TRENDS AND FUTURE PROSPECTS - Total-Reflection X-Ray Fluorescence Analysis and Related Methods - page 460

Figure7.13. TXRF spectrum of a silicon wafer contaminated with C, O, Fe, Cu, and Al up to
0.2 ng/cm 2 . The spectral peaks of these elements appear above a continuous background, which was
deconvoluted with respective fundamental parameters of the sample and experimental parameters
of the detector (its“response function”). Different components were taken into account, such as
Rayleigh and Compton scattering, resonant Raman scattering, and“bremsstrahlung”of photo-
electrons emitted by aluminum atoms with 0.2 ng/cm 2 . Figure from Ref. [32], reprinted with
permission from the American Chemical Society. Copyright2008, Trans Tech Publications.
The method of reference-free quantification was performed for the analysis
of particulate contaminations on a substrate by GI-XRF [63]. In order to
simulate aerosol particles, artificial nanoscaled structures were deposited on
silicon wafers. The surface was first covered with a photoresist and a defined
pattern of“dots”was imprinted by lithography. The dots had a diameter of
2.7 μ m and were arranged in seven rows of about 50 μ m horizontal distance.
Altogether, 2250 dots with a minimal distance of 50 μ m were deposited on an
area of about 350 μ m × 20 mm. The total area was covered with a thin metallic
layer. Afterward, the photoresist was removed and the dots appeared as
isolated flat cylinders or“pads”with a diameter of 2.7 μ m and a height of
only 20-100 nm. Only 0.2% of the total area was deposited with metallic pads.
The diameter was checked by scanning electron microscopy (SEM) images, the
height was determined by a profilometer, and the density was derived from
weighing the samples.
Two sets of samples were studied, covered with chromium and with
permalloy (66% iron and 34% nickel), respectively, and both sets had four
samples with a small nominal height of 10, 20, 50, or 100 nm. One additional
sample was produced with a 2 nm gold layer on top of chromium pads. These
artificial structures were investigated by GI-XRF. Measurements were carried
out at the FCM beamline in the PTB laboratory at the electron storage ring of
BESSY II [63].