Characterization of laser-fired contacts in PERC solar cells: SIMS and TEM analysis applying advanced preparation techniques

In this study we apply ion-beam supported preparation techniques for both mesa formation by trench sputtering and FIB ‘lift-out’ lamella cutting for dynamic SIMS and TEM analysis of laser-fired Al point contacts on Si, respectively. Detailed compositional and structural informations about the metallurgical contact formation process are obtained combining both characterization techniques. While TEM micrographs and microdiffraction patterns reveal a mixture of Al- and Si-crystals within the 1 mm thick Al rich re-solidified surface layer according to the Al–Si phase diagram, spatially resolved SIMS depth profiling indicates ppm-range Al-diffusion a few hundred nm into the buried, substantially undisturbed Si-lattice