Inductive broad-band sensors for electromagnetic waves
A broad-band sensor for a radio frequency plasma processing system that includes a reaction chamber housing an electrode within a vacuum processing environment. The sensor includes an inductive pickup positioned in the vacuum processing environment proximate to the electrode. The inductive pickup includes a wire formed into a loop extending in an azimuthal direction about a symmetry axis of the reaction chamber. A lead carrying an electric signal from the inductive pickup extends through a vacuum wall of the reaction chamber outside the vacuum processing environment. An attenuator circuit including an electrical resistance bridge couples the lead to a signal carrier extending outside the vacuum processing environment. The broad-band sensor has radio frequency detection capability for measuring electromagnetic surface modes within the plasma chamber and coupling the measured electromagnetic surface modes to the signal carrier.
1. A broad-band sensor for a radio frequency plasma processing system having a reaction chamber, the reaction chamber housing an electrode within a vacuum processing environment, the sensor comprising:
an inductive pickup positioned in the vacuum processing environment proximate to the electrode comprising a wire formed into a loop extending in an azimuthal direction about a symmetry axis of the reaction chamber;
a lead carrying an electric signal from the inductive pickup extending through a vacuum wall of the reaction chamber outside the vacuum processing environment;
an attenuator circuit comprising an electrical resistance bridge coupling the lead to a signal carrier extending outside the vacuum processing environment; and
wherein the broad-band sensor has radio frequency detection capability for measuring electromagnetic surface modes within the plasma chamber and coupling the measured electromagnetic surface modes to the signal carrier.
2. The apparatus of claim 1 , wherein the sensor further comprises an electrostatic shield positioned between the inductive pickup and a surface level of the electrode.
3. The apparatus of claim 1 , further characterized by a shunt capacitance between the lead and the electrode of less than about 20 picofarads.
4. The apparatus of claim 1 , wherein the broad-band sensor is positioned within a hole in the electrode with a top of the sensor substantially flush with a surface of the electrode.
5. The apparatus of claim 4 , wherein the hole is filled with a dielectric material exhibiting a dielectric constant less than 5.
6. The apparatus of claim 1 , wherein an electrical resistance of the electrical resistance bridge is in a range between 10 Ohms and 5,000 Ohms.
7. The apparatus of claim 1 , wherein:
the electrode comprises a hole filled with a dielectric material forming a substrate-supporting area of the electrode; and
the loop is embedded in the dielectric material and extends azimuthally around the substrate-supporting area of the electrode.
8. The apparatus of claim 1 , wherein the signal carrier comprises a coaxial cable and the lead is coupled to a center conductor of the coaxial cable.
9. The apparatus of claim 8 , wherein the electrical resistance bridge comprises a first resistor that is relatively larger than a second resistor to limit the electric drain of the inductive pickup while avoiding suppression of a desired sensor signal carrier by the pickup.
10. The apparatus of claim 9 , further characterized by a capacitance of less than about 20 picofarads from a junction between the first and second resistors to the electrode.
11. The apparatus of claim 9 , further comprising a shunt impedance matching resistor coupling a junction between the second resistor and a center conductor of the coaxial cable to a shield conductor of the coaxial cable.
12. The apparatus of claim 11 , wherein the impedance matching resistor is characterized by a resistance of about 50 Ohms to eliminate or reduce reflections of radio frequency power flowing through the broad-band sensor.
13. The apparatus of claim 1 , wherein the broad-band sensor has radio frequency detection capability in a radio frequency range from 10 kHz to at least 1 GHz.
14. The apparatus of claim 1 , wherein the sensor is positioned proximate to the electrode and the electromagnetic surfaces modes comprise fundamental and harmonic modes of radio frequency energy supplied to the plasma processing system associated with the electrode.
15. The apparatus of claim 1 , wherein the loop is positioned proximate to a substrate supporting area of the electrode and extends azimuthally around the substrate supporting area.
16. The apparatus of claim 15 , wherein the electromagnetic surfaces modes comprise modes propagating toward or away from the substrate supporting area of the electrode.
17. The apparatus of claim 16 , wherein the electromagnetic surfaces modes comprise surface voltage amplitudes and phases.
18. The apparatus of claim 17 , wherein the electromagnetic surfaces modes comprise surface currents.
19. The apparatus of claim 18 , wherein the electromagnetic surfaces modes comprise fundamental and harmonic modes of radio frequency energy supplied to the plasma processing system.
20. The apparatus of claim 19 , wherein the electromagnetic surfaces modes comprise axisymmetric modes and non axi-symmetric modes for the fundamental and harmonic modes.