Deutsche Tagung f ¨ur Forschung mit ... - SNI-Portal

Methoden und Instrumentierung Poster: Mi., 14:00–16:30 M-P6
Wafer contamination analysis and speciation as well as reference-free
nanolayer characterization employing X-ray spectrometry
Burkhard Beckhoff 1 , Rolf Fliegauf 1 , Michael Kolbe 1 , Matthias Müller 1 ,
Beatrix Pollakowski 1 , Jan Weser 1 , Gerhard Ulm 1
1 Physikalisch-Technische Bundesanstalt, Abbestraße 2-12, 10587 Berlin, Germany
Monochromatized synchrotron radiation has been used for the non-destructive investigation
of wafer surface contamination and nanolayered materials by X-ray spectrometry
in different beam geometries: varying the incident angle from close to zero degrees, i.e.
total-reflection geometry (T), over grazing incidence (GI) to conventional X-ray fluorescence
(XRF). In TXRF geometry only the surface is analyzed, whereas GIXRF and
XRF provide information from subsurface layers respectively the bulk of a sample.
The Physikalisch-Technische Bundesanstalt operates XRF equipment at a plane grating
monochromator beamline for undulator radiation in its laboratory at BESSY II.
The absolute lower levels of detection for TXRF of light elements range between 100 fg
and 1 pg with respect to a measuring time of 1000 s. For the explicit purpose of the
semiconductor industry, PTB can handle 25 mm through 300 mm silicon wafers in its
XRF and TXRF instrumentation [1] ensuring reference-free quantitation by calibrated
components [2].
Near-edge X-ray absorption fine structure (NEXAFS) investigations in conjunction
with TXRF are able to contribute to the speciation of low Z and organic compounds.
TXRF-NEXAFS experiments [1,3] of contaminants have been performed at the K
absorption edges of light elements and the L absorption edges of transition metals.
Reference-free quantification in X-ray fluorescence analysis requires the accurate knowledge
of all experimental values both in the excitation and detection channels as well as
of the fundamental parameters involved. The experimental data are accessible through
calibrated devices such as photodiodes, diaphragms and energy-dispersive detectors.
Besides the instruments’ contributions, the relative uncertainties of the XRF analytical
results are also affected by the tabulated fundamental parameters of the elements,
some of which only have estimated uncertainties. The layer thickness obtained for
transition metals as well as silicon dioxide layers by reference-free XRF has been compared
to the thicknesses determined by X-ray reflectometry. Both methods showed
the same results within the frame of their respective uncertainties [4]. For the speciation
of nanolayer compositions, grazing incidence XRF (GIXRF or GIXF) allows for
different penetration depths by varying the incident angle. At a given incident angle,
GIXRF can be combined with NEXAFS revealing the depth profile of the chemical
layer structure.
[1] B. Beckhoff et.al, ECS Proc. 2003-3 (2003) 120
[2] F. Scholze et al., Microchim. Acta (2006) online
[3] G. Pepponi et al., Spectrochim. Acta B 58 (2003) 2245
[4] M. Kolbe et al., Spectrochim. Acta B 60 (2005) 505