Cesium/Xenon dual beam sputtering in a Cameca instrument: Cesium/Xenon dual beam sputtering in a Cameca instrument

Although the use of cesium (or oxygen) primary ions in secondary ion mass spectrometry (SIMS) enabled its success in microelectronics, issues arise at ultra-low energies, as required for extreme depth resolution, as the sputter yield becomes very small such that one enters the regime of ion beam deposition instead of material erosion. A potential solution is then to lower the Cs supply by using a Cs/Xe co-sputtering as introduced by ION-TOF and explored extensively by J. Brison. In this work, we describe a somewhat similar implementation in a Cameca SC Ultra and assess its performance and impact on ion yields. Because of the specific Cameca instrumental configuration, one alternates with short time intervals between Cs+ and Xe+ primary ions in the same ion column. Depending on the time intervals used, this approach leads to either quasi-simultaneous sputtering (intervals similar to 80ms) or sequential (intervals >1s) sputtering. An exponential variation of the Si- yield is observed when the Cs beam fraction varies from 0 (Xe) to 1 (Cs) and is ascribed to the corresponding increase in the near surface Cs concentration, C-Cs. Moreover, we observed detailed timing effects of the beams implying that the same nominal C-Cs may lead to different secondary ion yields suggesting effectively a different C-Cs. These effects are further investigated by observing the finer details of Cs accumulation and migration mechanisms in situ. Finally, when analysing SiGe/Si layers, it is found that with increasing Cs/Xe ratio, the decay lengths tend to decrease whereas matrix effects at interfaces show an opposite trend. Copyright (c) 2014 John Wiley & Sons, Ltd.