Electron trapping in SiO2 due to electron-beam deposition of aluminum

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Abstract
Electron trapping in the SiO2 layer of n‐channel polycrystalline silicon‐SiO2‐silicon field‐effect transistors with electron‐beam‐evaporated aluminum was studied. The increased electron trapping was attributed to the x rays generated when the electron beam impinged on the aluminum target. Traps with low‐field capture cross sections greater than 10−13 cm2 are associated with the x‐ray‐induced positively charged centers, while traps with low‐field capture cross sections of about 1×10−15 cm2 are associated with the x‐ray‐induced neutral centers. For the silicon‐gate devices, both traps could be effectively reduced by annealing in dry forming gas at 550 °C for 20 min. As reported earlier, the capture cross section of the positively charged traps has a strong field dependence of approximately E−3ox and is approximately independent of temperature. The field dependence of the capture cross section of the neutral traps is much weaker, with roughly a σ =σ0 exp(−bEox) dependence, where σ0=1.6×10−15 cm2 and b=7.35×10−7 cm/V. A possible origin of these neutral traps is displaced bonds forming polarization potential wells.