Electron Beam-Induced Deposition for Atom Probe Tomography Specimen Capping Layers.

Area of Science:

• Materials Science
• Nanotechnology
• Surface Science

Background:

• In situ electron beam-induced deposition (EBID) is vital for preparing atom probe tomography (APT) specimens.
• Capping layers are essential for preserving near-surface features during APT analysis.
• Evaluating precursor effectiveness for EBID capping is critical for optimizing specimen preparation.

Purpose of the Study:

• To evaluate six precursors for in situ EBID capping layers in APT specimen preparation.
• To assess the utility of these depositions, focusing on near-surface feature retention at the specimen apex.
• To identify effective capping materials that minimize specimen damage and enhance APT analysis.

Main Methods:

• Six precursors were deposited onto silicon posts using EBID.
• Specimens were shaped into sub-70-nm radii needles using focused ion beam (FIB) milling.
• Depositions were assessed based on composition, uniformity, evaporation behavior, evaporation fields, and Ga+ ion penetration depth.

Main Results:

• Methyl cyclopentadienyl platinum trimethyl, palladium hexafluoroacetylacetonate, and dimethyl-gold-acetylacetonate [Me2Au(acac)] resulted in tip fracture above 3 kV.
• Me2Au(acac) with O2 was inconclusive due to underlying silicon evaporation.
• Dicobalt octacarbonyl [Co2(CO)8] and diiron nonacarbonyl [Fe2(CO)9] proved effective capping materials.
• Co2(CO)8 and Fe2(CO)9 exhibit distinct evaporation fields (36 V/nm and 21 V/nm, respectively), offering flexibility in matching specimen material evaporation fields.

Conclusions:

• Dicobalt octacarbonyl and diiron nonacarbonyl are suitable in situ capping materials for APT of silicon specimens.
• The differing evaporation fields of Co2(CO)8 and Fe2(CO)9 provide valuable options for optimizing APT analysis.
• Effective capping layers are crucial for high-resolution analysis of near-surface features in APT.