Model for noncollisional heating in inductively coupled plasma processing sources

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Abstract
Low pressure (<10 mTorr) inductively coupled plasma sources are being developed for etching and deposition of semiconductors and metals. In models for these devices, plasma dynamics are typically coupled to the electromagnetic fields through Ohm’s law, which implies that collisional heating is the dominant power transfer mechanism. In this article, we describe an algorithm to couple plasma dynamics to electromagnetic field propagation which self-consistently includes noncollisional heating effects as well. The algorithm makes use of kinetic information available from an electron Monte Carlo simulation to compute plasma currents that are then used in computation of the electromagnetic field. Results for plasma density and electric field amplitude are presented as a function of power and pressure, and are compared to results from models that consider only collisional heating. We find that noncollisional heating effects are important at pressures of less than 10–20 mTorr, a range that depends both on gas mixture and geometry. Noncollisional heating effects allow the wave to couple more efficiently to the plasma. As a result, the electric field amplitude required to deposit a given amount of power in the plasma is smaller than that needed when only collisional heating is considered. For a constant power deposition, this generally leads to lower plasma densities.