Wisman High Voltage Power Supply in the Field of Plasma Wide Range of Applications

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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 rises, a solid becomes a liquid and a gas.

For example, water becomes a solid called ice in its crystalline state, liquid water when the temperature rises, and a gas called water vapor when the temperature rises further. Thus, the amount of energy a substance possesses 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 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 rises further to an extremely high energy state of about a few thousand degrees Celsius, the electrons orbiting the nucleus separate (ionize) from the atoms and become unstable. This state is plasma.

In an 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 current is very easy to flow, which is also characterized by an increase in the movement of electrons due to the electromagnetic force.

Although plasma seems to be a special state, it is often observed in nature. Thunder and Aurora is one of them. In industry, it is also used to make fluorescent lamps, plasma torches and semiconductors.

Plasma in a semiconductor

Here are three examples of plasmas used in semiconductor manufacturing.

(1) Plasma enhanced Chemical Vapor Deposition (PECVD)

Plasma enhanced chemical vapor deposition (PECVD) is used to form silicon nitride films (SiN) and silicon oxide films (SiO 2) in silicon semiconductor manufacturing.

The feed gas supplied on the substrate is converted into plasma by direct current (DC), radio frequency (RF) current or microwave to activate neutral excitation particles. It is a method of forming a thin film by causing a chemical reaction on a substrate and depositing the resulting material.

Compared with the traditional 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 the substrate. Traditionally, wet etching methods using etching solutions have been used. However, in recent years, dry etching using etching gases or ions has become mainstream.

Plasma dry etching is a technique that etches the surface of a substrate by scraping it 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 point, the ions collide with the substrate, promoting a chemical reaction with the substances contained in the plasma. This makes it possible to precisely scrape the surface of the substrate at the atomic scale.

Unlike wet etching, no waste liquid is produced, so in addition to being a clean processing method, more accurate processing can be performed than wet etching.

Deeper etching can also be used to separate semiconductor chips, known as plasma cutting.

(3) Plasma cleaning

Plasma cleaning is a cleaning technology that uses plasma to decompose and vaporize organic matter such as oil attached to the surface of the substrate. In addition to being a dry cleaning method that does not use water or cleaning solutions, it also provides a high level of cleaning without leaving any residue.

Plasma cleaning can also make the surface of the treated object hydrophilic by breaking molecular bonds and modifying it with hydroxyl groups. In semiconductor manufacturing, it is also used to add hydrophilicity to patterned PDMS (dimethylpolysiloxane) surfaces to improve pattern adhesion.