Electron heating in reactive and magnetized capacitive radio frequency plasmas: From fundamental understanding to predictive control

• Applicants: Professor Dr. Julian Schulze; Dr. Li Wang
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas ; Communication Technology and Networks, High-Frequency Technology and Photonic Systems, Signal Processing and Machine Learning for Information Technology
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 428942393

Capacitively coupled radio frequency technological plasmas (CCP) are frequently used for etch and deposition processes on microscopic scales, that represent crucial steps in the production of computer chips in semiconductor manufacturing and are important for a variety of other applications of high societal relevance. Despite their importance to overcome the "chip crisis", the fundamentals of their operation under application relevant conditions, i.e. in complex reactive and electronegative gas mixtures, externally applied magnetic fields and under multi-frequency excitation, are not understood. Thus, plasma processes are mostly developed empirically until now. However, the ever increasing process requirements towards the control of energy distribution functions of electrons, ions, and reactive radicals in the plasma volume and at boundary surfaces, e.g. in the production of miniaturized transistors, require a knowledge based approach. This must be based on a fundamental understanding of the spatio-temporally resolved electron power absorption dynamics in the plasma and the effects of external control parameters on it such as the gas mixture, magnetic field, pressure and driving voltage waveform. In this project we investigate the spatio-temporally resolved electron power absorption dynamics in CCPs operated in different mixtures of Ar/CF4/O2 as an example of a commercially relevant reactive and electronegative gas mixture used frequently for dielectric plasma etching. By a synergistic combination of hybrid (fluid/kinetic) simulations and experiments in a reference reactor we study the effects of transversal magnetic fields and tailored multi-frequency driving voltage waveforms on the electron heating and the formation of process relevant distribution functions of electrons, ions, and neutral radicals as a function of external control parameters such as the pressure and gas mixing ratio. For this purpose a new hybrid simulation is implemented, benchmarked against existing fully kinetic simulations and validated experimentally based on multiple state-of-the-art plasma diagnostics. Compared to existing particle-in-cell kinetic simulations, the new code will be much faster, since heavy particles are treated as a fluid, while electrons are handled fully kinetically to describe non-local effects correctly. In this way radical densities and fluxes can be obtained. The synergistic combination of hybrid simulations and experiments will be used to reveal and understand new modes of electron heating in magnetized CCPs such as the magnetized Drift-Ambipolar mode and magnetically induced electric field reversals. The effects of Voltage Waveform Tailoring on energy distribution functions of different particle species in such complex discharges will be studied. Based on the obtained fundamental understanding concepts to control such distribution functions will be developed as the basis of knowledge based plasma process control.

• DFG Programme: Research Grants
• International Connection: Hungary
• Cooperation Partners: Dr. Zoltan Donko; Dr. Peter Hartmann