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 co- efficient, orientation-dependent diffusion under oxidizing conditions, and re- tarded 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 non- oxidizing ambient. A donor-type vacancy is responsible which has a presumed energy level of --Ev + 0.37 eV as suggested from the quenching experiments of Elstner and Kamprath. High concentration (>2 X I019 cm -a) B diffusions into Si over a 550~ 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 dif- fusivity. From this result, useful curves of surface concentration vs. resistivity and junction depth are presented.