[B._Beckhoff,_et_al.]_Handbook_of_Practical_X-Ray_(b-ok.org).pdf

To intralaboratory independent and complementary

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to intralaboratory, independent, and complementary methods of validation, 4 Siltronic AG, Central Research & Development, Burghausen, Germany
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500 C. Streli et al. such as instrumental neutron activation analysis (INAA) [90], and laser diode atomic absorption spectroscopy (LAAS) [91]. By applying modulation techniques and second harmonic generation (SHG) connected with the use of LiIO 3 laser diode radiation source, the relative stan- dard deviation of the background can be reduced due to the missing flicker noise of the hollow cathode lamp. In close cooperation with our laboratory, 5 LAAS has been developed by LaserSpec Analytik GmbH. 80807 M¨unchen, eventually in fusion with ATOMIKA Instruments and became a very sensi- tive analytical tool for Al at 396.15 nm (SHG) and K at 776.7 nm wavelength down to 5 ng/l and, respectively, 0.1 ng/l. LAAS is also an ideal tool of in situ analysis of various cleaning bathes on the production floor. In the referenced application, LAAS has surpassed the classical GFAAS [92] by one order of magnitude. Until an efficient SHG laser diode for Na is commercially avail- able, INAA will remain the most suitable validation method for Na down to an absolute amount of about 1 ng. 7.3.2 Analysis of Metallic Surface Contamination by Means of TXRF In the daily analytical routine, the merit of TXRF is the simplicity of the TXRF spectra and the broad range of linear response over four orders of magnitude. The spectral simplicity allows straightforward quality control of the analytical results and easy data management. The broad range of linear response provides facile ways of calibration control combined with automated sample preparation, measurement, and data evaluation. In this regard, com- peting microanalytical methods cannot defeat TXRF. Providing high uptime and reasonable throughput, TXRF proved to be an ideal at- and in-line mi- croanalytical tool of monitoring front-end cleanliness and process hygiene of wafer processes. The disadvantages of commercially available TXRF are the high investment costs, unsatisfactory detection limits (LOD) for light ele- ments, and the inability to analyze the target X-ray source metal. The latter issue was recently circumvented by applying bright synchrotron radiation (SR) sources [93]. Further development requests advanced sensitivity, particularly in spot-wise surface analytical application, and a broader choice of analytes including the light elements, as suggested by the presently valid International Technology Roadmap for Semiconductors [94]. 7.3.3 Historic Background Compton reported in 1923 that reflectivity on a flat target was increasing below a critical angle of 0.1 under conditions of total X-ray reflection. The high reflectivity of the sample support reduced the spectral background of the support and improved the LOD down to picogram levels in the early 1970s 5 Siltronic AG, Central Research & Development, Burghausen, Germany
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Methodological Developments and Applications 501 when Yoneda and Horiuchi applied the principle of TXRF, mainly, to ultra trace elemental microanalyses of biological samples in 1971 [95]. For more de-
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