Assessing the impact of secondary fluorescence on X-ray microanalysis results from semiconductor thin films: X-ray microanalysis of thin surface films and coatings

The impact of secondary fluorescence on the material compositions measured by X-ray analysis for layered semiconductor thin films is assessed using simulations performed by the DTSA-II and CalcZAF software tools. Three technologically important examples are investigated: Al_xGa_1-xN layers on either GaN or AlN substrates, In_xAl_1-xN on GaN and Si-doped (Sn_xGa_1-x)2O3 on Si. Trends in the differences caused by secondary fluorescence are explained in terms of the propensity of different elements to reabsorb either characteristic or bremsstrahlung X-rays and then to re-emit the characteristic X-rays used to determine composition of the layer under investigation. Under typical beam conditions (7-12 keV) the quantification of dopants/trace elements is found to be susceptible to secondary fluorescence and care must be taken to prevent erroneous results. The overall impact on major constituents is shown to be very small with a change of approximately 0.07 molar cation percent for Al_0.3Ga_0.7N/AlN layers and a maximum change of 0.08 at% in the Si content of (Sn_xGa_1-x)₂O₃/Si layers. This provides confidence that previously reported wavelength dispersive X-ray compositions are not compromised by secondary fluorescence.