What is plasma?
Plasma is a state of matter with higher energy than gas. Generally speaking, matter exists in three states: solid, liquid, and gas. As the temperature increases, the solid becomes a liquid and becomes a gas.
For example, water becomes a solid called ice in its crystalline state, liquid water when the temperature increases, and a gas called water vapor when the temperature increases further. Therefore, the energy possessed by matter determines its state of matter.
Matter usually has electrons moving around its nucleus. The nucleus is positively charged and consists of protons and neutrons. Instead, because the electrons are negatively charged, they are attracted to the nucleus by the Coulomb force and always move around the nucleus.
However, when the temperature of the gas is further increased to an extremely high energy state of about a few thousand degrees Celsius, the electrons orbiting the nucleus separate (ionize) from the atom and become unstable. This state is plasma.
In its ionized and unstable state, the plasma emits light and electromagnetic waves, and appears to glow as it releases energy and tries to return to a stable state. In addition, the flow of current is extremely easy, which is also characterized by the increased movement of electrons due to electromagnetic forces.
While plasma appears to be a special state, it is often observed in nature. Thunder and Aurora are one of them. Industrially, it is also used to make fluorescent lamps, plasma torches and semiconductors.
Plasma in Semiconductors
Below are three examples of the use of plasma in semiconductor manufacturing.
(1) Plasma Enhanced Chemical Vapor Deposition (PECVD)
Plasma-enhanced chemical vapor deposition (PECVD) is used for the formation of silicon nitride films (SiN) and silicon oxide films (SiO 2 ) in silicon semiconductor manufacturing.
The feedstock gas supplied on the substrate is converted into plasma by direct current (DC), radio frequency (RF) current or microwave to activate neutrally excited particles. It is a method of forming a thin film by causing a chemical reaction on a substrate and depositing the resulting substance.
Plasma Chemical Vapor Deposition
Compared with the conventional heat treatment method (thermal CVD method), it is characterized by the ability to form thin films at low temperatures. Because it does not use a heating device, it can handle uneven substrates and complex shapes.
(2) Plasma dry etching
Etching is the process of carving grooves and patterns into the surface of a substrate. Conventionally, a wet etching method using an etching solution is used. However, in recent years, dry etching using etching gas or ions has become mainstream.
Plasma dry etching is a technique for etching by scraping the surface of a substrate with plasma. Also known as chemical physical etching technology.
As with plasma CVD, the gas flows to the surface of the substrate and the gas becomes plasma. At this time, the ions collide with the substrate, promoting chemical reactions with substances contained in the plasma. This makes it possible to precisely scratch the surface of the substrate at the atomic scale.
Unlike wet etching, no waste liquid is generated, so in addition to being a clean processing method, more precise processing than wet etching is possible.
A deeper etch can also be used to separate semiconductor chips, called plasma dicing.
(3) Plasma cleaning
Plasma cleaning is a cleaning technology that uses plasma to decompose and vaporize organic substances such as oil attached to the surface of the substrate. Besides being a dry cleaning method that does not use water or cleaning solutions, it also provides a high level of cleaning that leaves no residue.
Plasma cleaning can also make the surface of the treated object hydrophilic by breaking molecular bonds and modifying it with hydroxyl groups. It is also used to add hydrophilicity to patterned PDMS (dimethylpolysiloxane) surfaces to improve pattern adhesion during semiconductor fabrication.
Plasma Chemical Vapor Deposition
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