Change in reflectance over time of samples terminated with 9–20 Å of Ir and a Si spacer. Displayed reflectance values are relative to their Si capped control sample. Samples with Ir thicknesses between 16 and 20 Å have a reflectance of and are temporally stable. Ir thicknesses between and 16 Å do not stabilize over the time period studied.
Area reflectivity scans of Si (left) and (right) terminated multilayer mirrors. The rectangular areas of reduced reflectivity correspond to electron beam exposure in the presence of residual water vapor . As reflected in the data scales of the individual scans, the Si terminated sample experiences a loss in relative reflectivity while the terminated sample is relatively stable ( loss). Note left and right images have different scales. The Si terminated ML data was provided by Sasa Bajt.
Relative amounts of Ir, C, , and O during electron beam exposure as measured by Auger electron spectroscopy during the accelerated lifetime test. Slow rate of change in relative percentages after 60 min of exposure is consistent with approach to steady-state conditions.
Relative amounts of Ir, Si, , C, and Mo as a function of depth in the near surface region of 9.5, 11.2, and 18.7 Å Ir capped multilayers as measured by sputtering AES. The overlap of Ir and Si distribution is consistent with the presence of an gradient. Note that only the 11.2 Å sample has a significant amount of at the surface.
Theoretical and experimental (after day exposure to air) reflectance values vs Ir thickness for Ir on Si capped multilayers. Theoretical reflectance values were calculated using a base model of the near surface region composed of elemental Ir and Si layers with a interface layer. Note the marked discrepancy between the model calculations and measurements for Ir thicknesses between and 16 Å.
Measured (◇) and fitted EUV reflectance (–) spectra as a function of wavelength for a terminated multilayer mirror. The fitted model calculations employ the near surface chemical composition illustrated in Fig. 7(c) to simulate the EUV optical response. Note the excellent agreement between model and measured results.
Near surface structure derived from best agreement model fits to the measured EUV reflectance spectra (e.g., Fig. 6) for capping layers with nominal thicknesses (as deposited) of 42 Å Si and (a) 9.5 Å, (b) 12 Å, and (c) 18.7 Å of Ir. Note that the presented structures agree with the sputtering AES results shown in Fig. 4.
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