo and Si targets was carried out by Nd:YAG laser irradiation using the third harmonic (λ=355 nm) with a pulse energy Ep=275 mJ and a pulse width τ=4…6 ns. Multilayers of 10…50 periods have been synthesized. Soft X-ray measurements in the EUV-range at near normal incidence show reflectivities Rs of typically 60%. From HRTEM, a high stack regularity and minimum interface roughness can be deduced. In contrast to conventional technologies (coating by sputtering or e-beam evaporation) the formation of a MoSix-interface layer happens only when depositing Mo on Si. Extremely sharp interface transitions from one individual layer to the other are observed and the total period is represented by a three-layer system. From TEM results, a structure model for PLD-prepared Mo/Si-multilayers has been deduced. The optical parameters of the layers were adapted by reflectivity curve fitting, so that the results measured in the EUV-range can be explained. Using this model, predictions of the ratio of the number of atoms NSi/NMo for the total stack were made and are in good agreement with results of RBS measurements. The use of the multilayers as X-ray optics requires an excellent homogeneity of the layer thickness across the entire mirror. It can be shown that the PLD technique is able to realize film uniformities with a standard deviation of the period thickness of less than 0.5%. This was confirmed by Cu–Kα-reflectometry and by near normal incidence measurements in the EUV range on 4 in. samples.

In the past, the successful application of PLD for X-ray multilayer synthesis has already been demonstrated for C-spacer systems. Recently, the method has also been tested for Mo/Si layer stacks. A UHV-coating machine has been used to prepare X-ray mirrors on 4 in. substrates. The ablation of both Mo and Si targets was carried out by Nd:YAG laser irradiation using the third harmonic (λ=355 nm) with a pulse energy Ep=275 mJ and a pulse width τ=4…6 ns. Multilayers of 10…50 periods have been synthesized. Soft X-ray measurements in the EUV-range at near normal incidence show reflectivities Rs of typically 60%. From HRTEM, a high stack regularity and minimum interface roughness can be deduced. In contrast to conventional technologies (coating by sputtering or e-beam evaporation) the formation of a MoSix-interface layer happens only when depositing Mo on Si. Extremely sharp interface transitions from one individual layer to the other are observed and the total period is represented by a three-layer system. From TEM results, a structure model for PLD-prepared Mo/Si-multilayers has been deduced. The optical parameters of the layers were adapted by reflectivity curve fitting, so that the results measured in the EUV-range can be explained. Using this model, predictions of the ratio of the number of atoms NSi/NMo for the total stack were made and are in good agreement with results of RBS measurements. The use of the multilayers as X-ray optics requires an excellent homogeneity of the layer thickness across the entire mirror. It can be shown that the PLD technique is able to realize film uniformities with a standard deviation of the period thickness of less than 0.5%. This was confirmed by Cu–Kα-reflectometry and by near normal incidence measurements in the EUV range on 4 in. samples.

Extreme Ultraviolet Lithography (EUVL), using 13 nm radiation, has a high probability to become the Next Generation Lithography of choice for resolutions of 50 nm and below. The work at CARL ZEISS focusses on the development of optical system design and core technologies necessary for the industrialization of EUVL optical systems.

Mo/Si 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/mm(2) were applied at the PTB 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 3x10(-8) mbar (without hydrocarbons) and 10(-7) mba. (with hydrocarbons) at EUV intensities of 3 mW/mm(2), respectively 0.2 mW/mm(2) 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/Si mirrors do not suffer from prolonged exposure to ozone.

Extensive optimization on the fabrication of Mo/Si multilayer systems is carried out at the FOM Institute Rijnhuizen using e-beam evaporation. The process is being optimized including parameters such as variation of the mirror's center wavelength, the metal fraction, deposition parameters, and the layer composition. Reflectivities of 69.5% are demonstrated at normal incidence, with values of 67 to 69% being routinely achieved, demonstrating the capabilities of the deposition process. Some evidence of smoothening to interface roughness values lower than the roughness of the initial substrate is given. Furthermore, investigation of the temporal behavior of the coatings does not indicate any loss of reflectivity over an eight-month period. An analysis of the multilayer composition and the interface roughness is given. The reflectivity measurements have been carried out at the PTB facilities at the electron storage rings BESSY I and BESSY II in Berlin. The results of measurements at both facilities are found to be identical and accuracy is discussed in detail.

Normal-incidence reflectivity data of Mo/Si multilayer systems are being reported for the EUV wavelength range.

Reported is the optimization of the fabrication of Mo/Si multilayer systems produced by e-beam evaporation and ion-beam smoothening. The impact of a number of coating parameters is verified such as variation of the mirror’s center wavelength and the metal fraction of the bilayer (Γ ratio), resulting in reflectivities up to 68.6% at normal incidence. Parallel to this experimental work, a numerical optimization based on experimentally determined multilayer properties is carried out on the throughput of multimirror lithographic systems for the 11–15 nm wavelength region using Mo/Si and Mo/Be coatings. The center wavelength, Γ ratio and layer stack have been optimized. The calculations show an optimum throughput for a 10-mirror Mo/Si system at 14.4 nm, assuming a light source with a wavelength independent spectrum.