GIXRF and XRR characterization of near surface
layers
D. Ingerle, G. Pepponi1, C. Streli, and P. Wobrauschek
Atominstitut, Vienna University of Technology, Stadionallee 2, A-1020 Vienna, Austria
1Fondazione Bruno Kessler, Via Sommarive 18, I-38123 Povo, Trento, Italy
Grazing Incidence X-Ray Fluorescence (GIXRF) analysis is a surface sensitive technique able to
provide information about the elemental composition, concentration profile / thickness of near
surface layers [1-7]. The technique is typically used for the characterisation of impurities or thin
film structures in/on semiconductor surfaces. While elemental identification and qualitative
evaluation of concentration is relatively straight forward a quantitative approach is only possible
with a pre-knowledge about the sample structure. In fact quantitative analysis is typically carried
out by fitting experimental data based on the simulation of the fluorescence intensity dependence
on the incidence angle of the primary radiation.
The physics behind the modelling of the fluorescence involves the calculation of the
electric/magnetic field intensity along the depth of the sample and the calculation of the induced
fluorescence. This model inherently includes the calculation of the reflected beam as well. Aim of
the experiment was thus the simultaneous acquisition of the fluorescence signal and the reflected xray beam which is a measure of the X-Ray Reflectivity (XRR) of the surface. The advantage of this
combined approach lies in the complementary information provided by these two techniques. GIXRF is clearly very sensitive to elemental gradients in the surface vicinity, whereas x-ray
reflectivity samples the electronic density gradient, and having a much better signal to noise ratio
can provide more precise information about film thickness.
For the collection of XRR data a Mythen microstrip detector[8] was added to the GI-XRF setup
already present at HASYLAB beamline L. This detector was developed for X-ray powder
diffraction experiments and consists of 1280 strips each having a width of 50µm. Thus the reflected
and diffracted beam can be recorded simultaneously over a large angular range without moving the
detector.
To test the setup and check the quality of the data obtained, a W/C Multilayer was used. Figure 1
shows a visual representation of X-ray intensities recorded by the Mythen detector. Each horizontal
line contains a full readout of the 1280 channels, representing different diffraction angles, and the
angle of incidence was varied for each line.
Figure 1: Diffraction pattern of a multilayer, horizontal: diffraction angle, vertical: incident angle.
The data show very low detector noise in the region where the primary beam was blocked by the
sample and the high dynamic range of the system, ranging over more than 5 orders of magnitude.
To create an evaluable representation equivalent to a conventional XRR spectrum, pixel along a
virtual line corresponding to the theta-2theta condition were summed. The result of this
computation is shown in Figure 2.
0
normalized reflectivity [a.u.]
10
measured reflectivity
calculated reflectivity
−1
10
−2
10
−3
10
−4
10
−5
10
0
5
10
15
20
25
grazing angle [mrad]
30
35
40
Figure 2: Extracted XRR spectrum and calculated data
Measurements with the new setup show promising results and the Mythen detector seems to work
very well. The data evaluation routine needs further work.
References
[1] D.K.G. de Boer, Glancing-incidence x-ray fluorescence of layered materials, Physical Review B 44
(1991) 498.
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Impurity Profiles in Semiconductor Silicon Using Time-of-Flight Secondary Ion Mass Spectrometry
and Total Reflection X-Ray Fluorescence Spectrometry, Journal of The Electrochemical Society 144
(1997) 3979-3983.
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[7] C. Streli, P. Wobrauschek, L. Fabry, S. Pahlke, F. Comin, R. Barrett, P. Pianetta, K. Lüning,
B.Beckhoff, Total-Reflection X-Ray Fluorescence (TXRF) Wafer Analysis, in: B. Beckhoff, B.
Kanngießer, N. Langhoff, R. Wedell, H. Wolff (Eds), Handbook of Practical X-Ray Fluorescence
Analysis, Springer Verlag, Heidelberg, 2006, pp. 498 - 554.
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Patterson, Mythen detector system, Nuclear Instruments and Methods in Physics Research Section
A, Volume 501, Issue 1, 21 March 2003, 267-272