3D-FIB Investigation of Cu Precipitates in c-Si after High Temperature Treatments

Besides x-ray fluorescence (XRF) and transition electron microscopy (TEM), 3-dimensional focused ion beam (3D-FIB) combined with scanning electron microscopy (SEM) is an additional method to investigate the transition metal distribution in crystalline silicon material leading to additional information on the 3D shape, size and distribution of precipitates. The 3D-FIB method has been used to investigate the transition metal precipitate distribution around extended crystal defects, showing a strong influence of crystallographic parameters on the precipitation behavior. In addition, the transition metal precipitate distribution after a phosphorous (POCl3) diffusion process and a corresponding temperature profile alone has been investigated. During POCl3 diffusion the transition metal precipitates dissolve and the transition metals move to regions with higher solubility leaving voids behind, which can still act as recombination active centers and have to be taken into account in further process treatments. The diffusivity and density of silicon self interstitials and the duration of the POCl3 diffusion is not sufficient to fill the voids. If only the temperature profile of a POCl3 diffusion is applied, the transition metal precipitates dissolve but return to the same sites during cool down due to a missing external getter sink.