Effect of O2 gas partial pressure on mechanical properties of SiO2 films deposited by radio frequency magnetron sputtering

The effect of O2 partial pressure on the mechanical properties of SiO2 films deposited by rf magnetron sputtering is studied. The sputtering rate of SiO2 in argon gas with added O2 gas is lower than that in pure argon gas, whereas the rate is independent of O2 partial pressure. The internal stresses in films are compressive, and the magnitude decreases from 0.8 GPa for films sputtered in pure argon gas to 0.4 GPa for films sputtered in argon gas with O2 gas partial pressure above 9×10−3 Pa. Although the internal stress decreases with increasing O2 partial pressure, the magnitudes of hardness and adhesion increase conversely. X-ray diffraction measurements indicate that the crystal structure of sputtered SiO2 films is amorphous at all O2 partial pressures investigated. The argon content in the film obtained from an electron probe microanalyzer decreases with increasing O2 partial pressure. An atomic force microscopy observation reveals that the surface topography of sputtered SiO2 films show a turnover from needle structure to a spherical structure, and the fracture section varies from columnar to no discernible features as O2 partial pressure is increased.