Mechanical Stress-Induced Damage on Breakdown Characteristic of Dielectric Thin Films in MOS Transistors

Mechanical Stress-induced deterioration of the breakdown characteristic of SiO₂ films was discussed analytically and experimentally. The decrease in the band gap of the oxide due to the crystal deformation is the main reason for the deterioration. The change rate was analyzed by the first principles calculation. The mechanism of the stress development in a MOS transistor structure was clarified by stress measurement of thin films. The intrinsic stress of the thin films used for the gate electrode of the transistor is the important factor for determining the residual stress in the oxide under the electrode. The residual stress in the silicon substrate before the oxide (SiO₂) formation (surface oxidation of the substrate) is another important factor which affects the quality of the oxide film. In particular, the density of the unstable atomic bonding of silicon near the Si/SiO₂ interface varies depending on the stress in the substrate.