Paper PS-MoA8
Control of Uniformity and Ion Energy Distributions in Tri-frequency Capacitively Coupled Plasmas Accounting for Finite Wavelength Effects

Monday, November 7, 2016, 4:00 pm, Room 104B

To provide additional means of control of capacitively coupled plasmas (CCPs) for semiconductor processing, multi-frequency systems are being investigated. Current plasma tools now have up to 3 frequencies. The source is typically a high frequency (50-150 MHz) intended to control ionization. The biases, typically low frequencies of a few to 10 MHz, are used to control ion energy distributions. At sufficiently high frequencies, the applied power takes on electromagnetic properties (as opposed to electrostatic) in which the electric field is wave-guided by the plasma sheath, causing constructive and destructive interference over the wafer. In extreme cases, a center-high electric field is produced along with a non-uniform center-high plasma density. The mixing of frequencies in tri-frequency systems (TF-CCPs) has the potential to mitigate finite wavelength effects while also providing opportunities to control IEDs.

In this work, TF-CCPs were investigated using a 2-dimensional hydrodynamic model with a full-wave FDTD (finite-difference-time-domain) solution of Maxwell’s equations. Results will be discussed for plasma uniformity and IEDs for Ar and Ar/C₄F₈/O₂ gas mixtures at 10s of mTorr, with frequencies of a few MHz, 10 MHz and up to 150 MHz with collective powers of up to 10-15 kW. We found that at these elevated powers, the ability to separately control ion fluxes and IEDs is at best difficult. For these conditions, the system should be viewed as a collective set of 3-frequencies that have symbiotic contributions, as opposed to separate contributions that can be uniquely controlled.

Work was supported by Samsung Electronics Ltd., Department of Energy Office of Fusion Energy Science and the National Science Foundation.