Detailed analysis of amorphous silicon passivation layers deposited in industrial in-line and laboratory-type PECVD reactors

Amorphous silicon (a-Si) layers for the passivation of p-type silicon wafer surfaces are investigated. The first main topic is the thermal stability of a-Si passivation. Here, an improved thermal stability in annealing (400 °C) and firing processes (wafer temp. 550 °C) could be achieved by stacking a-Si layers with PECVD SiOx layers of different thickness. Hydrogen depth profiling using nuclear reaction analysis shows a hydrogen concentration of 11 at% in the bulk of the a-Si. After firing of single layer a-Si samples a hydrogen concentration peak at the a-Si / c-Si interface could be observed. The second major topic of this paper is the deposition of a-Si layers using an industrial-type inline PECVD reactor. Excellent surface passivation (>1 ms on 1 Ohm cm FZ wafers) can be reported. These a-Si layers are further characterised using FTIR and spectroscopic ellipsometry.