The diffusion coefficient and solubilities of several metals (Ag, Cu, Au, Pd, and Ti) have been investigated by bias temperature stress (BTS) of normalmetal/SiO2/normalSi (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 false(N2false) , and forming gas false(N2H2false) . In dry N2 false(<3 normalppm H2Ofalse) , 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 4.5×10−13 cm2/normals . Copper diffusion has an activation energy of 1.82 eV in the temperature range of 350°–450°C in a forming gas environment false(<3 normalppm H2Ofalse) and a diffusion coefficient in SiO2 at 450°C of 1.2×10−11 cm2/normals . A thermodynamic model to predict the activation energy of the solid solubility of these metals in SiO2 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 SiO2 .

Fast electric field aided diffusion of silver in SiO2 has been observed for fields of 104 V/cm and temperatures as low as 275 °C. The diffusion coefficient of silver in SiO2 is estimated to be 10−13 cm2/s at 300 °C, with an activation energy of 1.24 eV. The consequences of Ag contamination in very large scale integrated metallization systems are discussed.

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