Observation and electronic characterization of "new" E′ center defects in technologically relevant thermal SiO₂ on Si: An additional complexity in oxide charge trapping

Using electron-spin resonance (ESR), we demonstrate that several E' variant precursors exist in a variety of technologically significant thermally grown thin SiO₂ films on Si. The E' variants include two varieties with the ubiquitous E_γ^' line shape (zero-crossing g=2.0005, O3≡Si·) and a second very narrow line shape (zero-crossing g=2.0019, structure unknown). We tentatively label the g=2.0019 defect EP for provisional E' and distinguish the E_γ^' variants E_γn^' (neutral) and E_γp^' (positive). We combine ESR, capacitance versus voltage electrical measurements, and charge injection sequences to compare the electronic properties of the defects. We find that paramagnetic EP defects are positively charged while paramagnetic E_γ^' centers can be either positively charged or, under some circumstances, neutral. We find that EP precursors have a very large capture cross section for holes (σ=10^-13 cm ²) and that paramagnetic EP defects have an even larger capture cross section for electrons (σ=10^-12 cm²). Both EP capture cross sections are an order of magnitude greater than those of the E_γp^' defects. We find that EP centers are distributed much more broadly throughout the oxide than either the E _γp^' or E_γn^' defects. We also find a two order of magnitude variation in EP density dependent upon processing variations. In addition, EP centers, unlike the E _γ^' variations, are not stable at room temperature. With their large capture cross section for holes and even larger capture cross section for electrons, EP defects may be relevant to device reliability and charge trapping under conditions of a low, relatively pure hole fluence such as in hot hole injection in short n-channel metal-oxide-semiconductor field-effect transistors.