Method and device for measuring an ion flow in a plasma

A device for measuring an ion flow from a plasma to a surface such as a probe in a vacuum enclosure constituting a plasma reactor, including:

• a probe internal to the enclosure and including a planar sensitive surface, said probe comprising a disk connected, by a substantially axial conductor, to a terminal of the measuring capacitor, the rear and lateral surfaces of the disk being surrounded by an insulator and a conductive sheath acting as-a screen and a guard ring;
• means external to the enclosure for periodically supplying the probe with a radio frequency voltage;
• a measuring capacitor external to the enclosure mounted in series between the supplying means and the probe;
• and
• means external to the enclosure for periodically measuring the potential variations across the measuring capacitor during its discharge.

A method for measuring ion flow from a plasma to a surface such as a probe, comprising the steps of:

• applying a radio frequency voltage to a first terminal of a measuring capacitor connected between a radio frequency voltage source and a plate-shaped probe in contact with said plasma, whereby said capacitor becomes charged at a self biasing potential of the plasma;
• periodically supplying the probe with radio frequency oscillation trains by means of said radio frequency voltage source and performing the measurement of said discharge rate, between two oscillation trains, after the damping of the radio frequency signal and before the potential of the probe is stabilized;
• and
• measuring a discharge rate of the capacitor when discharged by the ion flow arriving on the probe, wherein the value of the measuring capacitance is lower than the value of the capacitance of a thin layer deposited by the plasma on the probe.