Temperature dependent Cs retention, distribution, and ion yield changes during Cs+ bombardment SIMS

Abstract

Combining 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 at. %) to matrix elements. The MCs+ technique has had great success in quantifying the sample composition of III–V semiconductors. However, the MCs+ has been less effective at reducing the matrix effect for group IV materials, particularly Si-containing compounds. The lack of success in quantifying group IV materials is primarily attributable to the high Cs surface concentrations overloading the sample surface and lowering ion yields. The Cs overload issue is caused by the mobility and relocation of the implanted Cs to the surface during an analysis. Critical to understanding the material-dependent success of the MCs+ technique and elucidating the Cs mobility is understanding how Cs is incorporated and distributed into the sample and how the Cs surface concentration affects the ionization processes. The authors provide both new insight for improving the MCs+ technique by investigating the Cs retention, distribution, and ion yield differences between group III–V and IV materials and a greater understanding of the temperature-dependent mobility and relocation of the implanted Cs. There have been many studies on improving the MCs+ technique; however, our novel approach to use temperature as a means of controlling the Cs mobility has not been previously explored. Cesium build-up curves were acquired to assess the in situ Cs incorporation differences. By utilizing the newly developed variable temperature stage on our SIMS, cesium build-up curves were acquired over a wide range of temperatures (−150 to 300 °C) to show the temperature-dependent relocation of Cs and the effect it has on the ionization processes. Additionally, Cs ionization and neutralization were quantified as a function of Cs fluence and temperature. The Cs retention and distribution differences were determined ex situ by measuring the Cs concentration using heat-treatment x-ray photoelectron spectroscopy and heat-treatment medium energy ion scattering. These results allow for a more thorough understanding of the material-dependent success of the MCs+ technique, the Cs+-sample interaction, and the temperature component of the Cs mobility.