The presence and influence of ions in several reactor configurations used for plasma-assisted atomic layer deposition (ALD) are discussed. It is shown that the ion energies are often moderate or even negligible in direct plasma and remote plasma ALD reactors under processing conditions typically employed. Plasma-induced damage by ion bombardment is therefore not a major issue during most processes. It has furthermore been demonstrated that ion energies can be enhanced using substrate biasing, which can be used to tailor the material properties as demonstrated for several metal-oxides.

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. ~

In this work we studied the deposition of silver (Ag) by spatial-ALD on molybdenum layers serving as a growth model substrate. Mo-layers were selected for testing the suitability of spatial-ALD in fabricating MoO3/Ag/MoO3 tri-layer transparent conductor (TC) stacks used for light-management optimization in organic-based and perovskites solar cells. The presence of native MoO3 on the Mo surface was found to hinder the Ag coalescence. Therefore, an H2/N2 plasma pre-treatment was introduced before Ag deposition in order to reduce the native MoO3. It was concluded that this plasma pre-treatment was effective in promoting Ag wetting, as corroborated by scanning electron microscopy and ellipsometry measurements. Wetting/de-wetting properties as probed by rapid thermal annealing experiments and comparable XRD stress amplitude measurements supported the conclusion that, plasma pre-treatment ALD deposited MoO3 layers can act as wetting layers for subsequent Ag spatial-ALD. This can open up alternative pathways for the fabrication of TCs using ALD.

The crystallization behavior of thin strontium titanate (SrTiO3, STO) films with ~15 nm thickness was studied by Transmission Electron Microscopy (TEM). Amorphous STO films with [Sr]/([Sr]+[Ti]) ratio ranging from 0.51 to 0.65 were deposited at 350 {degree sign}C by plasma-assisted ALD and subsequently treated by rapid thermal annealing for crystallization. Different temperatures and annealing durations were employed to fully characterize the crystallization process. TEM analysis evidenced the influence of the STO composition and of the thermal budget applied on the grain size, cracks and void formation. In particular, Sr-rich layers ([Sr]/([Sr]+[Ti] {greater than or equal to} 0.6) showed a finer crystalline structure which was imputed to a higher nucleation probability at the onset of the crystallization process. By tuning the STO composition and the thermal budget of the annealing step it was demonstrated that it is possible to control the microstructure of the crystallized STO layers.

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