PLASMA MONITORING AND PLASMA DENSITY MEASUREMENT IN PLASMA PROCESSING SYSTEMS
A plasma processing system includes a processing chamber including a substrate support. A plasma generator is configured to selectively generate plasma in the processing chamber to treat a substrate arranged on the substrate support. An emitter is configured to transmit first terahertz waves through the plasma in the processing chamber. A detector is configured to receive second terahertz waves corresponding to the first terahertz waves transmitted through the plasma in the processing chamber.
1 . A plasma processing system comprising:
a processing chamber including a substrate support;
a plasma generator configured to selectively generate plasma in the processing chamber to treat a substrate arranged on the substrate support;
an emitter configured to transmit first terahertz waves through the plasma in the processing chamber; and
a detector configured to receive second terahertz waves corresponding to the first terahertz waves transmitted through the plasma in the processing chamber.
2 . The plasma processing system according to claim 1 , wherein:
the emitter and the detector are arranged on opposite sides of the processing chamber, and
the processing chamber includes first and second windows located adjacent to the emitter and the detector, respectively.
3 . The plasma processing system according to claim 2 , wherein the first terahertz waves pass through the first window and into the processing chamber, and the detector is configured to receive the second terahertz waves through the second window.
4 . The plasma processing system according to claim 2 , wherein an optical axis of the first window is aligned with a path of the first terahertz waves.
5 . The plasma processing system according to claim 1 , wherein the emitter and the detector are arranged inside of the processing chamber.
6 . The plasma processing system according to claim 1 , wherein:
the emitter includes a plurality of sub-emitters each configured to generate the first terahertz waves, and
the detector includes a plurality of sub-detectors configured to detect the second terahertz waves from each of the plurality of sub-emitters, respectively.
7 . The plasma processing system according to claim 6 , wherein:
a first path of the first terahertz waves from one sub-emitter of the plurality of sub-emitters is configured to pass over a center of a substrate, and
a second path of the first terahertz waves transmitted from another sub-emitter of the plurality of sub-emitters is configured to pass over an edge of the substrate.
8 . The plasma processing system according to claim 6 , wherein a first path of the first terahertz waves from one sub-emitter of the plurality of sub-emitters is closer to an upper portion of the processing chamber than a second path of the first terahertz waves from another sub-emitter of the plurality of sub-emitters.
9 . The plasma processing system according to claim 1 , wherein:
the emitter and the detector are arranged above a surface of a substrate, and
the first terahertz waves from the emitter are directed at and reflected by the substrate.
10 . The plasma processing system according to claim 1 , wherein the detector is configured to detect the second terahertz waves using frequency scanning.
11 . The plasma processing system according to claim 1 , further comprising a controller configured to control the emitter and the detector and to compare one or more characteristics of the second terahertz waves to one or more corresponding characteristics of reference terahertz waves and to estimate plasma density in response to the comparison.
12 . The plasma processing system according to claim 11 , wherein the controller is configured to:
determine an amplitude difference between the second terahertz waves and the reference terahertz waves, and
calculate the plasma density in the processing chamber based on the amplitude difference.
13 . The plasma processing system according to claim 11 , wherein the controller is configured to:
determine an RMS value difference between the second terahertz waves and the reference terahertz waves, and
calculate the plasma density in the processing chamber based on the RMS value difference.
14 . The plasma processing system according to claim 11 , wherein the controller is configured to:
determine a phase difference between the second terahertz waves and the reference terahertz waves, and
calculate the plasma density in the processing chamber based on the phase difference.
15 . The plasma processing system according to claim 11 , wherein the first terahertz waves are configured as continuous waves.
16 . The plasma processing system according to claim 14 , wherein the plasma generator includes:
a coil arranged adjacent to the processing chamber; and
an RF generator configured to supply power to the coil.
17 . The plasma processing system according to claim 16 , wherein the controller is further configured to adjust power supplied by the RF generator to the coil in response to the plasma density.
18 . The plasma processing system according to claim 16 , wherein the controller is further configured to communicate with a gas delivery system to adjust a gas flow rate to the processing chamber in response to the plasma density.
19 . A method for measuring plasma density comprising:
arranging a substrate on a substrate support in a processing chamber;
striking plasma in the processing chamber;
transmitting first terahertz waves through the plasma in the processing chamber;
receiving second terahertz waves corresponding to the first terahertz waves transmitted through the plasma; and
determining plasma density based on characteristics of the second terahertz waves.
20 . The method of claim 19 , further comprising measuring reference terahertz waves transmitted through the processing chamber before generating the plasma in the processing chamber.
21 . The method of claim 20 , wherein the determining the plasma density includes at least one of:
comparing an amplitude of the second terahertz waves with an amplitude of the reference terahertz waves; or
comparing a phase of the second terahertz waves with a phase of the reference terahertz waves.
22 . The method of claim 21 , wherein the plasma density is proportional to a difference between the amplitude of the reference terahertz waves and the amplitude of the second terahertz waves.
23 . The method of claim 22 , wherein the amplitude of the second terahertz waves is smaller than the amplitude of the reference terahertz waves.
24 . The method of claim 22 , wherein as the plasma density in the processing chamber increases, a transmittance of the second terahertz waves decreases and the difference between the amplitude of the reference terahertz waves and the amplitude of the second terahertz waves increases.
25 . The method of claim 21 , wherein the plasma density is proportional to a difference between the phase of the reference terahertz waves and the phase of the second terahertz waves.
26 . The method of claim 25 , wherein the phase of the second terahertz waves is different than the phase of the reference terahertz waves.
27 . The method of claim 25 , wherein as the plasma density in the processing chamber increases, a transmittance of the second terahertz waves decreases and the phase difference between the reference terahertz waves and the second terahertz waves increases.
28 . The method of claim 19 , wherein the receiving the second terahertz waves includes:
outputting the first terahertz waves into the processing chamber from an emitter arranged on one side of the processing chamber; and
detecting the second terahertz waves transmitted through the processing chamber from a detector arranged on the other side of the processing chamber.
29 . The method of claim 28 , wherein a path of the second terahertz waves between the emitter and the detector passes over the substrate.