Contamination Analysis

Using undulator radiation at electron storage rings, high photon fluxes of linear polarized radiation for the excitation in total-reflection X-ray fluorescence analysis (TXRF) for the contamination control on semiconductor surfaces can be achieved. At PTB's PGM beamline such high photon fluxes can be achieved in the soft X-ray range, up to about 1860 eV. Here, the absolute lower levels of detection for TXRF [1,2] of light elements such as C, N, Na, Mg and Al range between 100 fg and 1 pg with respect to a measuring time of 1000 s. Transition metals can also be analyzed through their L-fluorescence radiation.
For purposes of the semiconductor industry, PTB can handle 15 mm through 75 mm as well as 200 mm and 300 mm silicon wafers in its XRF and TXRF instrumentation. Routine analysis of wafer surfaces involves TXRF spectra deconvolution based on both detector response functions and physical modeling of background components such as resonant Raman scattering [3]. Furthermore, reference-free quantitation is ensured by calibrated components of the instrumentation employed.
Near-edge X-ray absorption fine structure (NEXAFS) investigations in conjunction with TXRF are able to contribute to the speciation of contaminants such as low Z compounds (B, C, N, O, F) or transition metals in the low pg range.