ToF‐SIMS depth profiling of insulating samples, interlaced mode or non‐interlaced mode?

Abstract

Dual-beam depth profiling strategy has been widely adopted in time-of-flight secondary ion mass spectrometry depth profiling, in which two basic operation modes, interlaced mode and non-interlaced mode, are commonly used. Generally, interlaced mode is recommended for conductive or semi-conductive samples, whereas non-interlaced mode is recommended for insulating samples, where charge compensation can be an issue. Recent publications, however, show that the interlaced mode can be used effectively for glass depth profiling, despite the fact that glass is an insulator. In this study, we provide a simple guide for choosing between interlaced mode and non-interlaced mode for insulator depth profiling. Two representative cases are presented: (i) depth profiling of a leached glass sample and (ii) depth profiling of a single-crystal MgO sample. In summary, the interlaced mode should be attempted first, because (i) it may provide data with reasonable quality, (ii) it is timesaving for most cases, and (iii) it introduces low H/C/O background. If data quality is the top priority and measurement time is flexible, non-interlaced mode is recommended because interlaced mode may suffer from low signal intensity and poor mass resolution. A big challenge is tracking trace H/C/O in a highly insulating sample (e.g., MgO), because non-interlaced mode may introduce strong H/C/O background, but interlaced mode may suffer from low signal intensity. Meanwhile, a C or Au coating is found to be very effective to improve the signal intensity. Surprisingly, the best analyzing location is not on the C or Au coating but at the edge (outside) of the coating.

Argon Cluster Sputtering Source for ToF-SIMS Depth Profiling of Insulating Materials: High Sputter Rate and Accurate Interfacial Information

“…+ peak area from 2.0 keV O 2 + non-interlaced mode sputtering was 100%, the relative peak area of the 28 Si + arising from 20 keV Ar n + non-interlaced mode sputtering was 50%. This indicates that for this glass sample, the ionization yield enhancement using O 2 + sputtering is only twice that using 20 keV Ar n + sputtering, which is much smaller than the enhancement value (~50 times) of Si + on a silicon wafer.…”

“…This means that with interlaced mode 20 keV Ar n + sputtering, the charge compensation is very effective, though it may not be as good as that with noninterlaced mode. As a comparison, interlaced and noninterlaced mode using 2.0 keV O 2 + sputtering show~6 times difference in mass resolution and~560 times difference in signal intensity for the 28 Si + signal. Interlaced and noninterlaced mode using 2.0 keV Cs + sputtering show~7 times difference in mass resolution and~30 times difference in signal intensity for the 18 …”

“…This advantage is especially important for deep depth profiling (e.g., ≥3 μm) because the measurement time is very long if Cs + or O 2 + sputtering is used. In Table 2, the signal intensity and mass resolution of the 28 Si + or 18 O -peak with non-interlaced mode 20 keV Ar n + sputtering is only slightly (5%-15%) better than that from interlaced mode. This means that with interlaced mode 20 keV Ar n + sputtering, the charge compensation is very effective, though it may not be as good as that with noninterlaced mode.…”

“…Charge compensation was used for all depth profiling measurements. The details for the adjustment of charge compensation and additional information for ToF-SIMS measurement can be found in our previous publication [28].…”

“…However, ionization yield enhancement may not be a problem for glasses or other oxide samples because these materials are generally ionic structures, guaranteeing Table 2). If defining the 28 …”