Method for obtaining uniform etch by modulating bias on extension member around radio frequency etch table

A method for obtaining a uniform etch on a semiconductor wafer being etched on an RF etch table in a plasma etch system, comprising,

• placing said semiconductor wafer on said RF etch table, said table having an extension member positioned adjacent its periphery, said extension member being electrically conductive and being insulated from the structures surrounding said table,
• generating a plasma above said etch table to thereby etch the surface of said wafer,
• protecting the surface of said extension member from ions extracted from said plasma to prevent the generation of unwanted metallic impurities, applying a bias potential to said extension member whereby the sheath of said plasma generated above said etch table is extended beyond the periphery of said etch table and above at least a portion of said extension member, and
• modulating said bias potential so as to produce a more uniform overall etch on said semiconductor wafer.