Sub-2 nm boron doping in silicon using novel ultra-thin SiO2 film produced by sol–gel dip coating as a capping layer

Abstract

Advancements in semiconductor electronics and sensor technologies demand a more robust doping approach and process to fabricate ultra-shallow doping with abrupt depth, particularly on complex structured surfaces. Molecular monolayer doping (MLD) is a potential approach, but is limited by the difficulty in depositing a high-quality SiO2 capping film without damaging the dopant molecular layer. In this work, a relative humidity condition during deposition of the film in the sol–gel dip-coating process is found to produce continuous, dense and stoichiometric ultra-thin SiO2 films of quality equivalent to that produced by complicated thermal oxidation/etching and sophisticated chemical vapor deposition and atomic layer deposition methods. Applying these ultra-thin SiO2 films as capping layers in the molecular MLD method, B doping in Si with sub-2 nm effective depth and sub-5 nm abrupt depth is achieved. Remarkably, around 82%–86% of doped B atoms in Si are found to be electrically active as estimated from sheet resistance measurements. The established sol–gel dip coating conditions to deposit ultra-thin SiO2 films are generic and can be extended to produce high-quality ultra-thin films of other metal oxide materials required for advanced technological applications.