Variation of Chemical Vapor Deposited SiO2 Density Due to Generation and Shrinkage of Open Space During Thermal Annealing

Abstract

Chemical vapor deposited (CVD) SiO2 using tetraethoxysilane has a low density compared with thermally grown SiO2, and the as-deposited film contains impurities. In addition, compressive stress exists in the Si–O–Si network. In this work, CVD SiO2 films annealed with various thermal budgets were evaluated using ellipsometry. Positron annihilation spectroscopy indicated that the desorption of residual impurities by thermal annealing generates open spaces in the films. Subsequent annealing shrinks the open spaces and relaxes the compressive stress with reconstruction of the Si–O–Si network. Consequently, the refractive index of CVD SiO2 shows turn-around characteristics with increasing annealing temperature.