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

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⁻³_ox 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(−bE_ox) 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.