WIDE BAND-PASS APPROACHES TO TOTAL-REFLECTION X-RAY-FLUORESCENCE USING SYNCHROTRON-RADIATION

Measurement and control of surface and near surface trace impurities on silicon wafers is a critical technology for the development and manufacture of leading-edge silicon VLSI circuits. Among the industry-standard methods for monitoring surface impurities are grazing-incidence X-ray methods employing rotating anode sources. In the semiconductor industry, the X-ray method is referred to as total reflection X-ray fluorescence spectroscopy (TRXRF or TXRF). Conventional-source TRXRF methods are not adequate for future industry needs. Beamline modifications and a special experimental chamber were designed and executed at the Stanford Synchrotron Radiation Laboratory to investigate the performance of synchrotron radiation based approaches to this application. Crystal monochromators, a Mo-C multilayer mirror, and filtered white light were examined as sources for TRXRF. The best experimental configuration surpassed previous attempts in the field. With it, two different semiconductor industry user groups were able to demonstrate significant improvements in the TRXRF detection limits for 3-d transition metals and for aluminum compared to standard conventional equipment. The design goals, equipment configuration and current performance level of this synchrotron-based TRXRF configuration are described in detail. Aspects of the experimental design under further development for even higher performance are discussed.