Quo Vadis total reflection X-ray fluorescence?

摘要

The multielement trace analytical method 'total reflection X-ray fluorescence' (TXRF) has become a successfully established method in the semiconductor industry,particularly,in the ultra trace element analysis of silicon wafer surfaces.TXRF applications can fulfill general industrial equirements on daily routine of monitoring wafer cleanliness up to 300 mm diameter under cleanroom conditions.Nowadays,TXRF and hyphenated TXRF methods such as 'vapor phase decomposition (VPD)-TXRF',i.e.TXRF with a preceding surface and acid digestion and preconcentration procedure,are automated routine techniques ('wafer surface preparation system',WSPS).A linear range from 10~8 to 10~(14) [atoms/cm~2] for some elements is regularly controlled.Instrument uptime is higher than 90%.The method is not tedious and can automaticaly by operated for 24 h/7 days.Elements such as S,Cl,K,Ca,Ti,V,Cr,Mn,Fe,Co,Ni,Cu,Zn,As,Br,Sn,Sb,Ba and Pb are included in the software for standard peak search.The detection limits of recovered elements are between 1X10~(11) and 1X10~(7) [atoms/cm~2] depending upon X-ray excitation energy and the element of interest.For the determination of low Z elements,i.e.Na,Al and Mg,TXRF has also been extended but its implementation for routine analysis needs further research.At present,VPD-TXRF determination of light elements is viable in a range of 10~9 [atoms/cm~2].Novel detectors such as silicon drift detectors (SDD) with an active area of 5 mm~2,10 mm~2 or 20 mm~2,respectively,and multi-array detectors forming up to 70 mm~2 are commercially available.The first SDD with 100 mm~2 (!) area and integrated backside FET is working under laboratory conditions.Applications of and comparison with ICP-MS,HR-ICP-MS and SR-TXRF,an extension of TXRF capabilities with an extremely powerful energy source,are also reported.