Plasma cleaning is the removal of contaminants and contaminants from surfaces using high-energy or dielectric barrier discharge (DBD) plasmas generated from gaseous species. https://www.tridentet.com/plasma-clean/ Gases such as argon and oxygen and mixed gases such as air and hydrogen/nitrogen are used. Plasmas are created by ionizing low-pressure gases (usually about 1/1000 of atmospheric pressure) using high-frequency voltages (typically kHz to >MHz), although atmospheric pressure plasmas are now common as well.
In a plasma, gas atoms are excited to higher energy states and ionized. When atoms and molecules "relax" to their normal, low-energy state, photons are emitted, producing the characteristic "glow" or light associated with plasmas. Different gases produce different colors. For example, oxygen plasma emits a light blue color.
Plasma activating species include atoms, molecules, ions, electrons, free radicals, metastables, and short-wave ultraviolet (vacuum UV, or VUV for short) photons. This mixture interacts with each surface introduced into the plasma.
Plasma is an effective, economical and environmentally friendly method for critical cleaning when the gas used is oxygen. VUV energy is very effective at breaking most organic bonds (ie, C-H, C-C, C=C, C-O, and C-N) in surface contaminants. This helps break down high molecular weight contaminants. A second cleaning action is performed by plasma-generated oxygen species (O2+, O2-, O3, O, O+, O-, ionized ozone, metastable excited oxygen, and free electrons) [2] . These species react with organic impurities to form HO, CO, CO2, and low molecular weight hydrocarbons. These compounds have relatively high vapor pressures and are expelled from the chamber during processing. The surface obtained is very clean. Figure 2 shows the relative carbon content in depth of the material before and after cleaning with excited oxygen [1].
Figure 2. Carbon content and material depth z: before sample treatment - diamond point and after 1 second treatment. - square point
If the part is made of a material that oxidizes easily, such as silver or copper, the process uses an inert gas such as argon or helium instead. Plasma-activated atoms and ions act like a molecular sandblast and can break down organic contaminants. These contaminants evaporate during processing and are exhausted from the chamber.
Most of these by-products are small amounts of gases such as carbon dioxide and water vapor with trace amounts of carbon monoxide. View full..