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

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• 作者：Thibault Alphazan ; Laurent Mathey ; Martin Schwarzwälder ; Tsung-Han Lin ; Aaron J. Rossini ; Raphaël Wischert ; Virginie Enyedi ; Hervé Fontaine ; Marc Veillerot ; Anne Lesage ; Lyndon Emsley ; Laurent Veyre ; François Martin ; Chloé Thieuleux ; Christophe Copéret
• 刊名：Chemistry of Materials
• 出版年：2016
• 出版时间：June 14, 2016
• 年：2016
• 卷：28
• 期：11
• 页码：3634-3640
• 全文大小：387K
• 年卷期：0
• ISSN：1520-5002

文摘

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.