INSTRUMENTATION FOR TXRF AND GI-XRF - Total-Reflection X-Ray Fluorescence Analysis and Related Methods - page 163

loaded into the sample holder one at a time and then set back after the
measurement. This process can be carried out automatically, even by a robot.
The sample positioning device is the core of those instruments that are
suitable for surface- and thin-layer analyses. The sample should be capable of
being adjusted in the reference plane and of being tilted around a horizontal
axis. The angle of incidence should be variable, preferably stepwise. This
quantity is the key parameter for recording the angular-dependent intensity
profiles and is the basis for surface- and thin-layer analyses. Apart from being
adjustable, the sample should be displaceable in order to set each spot of a
larger sample in the measuring position and to check the total surface.
Figure 3.13 depicts schematically a convenient device for an angle variation
and sample positioning with 6 degrees of freedom. However, an even simpler
device with ball-points and stepper motors may be sufficient. The wafer or
sample S is placed on a flat carrier C (made of float glass). As an attachment,
either a mechanical chuck is used, applying a slight pressure, or an electrostatic
chuck is designed to apply a specific voltage. The sample can be adjusted to the
tilt center, T, by a vertical shift, z , and this center can be driven into the
reference plane (see Figure 3.9) determined by the two horizontal axes, a and b ,
at right angles. For that purpose, the base B is shifted by z 0 . The sample surface
can further be adjusted with respect to the reference plane by a tilt correction of
Θ and χ . Each spot of the sample can be placed into the measuring position or
tilt center T by a lateral movement x and a rotation φ on the vertical axis.
Finally, the angle of incidence can be varied by a tilt Θ around the axis a lying on
the wafer surface.
Figure3.13. Schematic diagram of an angle variation and sample positioning device suitable for
thin-layer analysis by GI-XRF: B = solid base; C = flat carrier; S = flat sample or wafer; a and
b = horizontal axes spanning the reference plane, T = tilt center; x = lateral movement; Φ= rotation
on the vertical axis; Θ= tilt around axis a ; χ = tilt correction for axis b ; z = vertical shift of the sample,
z 0 = vertical shift of the base. Figure from Ref. [2], reproduced with permission. Copyright1996,
John Wiley and Sons.