XRD may give you the film thickness as well as the roughness, if the crystallites that form the film are elongated from the substrate to the air/vacuum surface. In that particular case, the average film thickness is identical to the crystallite size, and you may get the value from the peak broadening as mentioned above. If the films are smooth, then you will also observe side-lobes at both sides of the bragg-peak (see enclosure) and by a modelling, you may get the films roughness. In the attached example, the XRD evaluation results in a thickness of about 65.3 nm (+/- 1.5 nm) while an independent thickness measurement using profilometry and X-ray reflectivity gave 66.5 nm. Thus in that case, we can assume that the crystallites forming the films are of the same size as the film thickness. It should be noted, that prior to annealing, the crystallites were smaller, and thus the XRD evaluation did not reproduced the film thickness!
This implies that this kind of thickness estimation by XRD is dangerous!
Good luck, Dirk
I don't think it would be feasible by XRD however XRR will give your response.
https://www.researchgate.net/post/Can_we_find_the_thickness_of_film_from_XRD_peaks_If_yes_then_how
XRD may give you the film thickness as well as the roughness, if the crystallites that form the film are elongated from the substrate to the air/vacuum surface. In that particular case, the average film thickness is identical to the crystallite size, and you may get the value from the peak broadening as mentioned above. If the films are smooth, then you will also observe side-lobes at both sides of the bragg-peak (see enclosure) and by a modelling, you may get the films roughness. In the attached example, the XRD evaluation results in a thickness of about 65.3 nm (+/- 1.5 nm) while an independent thickness measurement using profilometry and X-ray reflectivity gave 66.5 nm. Thus in that case, we can assume that the crystallites forming the films are of the same size as the film thickness. It should be noted, that prior to annealing, the crystallites were smaller, and thus the XRD evaluation did not reproduced the film thickness!
This implies that this kind of thickness estimation by XRD is dangerous!
Good luck, Dirk
You need to perform X-ray reflectivity: i.e. the analogue to a classical Theta/2Theta measurement in the small angle range (Theta 0.1 to 2 degrees). For this you need to align you sample carefully in the beam and have a very collimated beam in the first place.
I am really surprised someone downvoted Jochen's comment on X-ray reflectivity. In fact, it is the first thing (or one of the first things) which comes to mind, when the problem is set to measure a thickness of an overlayer/film with X-rays. If one thinks about it, it is no different from the l-scan in the vicinity of a Bragg peak, shown, I suppose, by Dirk. That is, it doesn't matter much if you scan a crystal truncation rod/ (CTR), do an l-scan/rocking scan on the CTR or on the specular (0,0) rod, which corresponds to a reflected beam. It is essentially similar information. And to my mind, performing XRR is WAY EASIER than doing an l-scan around a Bragg peak, because you don't care about polar orientation of the crystal. To sum up, I encourage you, Ayed, when choosing the most appropriate technique, consider the XRR prior to the XRD.
Regards
A wonderful and comprehensive answer by Dirk Luetzenkirchen-Hecht. I would also recommend you do SEM cross-sectional facility to measure the exact film thickness to strengthen the results obtained from XRD. Good luck!
I fully agree with the arguments given for the use of both reflectivity (XRR) and diffraction (XRD) measurements. Both techniques can give access to thickness and roughness (that implies that the layer in question is rather smooth), but there are also some subtle differences that one should be aware:
- in XRR (Kiessig fringes), the contrast is ensured by the (electron) density contrast between the thin film(s)/ layer(s) and the substrate. Thus, there should exist in your system a different density layer or interface
- in XRD (Laue oscillations), the thickness obtained is a 'coherent' thickness (like before, result of interference phenomena) but is specific of the crystalline phase you select via the Bragg peak (is the thickness / number of planes with this Bragg spacing)
(can also see the following link:
http://www.diss.fu-berlin.de/diss/servlets/MCRFileNodeServlet/FUDISS_derivate_000000002709/06_ch3.pdf?hosts=)
Thus, in a simplified formulation, in one case one measures the 'total' thickness of the film( resulting from the change in density), in the 2nd case only the thickness of the 'crystalline' part selected via the Bragg peak. The information obtained can thus complementary, it can be interesting to perform both measurements for some samples and compare the results. One expects to get
thickness(XRR) > thickness(XRD)
Regards, Cristian
As mentioned above, x-ray reflectivity (XRR) is a very powerful method, that lets you determine thickness, density and roughness simultaneously. Here is a very good article that concisely compares four different methods to measure thickness from XRR data:
http://www.journals.cambridge.org/abstract_S0885715600009076
Ali, it depends on the material and the quality of the film if an XRD of a 20nm film will be successful. From my personal experience, 20 nm of e.g. a pure metal film are sufficient to be measured with a laboratory XRD system. However, if you have organic thin films, this may correspond to only a single monolayer for a large molecular strucutre, and thus, 20 nm may be difficult to do. You may enhance surface sensitivity using an asymmetric diffraction geometry at grazing incidence, but this is not feasible with many standard diffractometers that only allow the Theta-2Theta geometry. Good luck, Dirk
XRR is a sub-set of XRD around the main beam, yes? As is SAXS, I suppose, a sub-set. The XRR method is independent of the crystallinity of the layers. XRR, is only sensitive to density difference and flatness. XRR is limited to an observation depth of around 300-350nm or less.
Thanks for all the links. Please review the following and post comments when convenient.
https://www.researchgate.net/post/What_depths_can_one_typically_probe_with_XRR_X-ray_Reflectivity_Reflectometery
https://www.researchgate.net/post/Can_XRR_X-Ray_Reflectivity_be_implemented_in_the_Topographic_Mode_with_spatial_resolution_over_the_sample_surface_Is_there_value_for_such_analyses?_tpcectx=profile_questions
Yes. the thin film can be calculated by XRD
http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/13/653/13653832.pdf
Cyril! Good reference. Note that these links are no longer accessable directly. You'll need to cut/paste into Google to find it. Here are some note worthy excerpts from the article.
"The estimated uncertainty in thickness by the weighing method is ±0.1 micron. Taking this as the standard, i t is clear from Table I I that the x-ray diffraction method gives results within ±1 micron."
"7. CONCLUSION The x-ray diffraction method is a non-destructive and a fairl y fast method for the determination of thicknesses of thin films . The absorption technique can be used for both amorphous and polycrystalli/'ie films , when deposited on polycrystalline substrate. The diffraction technique can be used to determine the thickness of polycrystalline films deposited on polycrystalline or amorphous substrate. There is a close agreement between the value calculated from x-ray measurement and the thickness obtained by weiqhing method. The metallographic method also gives values within ±1 micron of the value determined by the weighing method. The accuracy of the x-ray method can be increased, if a calibration procedure is adopted."
Weight method not good enough for correlation yet!
"thickness(XRR) > thickness(XRD)"
XRR is a method that indicates a "gross" thickness parameter. Due to the super low angle of incidence most incident beams would illuminate the entire specimen surface along the equatorial plane up to the "critical angle". So whatever value is computed represents the entire specimen surface with no ability to detect spatial variations on the "topograph".
By examining the higher order (hkl) Bragg profiles it would be possible to detect film thicknesses as well. This may be accomplished with significantly higher spatial resolution compared with XRR with a 2D detector.
Tilting the 2D detector w.r.t. the exit diffracted beam is also another technique for enhancing the spatial resolution (and angular resolution) of data from XRR to XRD without expanding the diffractometer radius or being forced to use a synchrotron :-)
Watch this video!
"How can measure thin film thickness by XRD? Thin film on glass substrate."
Here is an example for a complex hetero epitaxial specimen with GaN-AlGaN-AlN-Si. I was able to use Origin Pro in order to do some curve fitting to extract peak parameters including peak positions, peak heights, peak widths and peak integrated intensities.
If I was to translate various topographic locations to the same detector pixel, while maintaining all other experimental conditions, then I should be able to directly compare the Bragg profiles to estimate contributing diffracting volumes and hence thicknesses of individual layers. This was not done for the current data set.
This method is very different from XRR "gross" measurements for estimating individual layer thickness and other parameters locally at each spatial voxel on the "flat" sample surface. I would think that with a sensitive detector and/or large data integration times, it would be possible to even quantify "mono layers" of Graphene perhaps. Yes?
Cristian Mocuta! Please post the reference for the text that you posted earlier. Thanks!
"Chapter 3
X-Ray Diffraction X-ray diffraction has been a well-established technique in the field of structural investigations for decades, applied not only by physicists. It represents an important tool for chemists and biologists, too, and played a decisive role in the discovery of the structure of the DNA in 1953. Any method that exploits x rays is based upon their discovery in 1895 by W. C. Röntgen by chance while studying the charge transport in gases [91]. This achievement was rewarded the first Nobel prize in the field of physics ever, in 1901. The first diffraction experiment was performed by Max v. Laue in 1912. Fig 3.1 displays the observed diffraction pattern. With this single photograph, Laue solved at once two major problems of his days: It clearly reveals the crystalline nature of solids and proves that x rays behave like waves. This finding was rewarded the Nobel prize in 1914. The following pages summarize the main aspects of the interaction of these "waves" with crystalline material."
What about the rest of it? Keenly interested :-)
Happy New Year to all!
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