Bulk and surface passivation by silicon nitride has become an indispensable element in industrial production of multicrystalline silicon (mc-Si) solar cells. Microwave PECVD is a very effective method for high-throughput deposition of silicon nitride layers with the required properties for bulk and surface passivation. In this paper an analysis is presented of the relation between deposition parameters of microwave PECVD and material properties of silicon nitride. By tuning the process conditions (substrate temperature, gas flows, working pressure) we have been able to fabricate silicon nitride layers which fulfill almost ideally the four major requirements for mcSi solar cells: (1) good anti-reflection coating (refractive index tunable between 2Á0 and 2Á3); (2) good surface passivation on p-type FZ wafers (S eff < 30 cm/s); (3) good bulk passivation (improvement of IQE at 1000 nm by 30% after short thermal anneal); (4) long-term stability (no observable degradation after several years of exposure to sunlight). By implementing this silicon nitride deposition in an inline production process of mc-Si solar cells we have been able to produce cells with an efficiency of 16Á5%.Finally, we established that the continuous deposition process could be maintained for at least 20 h without interruption for maintenance. On this timescale we did not observe any significant changes in layer properties or cell properties. This shows the robustness of microwave PECVD for industrial production.

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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.

A route, as followed by ECN, is described for development of Si N,:H layers deposited by microwave (MW) PECVD. which are suited for surface and bulk passivation of moSi solar cdls. First research was focussed on surface passivation and this resulted in the development of SIN layers that were Si-rich and where the hydrogen is mainly bonded to Silicon atoms. A disadvantage of such Si-rich layers is their large absorption at shorter wavelengths, which make them unsuitable as front side AR coatings. Further. these layers appeared to be less suitable for bulk passivation. The next step therefore was the development of SIN layers for bulk passivation. For good bulk passivation of solar cells by means of a thermal anneal of the SiN layers, we found that SIN layers with high N-H bonding concentralions are required. Fine-tuning of the deposition conditions of these layers, finally resulted in the development of a SiN layer type which combines the three desired properties: low absorption (good antireflection coating). good surface passivation ( S S~ on FZ wafers less than 50 cm/s) and good bulk passivation. ~