Paper AM+MP+NS-WeA8
Atomically Precise Tip Positioning for Automated Writing of Atomic-scale Devices

Wednesday, October 24, 2018, 4:40 pm, Room 102B

Hydrogen depassivation lithography has enabled unprecedented sub-nanometer precision in the positioning of dopant atoms in silicon,[1] advancing the field of silicon quantum electronics. It has also been used for localised atomic layer deposition of Si [2] and TiO₂[3].

In pursuit of our overall vision of Atomically Precise Manufacturing, we are pursuing a number of tactics towards automated fabrication of atomically precise structures. STM lithography vectors are automatically aligned to the surface atomic lattice, and patterns can be input as geometric shapes or arbitrary bitmaps. To improve tip position precision, we have developed real-time creep and hysteresis error correction. Using this, we have previously demonstrated open-loop atomic precision patterning over length scales up to 100 nm. Above this scale, where hysteresis errors are more significant, we are able to reduce the position errors by ~90%.

In parallel with real-time position corrections, we have developed automatic fiducial alignment routines. The tip position can either be aligned to previously-drawn patterns or to deliberate fiducial marks. A large pattern can therefore be stitched together from write fields within which atomic precision can be obtained. Thus, precise patterning can be scaled to large areas.

In the burgeoning field of Quantum Metamaterials[4], large arrays of single dopant atoms are required, with extreme position precision and very high yield. However, the yield of the current thermal process for P limits the yield to 70%[5].

Based on recent work on removal of H from surface PH₂ species[6], we are developing a tip-assisted incorporation process, which prevents the recombination and desorption process. For this application, we need to write single-dimer patterns to adsorb only one PH₃ molecule. For these small patterns, Automated Feedback Controlled Lithography is used, so as to remove exactly the required H atoms from the surface. We are working to improve the detection of the H atom removal, using not only the spike in tunnel current but also the change in the local barrier height [7].

1. M. Fuechsle, et al. Nat Nano 7 242-246 (2012) DOI:: 10.1038/nnano.2012.21

2. J. H. G. Owen et al., J. Vac. Sci. Technol. B 29, 06F201 (2011).

3. J. B. Ballard, J. H. G. Owen, et al. J. Vac. Sci. Technol. B, 32, 41804 (2014).

4. J. Salfi, et al. Nat. Commun., 7, 11342, (2016).

5. J. G. Keizer, S. Koelling, P. M. Koenraad, and M. Y. Simmons ACS Nano9 12537-12541 (2015)

6. Q. Liu, Y. Lei, X. Shao, F. Ming, H. Xu, K. Wang, and X. Xiao, Nanotechnology, 27(13), 135704, (2016).

7. F. Tajaddodianfar, S. O. R. Moheimani, J. Owen, and J. N. Randall, Rev. Sci. Instrum., 89(1), 13701, (2018)