| AVS 64th International Symposium & Exhibition | |
| Plasma Science and Technology Division | Wednesday Sessions |
| Session PS-WeA |
| Session: | Modeling of Plasmas |
| Presenter: | Steven Lanham, University of Michigan |
| Authors: | S.J. Lanham, University of Michigan M.J. Kushner, University of Michigan |
| Correspondent: | Click to Email |
Pulsing the power applied to inductively coupled plasma (ICP) systems has beneficial effects, such as lowering average ion energies and customizing the flux of reactive species to surfaces [1]. With pulsed plasmas being increasingly used in semiconductor fabrication, more of the processing time is in a transient regime. For example, in many ICP systems pulsing the power repeatedly transitions between electrostatic (E-mode) power deposition at the start of a power pulse and inductive (H-mode) power deposition later during the power pulse [2]. This transition results from the large variation of the electron density, particularly for electronegative gas mixtures, and plasma impedance during a pulse. For the highly electronegative gases often used for processing, the plasma can essentially extinguish in the afterglow of a pulse and require reigniting at the start of every pulse.
In this paper, we discuss mode transitions for power deposition in pulsed ICP systems based on results from a computational investigation. The Hybrid Plasma Equipment Model (HPEM), a 2-dimensional plasma multi-fluid model [3], was used to simulate the consequences of the E-H transition resulting from capacitive coupling in pulsed ICPs. We found that for highly electronegative gas mixtures, such as Cl2 at a few to tens of mTorr, the power initially applied at the beginning of a pulse is essentially purely capacitive. The dominance of sheath centric power deposition during startup can then launch electrostatic waves into the plasma, an outcome that is sensitive to antenna frequency and pulse repetition frequency. Choosing to operate with a ramped current or ramped power at the onset of a pulse can, in some instances, constrain operation to E-mode or allow a faster transition from E- to H-mode. The pulse power format has a first order effect – controlling current or controlling power – on the E-H transition, and the stability of the plasma.
[1] D. J. Economou, J. Phys. D. Appl. Phys. 47, 303001 (2014).
[2] M. Zaka-ul-Islam, Phys. Plasmas 23, 113505 (2016).
[3] M. J. Kushner, J. Phys. D. Appl. Phys. 42, 194013 (2009).
This work was supported by the National Science Foundation and the Department of Energy Office of Fusion Energy Science.