RESIDUAL-STRESSES IN EVAPORATED SILICON DIOXIDE THIN-FILMS - CORRELATION WITH DEPOSITION PARAMETERS AND AGING BEHAVIOR

Silicon dioxide thin films have been prepared by electron-gun evaporation under various deposition conditions. The residual stresses in SiO2 films were determined by measurements of the radius of curvature of Si and Ge substrates. The composition and density of films were deduced from Rutherford backscattering spectroscopy and elastic recoil detection analyses. The films were found to be stoichiometric (Si/O=1/2) under the deposition conditions investigated. The compressive residual stresses in films deposited at the base pressure (2×10-5 mbar) varied from -20 to -550 MPa as the substrate temperature increased from 20 to 285°C. At a substrate temperature of 200°C, the residual stresses varied from +70 to -180 MPa with decreasing oxygen pressure in the deposition chamber. The contribution of three types of stresses, namely thermal, intrinsic, and water-induced stresses, can be distinguished. The stress component resulting from the absorption of water molecules in porous SiO2 films was obtained from variation of residual stresses caused by the changeover of samples from air to vacuum. The level of this stress component was dependent on the density of films. An evolution of residual stresses from compressive to tensile with time of sample storage in a conventional clean-room environment was measured for all evaporated SiO2 films investigated in this study. In addition, the hydrogen content in films increased progressively with increasing aging time in air. The kinetics of this stress evolution was considerably reduced when the films were stored in vacuum. The origin of residual stresses and the stress aging mechanism are discussed. © 1995 American Institute of Physics.