No abstract

The field‐assisted transport of sodium ions through phosphosilicate normalglass‐SiO2 composite films on silicon substrates has been investigated. The effects of P2O5 concentration (in the 0 to 8 mole per cent [m/o] range), sodium contamination level (between 1011 and 1015 Na+ ions/cm2), field, temperature, and time have been quantitatively determined. For a limited quantity of transported sodium, this quantity is approximately proportional to the square root of biasing time; exponentially dependent on temperature and field, increases linearly with the initial sodium contamination level; and decreases drastically with increasing P2O5 concentration. For example, seven more orders of magnitude of time are required to drift a given number of Na+ ions through a PSGfalse(3.5%P2O5−125Aåfalse)/2025Aå SiO2 composite layer than through a 2150Aå thick layer of pure, thermally grown SiO2 . The results are consistent with a model based on the emission of Na+ ions from traps in the phosphosilicate layer. It was concluded that phosphosilicate glass films, having negligible intrinsic polarizability, can be used to effectively stabilize IGFET threshold voltages against changes (0.1V in 10 yr at 80°C under a field of 2×106V/normalcm ) due to the presence of large amounts of sodium.

not Available.

The hysteresis observed in capacitance-voltage (C-V) measurements on metal-sputtered silicon nitride—silicon structures indicates that carriers are injected predominantly as holes rather than electrons. Shifts in the C-V characteristic after bias-temperature stress at 300°C support this finding. In dc conduction measurements on these samples a linear relation was found between the logarithm of current and the square root of field. The slope of this plot and the independence of current on bias polarity indicate a bulk-limited conduction mechanism of emission of carriers from traps in the silicon nitride.

High conductivity observed in oxides grown on polycrystalline silicon has been previously speculated as being due to asperities on the silicon surface, which enhance the oxide field. Direct evidence of these asperities is shown here in SEM micrographs. The presence of the asperities is strongly correlated with the oxide conductivity (as controlled by the oxidation temperature).