Plasma processing apparatus and method of measuring amount of radio-frequency current in plasma
In the present invention, two coil-shaped probes each detecting the intensity of a magnetic field in a direction around a center axis of a processing space are provided in a process vessel of a plasma processing apparatus. Each of the probes detects an induced electromotive force generated in the coil, and a computer calculates an amount of radio-frequency current from the induced electromotive force, based on a predetermined calculation principle. A difference between the amounts of the radio-frequency current detected by the probes is calculated, and a loss radio-frequency current amount passing out of a plasma area between upper and lower electrodes is calculated, whereby the flow of the radio-frequency current in the plasma is known.
1. A plasma processing apparatus which has upper and lower radio-frequency electrodes facing each other in a process vessel and processes a substrate by supplying radio-frequency power to at least one of the radio-frequency electrodes and generating plasma in the process vessel, the apparatus comprising:
a probe which is disposed in the process vessel to detect a time varying magnetic flux density directed in a azimuthal direction around an up/down-direction center axis of the process vessel; and
a calculation part which calculates an amount of radio-frequency current passing in an axial direction in the plasma when the radio-frequency power is supplied, based on the time varying magnetic flux density detected by said probe,
wherein plural ones of said probe are provided at a plurality of positions in the up/down direction in the process vessel, and
wherein said calculation part subtracts an amount of the radio-frequency current detected by a probe close to one of the radio-frequency electrodes from an amount of the radio-frequency current detected by the probe close to the other radio-frequency electrode and calculates an amount of the radio-frequency current passing in a radial direction, based on an amount by which the radio-frequency current in the axial direction increases/decreases between said probes.
2. The plasma processing apparatus according to claim 1 , wherein each of said probes is formed in a coil shape, and an axis of the coil is directed in the azimuthal direction around the up/down-direction center axis of the process vessel.
3. The plasma processing apparatus according to claim 2 ,
wherein each of said probes detects an induced electromotive force generated in the coil, as the time varying magnetic flux density, and
wherein said calculation part calculates the amount of the radio-frequency current from the induced electromotive force.
4. The plasma processing apparatus according to claim 1 , wherein said probes are provided at heights between the upper and lower radio-frequency electrodes.
5. The plasma processing apparatus according to claim 1 , wherein said probes are provided on an outer side of the substrate held on one of the upper and lower radio-frequency electrodes in the process vessel.
6. The plasma processing apparatus according to claim 1 , wherein at least one of said probes is provided at a height immediately under the upper radio-frequency electrode, and at least another of said probes is provided at a height immediately above the lower radio-frequency electrode.
7. The plasma processing apparatus according to claim 1 , further comprising:
a control part which executes the calculation of the amount of the radio-frequency current between said probes during the processing of the substrate, and stops the processing of the substrate based on the calculated amount of the radio-frequency current and a preset threshold value of the amount of the radio-frequency current.
8. The plasma processing apparatus according to claim 1 , further comprising
an analysis part which decomposes the time varying magnetic flux density detected by each of said probes into frequency components included in the detected time varying magnetic flux density, and
wherein said calculation part calculates the amount of the radio-frequency current between said probes for each of the frequencies.
9. The plasma processing apparatus according to claim 8 , further comprising an adjustment part which adjusts an amount of the radio-frequency current with a specific frequency based on the amount of the radio-frequency current calculated for each of the frequencies.
10. The plasma processing apparatus according to claim 1 , wherein each of said probes is covered by an insulative cover.
11. The plasma processing apparatus according to claim 1 , wherein said probes are buried in a member facing the generated plasma.
12. The plasma processing apparatus according to claim 11 , wherein said probes are buried in a wall portion of the process vessel.
13. The plasma processing apparatus according to claim 11 , wherein the lowest probe is buried in an annular member surrounding an outer periphery of the substrate held on the lower radio-frequency electrode in the process vessel.
14. The plasma processing apparatus according to claim 1 , wherein said probes are movable up and down in the process vessel.