STRESS AND PLASTIC-FLOW IN SILICON DURING AMORPHIZATION BY ION-BOMBARDMENT

In situ wafer curvature measurements were performed during amorphization of silicon by MeV ion implantation. These measurements provide information about density changes and plastic phenomena in the implanted region. Experiments were performed for a variety of ions, a range of fluxes, and for temperatures between - 175 and 200-degrees-C. In all cases, the implanted region expanded due to the creation of damaged crystal, creating compressive stress in the implanted region on the order of 10(8) N/m2. Once heavily damaged or amorphous regions were formed, radiation-enhanced plastic flow of material out of the plane of the wafer occurred in order to relieve the stress created by the expansion. The value of the shear viscosity responsible for this phenomena could be measured by comparing samples with the same history but different stresses. For 2-MeV Xe implantation at room temperature and 10(11) ions/cm2 s, the radiation-enhanced shear viscosity is approximately 10(13) Ns/m2, which is at least four orders of magnitude smaller than the thermally activated shear viscosity. Possible contributions to flow from a homogeneous distribution of broken bonds and from fluid-like collision cascade regions are discussed.