Understanding the correlation of TXRF and surface SIMS

The measurement of the surface metal contamination on silicon wafers is an essential part of yield improvement during IC processing. Total reflection X-ray fluorescence (TXEF) and secondary ion mass spectrometry (SIMS) are widely used analytical tools to monitor contamination on semiconductor wafers. A comparison of SurfaceSIMS measurements of surface metal contamination on silicon wafers with TXRF analyses of the same wafers is presented. These two important surface analysis techniques are characterized by differing analytical areas and sampling depths. For Fe, agreement between SurfaceSIMS and TXRF results is good (generally within a factor of two) for silicon wafers from a variety of sources with contamination levels ranging from 8×10⁹ to 2×10¹⁵ atoms/cm². Differences between SurfaceSIMS and TXRF results occur for other elements (such as W and Cu) when the contamination is not uniform across the surface of the wafer (particles are present), or extends a significant depth below the surface of the wafer (as is frequently the case for ion-implanted wafers),