The continuous downscaling of the process size for semiconductor devices pushes the junction depths and consequentially the implantation depths to the top few nanometers of the Si substrate. This motivates the need for sensitive methods capable of analyzing dopant distribution, total dose and possible impurities. X-ray techniques utilizing the external reflection of X-rays are very surface sensitive, hence providing a non-destructive tool for process analysis and control.X-ray reflectometry (XRR) is an established technique for the characterization of single- and multi-layered thin film structures with layer thicknesses in the nanometer range. XRR spectra are acquired by varying the incident angle in the grazing incidence regime while measuring the specular reflected X-ray beam. The shape of the resulting angle-dependent curve is correlated to changes of the electron density in the sample, but does not provide direct information on the presence or distribution of chemical elements in the sample.Grazing Incidence XRF (GIXRF) measures the X-ray fluorescence induced by an X-ray beam incident under grazing angles. The resulting angle dependent intensity curves are correlated to the depth distribution and mass density of the elements in the sample. GIXRF provides information on contaminations, total implanted dose and to some extent on the depth of the dopant distribution, but is ambiguous with regard to the exact distribution function.Both techniques use similar measurement procedures and data evaluation strategies, i.e. optimization of a sample model by fitting measured and calculated angle curves. Moreover, the applied sample models can be derived from the same physical properties, like atomic scattering/form factors and elemental concentrations; a simultaneous analysis is therefore a straightforward approach. This combined analysis in turn reduces the uncertainties of the individual techniques, allowing a determination of dose and depth profile of the implanted elements with drastically increased confidence level.Silicon wafers implanted with Arsenic at different implantation energies were measured by XRR and GIXRF using a combined, simultaneous measurement and data evaluation procedure. The data were processed using a self-developed software package (JGIXA), designed for simultaneous fitting of GIXRF and XRR data. The results were compared with depth profiles obtained by Secondary Ion Mass Spectrometry (SIMS).
Dopant depth profiling and dose determination are essential for ultrashallow junction technology development. However they pose a challenge to the widely used dynamic secondary ion mass spectroscopy ͑SIMS͒ technique that suffers uncertainties due to an initial transient width comparable to the dopant depth distribution. In this work the authors report on the application of grazing incidence x-ray fluorescence ͑GIXRF͒ for arsenic in silicon dose and profile determination and its combination with SIMS in order to try to overcome the limitations of the latter in the topmost few nanometers. A polynomial variation of the sputtering rate is supposed in the first sputtering stage of the SIMS analysis and the parameters that regulate the magnitude of such correction are determined by a least square fitting of the angle dependent fluorescence signal. The total retained fluence was also measured by instrumental neutron activation analysis and synchrotron radiation soft x-ray GIXRF. The comparison among the total retained fluence determinations shows a good agreement among the techniques. Furthermore, from this first set of measurements it was clearly shown that the GIXRF profile correction is very sensitive to the SIMS profile in the very first nanometers. Therefore if matrix effects are present in the SIMS analysis beside the sputtering rate change, the tested sputtering rate correction can produce nonreliable profiles.
As Grazing Incidence X-ray Fluorescence (GIXRF) analysis does not provide unambiguous results for the characterization of nanometre layers as well as nanometre depth profiles of implants in silicon wafers by its own, the approach of providing additional information using the signal from X-ray Reflectivity (XRR) was tested. As GIXRF already uses an X-ray beam impinging under grazing incidence and the variation of the angle of incidence, a GIXRF spectrometer was adapted with an XRR unit to obtain data from the angle dependent fluorescence radiation as well as data from the reflected beam. A θ-2θ goniometer was simulated by combining a translation and tilt movement of a Silicon Drift detector, which allows detecting the reflected beam over 5 orders of magnitude. HfO2 layers as well as As implants in Silicon wafers in the nanometre range were characterized using this new setup. A just recently published combined evaluation approach was used for data evaluation.
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