Diffusion of Metals in Silicon Dioxide

Abstract

The diffusion coefficient and solubilities of several metals (Ag, Cu, Au, Pd, and Ti) have been investigated by bias temperature stress (BTS) of (MOS) structures using the candidate metal as the electrode. Temperatures ranged from 250° to 600°C, and the electric fields ranged from +106 to −106 V/cm in ambients of vacuum (10−6 torr), nitrogen, and forming gas . In dry , the activation energy for silver diffusion is found to be 1.24 eV in the temperature range of 275°–365°C. The diffusion coefficient for silver at 300°C in silicon dioxide is . Copper diffusion has an activation energy of 1.82 eV in the temperature range of 350°–450°C in a forming gas environment and a diffusion coefficient in at 450°C of . A thermodynamic model to predict the activation energy of the solid solubility of these metals in and an interstitial diffusion model, that includes both strain and electrostatic energies, which predicts the diffusion activation energy, have been developed. Diffusion coefficients are estimated from a closed form solution of the diffusion equation and the observed behavior of the metal in .