AVS 57th International Symposium & Exhibition
    Plasma Science and Technology Tuesday Sessions
       Session PS2-TuA

Paper PS2-TuA8
Self-Consistent Electrodynamics of Large-Area High-Frequency Capacitive Plasma Discharge

Tuesday, October 19, 2010, 4:20 pm, Room Galisteo

Session: Plasma Sources
Presenter: Z. Chen, Applied Materials Inc.
Authors: Z. Chen, Applied Materials Inc.
S. Rauf, Applied Materials Inc.
K. Collins, Applied Materials Inc.
Correspondent: Click to Email
Large-area capacitively coupled plasmas (CCP) generated by high frequency (HF, 3-30 MHz) and very high frequency (VHF, 30-300 MHz) RF sources are used for thin film deposition in the production of thin film transistors for flat panel display and thin film photovoltaic solar panels. Economic considerations are driving a rapid increase in substrate size and adoption of VHF sources for improved film quality and higher deposition rate. As a consequence of these trends, electromagnetic wave effects are becoming the dominant factor in determining processing uniformity. Because the effective RF wavelength in plasma depends upon both RF frequency and plasma process conditions such as RF power and gas pressure, a self-consistent model including both RF power delivery system and plasma discharge is highly desired to capture a more complete physical picture of plasma behavior. In this paper, we present a three-dimensional model for self-consistently studying both electrodynamic and plasma dynamic behavior of large-area (> 8 m2) CCP. The model couples Maxwell’s equations with transport equations for charged and neutral species in the time domain. Maxwell’s equations are discretized and solved using the finite-difference time-domain (FDTD) method. The plasma discharge is modeled by solving the continuity equations for charged and neutral species and the electron energy conservation equation. The complete RF plasma discharge chamber including RF power delivery sub-system, electrodes and plasma domain is modeled as an integrated system. The RF power source is naturally applied onto the transmission line of the RF feed system in the form of an electromagnetic wave. Based on the full-wave solution model, we are able to study the important limitations for processing uniformity imposed by electromagnetic wave effects in a rectangular reactor having electrode size of 3.05 m × 2.85 m. We examine the behavior of H2 plasmas in such a reactor at a pressure of 2 Torr when we incrementally scale the frequencies from 13.56 to 200 MHz and the power from 20 kW to 80 kW. We show that various rectangular harmonics of electromagnetic fields can be excited as RF frequency or power is increased. These rectangular harmonics, mathematically described by the hyperbolic functions, can create not only the plasma profiles where plasma density is high at the center and low at the corners of the reactor, but also the profiles where plasma density is high at the corners and along the edges of the reactor and low in the inner area. Such highly nonuniform plasma distribution at VHF or high power level is challenging to compensate and has important implications for large-area plasma processing.