Unified model of hole trapping, 1/f noise, and thermally stimulated current in MOS devices

Capture cross-section data from the literature and recent density-functional theory (DFT) calculations strongly suggest that the 1/f noise of MOS devices is caused by the thermally activated capture and emission of carriers at O vacancy centers near the Si-SiO₂ interface. At least two kinds of defects can contribute to the noise of unirradiated and irradiated devices. The first is a "dimer" vacancy associated with the E_δ\´ center, which is shown by DFT to be a metastable electron trap when the Si-Si spacing is stretched beyond its equilibrium value, as likely can occur in strained SiO₂ near the Si-SiO₂ interface. The second is a neutral or positively charged Eγ\´ center, which has two configurations. One is puckered (one of the Si atoms relaxes through its local bonding plane) and forms a dipole after electron capture (E(γ⁴)\´). The other is shown via DFT to be a different kind of puckered configuration, including a fivefold coordinated Si (E(γ⁵)\´); this does not form a dipole. These results strongly suggest a common model of charge exchange with O vacancies can account for much of the oxide-trap charge and 1/f noise in MOS devices. Applying this model to thermally stimulated current (TSC) experiments suggests hole emission in TSC may well be due to the thermal relaxation of a puckered Eγ\´ into a dimer E_δ\´. This can explain literature discrepancies between optical and thermal estimates of trapped-hole energies.