Direct TXRF (Direct Total X-Ray Fluorescence)

In TXRF X-rays (Cr, W, Mo or Ag) are made to impinge on the surface of a sample at glancing incidence (0.1°) such that total reflection occurs. The X-rays excite atoms in the top layers of the material and the fluorescence is detected by positioning a detector above the sample.

VPD-TXRF (Vapour Phase Decomposition - Total Reflectance X-Ray Fluorescence)

VPD-TXRF improves the detection limits of standard TXRF (by a factor of 300 on 200mm wafers) and also allows detection of the light elements including Na and Al by use of Cr X-ray excitation. In this technique the native oxide is dissolved by by exposure to HF in a VPD reactor. By scanning with a small droplet of HF and H₂O₂ the oxide layer is collected and permitted to dry. This dried residue is then analysed by TXRF. The information provided is from the entire wafer surface.

VPD-ICPMS (Vapour Phase Decomposition - Inductively Coupled Mass Spectrometry)

To improve on the detection limits of VPD-TXRF, VPD-ICPMS can be utilised.

In VPD-ICPMS the native oxide is dissolved with HF acid but instead of the droplet being allowed to dry it is removed after scanning and diluted before analysis by ICPMS.

The benefit is that almost the entire periodic table can be measured in one go.