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

Abstract

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 Eγ′ 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 Eγ′ variants Eγn′ (neutral) and Eγp′ (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 Eγ′ 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 cm2) 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 Eγp′ defects. We find that EP centers are distributed much more broadly throughout the oxide than either the Eγp′ or Eγn′ defects. We also find a two order of magnitude variation in EP density dependent upon processing variations. In addition, EP centers, unlike the Eγ′ 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.