Invited Paper PS2-TuA10
Electron Heating Mechanisms, Mode Transitions, and Non-Uniformities in Dual Frequency Capacitive Discharges
Tuesday, October 16, 2007, 4:40 pm, Room 607
The physics of capacitive discharges has recently been reinvigorated with the rise of interest in multiple-frequency excitation and the related need to widen the range of frequencies that are used. A major attraction of dual-frequency excitation is that it promises independent control of the ion flux and the ion energy. In some circumstances, a third frequency is added to further control the etching processes by modifying the ion energy distribution function at the substrate. In this paper, we focus on the consequences of multiple-frequency excitation on the electron heating mechanisms, and in turns on the plasma uniformity. We will discuss the collisionless and collisional electron heating mechanisms within rf sheaths, when they are driven by two frequencies. For typical discharge parameters, we find the result that the collisionless heating produced by the combination of two frequencies can be much larger than that of either acting alone. We will also address the issue of electromagnetic effects arising when the wavelength associated with the highest frequency becomes comparable to (or shorter than) the electrode size. In this situation, the electric field has two components, (i) the usual capacitive field perpendicular to the electrodes, (ii) and the inductive field, parallel to the electrode. The power deposited by the inductive field may be greater than the capacitive power. As in classical inductive discharges, the high frequency capacitive discharge experiences capacitive-to-inductive (E to H) transitions when the injected power, i.e. the voltage between the electrodes, is increased. Finally, both the capacitive and inductive powers are radially non-uniform, which can lead to severe problems of process uniformity.