The ellipsometric measurement of refractive indexes for films less than 50 nm thick is of dubious quality due to the significance of the size of random errors relative to the accuracy required to extract reliable index values from the measurements. In this study the various errors are quantitatively assessed as a function of the film thickness, and then compared with experimental data obtained from differently prepared silicon dioxide films on silicon. The new results confirm previous work that shows higher refractive indexes for thinner films. Transmission electron microscopy confirms the results. Graded and discrete layer models are compared.

Implantation of Si in does of 1015–1016 cm−2 into dry thermal oxides on silicon wafers produces a three-state MOS memory device. For both positive- and negative-going traps, gate voltage stress up to ±10 MV/cm−1 generates stable (±) oxide charge near the gate and (∓) charge near the substrate. Electron paramagnetic resonance (EPR) measurement on corona-field (≤11 MV/cm) stressed oxides reveals E′ centers in regions of positive charge, which may be recycled between the EPR-visible (+) state and the invisible neutral state. The correspondence of charge and EPR indicates a composite or Feigl-Fowloer-Yip E′ center, O3 3/4 Si:...+Si 3/4 O3, arising from nonstoichiometric Si fused into the SiO2 lattice. Upon trapping an electron, the center rebonds to yield O3 3/4 SiSi 3/4 O3. The charging parameters of the E′ center suggest tunneling of an electron from the (0→+) state, and are consistent with the theoretical prediction of the energy level and Franck–Condon relaxation. The three types of E′ centers observed in this and related studies are compared with the E′α, Eβ and E′γ variants of bulk amorphous silica.

Single wavelength ellipsometry, although used extensively in the microelectronics field for the measurement of film thicknesses and refractive indexes, does not usually yield reliable refractive indexes for dielectric films less than 50 nm thick due to instrumental errors and software limitations. Addressing this issue, we employ previously developed ellipsometric procedures that enable a reliable assessment of refractive index profiles for a variety of thermally grown and chemically vapor deposited (CVD) dielectric films on Si substrates down to about 10 nm thickness, and we compare the results in terms of the current understanding about the film‐substrate interface. In all cases studied we find that the interfacial region is optically different than the bulk film and that the precise film processing can substantively alter the nature of the interface region.