Interface Characterization of Dry-Etched Emitters
The electrical quality of a diffused phosphorous emitter can be significantly improved by etching back the defect-rich surface region (dead layer). This work focuses on the combination of a dry-etch process of the dead layer and a subsequent inline PECVD deposition of the anti-reflective coating (ARC). As we will show in the present work, the surface passivation of the ARC deposited on the plasma-etched surface is affected by a poor firing stability. At a critical temperature of about 800°C, the firing stability of the plasma-etched samples is no longer guaranteed. Therefore, the characteristics and the composition of the resulting Si/SiNx interface play a decisive role. To investigate the reason for the firing-instability of the dry-etched samples, the interface is analyzed by transmission electron microscopy (TEM) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The etch-back emitters show a porous interface structure with a roughness of about 10 to 20 nm and strong blistering effects in the SiNx layer.