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The effect of dissolved air on the density and the refractive index of liquid water is studied from 0 to 50 • C. The density effect is calculated from the best available values of Henry's constants and partial molar volumes for the components of air; the results are in agreement with some previous experimental studies, but not others. The refractive-index effect is calculated as a function of wavelength from the same information, plus the refractivities of the atmospheric gases. Experimental measurements of the refractive-index effect are reported at both visible and ultraviolet wavelengths; the measured and calculated values are in reasonable agreement. The magnitude of the refractive-index change, while small, is several times larger than a previous estimate in the literature.

A custom, flat field, extreme ultraviolet EUV spectrometer built specifically for use with low power light sources that operate under ultrahigh vacuum conditions is reported. The spectral range of the spectrometer extends from 4 nm to 40 nm. The instrument optimizes the light gathering power and signal to noise ratio while achieving good resolution. A detailed description of the spectrometer and design considerations are presented, as well as a novel procedure that could be used to obtain a synthetic wavelength calibration with the aid of only a single known spectral feature. This synthetic wavelength calibration is compared to a standard wavelength calibration obtained from previously reported spectral lines of Xe, Ar and Ne ions recorded with this spectrometer.2

Two techniques are presented for measuring the refractive index of fluids. The first is a reflective technique where liquid is applied to a rough surface to hold the liquid during measurement. Ellipsometric psi and delta data are acquired and analyzed to determine the fluid refractive index. The second technique is refractive and uses a hollow prism cell to contain the liquid. The fluid index is then determined using the prism minimum deviation technique. Both techniques have been applied over a very wide spectral range from the vacuum ultraviolet to the infrared and have been implemented on a research spectroscopic ellipsometer system (VUV-VASE®) with continuously variable angle of incidence. The refractive index of several candidate immersion fluids for 157 and 193 nm immersion lithography are reported over the spectral range from 156 to 1700 nm in a nitrogen-purged environment. The advantages and disadvantages of both techniques are discussed. Results were checked against values measured on very accurate prism minimum deviation equipment at NIST, and agreement with NIST has been found to be good on all fluids measured.

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