[B._Beckhoff,_et_al.]_Handbook_of_Practical_X-Ray_(b-ok.org).pdf

Multilayer monochromator selects a bandpass

Info icon This preview shows pages 562–564. Sign up to view the full content.

View Full Document Right Arrow Icon
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
Image of page 562

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
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
Image of page 563
Image of page 564
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern