7 July 1997 Polycapillary focusing optic for low-energy x-ray fluorescence
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Abstract
It has been suggested that low-energy-x-ray fluorescence (LEXRF) could be a surface analysis technique used for measuring elemental composition and thickness of thin films on a Si substrate. Conventional XRF, due to constraints on primary beam flux, requires close coupling of the sample to the source and illumination of a large area, making measurements inconvenient with limited spatial information. Polycapillary optics capture a large solid angle of x rays from a source and efficiently focus them to a submillimeter spot on the wafer with significant flux gains. Polycapillary optics do not suffer from the 1/r2 losses in going to longer source to sample distances. A prototype focusing optic has been constructed and characterized at Cu L (0.93 keV) and Al K (1.49 keV). The optic collects 0.043 sr of x rays from a point source and focuses the beam to a point 0.46 mm and 0.42 mm in diameter (FWHM) for the Cu L and Al K source, respectively. The optic is 76 mm in length and has an input and output focal length of 64 mm. Compared to the direct beam 100 mm away from the source, the average flux gains within the output focal spot (FWHM) are 94 and 168 times greater for Cu L and Al K, respectively. It is estimated that coupling this optic with a 18 W (1.8 kV 10 mA) Cu source would allow a 4 nm SiO2 layer on a Si wafer to be measured within 1 minute with a statistical accuracy of (sigma) equals 2%.
© (1997) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Ira Klotzko, Qi-Fan Xiao, "Polycapillary focusing optic for low-energy x-ray fluorescence", Proc. SPIE 3115, Hard X-Ray and Gamma-Ray Detector Physics, Optics, and Applications, (7 July 1997); doi: 10.1117/12.277672; https://doi.org/10.1117/12.277672
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