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First polarization-resolved measurement with the new EUV ellipso-scatterometer

15.05.2014

Fig. 1: Mechanics of the EUV ellipso-scatterometer. In the foreground: the arc guiding for the detector which allows the detector to be driven across one-quarter of the spherical surface and any orientations of the reflection planes to be realized. The manipulator for the sample (centre) permits rotations about three axes and three translations.

Fig. 2: Reflectance (measurement: circles) for S- and P-polarized radiation in the vicinity of the Brewster angle for an Mo/Si multilayer mirror. The dot-dash lines show a modelling which has been adapted to the measurement for S-polarized light. For P-polarized light, it does not completely agree with the measurement. This is due to the optical constants which are only insufficiently known in this spectral range and, thus, proves the need for corresponding measurements.

For many years, the Physikalisch-Technische Bundesanstalt (PTB) has been extending its measurement technology for the characterization of optical components in the extreme-ultraviolet spectral range (EUV). Thereby, it supports European companies which are worldwide leading in the development of EUV lithography for the manufacture of semiconductor components making use of radiation with a wavelength of 13.5 nm. Suitable measurement capabilities for polarization-resolved reflection measurements in the UV range had, however, so far been lacking at PTB. Therefore, a new EUV ellipso-scatterometer has been put into operation at the beamline for soft X-rays at BESSY II (Figure 1). The mechanics of this system, which does without grease lubrication, allows the reflection plane of a measurement to be freely oriented to the direction of the linear polarization of the incident radiation. In addition, a Brewster polarizer with a broadband-Mo/Si multilayer mirror has been established to furnish proof of the reflected radiation. This also allows the linear polarization degree of the reflected radiation to be measured and/or undesired polarization fractions of the incident radiation to be suppressed. In initial measurements, it has been possible to furnish proof of the high suppression of P-polarized radiation for reflection under the Brewster angle on an Mo/Si multilayer mirror (Figure 2). Polarization-resolved measurements are important for the characterization of mirrors for oblique incidence, for example in the case of lens systems with large numerical aperture, or of line structures on photomasks which have polarizing properties due to their geometry.

Contact:

F. Scholze, 7.12, e-mail: Opens window for sending emailFrank.Scholze(at)ptb.de