Effect of physical stress on the degradation of thin SiO/sub 2/ films under electrical stress

In this work, we demonstrate that for ultrathin MOS gate oxides, the reliability is closely related to the SiO/sub 2//Si interfacial physical stress for constant current gate injection (V/sub g//sup -/) in the Fowler-Nordheim tunneling regime. A physical stress-enhanced bond-breaking model is proposed to explain this. The oxide breakdown mechanism is very closely related to the Si-Si bond formation from the breakage of Si-O-Si bond, and that is influenced by the physical stress in the film. The interfacial stress is generated due to the volume expansion from Si to SiO/sub 2/ during the thermal oxidation, and it is a strong function of growth conditions, such as temperature, growth rate, and growth ambient. Higher temperatures, lower oxidation rates, and higher steam concentrations allow faster stress relaxation through viscous flow. Reduced disorder at the interface results in better reliability. Fourier transform infrared spectroscopy (FTIR) technique has been used to characterize stress in thin oxide films grown by both furnace and rapid thermal process (RTP). In conjunction with the Gibbs free energy theory, this model successfully predicts the trends of time-to-breakdown (t/sub bd/) as a function of oxide thickness and growth conditions. The trends of predicted t/sub bd/ values agree well with the experimental data from the electrical measurement.

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