Optimisation of sample preparation and analysis conditions for atom probe tomography characterisation of low concentration surface species

Abstract

The practicalities for atom probe tomography (APT) analysis of near-surface chemistry, particularly the distribution of low concentration elements, are presented in detail. Specifically, the challenges of surface analysis using APT are described through the characterisation of near-surface implantation profiles of low concentration phosphorus into single crystal silicon. This material system was chosen to illustrate this surface specific approach as low concentration phosphorus has significant mass spectra overlaps with silicon species and the near surface location requires particular attention to Focussed Ion Beam specimen preparation and deposition of various capping layers. Required changes to standard sample preparation procedure are described and the effects of changes in APT analysis parameters are discussed with regards to this specific material system. Implantation profiles of 14 kV phosphorus ions with a predicted peak concentration of 0.2 .at % were successfully analysed using APT using pulsed laser assisted evaporation. It is demonstrated that the most important factor in obtaining the most accurate implantation profile was to ensure all phosphorus mass peaks were as free of background noise as possible, with thermal tails from the Si 2+ ions obscuring the P 2+ ions being the major overlap in the mass spectrum. The false positive contribution to the phosphorus profiles from hydride species appears minimal at the capping layer/substrate interface. The initial capping layer selection of nickel was successful in allowing the analysis of the majority of the phosphorus profile but nickel and phosphorus mass spectra overlaps prevent optimum quantification of phosphorus at the surface.

Comparing the Consistency of Atom Probe Tomography Measurements of Small-Scale Segregation and Clustering Between the LEAP 3000 and LEAP 5000 Instruments

“…Ion implantation is a well understood industrial process commonly used in fabrication of integrated semiconductor electronics and the implantation and detection of single phosphorus ions within designated nanoscale volumes has already been demonstrated (Donkelaar et al, 2015). APT investigations of silicon implanted with 14 keV phosphorus ions with peak concentration of 0.2 at% have been carried out using the LEAP 3000 (Douglas et al, 2016) and LEAP 5000. An increase in detector efficiency could improve the ultimate detection limit of phosphorus in silicon for this application and allow more accurate characterization of low concentration diffusion and implantation profiles in general.…”

“…APT investigations of silicon implanted with 14 keV phosphorus ions with peak concentration of 0.2 at.% have been carried out using the LEAP 3000 (Douglas, 2016) and LEAP 5000. An increase in detector efficiency could improve the ultimate detection limit of phosphorus in silicon for this application and allow more accurate characterisation of low concentration diffusion and implantation profiles in general.…”

Atom Probe Tomography of Au–Cu Bimetallic Nanoparticles Synthesized by Inert Gas Condensation

“…The low-voltage cleaning was necessary to ensure minimal Ga + implantation in the final sample. 29 All samples were then analyzed in a Cameca LEAP 3000X-HR instrument. A pulsed laser mode (532 nm) was employed with beam energy varying from 0.05 to 0.3 nJ at a 100 kHz pulsing rate.…”

“…Details of the milling conditions are listed in Table . The low-voltage cleaning was necessary to ensure minimal Ga + implantation in the final sample . All samples were then analyzed in a Cameca LEAP 3000X-HR instrument.…”

Analytical challenges of determining composition and structure in small volumes with applications to semiconductor technology, nanostructures and solid state science

“…They present an analytic model to interpret the inaccuracy in the depth reconstruction of these devices. Douglas et al illustrate the challenges of surface analysis using atom probe tomography through the characterization of near-surface implantation profiles of low concentration phosphorus into single crystal silicon [11]. This system requires particular attention to specimen preparation using a focused ion beam and care during the deposition of various capping layers because phosphorus has significant mass spectra overlaps with silicon species and the near surface location.…”