Patent ID: 8613827

Claim:
An apparatus for processing a workpiece with free radicals from a light-emitting plasma including ions and the free radicals, comprising: a vacuum chamber including a processing space and a plasma cavity in communication with said processing space; a holder for the workpiece positioned in said processing space of said vacuum chamber; a vacuum 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 center slotted plate positioned between said plasma cavity and said processing space, said center slotted plate having a plurality of first slots; and an upper slotted plate positioned between said center slotted plate and said powered electrode and said upper slotted plate having a plurality of second slots; a lower slotted plate including a plurality of third slots, said lower slotted plate being arranged between said center slotted plate and said processing space; and a plurality of electrically-conductive spacers between said center slotted plate, said lower slotted plate, and said upper slotted plate, said plurality of electrically-conductive spacers providing an electrical contact between said center slotted plate, said lower slotted plate, and said upper slotted plate, wherein said lower, center, and upper slotted plates are electrically grounded to said vacuum chamber, said powered electrode is capable of exciting the process gas in said plasma cavity to generate the ions and the free radicals of the plasma in the plasma cavity between the upper slotted plate and the powered electrode, said first slots, said second slots, and said third slots are configured to transfer the free radicals in the plasma from said plasma cavity to said processing space and to substantially reduce the transfer of the ions in the plasma from said plasma cavity to said processing space, and said first slots are offset from said second slots such that said first slots are not aligned with said second slots in a direction extending from said plasma cavity toward said processing space and said first slots are offset from said third slots said first slots are not aligned with said third slots in the direction extending from said plasma cavity toward said processing space to substantially eliminate line-of-sight paths from said plasma cavity to said processing space for reducing light transfer from the plasma to the workpiece.