An apparatus arranged to process a workpiece with free radicals from a light-emitting plasma including ions and the free radicals, comprising: a vacuum chamber including a chamber lid (14, 402, 502), a processing space and a plasma cavity defined in said chamber lid in fluid communication with said process-ing space; a workpiece holder positioned in said processing space of said vacuum chamber; an exhaust port in said vacuum chamber adapted to evacuate said processing space and said plasma cavity; a process gas supply port in said vacuum chamber adapted to introduce a process gas to said plasma cavity; a powered electrode located within said plasma cavity; a grounded plate being an assembly that includes an upper slotted plate, a center slotted plate, and a lower slotted plate, said grounded plate being positioned between said plasma cavity and said processing space and being configured to be removable from the chamber lid, said center slotted plate having a plurality of first slots; said upper slotted plate having a plurality of second slots; and said lower slotted plate including a plurality of third slots, the apparatus further comprising a plurality of electrically-conductive spacers between said center slotted plate and said upper slotted plate, said plurality of electrically-conductive spacers (550, 551) providing an electrical contact between said center slotted plate and said upper slotted plate, and a plurality of electrically-conductive spacers between said center slotted plate and said lower slotted plate said plurality of electrically-conductive spacers providing an electrical contact between said center slotted plate and said lower slotted plate; said powered electrode being arranged to cooperate with said grounded plate to generate the plasma in the plasma cavity said first slots, said second slots, and said third slots being configured to prohibit the transfer of ions and electrons from said plasma cavity to said processing space and allowing the transfer of free radicals from said plasma cavity to said processing space, each of the slotted plates (516, 518, 520) having a slot arrangement (522, 524, 526) that cooperates for substantially eliminating line-of-sight paths in that said slot arrangement of at least one of said slotted plates (516, 518, 520) is offset spatially from said slot arrangement of at least another of said slotted plates, and wherein the relative spatial arrangement of the first, second and third slots (522, 524, 526), in cooperation with the inter-plate spacings, eliminates, prohibits, or at least substantially reduces line-of sight paths between the plasma cavity and the processing space. a vacuum chamber including a chamber lid (14, 402, 502), a processing space and a plasma cavity defined in said chamber lid in fluid communication with said process-ing space; a workpiece holder positioned in said processing space of said vacuum chamber; an exhaust port in said vacuum chamber adapted to evacuate said processing space and said plasma cavity; a process gas supply port in said vacuum chamber adapted to introduce a process gas to said plasma cavity; a powered electrode located within said plasma cavity; a grounded plate being an assembly that includes an upper slotted plate, a center slotted plate, and a lower slotted plate, said grounded plate being positioned between said plasma cavity and said processing space and being configured to be removable from the chamber lid, said center slotted plate having a plurality of first slots; said upper slotted plate having a plurality of second slots; and said lower slotted plate including a plurality of third slots, the apparatus further comprising a plurality of electrically-conductive spacers between said center slotted plate and said upper slotted plate, said plurality of electrically-conductive spacers (550, 551) providing an electrical contact between said center slotted plate and said upper slotted plate, and a plurality of electrically-conductive spacers between said center slotted plate and said lower slotted plate said plurality of electrically-conductive spacers providing an electrical contact between said center slotted plate and said lower slotted plate; said powered electrode being arranged to cooperate with said grounded plate to generate the plasma in the plasma cavity said first slots, said second slots, and said third slots being configured to prohibit the transfer of ions and electrons from said plasma cavity to said processing space and allowing the transfer of free radicals from said plasma cavity to said processing space, each of the slotted plates (516, 518, 520) having a slot arrangement (522, 524, 526) that cooperates for substantially eliminating line-of-sight paths in that said slot arrangement of at least one of said slotted plates (516, 518, 520) is offset spatially from said slot arrangement of at least another of said slotted plates, and wherein the relative spatial arrangement of the first, second and third slots (522, 524, 526), in cooperation with the inter-plate spacings, eliminates, prohibits, or at least substantially reduces line-of sight paths between the plasma cavity and the processing space.