Phosphorus out-diffusion during high temperature anneal of phosphorus-doped polycrystalline silicon and SiO2

Loss of phosphorus by evaporation, from doped polysilicon and SiO2 films, due to high temperature anneals has been investigated by use of neutron activation analysis technique. It is found that large amounts of phosphorus, as much as 99%, are lost from polysilicon films during inert ambient anneals. The loss is dependent on the temperature and time of anneal and on the initial phosphorus concentration. There is no loss in oxidizing ambients. For P-glass films phosphorus is lost only from the top layers of the film. The top layer, when free of phosphorus, acts as diffusion barrier for further loss from underlying P glass. Also the maximum loss from P glass is ambient dependent, being ∼10% in oxygen, 20% in argon, and over 35% in steam. Mathematical modeling of the phosphorus out-diffusion from polysilicon and P-glass films is discussed.