Patent ID: 7413672

Claim:
A method for controlling a substrate processing process, said substrate processing process being configured to process a substrate using plasma in a substrate processing chamber, comprising: providing a PIF (planar ion flux) measurement arrangement, said PIF measurement arrangement including at least a PIF probe that has a surface exposed to a plasma sheath of said plasma while said substrate is processed by said plasma; alternately creating a charging phase and a quiescent phase for said PIF arrangement using an energy source that is configured to provide energy to said plasma via said PIF probe; ascertaining a time t point2 , said time t point2 representing a time during said charging phase of said PIF measurement arrangement wherein a first potential difference across said plasma sheath equals to a plasma potential of said plasma; ascertaining a time t point3a , said time t point3a representing a time during said charging phase of said PIF measurement arrangement wherein a second potential difference across said plasma sheath equals a floating potential, said floating potential representing a value of a potential difference across said plasma sheath during said charging phase when no current flows through said PIF probe; and generating a control signal to create at least one of an alarm and a transition in said substrate processing process if a time difference between said time t point2 and said time t point3a meets a predefined condition.