Residual stress in thin silicon dioxide films has been studied as a function of storage time. Films of varying microstructure and impurity content were deposited by plasma-enhanced chemical vapor deposition. Initially, all the films exhibited compressive stress, the magnitude of which was found to increase rapidly with time for the first few hours after deposition. For all the deposited thin films, this increasing compressive stress eventually saturates and then begins to decrease with time. The time at which the transition occurs depends on film thickness and quality, whereas, for relatively thicker films deposited under identical conditions, a saturation in compressive stress after long aging time was observed. No existing model of thin oxide films successfully explains the observed time variation of stress. In this paper, the variation of film stress as a function of storage time and film properties, such as porosity and impurity content, is discussed. Three driving forces, namely, surface reactivity, silanol buildup, and water dipole interaction, each of whose contribution varies depending on film thickness and quality, have been identified as potential mechanisms behind stress change in oxide films. A unified model consisting of these driving forces can explain the time variation of stress behavior in oxide films, irrespective of film quality and thickness. ©1997 American Institute of Physics.