General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Driven by the need for improvement of the economical competitiveness of photovoltaic energy, the feasibility of high-rate ͑Ͼ1 nm/s͒ amorphous silicon nitride (a-SiN x :H) deposited by the expanding thermal plasma ͑ETP͒ technique has been explored with respect to the application of the a-SiN x :H as functional antireflection coating on crystalline silicon solar cells. First, the deposition rate and the a-SiN x :H film properties, such as refractive index, Si, N, and H atomic density, and hydrogen bonding configurations, have been mapped for various operating conditions. From ellipsometry, elastic recoil detection, and infrared spectroscopy, it has been shown that deposition rates up to 20 nm/s can be reached with a fair film homogeneity and that the refractive index and the N/Si ratio can fully be tuned by the plasma composition while the hydrogen content can be controlled by the substrate temperature. Good antireflection coating performance of the a-SiN x :H has therefore been observed for monocrystalline silicon solar cells. These cells with ETP a-SiN x :H yielded only slightly lower conversion efficiencies than high-quality reference cells due to a much lower degree of surface passivation. This lack of surface passivation has also been shown in a separate study on the surface recombination velocity. Furthermore, it has been tested whether the a-SiN x :H films lead to silicon bulk passivation, which is essential for solar cells based on cheaper, defective silicon stock material such as multicrystalline silicon. It has been proven that bulk passivation of the cells is indeed induced by the high-rate ETP deposited a-SiN x :H after a high-temperature step in which the metal contacts of the cells are processed. These results make the ETP technique an interesting candidate for high-throughput processing of competitive silicon solar cells.

A remote expanding thermal plasma operated on an Ar–H2–N2–SiH4 mixture has been studied by several plasma diagnostics to obtain insight into the plasma processes and the hydrogenated amorphous silicon nitride (a-SiNx:H) growth mechanism from the N2–SiH4 reactant mixture. From Langmuir probe measurements, ion mass spectrometry, and threshold ionization mass spectrometry, it is revealed that the Ar–H2–N2 operated plasma source leads mainly to N and H radicals in the downstream region. The H radicals react with the SiH4 admixed downstream creating a high SiH3 density as revealed by cavity ringdown spectroscopy. By cavity ringdown measurements, it is also shown that Si and SiH have a much lower density in the downstream plasma and that these radicals are of minor importance for the a-SiNx:H growth process. The ground-state N radicals from the plasma source do not react with the SiH4 injected downstream leading to a high N density under the a-SiNx:H deposition conditions as revealed by threshold ionization mass spectrometry. From these results, it is concluded that N and SiH3 radicals dominate the a-SiNx:H growth process and the earlier proposed growth mechanism of a-SiNx:H from the N2–SiH4 mixture [D. L. Smith et al., J. Vac. Sci. Technol. B 8, 551 (1990)] can be refined: During deposition, an a-Si:H-like surface layer is created by the SiH3 radicals and at the same time this a-Si:H-like surface layer is nitridated by the N radicals leading to a-SiNx:H formation. This growth mechanism is further supported by the correlation between the SiH3 and N plasma density and the incorporation flux of Si and N atoms into the a-SiNx:H films as deposited under various conditions.

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Silicon nitride (a‐SiNx:H) films deposited by the expanding thermal plasma at high rate (> 1 nm/s) have been studied for application as anti‐reflection coatings for multicrystalline silicon (mc‐Si) solar cells. Internal quantum efficiency measurements have revealed that bulk passivation is achieved after a firing‐through process of the a‐SiNx:H as deposited from NH3/SiH4 and N2/SiH4 plasmas. However, the a‐SiNx:H films deposited from N2/SiH4 show a lower passivation quality than those deposited from NH3/SiH4. This has been attributed to a poorer thermal stability of the films deposited from the N2/SiH4 plasma, resulting in structural changes within the film during the firing step. Copyright © 2002 John Wiley & Sons, Ltd.