Densification of Chemical Vapor Deposition Silicon Dioxide Film Using Ozone Treatment

Abstract

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 (∼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 (∼2.13 g/cm3), a low-density center layer (∼2.03 g/cm3), and a high-density bottom layer (∼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.