Surface passivation of boron diffused junctions by borosilicate glass and in situ grown silicon dioxide interface layer

An in situ oxidation during the boron tribromide (BBr 3 ) diffusion process to form $p^{+}$ doped junctions on crystalline Si solar cells leads to the formation of stack layer system consisting of borosilicate glass (BSG; a binary B 2 O 3 -SiO 2 system) and a SiO 2 layer at Si interface. We present a method to passivate the $p^{+}$ doped regions by using this in situ grown SiO 2 in combination with a PECVD deposited SiN x layer. We show that the etching rate of the BSG layer, in a HF acid solution, varies over the wafer, depending on its local B 2 O 3 content in BSG, and is markedly higher than that of the SiO 2 layer. This difference in the etching rates can be used to controllably etch back the BSG layer in order to obtain a thin and uniform passivating oxide layer for solar cells application. Using this oxide/SiN x stack we obtained implied $V_{OC}$ of 705 mV and $J_{\theta e}$ as low as 14 fA/cm 2 on symmetrically diffused boron emitters on n-type Cz wafers. These passivation results are comparable, on similar structure and boron emitters, with today's state-of-the-art Al 2 O 3 based passivation methods. Moreover, we have successfully implemented this passivation method into mass-production of n-PERT and pilot-production of IBC solar cells, avoiding the need of adopting additional process steps and costs, which are otherwise needed for $p^{+}$ boron emitter passivation.