A simple two-step phosphorus doping process for shallow junctions by applying a controlled adsorption and a diffusion in an oxidising ambient

A simple phosphorus doping technique for shallow junctions is presented. The low pressure doping process was carried out in a single RTP reactor chamber by using a two-step process: a controlled adsorption of phosphorus on the silicon surface and a rapid thermal diffusion in an oxidising ambient without the deposition of an oxide capping layer. A low concentration of 50 vpm phosphine diluted in hydrogen allowed a sufficient phosphorus supply while the deposition of phosphorus on the reactor walls was insignificant. The phosphine decomposed on the clean silicon surface at a temperature of 550 °C, at which the silicon surface is saturated by the adsorbed phosphorus. The shallow junctions were defined by successive rapid thermal annealing at temperatures above the adsorption temperature. An oxygen pressure of 4.2 × 103 Pa during the annealing prevented the phosphorus from desorption. Therefore, a deposition of an additional oxide-capping layer was not necessary, allowing more simple processing. This doping method provides shallow junctions of depths below 100 nm with sheet resistances below 1000 Ω/sq.