Question about plasma ignition

[gofightwin]

Hi,

I am an EE studying some plasma physics. I am doing alright with it, but this question cropped up in my head a few days ago, and I've come to find out that most text-books don't devote a lot of time to it.

I am interested in microfabrication, and plasma reactors are central to a lot of fab. steps, that's sort of what lead me down this path. In microfab., there a lot of plasma tools which rely on an initial or intermittent arc to ignite the plasma, I think this sort of ignition is understandable.

However, I don't think all reactors use an arc to get things started. In some reactors, the gas is still 'excited' by an RF signal, but I think something other than an arc starts things off. Some textbooks just say that this signal excites or heats the gas, etc, and that's about as far as I've gotten.

My best guess so far is that some kind of dielectric heating occurs in the gas, but after this I don't know. Perhaps there is a tiny arc that starts almost ALL plasmas? It doesn't seem like it, but I can't really find a description of this mystery ignition method I'm asking about, ha.

Any ideas?
Thanks

 

[AJ Bentley]

Ignite?

A plasma is normally formed by ionisation of gas. That can be done in a variety of ways but I've never heard anyone refer to it as 'ignition'. Ignition normally suggests a chemical reaction between oxygen and a flammable material that continues exothermically.

In my experience, a plasma is usually generated and maintained by an external energy source.