Commonly used process gases for plasma cleaning machines include oxygen, argon, nitrogen, compressed air, carbon dioxide, hydrogen, carbon tetrafluoride, etc. It ionizes the gas to generate plasma to perform surface treatment on the workpiece. Whether it is cleaning or surface activation, different process gases are selected to achieve the best treatment effect. Then how to choose the common process gas of the plasma cleaning machine?
Oxygen is a commonly used active gas for plasma cleaning. It belongs to a physical + chemical treatment method. The ionized body produced after ionization can physically bombard the surface to form a rough surface. At the same time, the highly reactive oxygen ions can chemically react with the molecular chain after the bond is broken to form a hydrophilic surface of the active group, achieving the purpose of surface activation; the elements of the organic pollutants after the bond is broken will interact with the highly reactive oxygen ion A chemical reaction takes place to form molecular structures such as CO, CO2, and H2O, leaving the surface to achieve the purpose of surface cleaning. Oxygen is mainly used for surface activation of polymer materials and removal of organic pollutants, but not suitable for easily oxidized metal surfaces. The oxygen plasma under vacuum plasma state is light blue, and it is similar to white under partial discharge conditions. The discharge environment light is relatively bright, and it may appear that there is no discharge in the vacuum chamber when observed with the naked eye.
Argon gas is an inert gas. The ion body produced after ionization will not chemically react with the substrate. In plasma cleaning, it is mainly used for physical cleaning and surface roughening of the substrate surface. The biggest feature is in surface cleaning. Will not cause surface oxidation of precision electronic devices. Because of this, argon plasma cleaners are widely used in semiconductor, microelectronics, wafer manufacturing and other industries. The plasma produced by the ionization of argon in a vacuum plasma cleaner is dark red. Under the same discharge environment, the color of plasma generated by hydrogen and nitrogen is red, but the brightness of argon plasma will be lower than that of nitrogen and higher than that of hydrogen, which is better to distinguish.
1. Surface cleaning
In the process of removing particles on the surface of wafers, glass and other products, Ar plasma is usually used to bombard the particles on the surface to achieve the effect of particles being broken up and loose (detached from the surface of the substrate), and then combined with ultrasonic cleaning Or centrifugal cleaning and other processes to remove particles on the surface. Especially in the semiconductor packaging process, argon plasma or argon hydrogen plasma is used to clean the surface after the wire bonding process is completed to prevent wire oxidation.
2. Surface roughening
The surface roughening of the plasma cleaner is also called surface etching. Its purpose is to increase the surface roughness of the material to increase the bonding, printing, welding and other processes. The surface tension after treatment by the argon plasma cleaner will increase significantly. The plasma generated by the reactive gas can also increase the roughness of the surface, but the particles produced after argon ionization are relatively heavy. The kinetic energy of argon ions under the action of the electric field will be significantly higher than that of the reactive gas, so the roughening effect will be even greater. Obviously, it is most widely used in the surface roughening process of inorganic substrates. Such as glass substrate surface treatment, metal substrate surface treatment, etc.
3. Reactive gas assist
In the activation and cleaning process of the plasma cleaner, the process gas is often mixed to achieve better results. Because the molecules of argon are relatively large, the particles produced after ionization are usually mixed with active gases during surface cleaning and activation. The most common is the mixture of argon and oxygen. Oxygen is a highly active gas, which can effectively decompose organic pollutants or the surface of organic substrates, but its particles are relatively small, and the bond breaking and bombardment capabilities are limited. If a certain proportion of argon is added, the generated plasma The ability of the body to break bonds and decompose the surface of organic pollutants or organic substrates will be stronger, and the efficiency of cleaning and activation will be accelerated. The combination of argon and hydrogen is used in the bonding and bonding process. In addition to increasing the roughness of the pad, it can also effectively remove the organic pollutants on the surface of the pad, and at the same time reduce the slight oxidation of the surface, in semiconductor packaging and SMT, etc. It is widely used in the industry.
Hydrogen Hydrogen is similar to oxygen and is a highly reactive gas that can activate and clean the surface. The difference between hydrogen and oxygen is mainly that the reactive groups formed after the reaction are different. At the same time, hydrogen has reducing properties and can be used to remove the microscopic oxide layer on the metal surface and is not easy to damage the surface sensitive organic layer. Therefore, it is widely used in microelectronics, semiconductor and circuit board manufacturing industries. Because hydrogen is a dangerous gas, it will spontaneously explode when it merges with oxygen when it is not ionized. Therefore, it is generally forbidden to mix the two gases in plasma cleaning machines. In the vacuum plasma state, hydrogen plasma is red, similar to argon plasma, and slightly darker than argon plasma under the same discharge environment.
The plasma formed by the ionization of nitrogen can have a bonding reaction with part of the molecular structure, so it is also an active gas, but compared to oxygen and hydrogen, its particles are heavier. Normally, this gas is used in plasma cleaning machine applications. A gas defined between the active gas oxygen, hydrogen and the inert gas argon. It can achieve a certain bombardment and etching effect while cleaning and activating, and at the same time, it can prevent oxidation of some metal surfaces. The plasma formed by the combination of nitrogen and other gases is usually applied to the treatment of some special materials. Nitrogen plasma is also red in the vacuum plasma state. Under the same discharge environment, nitrogen plasma is brighter than argon plasma and hydrogen plasma.