Excellent passivation of thin silicon wafers by HF-free hydrogen plasma etching using an industrial ICPECVD tool

In this work, hydrogen plasma etching of surface oxides was successfully accomplished on thin (∼100 µm) planar n-type Czochralski silicon wafers prior to intrinsic hydrogenated amorphous silicon [a-Si:H(i)] deposition for heterojunction solar cells, using an industrial inductively coupled plasma-enhanced chemical vapour deposition (ICPECVD) platform. The plasma etching process is intended as a dry alternative to the conventional wet-chemical hydrofluoric acid (HF) dip for solar cell processing. After symmetrical deposition of an a-Si:H(i) passivation layer, high effective carrier lifetimes of up to 3.7 ms are obtained, which are equivalent to effective surface recombination velocities of 1.3 cm s–1 and an implied open-circuit voltage (Voc) of 741 mV. The passivation quality is excellent and comparable to other high quality a-Si:H(i) passivation. High-resolution transmission electron microscopy shows evidence of plasma-silicon interactions and a sub-nanometre interfacial layer. Using electron energy-loss spectroscopy, this layer is further investigated and confirmed to be hydrogenated suboxide layers. (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)