Radio-Frequency Capacitive Discharges

Yuri P. Raizer, Mikhail N. Shneider, Nikolai A. Yatsenko

• Publisher: CRC Press
• Year: 2017
• ISBN:
  9781351419956
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Physical & Theoretical Chemistry

The first publication of its kind in the field, this book describes comprehensively and systematically radio-frequency (rf) capacitive gas discharges of intermediate and low pressure and their application to gas laser excitation and to plasma processing. Text presents the physics underlying rf discharges along with techniques for obtaining such discharges, experimental methods and results, and theoretical and numerical modeling findings. Radio-Frequency Capacitive Discharges is written by well-known specialists in the field, authors of many theoretical and experimental works. They provide simple and clear discussions of complicated physical phenomena. A complete review on the state of the art is included. This interesting new book can be used as a textbook for students and postgraduates and as a comprehensive guidebook by specialists.

1

Basic Principles of the RF Capacitive Discharge

This chapter is an introduction to the physics of radio-frequency (RF) capacitive discharges. It describes various techniques for the excitation of RF field in a gas and the behavior of electrons (the majority charge carriers in fast oscillating electric fields), the electrodynamic characteristics of discharge plasma and their influence on an oscillating field. The production and loss of electrons and the plasma maintenance are discussed briefly. Basic data on the structure and behavior of RF discharges are given, and the formation of space charge sheaths at the electrodes and of constant potential in RF plasma is explained. A simplified RF discharge model is analyzed in order to provide a basis for further discussion of experimental data. Evidently, one cannot do an experiment and understand the results obtained without a simplified initial model of the phenomenon under study. The model will also serve as a starting point for consideration of the details of more complicated theories.

1.1 Excitation of an RF discharge

The RF range commonly used in discharge practice is f=ω/2π≃1−100 MHz. RF discharges can be subdivided into inductive and capacitive discharges differing in the way an RF field is induced in the discharge space. Inductive methods are based on electromagnetic induction so that the created electric field is a vortex field with closed lines of force. In capacitive methods, the voltage from an RF generator is applied to the electrodes, the lines of force strike them and the resultant field is essentially a potential field.

A simple and commonly used schematic representation of the inductive discharge is shown in Figure 1.1(a). RF current from an external source is passed through a coil which in practice may have even one or a few turns. The magnetic field in the coil is alternating and directed along the coil axis. A circular electric field is induced in the coil and its lines of force are concentric with the primary RF current. This electric field can initiate and maintain a gas discharge. For this purpose, a dielectric tube or a vessel filled with a gas under study at a required pressure is placed inside the coil, or a gas is pumped through the tube to produce a plasma jet. The inductive discharge is in principle electrodeless.

FIGURE 1.1
Basic ways of exciting RF discharges: (a) inductive discharge; (b)−(e) capacitive discharges with (b) plane naked electrodes, (c) coated electrodes, (d) external electrodes, and (e) with the earth as the other ‘electrode’ (torch single-electrode discharge).

A schematic diagram of a conventional capacitive discharge is shown in Figure 1.1(b,c). Two parallel disc electrodes are placed in a vessel filled with a gas at a certain pressure, and RF voltage is applied to the electrodes. These may be identical or vary in diameter; the latter will be shown below to be advantageous for some applications. Since the ac circuit should not necessarily be closed and may contain some nonconducting sections, the electrodes can be insulated from the conducting discharge plasma with dielectric material. This provides a possibility, often used in practice, to mou...

Table of contents

• Cover Page
• Title Page
• Copyright Page
• Preface
• 1 Basic Principles of the RF Capacitive Discharge
• 2 Moderate-Pressure RF Discharges
• 3 Low-Pressure RF Discharges and Asymmetry Effects
• 4 Experimental Methods and Measurements
• 5 Application of RF Capacitive Discharges for Gas Laser Excitation and Plasma Technology
• References
• Index