Controlled deterministic implantation by nanostencil lithography at the limit of ion-aperture straggling

Abstract

Solid state electronic devices fabricated in silicon employ many ion implantation steps in their fabrication. In nanoscale devices deterministic implants of dopant atoms with high spatial precision will be needed to overcome problems with statistical variations in device characteristics and to open new functionalities based on controlled quantum states of single atoms. However, to deterministically place a dopant atom with the required precision is a significant technological challenge. Here we address this challenge with a strategy based on stepped nanostencil lithography for the construction of arrays of single implanted atoms. We address the limit on spatial precision imposed by ion straggling in the nanostencil-fabricated with the readily available focused ion beam milling technique followed by Pt deposition. Two nanostencils have been fabricated; a 60 nm wide aperture in a 3 μm thick Si cantilever and a 30 nm wide aperture in a 200 nm thick Si3N4 membrane. The 30 nm wide aperture demonstrates the fabricating process for sub-50 nm apertures while the 60 nm aperture was characterized with 500 keV He(+) ion forward scattering to measure the effect of ion straggling in the collimator and deduce a model for its internal structure using the GEANT4 ion transport code. This model is then applied to simulate collimation of a 14 keV P(+) ion beam in a 200 nm thick Si3N4 membrane nanostencil suitable for the implantation of donors in silicon. We simulate collimating apertures with widths in the range of 10-50 nm because we expect the onset of J-coupling in a device with 30 nm donor spacing. We find that straggling in the nanostencil produces mis-located implanted ions with a probability between 0.001 and 0.08 depending on the internal collimator profile and the alignment with the beam direction. This result is favourable for the rapid prototyping of a proof-of-principle device containing multiple deterministically implanted dopants.

Dynamics of a single-atom electron pump

“…This is in agreement with what has been recently observed experimentally by several groups617 and observed in the experiment presented here, and could be further investigated by high-precision measurements on single-atom electron pumps to determine the effect of the relaxation rate on the pumping accuracy. The model allows to benchmark against the position of the atom in the channel of the silicon transistor and shows that the single-atom pumps performances are unaffected by displacements of the atom up to a few tens of nm, which are at reach of the precision achieved by the current atom placement technologies42. Lastly, the accuracy of these pumps could be enhanced by working with more effective pulse shapes and by increasing the relaxation rate to the ground state of the atom, making single-atom electron pumps an even more attractive alternative to dynamical quantum dot charge pumps.…”

Alternatives for Doping in Nanoscale Field‐Effect Transistors

“…If doping in the channel was completely avoided or if alternatively a junctionless transistors (with the same dopant concentration in source/drain and channel) was considered, the low total number of dopants in the source/drain extensions (and channel, in the case of a junctionless devices) results in variability . Therefore, a great deal of research work has been devoted to the realization of deterministic single ion implantation with low energies. If this is combined with a flash lamp anneal for dopant activation a deterministic distributions of dopants would become feasible.…”

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

“…As the planar straggle [22] of the implantation of the 14 kV phosphorus ions is over two orders of magnitude greater than the diameter of the flat top micro post, the implantation into the top of the post should be analogous to a larger, planar surface apart from those regions immediately adjacent to the post edge. Therefore this approach is likely suitable for APT analysis of low energy implants where the implantation profile peak is within a typical APT analysis depth of a few hundred nm.…”