My project focuses on making a plasma density measuring sensor for a PE-CVD chamber (Plasma Enhanced Chemical Vapor Deposition Chamber) . It has a capacitively coupled plasma which is powered by 13.56MHz RF power supply with 300-1000 Watts of power. At this RF frequency I expect lot of noise to be generated that would make the sensor output very difficult to read. The sensor will be placed inside the plasma chamber. Therefore I would like to measure the RF interference that would occur when the sensor is active. But I have no way of taking wires out of the chamber, since its vacuum sealed. Could you tell me how to do this with an Oscilloscope or a Spectrum Analyzer outside of the chamber? Do I need an antenna for this? And is it technically possible to do this outside the chamber?
Hi Indula, I cant really see it being practical to try and measure from outside the chamber, as your readings will be swamped by interference generated on the outside (which is more likely to be much more noisy than on the inside.)
For cheap electrical feed throughs to a vacuum chamber, you can use PCBs with pins / connectors soldered to both sides of the PCB and Oring sealed to the surface. Otherwise you could look at using some magnetic inductively coupled device.
For measuring a plasma density though I would think a non electrical way would be much better as there will be SO much interference. Can you not do it by looking at the optical spectrum / intensity of the plasma?
Thank you for your answer! Phil Denby
Is there any way of eliminating the noise generated here, if I keep the circuitry inside the chamber? Would that be enough using a simple RF filter if I'm measuring the current generated on the sensor due to plasma ? I expect the current waveform would also be in RF frequency and hence interference from RF noise would make filtering practically difficult. Is there a way around this ?
Hi Indula, I think the simplest most effective way would be putting the electronics inside a metal enclosure in your system. You could use some sort of fine metal mesh for most of it to allow fast pumping, but this should shield all the electronics very effectively.
- Badges
- Science topic
- Similar topics
- Phytochemistry
- Extracts