Type of presentation: Poster

IT-17-P-2966 Crystallographic calibration of Si-based atom probe reconstructions for enhanced short-range ordering information.

Breen A. J.^{1, 2}, Ceguerra A. V.^{1, 2}, Araullo-Peters V. J.^{1, 2}, Moody M. P.³, Ringer S. P.^{1, 2}

¹Australian Centre for Microscopy and Microanalysis, The University of Sydney, NSW 2006, Australia, ²School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, NSW 2006, Australia, ³Department of materials, The University of Oxford, Parks Road, OX13PH, Oxford, UK

andrew.breen@sydney.edu.au

Atom probe tomography (APT) enables the position and chemical identity of millions of atoms to be reconstructed in 3D with sub-nm precision. However, the spatial resolution is still generally not high enough to unequivocally determine the lattice positioning of atoms in crystalline materials. This presents a significant roadblock in understanding structure-property relationships at the atomic level. An important example is the need to more accurately characterise the dopant positioning within the ultra-shallow junctions of the latest generation of transistor devices that are now usually only several nm deep. Subtle differences in dopant positioning can have significant influence on device performance and this must be controlled more accurately if continual size reductions are to occur.

In this study, we have developed methods to study the short-range ordering of dopants within silicon in unprecedented detail using APT. Latent crystallographic structure can be detected within the reconstructions with the help of newly developed crystallographic mapping tools. After doing this, it is apparent that the detected crystal structure is slightly different to the theoretical structure in size and shape, even after careful calibration using the method described by Gault et al. (Gault, et al., 2009). This is most likely due to assumptions used in the initial reconstruction algorithm. Further crystallographic calibration, using linear transformations of the reconstructed atom co-ordinates, is then used to perfectly restore the latent crystal structure. However, we have found that the spatial noise present is still high enough to be detrimental to the measured short-range ordering. Lattice rectification approaches (Moody, et al., 2011), where atoms are repositioned to the closest lattice site, are then used to restore this short-range order and the results are compared and discussed. This work provides a significant contribution to lattice based atom probe studies of doped silicon.

Gault, B., Moody, M.P., de Geuser, F., Tsafnat, G., La Fontaine, A., Stephenson, L.T., Haley, D. & Ringer, S.P. (2009). Advances in the calibration of atom probe tomographic reconstruction. Journal of Applied Physics 105(3).

Moody, M.P., Gault, B., Stephenson, L.T., Marceau, R.K.W., Powles, R.C., Ceguerra, A.V., Breen, A.J. & Ringer, S.P. (2011). Lattice Rectification in Atom Probe Tomography: Toward True Three-Dimensional Atomic Microscopy. Microscopy and Microanalysis 17(2), 226-239.

The authors acknowledge scientific and technical input from the AMMRF node at The University of Sydney, particularly Baptiste Gault, Leigh Stephensen, Takanori Sato and Julie Cairney. The authors are also grateful to the ARC for providing funding. We also thank the ANFF at the University of NSW, particularly Joanna Szymanska, for Bosch processing of Si wafers.

Fig. 1: The latent crystallographic information within a Sb doped Si reconstruction. (a) The tomographic atom probe reconstruction. A thin red slice has been cropped out for crystallographic analysis. (b) 2D density map of Si. (C) 1D spatial distribution maps (SDM) of detected planes within the reconstruction (d) 2D SDM of {001} planes.