|AVS 54th International Symposium|
|Plasma Science and Technology||Tuesday Sessions|
|Presenter:||S. Rauf, Applied Materials, Inc.|
|Authors:||S. Rauf, Applied Materials, Inc.
K. Bera, Applied Materials, Inc.
K. Collins, Applied Materials, Inc.
|Correspondent:||Click to Email|
Capacitively coupled plasma (CCP) discharges are widely used for dielectric etching in the semiconductor industry. Operating frequencies, especially the source frequency in multi-frequency CCP systems, have generally increased in recent years to be able to generate high electron-density discharges with moderate ion energy. Concomitantly, economic considerations are driving towards radially larger plasma discharges. The combination of higher driving frequencies and larger plasma size means that electromagnetic effects start to play a more important role in determining plasma behavior. Understanding the physics of VHF plasmas is therefore critical for assessing the scalability of CCPs to future generations of dielectric etching technologies. This paper uses a computational model to elucidate the physics of VHF CCP discharges. The 2-dimensional model includes the full set of Maxwell equations in their potential formulation. The equations governing the vector potential, A, are solved in the frequency domain after every cycle for multiple harmonics of the driving frequency. Current sources for the vector potential equations are computed using the plasma characteristics from the previous cycle. The coupled set of equations governing the scalar potential, φ, and drift-diffusion equations for all charged species are solved implicitly in time. The model also includes the electron temperature equation, Kirchhoff equations for the external circuit, and continuity equations for neutral species. Our simulations focus on a 180 MHz CCP discharge, and examine the effect of inter-electrode spacing, driven electrode diameter, grounded electrode size and magnetic field on the plasma characteristics. It is found that the electrostatic component of the electric field peaks in the sheath region, where there is an imbalance between positive ion and electron concentrations. Electromagnetic fields are generated by current flowing through the discharge. The electromagnetic component of the electric field peaks in the center of the chamber due to the standing wave effect. The electromagnetic fields have a strong influence on charged species location and concentration at 180 MHz. However, besides the operating frequency, the plasma reactor design (inter-electrode spacing and electrode sizes) also determines the relative importance of the electromagnetic fields in plasma dynamics.