Effects of substrate materials and deposition parameters on film stress

An on-line thin film stress measuring system based on Hartmann-Shack sensor technique is introduced to measure the film stress of SiO₂, TiO₂, Ta₂O₅, Al₂O₃ and ITO films at different thickness which are prepared by ion assisted deposition, and the effects of substrate materials and preparation parameters on the stresses of SiO₂ and TiO₂ are investigated in details. The results show that the film stress as a function of the film thickness is linear in the initial stage of coating, and the film stress tends to be a stable value when the film thickness reaches a certain value. The thermal stress which resulted from the different coefficients of thermal between substrates and thin films can be diminished by choosing suitable substrates. In terms of TiO₂ films, the thermal stress plays a major role when the substrate temperature is below 150°C, but the compressive stress which resulted from the dense structure of films is dominant while the substrate temperature is above 150°C. However, the thermal stress in SiO₂ films is always dominant at different deposition temperatures. The tensile stress in SiO₂ films is mainly caused by the effects of ion assisted sputtering when the chamber pressure is below 1.7×10^-2 Pa, and the tensile stress in SiO₂ films increases with the vacuum chamber's pressure increasing when it is above 1.7×10^-2 Pa, but the refractive index decreases.