Methods and apparatus for determining the endpoint of a cleaning or conditioning process in a plasma processing system

A method of determining an endpoint of a process by measuring a thickness of a layer, said layer being deposited on said surface by a prior process, comprising:

• providing a sensor that is recessed from said surface, wherein said sensor is configured to measure said thickness;
• exposing said plasma chamber to a plasma, wherein said thickness is changed by said exposing;
• determining said thickness as a function of time;
• and
• ascertaining a steady state condition in said thickness, said steady state condition being characterized by a substantially stable measurement of said thickness, a start of said steady state condition representing said endpoint.

An apparatus for determining an endpoint of a process by measuring a thickness of a layer, said layer being deposited on said surface by a prior process, comprising:

• means for providing a sensor that is coplanar with said surface, wherein said sensor is configured to measure said thickness;
• means for exposing said plasma chamber to a plasma, wherein said thickness is changed by said exposing;
• means for determining said thickness as a function of time;
• and
• means for ascertaining a steady state condition in said thickness, said steady state condition being characterized by a substantially stable measurement of said thickness, a start of said steady state condition representing said endpoint.