DIFFERENT FIELDS OF APPLICATIONS - Total-Reflection X-Ray Fluorescence Analysis and Related Methods - page 341

Figure5.13. TXRF results of a wafer mapping for the elements S, Br, Fe, and Ca. About 225
different spots with an area of 0.5 cm 2 were investigated on an 8 inch wafer. Figure from Ref. [149],
reproduced with permission. Copyright1993, Elsevier.
The lateral resolution is determined by the observation area of the detector,
which is on the order of 0.5 cm 2 . Contaminants are in the range of 10 11 to some
10 13 atoms/cm 2 . The nonuniform distribution differs for the individual ele-
ments. Such results can give a first hint of existing contaminations. The
information they provide may give valuable clues as to the source of the
contamination and can help reduce or avoid them.
Sweeping TXRF is a new approach to directly check a whole wafer for
contamination within a reasonable period of time [156]. To this end, the wafer is
moved step-by-step automatically in a helical way and a mapping is carried out.
Figure 5.14 shows a map of four transition metals represented by 221 colored
spots on the wafer. The level of concentration equivalent to the detection limits
is 10 10 atoms / cm 2 . Only about 20 min was needed for the control of this 12 inch
silicon wafer. By the addition of all spectra, a mean value and a standard
deviation can also be evaluated for each contaminant. This technique can also