Contamination control in plasma contouring the plasma sheath using materials of differing rf impedances

摘要

The disclosure relates to a plasma processing apparatus including a wafer supporting pedestal (30) which is designed to reduce particle trapping phenomena. In a region of the pedestal surface which surrounds or abuts the wafer (10), the pedestal has a cover (40) in the form of a flat annular disk. The cover is formed from a material having a permittivity which is substantially equal to or greater than that of the wafer surface. As a result, the sheath boundary is reshaped to reduce particle trapping.