Boron Diffusion in Silicon‐Concentration and Orientation Dependence, Background Effects, and Profile Estimation

Abstract

Boron is almost universally used as a p‐type dopant in Si devices. Since this dopant is introduced into the Si lattice under a wide range of diffusion conditions, effects are often observed which appear anomalous because the mechanism of B diffusion is not completely understood. Anomalous effects that have been observed include a concentration‐dependent diffusion coefficient, orientation‐dependent diffusion under oxidizing conditions, and retarded or accelerated diffusion in the presence of n‐type impurities. This paper discusses a model of B diffusion which can be used to explain these observed effects. Data and arguments are presented which show that B diffuses via a monovacancy mechanism when the diffusion is performed in a nonoxidizing ambient. A donor‐type vacancy is responsible which has a presumed energy level of as suggested from the quenching experiments of Elstner and Kamprath. High concentration B diffusions into Si over a 550°C temperature range in neutral ambients result in profile data that fit a normalized universal curve which is a polynomial approximation to the solution of the diffusion equation with concentration‐dependent diffusivity. From this result, useful curves of surface concentration vs. resistivity and junction depth are presented.