Elastic and plastic relaxation of densified SiO2 films

Ion- and plasma-assisted deposition has been extensively used for the fabrication of high-performance optical films with dense and smooth microstructures that are essential for applications such as low-loss and environmentally stable optics. SiO(2) is a well-known amorphous material suitable for energetic deposition. SiO(2) single layers and SiO(2)-based single-cavity narrow-bandpass filters were prepared by plasma-ion-assisted deposition. The refractive index and film thickness were determined by variable-angle spectroscopic ellipsometry. The high compressive stress of the densified film was correlated to increased packing density. The center wavelength shift of the narrow-bandpass filters as a function of sample-temperature as well as high-temperature annealing was determined via spectral transmission measurement. Structural relaxation of the densified SiO(2) films was observed from the variation of the refractive index and physical thickness for the single layers and the center wavelength shift for the narrow-bandpass filters, suggesting elastic and plastic deformation of the densified films corresponding to a reversible and an irreversible center wavelength shift, respectively.