NOVELTY - The apparatus comprises a chamber (100) having a showerhead disposed in an opposing relationship to a substrate support (108), and a first gas source (122A) and a second gas source (120B). The first and second gas sources are present in fluid communication with discrete reaction zones of the showerhead. The reaction zones comprises a first reaction zone contained in a space between a first side of the showerhead and the substrate support, and a second reaction zone contained within an opposing second side of the showerhead.    USE - The apparatus is useful for depositing thin films on a substrate, where the thin films are useful for photovoltaic devices or solar cells.    ADVANTAGE - The apparatus can be effectively and economically depositing the thin films on the substrate with high stability and without light induced degradation effects.    DETAILED DESCRIPTION - The apparatus comprises a chamber (100) having a showerhead disposed in an opposing relationship to a substrate support (108), and a first gas source (122A) and a second gas source (120B). The first and second gas sources are present in fluid communication with discrete reaction zones of the showerhead. The reaction zones comprises a first reaction zone contained in a space between a first side of the showerhead and the substrate support, and a second reaction zone contained within an opposing second side of the showerhead. The first reaction zone is placed in electrical communication with a radio frequency (RF) power supply (114). The second reaction zone is electrically isolated from the first reaction zone, and comprises filaments coupled to a direct current power source. The chamber comprises electrical connectors coupled between the direct current power source and the filaments and RF insulators. Each electrical connectors is shielded from RF energy by the RF insulator. One of the RF insulators comprises ferrite rings, an insulative tube having a rod disposed to support and to electrically connect a bracket assembly supporting the filaments in the second reaction zone. The rod is disposed through an opening in a lid plate of the showerhead. The showerhead is present in fluid communication with a heat exchanger that maintains a temperature of the second reaction zone at 70-80 degrees C. An INDEPENDENT CLAIM is included for a method for forming a thin film on a substrate.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic cross-sectional view of a chamber.    Chamber (100)    Substrate support (108)    Radio frequency power supply (114)    Second gas source (120B)    First gas source. (122A)