Generation and loss of hydrogen-boron pairs in fired silicon wafers

Abstract

A dark anneal of fired B-doped samples is known to generate HB pairs which is followed by a loss of HB upon a prolonged anneal. In this paper, the reported data on the evolution of the total concentration of free and trapped ions, C = [H+] + [HB] (with a dominant contribution of HB) are used to extract the model parameters α (the dissociation coefficient of quenched-in hydrogen dimers, H2A), χ (the constant relating [H2A] and [HB] under equilibrium), β (the kinetic coefficient for the production of stable dimers, H2C). A loss of HB can be caused also by hydrogen out-diffusion; the computed diffusion-limited loss, surprisingly, is well faster than the observed loss. The reasons for this discrepancy are discussed. One possibility is that the hydrogen is trapped by boron initially into a metastable state with subsequent transformation into a stable state, of a lower effective diffusivity. This concept is supported by a peculiar evolution of [HB] observed under room-temperature illumination.