This work describes recent progress in implementation and applications of synchrotron radiation total reflection x-ray fluorescence (SR-TXRF) to measure trace metals on wafer surfaces. To date, we have achieved state-of-the-art transition metal sensitivity of 3×108 atoms/cm2 (˜3fg) for 1000 sec. counting time for impurities which have an monolayer-like distribution on the surface and <1fg for droplet-like impurities. Recent instrumentation breakthroughs include reduction of detector parasitic backgrounds (particularly Cu) to below our present detection limit, 150 and 200mm whole-wafer handling, wafer-mapping capability and a cleanroom mini-environment. With these upgrades, measurements were made of wafers from various steps in the integrated circuit fabrication process. These results demonstrate that synchtron radiation brings TXRF into a new and useful regime. Further developments are underway to increase throughput and access for broader application.
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Synchrotron radiation experiments were performed at the Stanford Synchrotron Radiation Laboratory (SSRL) which is funded by the Department of Energy (DOE), Office of Basic Energy Sciences. The detector development work was supported by a DOE Cooperative Research and Development Agreement between the Hewlett-Packard Co. and SSRL through the Stanford Linear Accelerator Center.
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Fischer-Colbrie, A., Laderman, S.S., Brennan, S. et al. State-of-the-Art Evaluation of Ultra-Clean Ulsi Processes. MRS Online Proceedings Library 477, 403–407 (1997). https://doi.org/10.1557/PROC-477-403