Multilayer monochromator selects a bandpass

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multilayer monochromator selects a bandpass continuously tunable between 800 eV and 20000 eV. Typical flux at the output of this monochromator is of the order of 10 14 photon per second. The X-ray beam passes then in the Experimental Hutch: a lead shielded enclosure kept in class 100 by filters and laminar flow hoods and that hosts 7 Personnel funding has been provided through the MEDEA platform, while capital funding has been provided by the LETI and TELECOM companies
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542 C. Streli et al. the TXRF measuring chamber and the ancillary wafer-handling devices for automatic loading and unloading of the wafers. Because of the need to handle photon energies as low as 800 eV, the entire beamline, TXRF chamber, and detection system are in vacuum with no win- dow to intercept the beam. The optical layout of the installation is completed by a silicon post- monochromator that can be inserted in the beam path after the multi- layer monochromator; this monochromator selects a bandpass of few eV for performing, when required, XAS measurements around selected absorption edges for analyzing chemical and geometrical atomic structure around the contaminant species. Finally, a mirror for rejecting the higher harmonics transmitted by the monochromator is installed upstream the wafer analysis station. This mirror is of the bimorph type and can be piezoelectrically bent longitudinally to focus the radiation in the vertical direction and increase then the photon density on a particular area of the wafer. The TXRF Station The TXRF end-station is at the core of the beamline. The station encompasses an atmospheric loading robot that transfers the wafers from standard cassettes to an indexer to azimuthally orient and center it before passing introduction into the load-lock vessel. The load-lock can host up to five 200 mm and five 300 mm wafers. After pump-down of the load-lock, one wafer at a time can be transferred to the main TXRF chamber for analysis. The TXRF system is sketched in Fig. 7.74: a large, rugged hexapode actuator installed in air just below the vacuum chamber is coupled through a bellow and a rotary feedthrough to the electrostatic chuck that flattens and holds the wafer in vacuum. All the alignment procedures of the wafer on the X-ray beam are performed via the air operated hexapode and transmitted through the bellow and the rotary feedthrough to the vacuum chuck. The Detection Scheme The operation scheme of the station was selected on the basis of a few geomet- rical constraints; on the one hand it was desirable to have the wafer loading, unloading, and alignment procedures to be performed in an horizontal plane for ease of operation; on the other, the fluorescence detectors should look along the horizontal polarization plane of the radiation to minimize the col- lection of elastically scattered photons. A third important constraint is that the radiation beam cannot be focused down into a small region of the wafer because any single element detector would be easily saturated. As a result
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  • Spring '14
  • MichaelDudley

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