Patent ID: 7544269

Claim:
A monitoring system for use in a plasma chamber, said monitoring system comprising: a microwave mirror having a first reflecting surface provided on an inner surface of a wall of the plasma chamber arranged opposite a substrate holder of the plasma chamber such that the first reflecting surface can be immersed in a plasma and the substrate holder or a substrate thereon or both provide a second reflecting surface, wherein said first and second reflecting surfaces provide a microwave resonator; a non-plasma power source coupled to a first aperture in said first reflecting surface such that said power source provides a microwave signal extending along an axis generally perpendicular to a substrate plane and incident on a discrete area of the substrate plane which is only a portion of an entire area of a support surface of the substrate holder in order to monitor spatial resolution of electron density along the substrate plane; a first microwave window provided on an outer surface of the wall of the plasma chamber that includes the reflecting surface such that the first microwave window is outside the plasma chamber and provided between the power source and the aperture; a detector coupled to a second aperture of said first reflecting surface, said detector being configured to measure at least one resonant frequency of said microwave resonator; and a control system connected to said detector and configured to process said at least one signal, said control system being configured to determine an electron density from said at least one resonant frequency.