NOVELTY - Process gas mixture (I) is flown into a processing chamber and plasma is generated. Silicon-nitride-containing layer (I) is deposited on substrate(s) in the chamber. The flow of mixture (I) is stopped, mixture (II) is flown, and silicon-nitride-containing layer (II) is deposited on layer (I), to form a dual stack silicon-nitride layer (801). Mixture (II) is chosen from gas mixtures consisting of silane and nitrogen, silane, nitrogen and ammonia, and silane and ammonia. Mixture (I) includes a total precursor gas mixture and a hydrogen gas diluent.    USE - Formation of dual stack silicon-nitride layer as antireflective coating/passivation layer on solar cell substrate.    ADVANTAGE - The method enables formation of dual stack silicon-nitride layer with suitable refractive index, mass density, and hydrogen concentration so that the layer serves as an antireflective coating/passivation layer. The deposition chamber throughput is enhanced. The antireflective coating enhances the efficiency of solar cell.    DETAILED DESCRIPTION - Process gas mixture (I) is flown into a processing chamber and a plasma is generated. Silicon-nitride-containing layer (I) is deposited on substrate(s) in the processing chamber. The flow of mixture (I) is stopped, process gas mixture (II) is flown into the processing chamber, and silicon-nitride-containing layer (II) is deposited on layer (I) to form a dual stack silicon-nitride layer. Mixture (II) is chosen from gas mixtures consisting of silane and nitrogen, silane, nitrogen and ammonia, and silane and ammonia. Mixture (I) includes a total precursor gas mixture and a hydrogen gas diluent. The flow rate of hydrogen gas diluent is equal to or greater than the flow rate of total precursor gas mixture.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic side view of a solar cell having a dual stack film formed on the light-receiving surface of an emitter region.    Solar cell (800)    Dual stack silicon-nitride layer (801)    Interface layer (801A)    Bulk silicon-nitride layer (801B)    Emitter region (803)