Boron and phosphorus diffusion through an SiO2 layer from a doped polycrystalline Si source under various drive-in ambients

Abstract

The diffusion of boron and phosphorus into thermally grown SiO2 from a doped polycrystalline Si source has been found to be dependent on drive-in ambients and to be especially fast in an H2 ambient. Diffusion coefficients have been calculated by the two boundary diffusion model. It was found that the diffusion coefficient of boron in SiO2 is about two orders of magnitude larger than that of phosphorus. This fact is very important for Si gate processes. For P-channel Si gate transistors, boron diffused in the gate SiO2 film from the doped polycrystalline Si gate electrode causes new types of instabilities in transistor characteristics.