Periodic Arrays of Dopants in Silicon by Ultralow Energy Implantation of Phosphorus Ions through a Block Copolymer Thin Film

In this work, block copolymer lithography and ultralowenergy ionimplantation are combined to obtain nanovolumes with high concentrationsof phosphorus atoms periodically disposed over a macroscopic areain a p-type silicon substrate. The high dose of implanted dopantsgrants a local amorphization of the silicon substrate. In this condition,phosphorus is activated by solid phase epitaxial regrowth (SPER) ofthe implanted region with a relatively low temperature thermal treatmentpreventing diffusion of phosphorus atoms and preserving their spatiallocalization. Surface morphology of the sample (AFM, SEM), crystallinityof the silicon substrate (UV Raman), and position of the phosphorusatoms (STEM- EDX, ToF-SIMS) are monitored during the process. Electrostaticpotential (KPFM) and the conductivity (C-AFM) maps of the sample surfaceupon dopant activation are compatible with simulated I-V characteristics, suggesting the presenceof an array of not ideal but working p-n nanojunctions. Theproposed approach paves the way for further investigations on thepossibility to modulate the dopant distribution within a silicon substrateat the nanoscale by changing the characteristic dimension of the self-assembledBCP film.