An RPCVD apparatus for forming a film comprising: one or more plasma generators (200a-d) to generate a plasma from a source comprising nitrogen; a reaction chamber in which to react a metal organic reagent with a reactive nitrogen species derived from the nitrogen plasma so as to deposit a film on one or more substrates ; a showerhead having: at least one gas chamber ; one or more plasma inlets (304a-d) to deliver plasma from the one or more plasma generators (200a-d) into the reaction chamber ; and a plurality of gas inlets to deliver gas from the at least one gas chamber into the reaction chamber ; a susceptor for supporting one or more substrates in the reaction at a surface of the susceptor between a central region and an outer region of the susceptor ; the susceptor being configured to rotate relative to the showerhead around an axis of rotation; wherein at least one of the plasma inlets (304a-d) is located at a position that is between a central region and an outer region of the showerhead and off-centre from the axis of rotation, wherein the gas inlets are distributed in a pattern at a surface of the showerhead between the central region and the outer region of the showerhead: wherein the gas inlets each direct gas having a respective spatial distribution of gas at the surface of the susceptor ; characterised in that the plasma generators (200a-d) generate plasma in line of sight of the susceptor and the plasma inlets (304a-d) have openings that are larger than openings of the gas inlets ; and wherein the gas inlets are configured such that a combination of all of the spatial distributions of gas provides a uniform distribution of gas density on the surface of the susceptor between a central region and an outer region of the susceptor , for a full rotation of the susceptor . one or more plasma generators (200a-d) to generate a plasma from a source comprising nitrogen; a reaction chamber in which to react a metal organic reagent with a reactive nitrogen species derived from the nitrogen plasma so as to deposit a film on one or more substrates ; a showerhead having: at least one gas chamber ; one or more plasma inlets (304a-d) to deliver plasma from the one or more plasma generators (200a-d) into the reaction chamber ; and a plurality of gas inlets to deliver gas from the at least one gas chamber into the reaction chamber ; at least one gas chamber ; one or more plasma inlets (304a-d) to deliver plasma from the one or more plasma generators (200a-d) into the reaction chamber ; and a plurality of gas inlets to deliver gas from the at least one gas chamber into the reaction chamber ; a susceptor for supporting one or more substrates in the reaction at a surface of the susceptor between a central region and an outer region of the susceptor ; the susceptor being configured to rotate relative to the showerhead around an axis of rotation; wherein at least one of the plasma inlets (304a-d) is located at a position that is between a central region and an outer region of the showerhead and off-centre from the axis of rotation, wherein the gas inlets are distributed in a pattern at a surface of the showerhead between the central region and the outer region of the showerhead: wherein the gas inlets each direct gas having a respective spatial distribution of gas at the surface of the susceptor ; characterised in that the plasma generators (200a-d) generate plasma in line of sight of the susceptor and the plasma inlets (304a-d) have openings that are larger than openings of the gas inlets ; and wherein the gas inlets are configured such that a combination of all of the spatial distributions of gas provides a uniform distribution of gas density on the surface of the susceptor between a central region and an outer region of the susceptor , for a full rotation of the susceptor . <EOS>