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Evaluation of contamination of power semiconductor device wafers by total reflection X-ray fluorescence spectrometer

Winter 2013, Volume 29, No. 1
Hiroshi Kohno

TXRF spectrometers are widely used as evaluation instruments for measuring contamination in the semiconductor fabrication process. This is mainly because the TXRF technique allows non-destructive analysis for almost all elements (Na~U) in the periodic table.

TXRF spectroscopy is possible due to the property of X-rays as they irradiate a flat surface, such as a Si wafer or glass. Each material has a unique critical angle. If the incident angle of the X-rays is above the critical angle, the X-rays penetrate the surface deeply; if the incident angle is smaller than the critical angle, the X-rays are reflected off the surface totally, or what is termed total reflection. In the total reflection condition, any 􀃀uorescence X-rays will occur only from contamination on the surface and the surface material will not add background noise to the measurement. The penetration depth of the incident X-rays under the conditions of total reflection is theoretically around 5 nm, and thus TXRF is classified as a surface analysis. TXRF’s outstanding S/N ratio makes the detection of contamination on the surface of a sample possible with high sensitivity.


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