We present new calculations of electron inelastic mean free paths (IMFPs) for 200–2000 eV electrons in 27 elements (C, Mg, Al, Si, Ti, V, Cr, Fe, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt, Au and Bi) and four compounds (LiF, SiO2, ZnS and Al2O3). These calculations are based on an algorithm due to Penn which makes use of experimental optical data (to represent the dependence of the inelastic scattering probability on energy loss) and the theoretical Lindhard dielectric function (to represent the dependence of the scattering probability on momentum transfer). Our calculated IMFPs were fitted to the Bethe equation for inelastic electron scattering in matter; the two parameters in the Bethe equation were then empirically related to several material constants. The resulting general IMFP formula is believed to be useful for predicting the IMFP dependence on electron energy for a given material and the material-dependence for a given energy. The new formula also appears to be a reasonable but more approximate guide to electron attenuation lengths.

Calculations of electron inelastic mean free paths for 31 materials

High resolution Si 2p photoelectron spectra obtained with synchrotron radiation are used to determine the distribution of oxidation states in the intermediary layer at the SiO2‐Si interface. A ratio of 0.4:0.3:0.3 is found for the Si3+:Si2+:Si1+ intensities independent of Si surface orientation and oxide thickness. The interface is not completely abrupt (5±1 A width).

Probing the transition layer at the SiO2‐Si interface using core level photoemission

Chemical and electronic structure of the SiO2/Si interface

The bonding of Si atoms at the SiO2/Si interface is determined via high-resolution core level spectroscopy with synchrotron radiation. For oxides grown in pure O2, the SiO2/Si interface is found to contain Si atoms in intermediate oxidation states with a density of 1.5 ± 0.5 × 1015 cm−2. From the density and distribution of intermediate oxidation states, models of the interface structure are obtained. The interface is not abrupt, as evidenced by the non-ideal distribution of intermediate oxidation states and their high density (about 2 monolayers of Si). The finite width of the interface is explained by the bond density mismatch between SiO2 and Si. Annealing in H2 is found to influence the electrical parameters by removing the Pb centers that pin the Fermi level. The distribution of intermediate oxidation states is not affected.

Microscopic structure of the SiO2/Si interface.

ESCA (electron spectroscopy for chemical analysis) measurement results on thin SiO2/Si samples are examined comprehensively, critically, and in detail to show that it is possible to correlate these results with MOS (metal–oxide–semiconductor) device characteristics such as flatband (threshold) voltage, oxide breakdown field, mobile‐ion density, hole and electron trap density, and hot‐carrier lifetime. Up to now, much effort has been made to detect SiOx phases at SiO2/Si interfaces since they are thought to have a significant effect on MOS device characteristics. However, correlating the SiOx phases with device characteristics is difficult and involves overcoming two problems. First, the chemical state is difficult to determine exactly due to x‐ray irradiation effects. Second, the amount of defects and impurities which influence device characteristics is usually below the ESCA detection limit (1012–1013 cm−2) in device‐quality SiO2/Si samples. Investigation of the first problem led to the conclusion that i...

Electron spectroscopic analysis of the SiO2/Si system and correlation with metal–oxide–semiconductor device characteristics

The distributions of intermediate oxides (SiOx, 0<x<2) in ultrathin oxide films formed on (100), (111), and (110) surfaces were investigated by using the nondestructive measurements of Si 2p photoelectron spectra. The experimental observations can be understood as follows: (1) the abrupt interfaces are formed for three crystal orientations; (2) the interface formed at 1000 °C on (100), (111), and (110) surface consists mainly of SiO, Si2O, and the mixture of SiO and Si2O, respectively; (3) Si2O3 is distributed in the oxide films for three crystal orientations.

Si-SiO2 interface structures on Si(100), (111), and (110) surfaces

The Si-SiO2 interface structures of thermally grown oxide films on (100) surfaces were studied using three types of depth profiling measurement. Analysis of these measurements confirms the interface structures determined previously by nondestructive depth profiling.1) The appicability of chemical depth profiling to the study of interface structures was also studied. A new method of spectral analysis, used successfully in the present measurements, is presented.

Depth Profiling of Si–SiO 2 Interface Structures

The effect of argon ion bombardment on a silicon oxide film prepared on a Si(111) surface by dry oxidation was investigated by measuring partial yield spectra in addition to the oxygen induced Si 2p core level shift. The experimental observations can be understood such that the SiO2 network is decomposed at the initial stage of argon ion bombardment. In the following stage of bombardment, the silicon oxide films are sputter etched resulting in a decrease in the oxide film thickness.

Initial stage of sputtering in silicon oxide

Based on the observation of crystal orientation dependence of Si 2p photoelectron spectra, the orientation dependence of interface structures and the distribution of intermediate oxidation states of Si in the oxide film were determined. The effects of oxidation condition on the structures of interfacial transition layer and SiO2 were found.

Dependence of Si‐SiO2 interface structures on crystal orientation and oxidation conditions

The Si-SiO2 interface structures are shown to depend on crystal orientations from the destructive and nondestructive measurements of Si 2p photoelectron spectra. The intermediate oxides, Si2O3,which corresponds to Si-Si bonds, are found to be distributed in the oxide films for three orientations.

Toshihisa Suzuki

Papers

Si-SiO2 interface structures on Si(100), (111), and (110) surfaces

Depth Profiling of Si–SiO 2 Interface Structures

Initial stage of sputtering in silicon oxide

Dependence of Si‐SiO2 interface structures on crystal orientation and oxidation conditions

Si-SiO2 Interface Structures on (100), (110), and (111) Surfaces