Effective attenuation length of Al Kα-excited Si2p photoelectrons in SiO2, Al2O3 and HfO2 thin films

The inelastic mean free path is extensively used as a measure of the surface sensitivity of electron spectroscopies such as XPS and AES. However, the elastic scattering of electrons can considerably influence their propagation in the solid resulting in larger than expected photoelectron counting rate at emission angles close to the surface. Therefore, the effective attenuation length (EAL) turned out to be more relevant in describing the signal attenuation with depth. The NIST database was developed recently to calculate the EAL values for different materials, experimental geometries, and electron energies. The aim of this work is to check experimentally the predicted EAL values for SiO2, Al2O3 and HfO2 dielectrics used in microelectronics. EALs of Al Kα-excited Si2p photoelectrons in the high-k layers were estimated assuming exponential decay of the substrate signal. Similar measurements were also carried out for SiO2 films grown on Si substrates. The obtained EAL values for SiO2 and Al2O3 are in good agreement with the corresponding values predicted by the NIST database while only an approximate EAL value could be obtained for HfO2 due to layer imperfections.