NOVELTY - The expanding thermal plasma (ETP)-based thin film deposition assembly (100) comprises a deposition chamber including a first ETP source to produce a plasma plume, a system (122) to transport a substrate (120) through the plasma plume along a substrate transport path having a substrate transport path direction, a mask (128) partly disposed in the plasma plume during operation and shaped to shield a portion of the substrate transport path, and a second ETP-source disposed downstream of the first ETP-source.    USE - The thin film deposition assembly is useful for depositing a hydrogenated silicon nitride layer (claimed) on a top of a substrate in the fabrication of a solar cell, where the assembly is expanding thermal plasma-based thin film deposition assembly.    ADVANTAGE - The expanding thermal plasma-based thin film deposition assembly is capable of effectively, accurately and economically depositing the hydrogenated silicon nitride layer on the top of the substrate thus optimizing the optical and electronic properties of the solar cell.    DETAILED DESCRIPTION - The expanding thermal plasma (ETP)-based thin film deposition assembly (100) comprises a deposition chamber including a first ETP source to produce a plasma plume, a system (122) to transport a substrate (120) through the plasma plume along a substrate transport path having a substrate transport path direction, a mask (128) partly disposed in the plasma plume during operation and shaped to shield a portion of the substrate transport path, and a second ETP-source disposed downstream of the first ETP-source such that the substrate transported along the substrate transport path is partially exposed to the plasma plumes produced by the ETP-sources. The plasma plume comprises a number of concentric deposition zones of which each has a relative composition of chemical components. The shielded portion of the substrate transport path extends in the direction of the substrate transport path and bridges a first deposition zone while an extremity of the shielded portion is located in a second deposition zone. The mask is a plate-like member, extends across the substrate transport path, merely extends in a downstream or upstream half of the plasma plume, and has an upstream edge and a downstream edge. The upstream and/or downstream edge has a profile of projections (129) that extend into the plasma plume during operation so as to equally shield the portions of the substrate transport path. The profile of the upstream and/or downstream edge of the mask is partially curved. The first deposition zone is a peripheral deposition zone located on the outside of the plasma plume. The second deposition zone has a higher relative content of hydrogen than the first deposition zone. The shielded portion of the transport path and the second deposition zone are dimensioned such that the path and the zone have a width that is equal to or greater than a width of the substrate, where widths are measured transverse to the direction of the substrate transport path thus allowing the entire substrate to be transported into or out of the second deposition zone without exposing to the first deposition zone. The plasma plumes produced by the ETP-sources differ in overall relative chemical composition, plasma flow rate and overall plasma density, and the plasma plumes are masked to shield a selected portion of the substrate transport path. An INDEPENDENT CLAIM is included for a method for depositing a thin film.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic cross-sectional view of a thin film deposition assembly.    Thin film deposition assembly (100)    Expanding thermal plasma plume (116)    Substrate (120)    Substrate transport system (122)    Mask (128)    Projections. (129)