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1、 What is plasma?
Plasma is the fourth material state except
for solid, liquid, and gas. It is mainly formed by the dissociation of gas
under the action of a high electromagnetic field to form a highly active
substance composed of electrons (with a negative charge), positive ions (with a
positive charge), free radicals, and neutral gas molecules. It will emit light
under the condition of common production. Generally, the number of positive
charges in plasma is equal to negative The number of charges, so the whole is
quasi-neutral. The lightning, fluorescent lamp, and neon lamp in our daily life
are the phenomena of plasma luminescence.
2、 Generation of
plasma
There are many ways to generate plasma, but
both generation and maintenance need external energy input. The electrons get
energy from the external electromagnetic field, and then inelastic collision
produces excitation and dissociative adsorption Secondary electrons, atoms,
molecules, and ions are produced by the reactions of attachment, disassociation,
ionization, and recombination. However, in the dissociation collision, the
electrons may reabsorb with gas ions, or disappear due to drift and diffusion
away from the electromagnetic field. Therefore, when the electrons are
generated and disappeared, they will not be able to form a new type of material
When the rate is equal, the plasma is stable. Here are four commonly used
plasma generation methods for etching
CCP:Capacitively
Coupled Plasma
ICP:Inductively
Coupled Plasma
TCP:Transformer Coupled
Plasma
ECR:Electron
Cyclotron Resonance
3、 Parameters of
plasma
a. Mean free path (MFP)
The average distance a particle can move
before it collides with it. The MFP is inversely proportional to the ambient
pressure P. the higher the pressure, the shorter the MFP, the lower the
pressure, and the longer the MFP. This is why plasma is produced in a
low-pressure approximate vacuum environment, because at atmospheric pressure
(760 Torr), the MFP of electrons is very short, and it is difficult to obtain
enough ability to use gas ionization.
Ionization degree:
b. The ratio of electron concentration to
the sum of ion and neutral particle concentration in plasma. The ionization
degree mainly depends on the energy of electrons in the plasma. The ionization
degree in most plasma reaction chambers is less than 0.01%, the ionization
degree of high-density plasma is about 1% ~ 5%, and the ionization degree at
the center of the sun is about 100%.
4、 Application of
plasma
At present, plasma technology is widely
used in various industries, such as semiconductor industry, biomedical
industry, food and chemical industry, automobile parts industry, etc,