Gas feeding molecular phosphorous ion source for semiconductor implanters.

Phosphorus is a much used dopant in semiconductor technology. Its vapors represent a rather stable tetratomic molecular compound and are produced from one of the most thermodynamically stable allotropic forms of phosphorus-red phosphorus. At vacuum heating temperatures ranging from 325 °C, red phosphorus evaporates solely as P4 molecules (P4/P2 ∼ 2 × 10(5), P4/P ∼ 10(21)). It is for this reason that red phosphorus is best suited as a source of polyatomic molecular ion beams. The paper reports on experimental research in the generation of polyatomic phosphorus ion beams with an alternative P vapor source for which a gaseous compound of phosphorus with hydrogen - phosphine - is used. The ion source is equipped with a specially designed dissociator in which phosphine heated to temperatures close to 700 °C decomposes into molecular hydrogen and phosphorus (P4) and then the reaction products are delivered through a vapor line to the discharge chamber. Experimental data are presented reflecting the influence of the discharge parameters and temperature of the dissociator heater on the mass-charge state of the ion beam.