The origins of self-bias on dielectric substrates in RF plasma processing

Negative biasing of dielectric substrates in plasmas is frequently applied to thin film deposition and etching in order to control impact energies onto the surface, which is usually done by contacting the dielectric substrates to an RF-driven electrode. The value of the bias on the surface of a dielectric substrate is difficult to monitor during plasma processing. In this work, we show that the self-bias on a dielectric substrate is determined by the plasma conditions as well as the thickness of the dielectric substrate. The difference between the actual self-bias on the surface of a dielectric substrate and the self-bias on the driven electrode can be very large. We propose a simple model to interpret the experimental results, in which the electron temperature and the plasma density as well as the dielectric thickness or dielectric constant play an important role in determining the actual bias on the dielectric substrate.