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How does electron flow occur in DC sputtering with dielectric substrates?

In my thin-film deposition work, I frequently use DC magnetron sputtering for metals. The standard model assumes a closed electrical circuit. However, when I place a glass or ceramic substrate on the anode, this model seems to break down, as charge would accumulate on the insulator. I'm trying to reconcile the practical success of the technique with the fundamental electrical principles.

 

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By Hamid Khan Answered 1 year ago

This is a classic practical hurdle. I've set up many sputter systems where this initially seems problematic. The key is that in a robust DC plasma, the insulating substrate surface does charge positively initially, but this actually attracts a sufficient flux of secondary electrons from the plasma itself. These electrons neutralize the positive charge in a dynamic, localized equilibrium. Furthermore, if the substrate holder has any slight conductivity or uses a grounded metal mask, it provides a subtle bleed path. So, the "circuit" closes through the plasma and these transient surface currents, not through the bulk insulator.

 

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