The 4MeV Xe-ion bombardment of a thin thermally-grown film on a Si substrate led to 4 effects; each of which was reflected by a characteristic change in the mechanical stress state of the film. These changes were: a densification which was attributed to a beam-induced structural change in the silica network, a stress relaxation caused by bombardment-enhanced plastic flow, anisotropic expansion plus stress generation, and a transient stress relaxation which was attributed to the annealing out of point defects. By using sensitive wafer-curvature measurements, in situ measurements were made of the in-plane mechanical stresses were made during and after ion bombardment at 95 to 575K. It was found that the structural transformation led to a state with an equilibrium density that was 1.7 to 3.2% higher than that in the initial state; depending upon the bombardment temperature. Due to the constraints imposed by the substrate, this transformation caused a tensile in-plane stress in the oxide film which was relieved by plastic flow. This led to densification of the film. The anisotropic strain-generation rate decreased linearly with temperature. The spectrum of bombardment-induced point defects, as deduced from the stress changes following bombardment, peaked at below 0.23eV and extended up to 0.80eV. All 4 bombardment-induced effects could be explained by using a thermal spike model.

Origin of MeV Ion Irradiation-Induced Stress Changes in SiO2. M.L.Brongersma, E.Snoeks, T.Van Dillen, A.Polman: Journal of Applied Physics, 2000, 88[1], 59-64