Atom probe tomography enables atomic-resolution characterization of sample structure and elemental composition. This technique, which removes individual atoms from the sample surface (as ions) and measures their identity with a mass spectrometer, requires that the sample is in the form of a sharp tip to eject the ions for analysis. Focused ion beam (FIB) milling is well suited for this particular type of sample preparation as it can remove highly precise quantities of material. When coupled with a scanning electron microscope (SEM), as in DualBeam (FIB-SEM) instruments, the milling process can be visually monitored in real-time.
The fundamental criteria for a good APT sample are:
- Site-specific and non site-specific sample preparation capability
- Needle-shaped specimen with tip radius typically less than 50 nm
- Uniform, circular cross-section of the tip to produce a radially symmetric electric field
- Correct taper angle for significant evaporation events to occur
- Minimal damage introduced to the tip during specimen preparation (apex region of needle should represent original sample in terms of microstructure and composition)
Thermo Scientific DualBeam instruments offer gallium FIB and plasma FIB (PFIB) milling for high-quality APT sample preparation. With the Thermo Scientific Helios Hydra DualBeam, a range of plasma ion species (oxygen, argon, nitrogen, or xenon) can uniquely be applied within the same instrument to determine which ion is best suited for milling a given sample. The process can also be automated with Thermo Scientific Autoscript Software, greatly reducing the burden of repetitive sample preparation.
Atom Probe Semiconductor Sample Preparation
The shrinking of semiconductor devices means smaller and smaller architectures are used in their design process, requiring higher resolution characterization. Atom probe tomography (APT) is increasingly used in advanced semiconductor analysis, as it enables detection, visualization, and analysis of these structures, along with elemental composition, at very low concentrations.
However, APT requires the preparation of high-quality, high-yield, and site-specific atom probe tips. This can be a daunting challenge due to the strict criteria applied to these tips. For example, the needle-shaped specimen needs a tip radius of less than 50 nm, a uniform circular cross-section to produce a radially symmetric electric field, correct taper angle for evaporation events to occur, and minimal damage introduced to the tip during preparation.
Focused ion beam (FIB) milling using DualBeam (combined FIB and scanning electron microscopy) technology is ideally suited for this particular type of preparation, as milling allows for highly precise quantities of material to be removed while being monitored in real time. Thermo Fisher Scientific has introduced Thermo Scientific Atom Probe LX Software and the Thermo Scientific Helios 5 FX DualBeam, brand new sample preparation technology that automates the atom probe tip milling process, making it reliable, precise, and repeatable.
These high-quality tips allow you to detect phenomena such as etch-related impurities (e.g. fluorides, chlorides) at interfaces, hydrogen distribution within features, heavy metal diffusion into the gate oxide, and lateral diffusion of dopants in epi-layers. See the Helios 5 FX DualBeam product page for more information.
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