Electromagnetic and thermal analyses of Faraday shield of various materials and structures for an ICP source

Abstract

Faraday shield (FS), a thin-wall metal structure with slits, is used in inductive coupled plasma (ICP) sources to protect the ceramic tube from plasma erosion and eliminate capacitive coupling. Electromagnetic energy is coupled into the driver through the slits, which makes FS an important component of ICP sources. Material and structure, which are critical for FS, should have effects on the distribution of electromagnetic field and temperature. In this contribution, discussions on various materials and structures’ impact on electromagnetic and thermal performance arise. FS made of copper, aluminum, molybdenum and stainless steel, as well as FS of different thickness, slit width, slit numbers and slit shapes, are investigated by numerical simulations referring to the parameters of an actual ICP source. Electromagnetic field, RF power loss, temperature and stress of different FS are compared. The results show that Mo has similar electromagnetic performance with Cu but better thermal performance than Cu for FS. As for structure, RF power transfer efficiency decreases slightly as FS thickens. Appropriate slit width and number are required to allow a sufficient RF coupling and acceptable plasma heat flux to ceramic tube. RF efficiency of z-shaped slotted FS and normally slotted FS is almost the same.