Simulation of the Anneal of Ion Implanted Boron Emitters and the Impact on the Saturation Current Density

Recently, the interest for the implementation of local ion implantation for emitter formation has been renewed, as it results in high cell efficiencies [1], while the amount of process steps is reduced. After implantation, a thermal diffusion (annealing) is necessary for the removal of the ion-induced damage, the activation of dopants and the formation of the desired profile shape. The goal is to change the implanted retrograde near surface (10-100 nm) inactive profile, into a damage free, box-like shaped, and fully active emitter (or BSF) with a low saturation current density (J0e).Here, we study different post-implantation annealing schemes, to achieve high performance boron emitters for n-type IBC solar cells. We show experimentally, that the use of oxygen gas during the boron anneal has an impact on the electrical performance (J0e) of the emitter. On the other hand, the obtained J0e values are higher than those obtained by the standard diffusion approach. Hence, in order to understand these results and optimize the implant/anneal process, the modeling of the profile shape and the damage evolution would be extremely valuable. In this work, we report on our initial simulation results, and we demonstrate the impact of oxygen on the evolution of the profile shapes of the implanted B-emitters after anneal, taking into account boron diffusion kinetics mechanisms such as Transient Enhanced Diffusion (TED) and Oxidation Enhanced Diffusion (OED). Moreover, we monitor the residual damage and we make a first effort to correlate the increase on the J0e values with the residual damage levels. Throughout this work, we adopt the process simulator tool Sentaurus Process.