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XRD/XRR v. AFM for Film Thickness

  1. Jul 7, 2010 #1
    Currently in our lab we have a WEDGE shaped sample that we would like to be able to know the thickness at various points along it. Our sample is about 5mm x 5mm. The wedge SHOULD extend from one side to the other. At the highest point, the wedge is 50nm, and then drops down, hopefully at a constant rate, to 0nm at the other side.

    **Special Note**
    The wedge is made of PZT and is between two layers of LSMO, with the layer on top of the wedge measuring a constant 5nm.

    We were thinking about using the XRR/XRD to find the thickness, but I've recently been told to try the Atomic Force Microscope because of our unique shape, and even perhaps the Scanning Electron Microscope.

    I have no personal experience using either the AFM or the SEM and have no idea how they would compare to using the XRR

    Thoughts/ Concerns from the forum please.
  2. jcsd
  3. Jul 7, 2010 #2

    I think all three of the techniques you mention could answer your question:

    XRR: thickness interference fringes in XRR can be modeled with the Parratt formalism (e.g. using Parratt32.exe), and give very reliable thickness and roughness values (~0.1 nm precision for good data and fits). As your sample shape is non-standard, you would have to constrict your x-ray beam to ~0.1 mm sideways, so as to not sample the whole wedge but just a part of it. This is doable on a good reflectometer, but you sacrifice a lot of flux, which makes it challenging

    AFM: I do not know what the abbreviations of your materials stand for, but if you can make a scratch down to the substrate you can scan the scratch then and (taking care to look beyond the bulge) extract film thickness. z-resolution should be up to 0.5 nm.

    SEM / TEM: You could break your sample an look at the cross section. IN SEM one would expect a resolution of 10nm, TEM where sample preparation would be much more involved can get much more precise.

    I would try AFM first (simplest), then XRR.
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