Radio Frequency Plasma (RF Plasma)

Basic properties of plasma

From a physical point of view, the definition of "plasma" is:

An electrically neutral, highly ionized gas composed of ions, electrons, and neutral particles. It is a state of matter that is considered to be different from solids, liquids, and ordinary gases.

A state of matter in which some or all of the electrons have been separated from their parent atoms. Negatively charged electrons and positively charged ions move independently. Plasma is often associated with extremely high temperatures.For example, most of the sun is made up of plasma.

Plasma is a low-density gas composed of electrons, positive ions, and neutral particles, and the overall performance is electrically neutral, which is considered the fourth state of matter. Strictly speaking, almost all gases in space can be called "plasma", although only a small fraction of atoms are ionized when the temperature is below about 726.85°C. The very low density in space allows electrons to travel without much hindrance, so space is almost a perfect conductor of electricity. Although electric charges can move freely, on average, cosmic plasma is always neutral, even in a very small volume (say a million kilometers). Plasma in space is permeated by a magnetic field.

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How plasma happens

The plasma with an excitation frequency of 40 kHz is the ultrasonic plasma: a physical reaction;

The plasma with an excitation frequency of 13.56MHz is a radio frequency plasma: physical reaction + chemical reaction;

Plasma with an excitation frequency of 2.45 GHz is a microwave plasma: a chemical reaction.

 

RF (Radio Frequency) power is widely used in plasma generation, especially in applications such as semiconductor manufacturing, surface treatment, and plasma etching. Here's a simple explanation of how RF power creates plasma:

RF generator: The process starts with an RF generator, which produces high-frequency alternating current (AC) power.

Electrode: This RF power is supplied to the electrode inside the vacuum chamber. The configuration of these electrodes can vary, but typically one electrode is energized (connected to the RF generator) and the other is grounded.

Electric field: The application of RF power creates an oscillating electric field between the electrodes. As the voltage increases, so does the strength of the electric field.

Ionization: In the presence of gases such as argon, oxygen, or nitrogen in the chamber, a strong electric field ionizes gas molecules. The electrons in the gas atoms gain enough energy to escape their atomic orbitals, resulting in the production of ions and free electrons.

Collision and excitation: Free electrons gain kinetic energy from an electric field and travel quickly through the gas. These electrons collide with other gas atoms to further ionize them and produce more free electrons and ions in a chain reaction. This process is known as collisional ionization.

Plasma formation: As this process continues, the density of ions and electrons increases, leading to the formation of plasma – a group of charged particles that are generally electrically neutral but highly reactive.

Plasma maintenance: A continuous supply of RF power is necessary to maintain the electric field, maintain the ionization process, and keep the plasma state stable. The frequency and power level of the RF signal can be adjusted to control the characteristics of the plasma.