Continuous Growth of Low‐Temperature Si Epitaxial Layer with Heavy Phosphorus and Boron Doping Using Photoepitaxy

Abstract

We grew p+‐n+ silicon epitaxial layers, heavily doped with phosphorus and boron, continuously at 650°C using low‐temperature photoepitaxy. The n+ photoepitaxial layer with a phosphorus concentration above 1017 cm−3 grown on p− substrate shows high‐density surface pits, and as a result, poor crystal quality. However, when this n+ photoepitaxial layer is grown continuously on a heavily boron‐doped p+ photoepitaxial layer, these surface pits are drastically decreased, disappearing completely above a hole concentration of 1019 cm−3 in the p+ photoepitaxial layer. The phosphorus activation ratio and electron Hall mobility in the heavily phosphorus‐doped n+ photoepitaxial layer were also greatly improved. We investigated the cause of the surface pitting using a scanning transmission electron microscope, secondary ion mass spectroscopy, and energy‐dispersive x‐ray spectroscopy. We thus characterized the precipitation of phosphorus atoms on the crystal surface at the initial stage of the heavily phosphorus‐doped n+ photoepitaxial layer growth. Continuous p+‐n+ growth prevented phosphorus atoms from being precipitated. Using these p+‐n+ layers, we made p+‐n+ junction diodes and bipolar devices with superior electrical characteristics. The very low growth temperature enabled us to obtain extremely abrupt impurity profiles of boron and phosphorus.