Epitaxial deposition of a silicon layer on a heavily doped silicon substrate

摘要

Limited doping of an epitaxial silicon layer by arsenic and phosphorus from a strongly doped monocrystalline silicon substrate includes a stage involving the deposition of a weak dose of germanium on the surface of the substrate, followed by a stage involving the desorption of arsenic or phosphorus atoms present on the surface of the substrate. Germanium is deposited in the gas phase in the presence of hydrogen. The germanium can be deposited in a first stage of epitaxial deposition of silicon by introducing a germanium gas composition into the epitaxial gas phase in order to form a germanium/silicon alloy. The first stage is carried out with a growth rate selected to allow desorption of surface arsenic or phosphorus atoms in parallel with the growth of silicon. The weak dose of germanium is deposited at around 1100 degrees C during an annealing stage preceding epitaxial deposition or, alternatively, during the first stage of epitaxial deposition of the silicon layer. The conditions and duration of the first stage of silicon epitaxial deposition and annealing are chosen such that the thin silicon layer forms a diffusion barrier against arsenic or phosphorus atoms in the additional silicon layer. Desorption of surface arsenic or phosphorus atoms from the substrate is carried out by sweeping the substrate surface with hydrogen gas. The hydrogen gas flow rate is increased at least during the period of exposure of germanium to hydrogen. Epitaxial deposition of the silicon layer can be carried out by deposition of a thin silicon layer, annealing and then deposition of another silicon layer to the required thickness. Deposition of silicon is carried out at around 1050 degrees C.