DEGRADATION OF DIELECTRIC-BREAKDOWN FIELD OF THERMAL SIO2-FILMS DUE TO STRUCTURAL DEFECTS IN CZOCHRALSKI SILICON SUBSTRATES

We used heat treatment to intentionally introduce various structural d efects in Czochralski silicon substrates. The type, size, and number d ensity of the induced defects were surveyed with transmission electron microscopy, and the defects were then incorporated into SiO2 films (1 0-50 nm thick) during thermal oxidation in dry O-2. The effect of the defects on dielectric strength of the SiO2 films was-examined with a t ime zero dielectric breakdown method. Larger platelet oxygen precipita tes caused greater decreases of the breakdown field, and precipitates smaller than the SiO2 film thickness did not appreciably reduce the br eakdown field. Every large platelet oxygen precipitate incorporated in the SiO2 film caused a degradation. Octahedral oxygen precipitates ca used little degradation. The breakdown field was higher than 7 MV/cm a nd did not depend much on the SiO2 film thickness and precipitate size . We discussed possible mechanisms for the degradation due to both kin ds of precipitates. Oxidation-induced stacking faults formed by a surf ace oxidation did not markedly reduce the breakdown field when only se gments of dislocations and stacking faults were incorporated in the Si O2 film. Another serious degradation was caused by pits that were form ed by dissolving octahedral oxygen precipitates in a HF solution. The breakdown field was lower for thicker oxide films, and it recovered as the pit shape became smoother during chemical etching. We proposed th at this degradation was caused by a local thinning of SiO2 film due to stress generated in the oxidation of pits. These results suggest that voids rather than the other reported grown-in defects play the most i mportant role in the degradation observed for as-grown silicon. (C) 19 96 American Institute of Physics.