Anomalous stress in thermal oxide of polycrystalline Si

Abstract
The thermal oxide of polycrystalline Si (poly‐Si oxide) is found to be under a compressive stress two or more times larger than the stress in the thermal oxide of single‐crystalline Si (single‐Si oxide). The stress in poly‐Si oxide depends largely on poly‐Si growth temperature, oxidation temperature, and oxide thickness, especially for oxides less than 200 nm thick. The surface valleys formed at poly‐Si grain boundaries relate to this phenomena. The behavior of stress variations with oxide thickness is not substantially affected by oxidation temperature. The temperature dependence (room temperature to 800 °C) of stress in poly‐Si oxide is similar to that in single‐Si oxide. Consequently, the large stress generation in poly‐Si oxide is not due to oxide characteristics but to poly‐Si surface morphological conditions.

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