Densification of Chemical Vapor Deposition Silicon Dioxide Film Using Ozone Treatment

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Silicon dioxide (SiO2) films formed by chemical vapor deposition (CVD) have been treated with ozone (O3) or oxygen (O2) gas ambient at 450 °C. Density depth profiles of the SiO2 films were investigated using X-ray reflectivity analysis with synchrotron radiation. The density depth profile of the base CVD-SiO2 film without the O3 or O2 treatment is low (${\sim}2.03$ g/cm3) and constant. That of the CVD-SiO2 film with the O3 treatment is not constant. The O3-treated CVD-SiO2 film is composed of a middle-density top layer (${\sim}2.13$ g/cm3), a low-density center layer (${\sim}2.03$ g/cm3), and a high-density bottom layer (${\sim}2.24$ g/cm3). The density depth profile of the CVD-SiO2 film treated with O2 gas agrees with that of the base CVD-SiO2 film. The temperature or presence of O2 molecules during the O3 treatment at 450 °C does not affect the densification of the base CVD-SiO2 film. Therefore, the active species that densify the base CVD-SiO2 film during the O3 treatment are oxygen (O) radicals generated by the thermal decomposition of O3 molecules. The middle-density top layer near the SiO2 surface is formed by the reconstruction of a Si–O network with the oxidation of oxygen vacancies in the base CVD-SiO2 film with O radicals. The high-density bottom layer near the SiO2/Si interface is formed by the oxidation of the silicon substrate with O radicals that diffuse through the low-density base CVD-SiO2 film. The penetration length of O radicals in the base CVD-SiO2 film is very large because the thickness of the high-density bottom layer does not depend on the thickness of the base CVD-SiO2 film up to 16.8 nm at least. Therefore, this densification method for the CVD-SiO2 film with O3 treatment can be applied to the formation of either thin or thick SiO2 films.
2009-10-25

Densification of Chemical Vapor Deposition Silicon Dioxide Film Using Ozone Treatment

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