Monolayer Doping of Silicon through Grafting a Tailored Molecular Phosphorus Precursor onto Oxide-Passivated Silicon Surfaces

• Published in: Chemistry of materials Vol. 28; no. 11; pp. 3634 - 3640
• Main Authors: Alphazan, Thibault, Mathey, Laurent, Schwarzwälder, Martin, Lin, Tsung-Han, Rossini, Aaron J, Wischert, Raphaël, Enyedi, Virginie, Fontaine, Hervé, Veillerot, Marc, Lesage, Anne, Emsley, Lyndon, Veyre, Laurent, Martin, François, Thieuleux, Chloé, Copéret, Christophe
• Format: Journal Article
• Language: English
• Published: American Chemical Society 14.06.2016
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.5b04291

Monolayer doping (MLD) of silicon substrates at the nanoscale is a powerful method to provide controlled doses of dopants and defect-free materials. However, this approach requires the deposition of a thick SiO2 cap layer to limit dopant evaporation during annealing. Here, we describe the controlled surface doping of thin oxide-passivated silicon wafers through a two-step process involving the grafting of a molecular phosphorus precursor containing a polyhedral oligomeric silsesquioxane (POSS) scaffold with silica-like architecture and thermal annealing. We show that the POSS scaffold favors the controlled formation of dopant-containing surface species with up to ∼8 × 1013 P atoms cm–2 and efficiently avoids phosphorus evaporation during annealing for temperatures up to 800 °C. Silicon doping is demonstrated, in particular, by grafting the POSS phosphorus triester on SiO2/Si wafers with optimized surface preparation (thin SiO2 layer of 0.7 nm) and annealing temperature (1000 °C), which provides phosphorus doses of ∼7 × 1012 P atoms cm–2 in the silicon substrates together with a decrease of their sheet resistance. A detailed study of the surface chemistry on SiO2 nanoparticles used as a high-surface-area model yields the grafting mechanism and the structure of the surface species. We show that the POSS scaffold is conserved upon grafting, that its size controls the final P-surface density, and that it behaves as a self-protecting ligand against phosphorus volatilization during the annealing step. We thus demonstrate that the use of custom-made dopant precursors with self-capping properties is a promising approach to tune medium to low doping doses in technologically relevant semiconductors.