Marion L. Scott

Optical constants for thin films of C, diamond, Al, Si, and CVD SiC from 24 Å to 1216 Å

A method for deriving optical constants from reflectance vs angle of incidence measurements using a nonlinear least-squares curve-fitting technique based on the chi(2) test of fit is presented and used to derive optical constants for several thin-film materials. The curve-fitting technique incorporates independently measured values for the film surface roughness, film thickness, and incident beam polarization. The technique also provides a direct method for estimating probable errors in the derived optical constants. Data are presented from 24 A to 1216 A for thin-film samples of C, synthetic diamond, Al, Si, and CVD SiC. Auger electron spectroscopy depth profiling measurements were performed on some of the samples to characterize sample composition including oxidation and contamination.

Optical constants for thin films of Ti, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Ir, Os, Pt, and Au from 24 A to 1216 A

Reflectance vs incidence angle measurements have been performed from 24 A to 1216 A on electron-beam evaporated samples of Ti, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt, and Au, and using a nonlinear least-squares curve-fitting technique, the optical constants have been determined. Independently measured values of the incident beam polarization, film thicknesses, and film surface roughnesses are incorporated into the derivation of the optical constants. Additionally, Auger electron spectroscopy depth profiling measurements have been performed on each sample to characterize sample composition including oxidation and contamination.

Extreme ultraviolet reflectance degradation of aluminum and silicon from surface oxidation

We have performed in situ oxide contamination and XUV reflectance vs angle of incidence studies on fresh aluminum and silicon films evaporated in an ultrahigh vacuum system (base pressure 2 x 10(-10)Torr). Our ellipsometric measurements indicate that a surface monolayer of oxide forms on aluminum (1 h at 2 x10(-8) Torr oxygen) and silicon (1 h at 10-(7) -Torr oxygen). The monolayer formation time is inversely proportional to oxygen pressure. Our reflectance vs angle of incidence measurements at 58.4-nm wavelength indicate that unoxidized aluminum and silicon coatings can be used as multifacet retroreflectors with net retroreflectances in excess of 75% for aluminum and 50% for silicon.

Measurement of n and k in the XUV by the Angle-of-Incidence, Total-External-Reflectance Method

Publisher Summary This chapter discusses the measurement of n and k in the extreme ultraviolet (XUV) by the angle-of-incidence, total-external-reflectance (AOITER) method. All the methods that have been developed and employed over the years to determine the optical constants of materials are not useful in the XUV because of the lack of appropriate optics such as quarterwave plates, high absorption of materials, and extreme dispersion in both n and k typical of this spectral region. Another complication inherent in making measurements in the XUV is the absorption of air in this spectral region, which necessitates the use of vacuum chambers for any optical measurements to be performed. There are several general considerations concerning the determination of the optical constants of a material in the XUV. One of the complications in using any reflection or transmission method for the determination of the optical constants of a material in the XUV is the potential presence of contamination layers on the surface of the material. There are potential systematic errors in the measurement of n and k using the AOITER method. If the polarization of the XUV beam is unknown, it is also a potential source of error in analyzing the AOITER data for values of n and k . Another example of a potential error that occurs is spatially nonuniform detector sensitivity. This error can be minimized by always requiring that the reflected beam strike the same spot on the detector method.

Extreme ultraviolet multilayer reflectors

We have investigated the design, fabrication, and reflectance measurements of a multilayer silver/silicon reflector for use at 58.4 nm. Our results indicate that reflectors in the extreme ultraviolet do not perform as well as predicted due to the presence of surface oxides and other surface contamination layers. In addition, we have found that the correct optical constants for silver have now been published. We find also that these multilayer coatings can be utilized as reflective polarizers in the EUV with an extinction ratio of 75:1 and a throughput of 28% for the s‐polarized component of the beam.

Chapter 9 – Measurement of n and k in the XUV by the Angle-of-Incidence, Total-External-Reflectance Method

Publisher Summary nMany complications are observed when determining the optical constants of materials such as the lack of appropriate optics, the high absorption of the materials, and absorption of air that necessitates the use of vacuum chambers for any optical measurements to be performed. The phenomenon of total external reflectance is encountered in many materials. This effect is analogous to the total internal reflectance observed in the visible spectrum, when light that is propagating in a dense medium is obliquely incident at an interface between this dense medium and a less dense medium. The existence of the total external reflectance at a given wavelength for a specific material implies that the complex index of refraction can be determined quite accurately, by making measurements of reflectance versus angle of incidence and performing the necessary analysis. General considerations concerning the determination of the optical constants of a material in the extreme ultraviolet (XUV) include: contamination and surface roughness, vacuum deposition and in situ reflectance measurement, and potential errors.

XUV projection lithography: is optical surface contamination an important limitation?

We report results of an extensive set of oxide and carbon film contamination experiments with Al, Si, Rh, and Ag films and surfaces to quantify the film growth rates and parameter dependencies. These four materials were selected initially because they exhibit total external reflectance at moderate angles of incidence, e.g., > 45 degree(s), as needed for high- reflectance multifacet mirrors. In addition, these materials are candidate films for single- surface and multilayer mirrors at normal incidence as well as transmission filters in XUV projection lithography optical systems. (Abstract only)

Development of an XUV-IR free-electron laser user facility for scientific research and industrial applications

Los Alamos has designed and proposes to establish an XUV-IR free-electron laser (FEL) user facility for scientific research and industrial applications based on coherent radiation ranging from soft x rays as short as 1 nm to far-infrared wavelengths as long as 100 micrometers . As the next-generation light source beyond low-emittance storage rings with undulator insertion devices, this proposed national FEL user facility should make available to researchers broadly tunable, picosecond-pulse, coherent radiation with 104 to 107 greater spectral flux and brightness. The facility design is based on two series of FEL oscillators including one regenerative amplifier. The primary series of seven FEL oscillators, driven by a single, 1-GeV rf linac, spans the short-wavelength range from 1 to 600 nm. A second 60-MeV rf linac, synchronized with the first, drives a series of three Vis/IR FEL oscillators to cover the 0.5 to 100-micrometers range. This paper presents the motivation for such a facility arising from its inherently high power per unit bandwidth and its potential use for an array of scientific and industrial applications, describes the facility design, output parameters, and user laboratories, makes comparisons with synchrotron radiation sources, and summarizes recent technical progress that supports the technical feasibility.

UHV Aluminum Grazing Incidence Reflectance At Extreme Ultraviolet Wavelengths

We have developed a multi-facet retroreflecting mirror substrate structure which can be coated with a fresh aluminum film in an ultra-high vacuum (UHV) system and subsequently used for in situ reflectance measurements in the extreme ultraviolet (XUV). We utilize a gas discharge XUV source in combination with a 0.2 m Minuteman monochromator to illuminate the 9-facet mirror with a series of XUV wavelengths. The XUV beam is incident on each of the nine facets at 80 degrees (from normal). An imaging microchannel plate detector is utilized to measure both the incident beam and the retroreflected beam in the UHV chamber. Maintenance of an ultra-high vacuum level during the thin film deposition and the subsequent reflectance measurements provides assurance that the fresh aluminum film does not form an oxide surface layer which would adversly affect the XUV reflectance measurements. Results of these reflectance measurements will be discussed.

Optical Constants For 22 Thin Film Materials In The 10 eV To 500 eV Photon Energy Region

Reflectance measurements were used to derive the optical constants of 22 materials for 36 photon wavelengths from 24 Å to 1216 Å. The samples studied are thin films of the transition metals Ti, Zr, Nb, Mo, Ru, Rh, Pd, Hf, Ta, W, Re, Os, Ir, and Pt, the noble metals Ag and Au, and films of C, diamond, Al, Si, CVD-SiC and a-SiC. We describe the experiment and also the data reduction technique used to derive the optical constants from the reflectance versus incidence angle data. A summary of the results is presented.