Plasma cleaning eliminates organic contaminants from treated surfaces via a chemical reaction or physical ablation of hydrocarbons. Process gases that are chemically reactive (air, oxygen) react with hydrocarbon monolayers to create gaseous products that are swept away by the plasma cleaner chamber’s continuous gas flow. Wet chemical methods such as piranha etching, which include hazardous chemicals, increase the risk of reagent contamination, and risk etching treated surfaces, can be replaced by plasma cleaning.
Gas atoms are stimulated to higher energy states and ionised in plasma. When atoms and molecules’relax’ to their usual, lower energy states, a photon of light is released, resulting in the “glow” or light associated with plasma. Colors are produced by several gases. The colour of oxygen plasma, for example, is bright blue.
Atoms, molecules, ions, electrons, free radicals, metastables, and photons in the short wave ultraviolet (vacuum UV, or VUV for short) spectrum are among the active species in a plasma. Any surface placed in the plasma interacts with this mixture.
If the gas used is oxygen, the best plasma clean is an effective, economical, environmentally safe method for critical cleaning. The VUV energy is very effective in the breaking of most organic bonds (i.e., C–H, C–C, C=C, C–O, and C–N) of surface contaminants. This helps to break apart high molecular weight contaminants. A second cleaning action is carried out by the oxygen species created in the plasma (O2+, O2−, O3, O, O+, O−, ionised ozone, metastable excited oxygen, and free electrons).[2] These species react with organic contaminants to form H2O, CO, CO2, and lower molecular weight hydrocarbons. These compounds have relatively high vapor pressures and are evacuated from the chamber during processing. The resulting surface is ultra-clean. In Fig. 2, a relative content of carbon over material depth is shown before and after cleaning with excited oxygen
If the item is made of easily oxidised metal like silver or copper, inert gases like argon or helium are used instead. Plasma stimulated atoms and ions function like a molecular sandblast, allowing organic pollutants to be broken down. During the processing, these impurities evaporate and are expelled from the chamber.
Small amounts of gases, such as carbon dioxide and water vapour, with trace amounts of carbon monoxide and other hydrocarbons, make up the majority of these by-products.
Contact angle measurements can be used to determine whether or not organic elimination is complete. Water has a high contact angle with the device when an organic contamination is present. When contaminants are removed, the contact angle is reduced to that of contact with the pure substrate. Surface cleaning and sterilisation applications are frequently validated using XPS and AFM.
Treatment through direct contact with plasma (capable of contraction to microarcs) could be detrimental if the surface to be treated is coated with a patterned conductive layer (metal, ITO). Cleaning by neutral atoms heated in plasma to a metastable state can be used in this scenario. The same applications to the surfaces of glass samples coated with Cr and ITO layers yielded the same results.
A water droplet’s contact angle decreases after treatment, becoming less than it was on the untreated surface. The droplet footprint relaxation curve for a glass sample is given in Fig. 4. Figure 4 inset shows a shot of the identical droplet on an untreated surface. The surface relaxation time for the data shown in is around 4 hours.
Plasma ashing is a carbon-removal method that only relies on plasma cleaning. O2 gas is always used for plasma ashing.Read More
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