A Fundamental Study on the Relocation, Uptake, and Distribution of the Cs⁺ Primary Ion Beam During the Secondary Ion Mass Spectrometry Analysis

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Virginia Tech


Combining cesium (Cs) bombardment with positive secondary molecular ion detection (MCs+) can extend the analysis capability of Secondary Ion Mass Spectrometry (SIMS) from the dilute limit (<1%) to matrix elements. The MCs+ technique has had great success in quantifying the sample composition of III-V semiconductors as well as dopants and/or impurities; however, it has been less effective at reducing the matrix effect for IV compounds, particularly Si-containing compounds, due to Cs overloading at the surface during the analysis from the Cs primary ion beam. The Cs overloading issue is attributable to the mobility and relocation of the implanted Cs to the surface; this effect happens almost instantaneously. Once the surface is overloaded with Cs, the excess Cs begins to reneutralize the ionization Cs and, as a result, the MCs+ technique is ineffective at reducing the matrix effect.

This research provides new insights for improving the MCs+ technique and elucidating the Cs mobility. A combination of multiple experimental techniques and theoretical modeling was implemented to assess the Cs retention, up-take, and distribution differences between group III-V and IV materials. Early experiments revealed a temperature-dependent component of the Cs mobility, prompting an investigation of this phenomenon. Therefore, we designed, built, and installed a variable temperature stage for our SIMS with temperatures ranging from -150 to 300 C. This enabled us to study the temperature-dependent component of the Cs mobility and the effect it has on the secondary ion emission processes. Additionally, a method was devised to quantify the amount of neutralization and ionization due to the relocated Cs. The results allow for a more thorough understanding of the material dependence on the Cs+-sample interaction and the temperature component of the Cs mobility.



Secondary Ion Mass Spectrometry, Cs+, MCs+, Temperature, Cs Relocation