Densification, anisotropic deformation, and plastic flow of SiO2 during MeV heavy ion irradiation

The response of SiO₂ thin films and implantation masks to 4.0 MeV Xe irradiation is studied. Trenches in silica deform dramatically after irradiation with 3X10¹⁵ ions/cm². In situ wafer curvature measurements show that thin planar silica films first densify by 3.6% during irradiation. The resulting stress then relaxes viscously by radiation-enhanced Newtonian flow. At a flux of 3X10¹⁰ Xe ions/cm²s the measured shear viscosity was 6X10¹³Pa s. We find evidence that an irradiation induced anisotropic deformation mechanism is present in the silica films. In equilibrium, this deformation leads to an average compressive saturation stress as large as 4.5X10⁷ Pa.