What is plasma?
Plasma can be defined as the fourth state of matter because it is not a liquid, solid or gas. In general, at low pressures (such as in the upper atmosphere and fluorescent lamps) or at very high temperatures (such as in stars and nuclear fusion reactors), it is an ionized gas composed of positive ions and free electrons in proportions that cause almost no total electrical charge.
A plasma includes ions, electrons, neutral gas atoms or molecules, UV light as well as excited gas atoms and molecules capable of carrying a large amount of internal energy.
All of these components may interact with the surface during plasma treatment. The effects of the plasma process can be fully adjusted or determined by the gas mixture, power, pressure, etc.
Although plasma is abundant in the universe, it is relatively rare in the world. Lightning and aurora are the main examples of naturally occurring plasma.
Using Plasma Technology
Organic surface pollutants are unlikely to be seen by nonexperts, but these pollutants greatly affect the ability of an object to interact with other materials. When a surface plasma treated, we can remove these contaminants.
Furthermore, the plasma treatment can increase or decrease the wettability by forming the surface. This allows any type of printing, painting or coating to adhere to the surface of the object.
Many universities undergo plasma treatment of various substrates for educational and laboratory studies. In addition, plasma treatment is performed by medical facilities and research laboratories working on new medical procedures.
Manufacturing plants use plasma processes to completely clean their products before bonding or printing.
For example, a facility that produces a medical catheter will most likely use vacuum plasma technology to clean the catheter and tubing before they are interconnected. This strengthens the bond and provides a durable, quality product.
When producing a small integrated circuit (IC) chips, plasma etching is used to engrave a layer of material with only a few atomic thicknesses. Nano IC chips are produced using plasma in clean rooms with as little as 10nm between transistors.
This requires a very precise and smooth production process. A photoresist is used to block the etching in the desired order, thereby engraving and eroding only areas where the photoresist is absent. This allows any pattern to be processed meticulously, with minimal or no error.
How to Perform Vacuum Plasma Treatment?
To subject a product to be plasma treated, firstly plasma is created. A gas or gas mixture is added to a closed, low-pressure vacuum plasma cabinet. These gases are then energized by the RF (radio frequency) power generated between an electrode array. The active ions in these gases accelerate and begin to vibrate.
This vibration purifies the surfaces in the room from contaminants. During this process, the UV light is emitted by the excited gas molecules and atoms in the plasma. That’s what makes plasma shine. Temperature control systems are often used to control the wear rate.
At temperatures between 60 and 90 degrees Celsius, the process can be four times faster than plasma treatment at ambient temperature. For parts that are temperature-sensitive or use temperature-sensitive components, plasma etching can be reduced to fifteen degrees.
Pre-programmed versions of all temperature control systems and integrated in the software of the plasma system are also frequently used in the industry. The settings are saved with each plasma recipe for easy replication of the process.
Changes to the process can be made by introducing different gases into the cabinet. Commonly used gases include O2, N2, Ar, H2 and CF4. These five gases, used singly or in combination, are used in most of the world’s laboratories for plasma processing.
Plasma treatment usually takes about five to eight minutes. When the plasma treatment is complete, a vacuum pump removes contaminants from the process. The remaining products in the container are now clean, sterilized and ready for bonding or further processing.
What is Plasma Cleaning?
Plasma cleaning is the process of removing all organic matter from the surface of an object using an ionized gas called plasma. This is usually accomplished in a vacuum chamber using oxygen and/or argon gas.
The cleaning process is environmentally safe as it does not contain any solid chemicals. Plasma often leaves a free radical on the surface being cleaned in order to further increase the bondability of the surface.
What is Plasma Ash?
Plasma ashing is the removal of carbon from products during cleaning or manufacturing processes. In a high frequency plasma cleaner, oxygen is used to ensure that 100 percent of the organic matter is removed by the plasma. All contaminants removed are pumped out of the room by the vacuum system.
The purpose of plasma ashing is, to completely remove organic matter including water vapor and volatile carbon oxides. Oxygen plasma removes 100% of the organic matter and leaves no residue in the sample.
However, if inorganic contaminants are present in the sample before processing, they will still be present in the sample. Plasma ashing is always carried out with oxygen (O2) gas.
A slice of a meteorite is placed inside an oxygen plasma cleaner, which removes organics from the outside of surfaces. Image Source: NASAJPL-Caltech
Pollution / Pollution Removal
Low-pressure plasma cleaners are an affordable, safe and economical way to clean.
It is used to remove contaminants from the surface of the treated substrates without affecting the properties of the bulk material.
Plasma is widely used in the circuit board industry, including PCB cleaning before conformal coatings and cleaning of lead frames during the packaging process.
Plasma treatment provides significant advantages over other surface cleaning techniques. It can be used for a wide range of materials (metals, plastics, glass, ceramics, etc.).
This is an environmentally friendly choice. Plasma cleaning eliminates the need for hazardous chemical solvents.
Significant cost savings can be achieved without having to address the environmental hazards of other processing methods. Oxygen is generally a suitable process gas.
Where solvents may leave a residue after treatment, the plasma cleaner may provide a completely residue- free end product.
The process eliminates mold release agents, antioxidants, carbon residues, oils and all types of organic compounds.
The surface of a MEMS device is cleaned with bright, blue oxygen plasma in a plasma etcher to rid it of carbon contaminants. (100mTorr, 50W RF) Image Source: Maxfisch / CC 0 1.0
Plasma Sterilization
A plasma cleaner is the best solution for removing microbial contamination.
Many medical and manufacturing plants rely on plasma because it greatly improves aggressive surfactants and organic solvents.
It provides a level of equality and rigor that other sterilization methods cannot easily compete with.
Plasma systems can produce superior results by penetrating into the reach of solvents due to surface tension limitations.
Oxygen Argon Plasma Cleaning etc. Hydrogen Plasma Cleaning
By using different types of gas (oxygen, argon, nitrogen, hydrogen, helium, etc.), the plasma can change various properties on the substrate surface.
These features include, but are not limited to:
• Modified surface tension / surface energy / contact angle characteristics.
• Improved bonding and bonding between surfaces.
• Hydrogen plasma is highly effective in removing oxide from glass or metal products.
• Modified surface wettability (increasing or decreasing the viscosity of liquids) to form hydrophilicity or hydrophobia – useful in pretreatment, painting and coating applications.
• Coating processes: adhesion, wettability, corrosion and wear resistance, electrical conductivity and insulation, magnetic response, reflective / reflective, anti-reflective, microbial, scratch-resistant, waterproofing, coloring, etc.
Plasma Activation
Plasma activation is the process of processing a polymer to enhance its ability to stain or print on it. This is done using oxygen plasma to oxidize the outer layer of the polymer. In easily oxidized metals, argon is used.
This not only produces a clean product, but also increases the polar groups, thereby directly enhancing the printability and interoperability of the polymer product. Oxygen argon plasma is also used for plasma activation.
Prepared by: B. Serhat Cengiz
Resources
• www.tstar.com/materials-surface-enhancements
• www.sciencedirect.com/topics/engineering/chemical-finishing
• www.henniker-plasma.nl/en/plasma-technology
• tantec.com/the-basics-of-plasma-treatment.html
• pubs.acs.org/doi/10.1021/acsenergylett.8b00184
• pluto.space.swri.edu/image/glossary/plasma.html5
