The effect of implantation dose on the microstructure of silicon nanocrystals in SiO2

Si nanocrystals were formed by the implantation of Si+ into a SiO2 film, deposited on (100) Si, followed by high-temperature annealing. Transmission electron microscopy?(TEM) was used to examine the effect of implantation dose on the microstructure of the Si nanocrystals?(Si?nc) in the SiO2 film. The size and spatial distribution and concentration of the Si?nc in four passivated samples with different implantation doses were investigated using the dark-field imaging technique. The thickness of all the samples was determined by electron energy-loss spectroscopy?(EELS). The structure of the Si?nc in all the samples was determined using selected area electron diffraction. It was found that the average diameter of the Si?nc changes from?2.7 to 3 and to 3.3?nm for the samples with implantation doses of 6 ? 1016, 8 ? 1016 and 1 ? 1017?cm?2; however, it ranges from?2 to 22?nm in the sample with an implantation dose of 3 ? 1017?cm?2. The size of the Si?nc is comparatively homogeneous throughout the whole implanted layer in the samples with implantation doses of 6 ? 1016 and 8 ? 1016?cm?2, while in the samples with implantation doses of 1 ? 1017 and 3 ? 1017?cm?2, the Si?nc in the middle region of the implanted layer are bigger than those near the surface or the bottom of the layer. From TEM experimental results, the concentration of the Si?nc is estimated to be 6 ? 1018, 4 ? 1018 and 4 ? 1018?cm?3 for the samples with implantation doses of 6 ? 1016, 8 ? 1016 and 1 ? 1017?cm?2, respectively. For the sample with an implantation dose of 3 ? 1017?cm?2, the concentration for the Si?nc of 3?nm is around 5 ? 1018?cm?3; the concentration for Si?nc of 6?nm is around 2 ? 1018?cm?3; and the concentration for the 12?nm group is about 1 ? 1018?cm?3. In addition, the concentration determined from TEM experiments is compared with the calculated one. Combining the TEM results with a Monte Carlo simulation, we also discuss the sputtering effect and the depth distribution of the Si ions implanted in SiO2.