Definition:Quasineutral gas that exhibits collective behavior in the presence of electromagnetic field
Fourth state of matter, posses different properties than gases
History: Irving Langmuir studied in 1929 plasma as a ionized gas in vacuum tubes
Purpose: Use of nonthermal energy (electric fields) for various processes at low temperature such as etching and deposition
How is it created:
an electric field is applied between two electrodes (negative bias on cathode and positive bias on anode)
a gas is introduced in the chamber
electrons are accelerated towards the anode
electrons collide with gas molecules, and a few processes occur as an effect of collisions:
dissociation: neutral atoms are removed from the molecule, they can deposit on surfaces, react with other atoms, etc.
ionisation: ions are created by removing an electron from the molecule, the ions are attracted by the cathode, which will be bombarded and maybe sputtered
excitation, radicals are formed, the radicals will deexcite (electron will return to ground zero of energy) and emit a photon, the photons have different colours (orange, pink, purple, blue, yellow) depending on the wavelength/excitation energy and thus plasma (named also glow discharge) will illuminate and heat the objects nearby
Excitation due to electron collision, and photon emission are presented in the next animation (in the middle is the nucleus of the atom; the electron moves around the nucleus having an energy level; after the collision the electron jumps to a higher energy level and after a few miliseconds it returns to the ground state energy, emitting a photon with the energy equal to the the difference between the two energy levels)
Substrate preparation
