Effects of detector dead-time on quantitative analyses involving boron and multi-hit detection events in atom probe tomography

Abstract

In atom probe tomography (APT), some elements tend to field evaporate preferentially in multi-hit detection events. Boron (B) is one such element. It is thought that a large fraction of the B signal may be lost during data acquisition and is not reported in the mass spectrum or in the 3-D APT reconstruction. Understanding the relationship between the field evaporation behavior of B and the limitations for detecting multi-hit events can provide insight into the signal loss mechanism for B and may suggest ways to improve B detection accuracy. The present work reports data for nominally pure B and for B-implanted silicon (Si) (NIST-SRM2137) at dose levels two-orders of magnitude lower than previously studied by Da Costa, et al. in 2012. Boron concentration profiles collected from SRM2137 specimens qualitatively confirmed a signal loss mechanism is at work in laser pulsed atom probe measurements of B in Si. Ion correlation analysis was used to graphically demonstrate that the detector dead-time results in few same isotope, same charge-state (SISCS) ion pairs being properly recorded in the multi-hit data, explaining why B is consistently under-represented in quantitative analyses. Given the important role of detector dead-time as a signal loss mechanism, the results from three different methods of estimating the detector dead-time are presented. The findings of this study apply to all quantitative analyses that involve multi-hit data, but the dead-time will have the greatest effect on the elements that have a significant quantity of ions detected in multi-hit events.

Atom Probe Tomography: Development and Application to the Geosciences

“…However, while gross differences between elemental sensitivities are avoided, more subtle effects can still be present and may result in chemical or isotopic compositional biases. The position‐sensitive detector has some dead time associated with the impact of each ion, so that a high flux of multiple‐ion events will lead to a loss of data, which may preference particular mass peaks (Thuvander et al , , Meisenkothen et al , Thuvander et al ). The precise nature of the dead time, which may include spatial proximity as well as coincidence limits, can be complex and will depend on the specific construction of the detector hardware (Peng et al ).…”

Atom Probe Tomography of TiSiN Thin Films

“…This region is called the dead zone and the period of time is called the dead time. They are related in such a way that the dead time decreases with distance from the detection event [37]. If a second ion hit the detector within the dead zone, at most one ion will be detected.…”

Quantification of dopant species using atom probe tomography for semiconductor application

“…The most common dopant elements in the silicon semiconductors are B (for p‐doping) and P (for n‐doping). Although there are a few APT studies of B quantification, only Meisenkothen et al reported there is 20% to 36% B signal lost in B implanted (B dose of 1.5e15 atoms/cm 2 ) of Si standard sample. It is well understood that B determined by the APT is always smaller than the SIMS value, but the loading dependence on concentration is not established yet.…”

“…However, deviation was as small as 14% in the low dose sample of 1.20e14 atoms/cm 2 . The data of Meisenkothen et al6 were plotted in the same figure for comparison…”