Low-temperature plasma is usually used to clean the surface of materials. It has the characteristics of high action strength and low penetration ability, simple and effective process treatment, environmental protection and energy saving. It can undergo a series of complex physical reactions or chemical reactions with the surface of materials.

Plasma cleaning principle

Plasma cleaning is that the plasma impacts the surface of the material to be cleaned through its internal particles with specific reactivity or high energy, such as ions, electrons, excited atoms and molecules, and free radicals. The pollutants or microparticles attached to the surface are peeled off or react with the organic matter on the surface of the product to form volatile gases, which are discharged with the vacuum pump to achieve the purpose of cleaning the surface of the material. It belongs to the dry cleaning technology, which can effectively remove the pollutants on the surface of the material to be cleaned without destroying the surface characteristics of the material. It has obvious advantages and can replace the traditional wet cleaning technology.

Plasma cleaning principle diagram

The plasma cleaning process is as follows :

Radio frequency excitation produces plasma→excitation state ( atom group, ion, neutral molecule )→plasma sputtering, etching→cleaning reaction

The RF excitation cleaning gas generates plasma, and the excited particles sputter and etch on the surface of the material to be cleaned to perform the plasma cleaning reaction. Because there are active particles such as electrons, ions and free radicals in the plasma, it is easy to undergo physical or chemical reactions with the solid surface. ( 1 ) The effect of free radicals such as atomic groups on the surface of the product to be cleaned : plasma free radicals are more than electrons, and are electrically neutral. The free radicals in the excited state have high energy and are easy to combine with the molecules on the surface of the product to continuously generate new free radicals. The newly formed free radicals also have high energy and are easy to cause decomposition reactions to produce small molecules and new free radicals, which cause the substances on the surface of the product to undergo continuous chemical reactions and eventually decompose into volatile substances such as water and carbon dioxide. ( 2 ) The effect of electrons on the surface of the product : electrons impact the surface of the product, prompting the gas molecules attached to the surface of the product to produce chemical decomposition or desorption. And a large number of electrons accumulate on the surface of the product, which is easy to cause chemical reactions. ( 3 ) The effect of ions on the surface of the product : usually positively charged cations will accelerate the movement to the negatively charged surface, resulting in atoms or molecules on the surface of the product to obtain greater kinetic energy, and ultimately escape from the surface of the product. This phenomenon is called sputtering phenomenon. ( 4 ) The effect of ultraviolet light on the surface of the product : it has strong light energy and strong penetration ability. It can break the molecular bonds attached to the surface of the product, and can penetrate the surface of the product and react up to several microns. In short, the surface of the product is cleaned by using the activation properties of various high-energy substances in the plasma, and the oxides and pollutants attached to the surface of the product to be cleaned are desorbed.