Fluctuation electron microscopy on silicon amorphized at varying self ion-implantation conditions

摘要

The medium range order of self-ion-implanted amorphous silicon was studied by variable resolution fluctuation electron microscopy and characterized by the normalized variance V(k,R). The ion-implantation was conducted at sequentially increasing ion energies ranging from 50keV to 300keV. Two silicon-on-insulator wafers were amorphized at different implantation conditions. From each material, one as-prepared and one ex situ annealed specimen were chosen for analysis. Fluctuation electron microscopy on cross-sectional prepared samples confirms the presence of medium range order due to the amorphization process. We propose three explanations on how the observed medium range order is created by silicon ion-implantation. Two of these suggestions involve paracrystals formed by thermal spikes while a third explanation assumes a medium range order due to nanoscale regions unaffected by the amorphization. Although the two amorphized silicon samples reveal different local structures due to the ion-implantation process, no difference in the self-diffusion behavior is evident, which demonstrates that self-diffusion mainly proceeds within the amorphous phase.