Probe for measuring characteristics of an excitation current of a plasma, and associated plasma reactor
View Patent ↗A probe for measuring electrical characteristics of an excitation current of a plasma is provided. The probe is mounted on a conductive line that includes an inner conductor and an outer conductor. The probe includes a current sensor and a voltage sensor. The current sensor includes a groove formed in the ground of one of the conductors in order to form a detour for the current flowing through the conductor, and a point for measuring electric voltage between a ground connected to the conductor and a point of the groove. The current sensor thus is able to measure a voltage proportional to the first time derivative of intensity (I plasma ) of the excitation current. The voltage sensor is a shunt sensor capable of measuring a voltage proportional to the first time derivative of the voltage (V plasma ) of the excitation current. A plasma reactor including a probe of the aforementioned type is also provided.
1. A probe for measuring electrical characteristics of an excitation current of a plasma, said probe comprising a current sensor and a voltage sensor, said probe being mounted on a conducting line which includes an inner conductor and an outer conductor, wherein the current sensor comprises:
a groove formed in a mass of one of the conductors to form a diversion for current traversing the conductor, and
a point for measuring the electrical voltage between an earth or a ground connected to the conductor and a point on the groove,
the current sensor measuring a voltage proportional to a first temporal derivative of the excitation current, and
the voltage sensor is a derivative sensor, measuring a voltage proportional to a first temporal derivative of the excitation current voltage.
2. A probe according to claim 1 , wherein the excitation current is an alternating RF current.
3. A probe according to claim 1 , wherein the groove creates a current diversion with a length of about centimeter.
4. A probe according to claim 1 , wherein the current sensor and the voltage sensor are both installed on the outer conductor.
5. A probe according to claim 1 , wherein the said voltage sensor includes a conical transmission line, terminated by a curved surface capacitively coupled to the conductor other than that on which the said voltage sensor is mounted.
6. A probe according to claim 5 , wherein a coupling capacitance between the curved surface and the conductor other than that on which the voltage sensor is mounted, is about 0.3 pF.
7. A probe according to claim 1 , wherein the current sensor and the voltage sensor are installed at the same level in a current path at the surface of the conductor.
8. A probe according to claim 1 , wherein the conducting line is a cylindrical coaxial line.
9. A probe according to claim 1 , wherein the conducting line is a radial coaxial line.
10. A probe according to claim 1 , additionally comprising means for measuring the phase offset between the current and the voltage of the excitation current.
11. A plasma reactor that comprises an RF generator additionally comprising a probe according to claim 1 .
12. A reactor according to claim 11 , wherein the probe is disposed between an impedance matching circuit connected to the RF generator and an RF electrode for excitation of the plasma.
13. A reactor according to claim 11 , wherein the probe is disposed between the RF generator and a matching unit, on a matched line.