Ion implantation and annealing of crystalline oxides

The technique of ion implantation is being investigated as a general method for altering the near-surface properties of insulating materials. The primary motivation behind these investigations is to develop ion implantation as a practical means of controlling and improving the near-surface mechanical, optical, or electronic properties of insulators. Changes in these properties depend on the microstructures and compositions developed in the material during the ion implantation process and subsequent thermal treatments. In many cases, structures and compositions can be produced by implantation and thermal annealing that cannot be achieved by conventional techniques. In this work, the response of a wide range of crystalline oxides to ion implantation and subsequent thermal processing will be reviewed. The materials treated here include Al₂O₃, LiNbO₃, CaTiO₃, SrTiO₃, ZnO, and MgO, as well as the non-oxide materials Si₃N₄ and SiC. The response of these insulators to ion implantation varies widely and depends on the specific material, the implantation species and dose, and the implantation temperature. Ion implantation produces displacement and other damage in the near-surface region, and in many cases, the surfaces of originally crystalline insulators are turned amorphous. Thermal annealing can often be used to restore crystallinity to the damaged near-surface region, and additionally, metastable solid solutions can be produced. For a number of oxide materials, the annealing behavior has been studied in detail using both Rutherford backscattering-ion channeling techniques and transmission electron microscopy. These studies show that, in some materials, the annealing behavior is quite simple and takes place by solid-phase epitaxial crystallization where the amorphous-to-crystalline transformation occurs at an interface that moves toward the free surface during the annealing process. In such materials, the regrowth kinetics have been measured, and the associated activation energies for crystallization have been determined. The formation of metastable solid solutions during crystallization of the amorphous phase will also be discussed.