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Figure 2. Measured reflectance of a typical Mo/Si multilayer compared to the calculated reflectances for an ideal multilayer, a multilayer with rough interfaces, and a multilayer with rough interfaces and an oxidized surface.

Figure 2 Measured reflectance of a typical Mo/Si multilayer compared to the calculated reflectances for an ideal multilayer, a multilayer with rough interfaces, and a multilayer with rough interfaces and an oxidized surface.

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Figure 1. Reflectance response of typical Mo/Si and Mo/Be multilayer mirror coatings measured at 5° from normal inci- dence. Peak reflectances of 70.2% and 67.5% are routinely achieved for Mo/Be and Mo/Si, respectively. The EUV projection lithography system throughput is a strong function of the multilayer reflectance because of the seven reflection design.4 It is therefore critical that the multilayer mirrors have the highest possible normal incidence reflec- tance. Mo/Si and Mo/Be are today’s material pairs of choice due to both their superior optical properties in the EUV wave- length region and their structural properties on the sub-nanometer scale. They are the only material pairs for which multi- layer mirrors with normal incidence reflectances higher than 60% were achieved in the EUV spectral region. 7.8
Figure 1. Reflectance response of typical Mo/Si and Mo/Be multilayer mirror coatings measured at 5° from normal inci- dence. Peak reflectances of 70.2% and 67.5% are routinely achieved for Mo/Be and Mo/Si, respectively. The EUV projection lithography system throughput is a strong function of the multilayer reflectance because of the seven reflection design.4 It is therefore critical that the multilayer mirrors have the highest possible normal incidence reflec- tance. Mo/Si and Mo/Be are today’s material pairs of choice due to both their superior optical properties in the EUV wave- length region and their structural properties on the sub-nanometer scale. They are the only material pairs for which multi- layer mirrors with normal incidence reflectances higher than 60% were achieved in the EUV spectral region. 7.8
multi- Figure 4. The effect of substrate roughness upon multilaye: x layer peak reflectance. Substrates were Zerodur flats with varyin; levels of surface roughness. Roughness values shown corre spond to the high spatial frequency component as measurec by atomic force microscopy on 2 im square scans. Figure 3. Calculated peak reflectances for ideal Mo/Si multi- F layers with a variety of increasingly thicker capping layer p materials on top of the last Si layer. le
multi- Figure 4. The effect of substrate roughness upon multilaye: x layer peak reflectance. Substrates were Zerodur flats with varyin; levels of surface roughness. Roughness values shown corre spond to the high spatial frequency component as measurec by atomic force microscopy on 2 im square scans. Figure 3. Calculated peak reflectances for ideal Mo/Si multi- F layers with a variety of increasingly thicker capping layer p materials on top of the last Si layer. le
Figure 6. Temporal stability of stress for a typical Mo/Si multilayer. After the initial relaxation period of about 10 days, subsequent stress changes are not expected to affect the performance of an EUV lithography system. Figure 5. Temporal stability of peak reflectance and peal wavelength for a typical Mo/Si multilayer.
Figure 6. Temporal stability of stress for a typical Mo/Si multilayer. After the initial relaxation period of about 10 days, subsequent stress changes are not expected to affect the performance of an EUV lithography system. Figure 5. Temporal stability of peak reflectance and peal wavelength for a typical Mo/Si multilayer.
Figure 7. Layout of the DC magnetron sputter system used to deposit multilayer coatings.
Figure 7. Layout of the DC magnetron sputter system used to deposit multilayer coatings.
Figure 8. Spatial uniformity of Mo/Si multilayer film thick- ness has been improved from 5.2% peak-to-valley to better than 0.4% over a 140 mm diameter region on flat Si sub- strates. Mo/Be multilayers have 0.1% uniformity over 100 mm diameter. 3.2 Uniform multilayer coatings
Figure 8. Spatial uniformity of Mo/Si multilayer film thick- ness has been improved from 5.2% peak-to-valley to better than 0.4% over a 140 mm diameter region on flat Si sub- strates. Mo/Be multilayers have 0.1% uniformity over 100 mm diameter. 3.2 Uniform multilayer coatings
Figure 9. Thickness gradient of multilayers deposited on a 10x Schwarzschild camera for a prototype EUV lithogra- phy system. Figures 9a and 9b represent the primary and secondary mirrors of the Schwarzschild system, respec- tively. The solid line is the target value, the dashed lines represent the boundaries of the specifications, and the symbols are the measured values for three subsequent depositions,
Figure 9. Thickness gradient of multilayers deposited on a 10x Schwarzschild camera for a prototype EUV lithogra- phy system. Figures 9a and 9b represent the primary and secondary mirrors of the Schwarzschild system, respec- tively. The solid line is the target value, the dashed lines represent the boundaries of the specifications, and the symbols are the measured values for three subsequent depositions,
Figure 10. Optical throughput loss expected from optic-to- optic mismatch of peak wavelength for an optical system with 7 multilayer mirrors. The narrower bandpass of Mo/Be mirrors (0.27 nm FWHM) results in higher loss than for Mo/Si (0.54 nm FWHM). We currently achieve wavelength matching of 0.017 nm at 1 standard deviation.
Figure 10. Optical throughput loss expected from optic-to- optic mismatch of peak wavelength for an optical system with 7 multilayer mirrors. The narrower bandpass of Mo/Be mirrors (0.27 nm FWHM) results in higher loss than for Mo/Si (0.54 nm FWHM). We currently achieve wavelength matching of 0.017 nm at 1 standard deviation.
Related topics:
RadiationOptical CoatingsExtreme Ultraviolet LithographyEUV Lithography
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