Observations of Lattice Distortions near Silicon Surfaces Implanted with Low-Energy Nitrogen Ions by Reflection X-ray Topography

Mirror-polished Czochralski-grown wafers with near-(100)-oriented surfaces were implanted with N+ at 8 keV energy at a dose of 1 ×1015 cm-2. Lattice distortions produced by the implantation process were observed by X-ray double-crystal topography using extremely asymmetric reflection. The intensity contrast caused by the lattice extensions in thin layers was clearly visualized. By annealing at 700°C for more than 90 min, the imperfect crystal in the ion-implanted region evidently recovers to a more perfect one, except for the boundary of the implanted region. The lattice distortions at the boundary, consisting of a narrow striated region, are thought to be due primarily to variations in the lattice spacing that has been deformed nonelastically. From a series of topographs taken by changing the glancing angle from the low-angle to the high-angle side of the Bragg peak, the differences in lattice spacing between the striated portions and the unimplanted regions were estimated.