Physical Limitations to Sputter Profiling at Interfaces — Model Experiments with Ge/Si Using KARMA

Abstract

The shape of depth profiles obtained by sputtering and the depth resolution are ultimately determined by transport processes in the collision cascade initiated by the primary ion. The limitations to sputter profiling imposed by these processes are investigated experimentally at Ge/Si interfaces prepared in situ. This system is considered a model system as most of the non-coilisional factors are suppressed or at least well controlled. We use the novel technique KARMA (Kombinierte Auger/Röntgen Mikro-Analyse—Combined Auger/Röntgen Microanalysis), which provides an unequivocal depth scale on the sputter profile and a precise escape depth correction via a self-consistent determination of the electron mean free paths. It is found that the shape of the depth profiles is asymmetric in general. The broadening and distortions are caused by recoil mixing in the collision cascade, in qualitative and quantitative agreement with theoretical calculations. The original interface position is not displaced on the depth profile and can be determined with good precision. The dependence of the broadening on the mass and energy of the bombarding noble gas ions is found to agree well with the theoretical predictions. The depth resolution is independent of depth, as far as determined by collisional processes, once the top layer thickness exceeds several times the projected ion range.

“KARMA: The force generated by a person’s actions held in Hinduism and Buddhism to perpetuate transmigration and in its ethical consequences to determine his destiny in his next existence.” Webster’s Collegiate Dictionary, 1973