Plasma-stimulated great reduction of diffusion activation energies for B, Al, and Ag in Si

Abstract

This work made an in-depth study on the transport of B, Al and Ag ions in an inductively coupled plasma-Si system. The plasma-stimulated impurity ion transport is demonstrated to be described by an implantation-diffusion two-step process rather than a pure diffusion process reported previously. The first step is impurity ion implantation under sheath voltage induced by plasma, which determines the impurity ion quantity into Si. The second step is plasma-stimulated impurity ion diffusion, which determines impurity ion transport depth in Si. An approximate solution to this implantation-diffusion process is deduced. Plasma-stimulated diffusion coefficients (D) for B, Al and Ag ions in Si are obtained by fitting the measured secondary ion mass spectroscopy concentration profiles with this equation. Furthermore, plasma-stimulated diffusion activation energies for B, Al and Ag ions in p-Si at 0-120 ºC are determined to be 0.22, 0.36 and 0.18 eV by Arrhenius plots, which are much lower than diffusion activation energies of 0.4-0.7, 1.2 and 1.15 eV for interstitial B, Al and Ag ions in Si without plasma reported in literatures. The great reduction of diffusion activation energy makes it possible for impurities to diffuse at room temperature or lower temperatures. The view of plasma-stimulated impurity ion transport is of significant importance on semiconductor technology and device degradation research.