Commonly used process gases for plasma cleaning machines are oxygen, argon, nitrogen, compressed air, carbon dioxide, hydrogen, carbon tetrafluoride, etc. It ionizes the gas to generate plasma for surface treatment of the workpiece. Whether it is cleaning or surface activation, different process gases will be used to achieve the best treatment effect. So how to choose the common process gas of the plasma cleaning machine?

oxygen

Oxygen is an active gas commonly used in plasma cleaning, which belongs to a physical + chemical treatment method. The ions generated after ionization can physically bombard the surface to form a rough surface. At the same time, the highly active oxygen ions can chemically react with the broken molecular chain to form a hydrophilic surface of the active group, so as to achieve the purpose of surface activation; the elements of the organic pollutants after the broken bonds will interact with the highly active oxygen ions. A chemical reaction occurs to form molecular structures such as CO, CO2, H2O, etc., which are separated from 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 it is not suitable for easily oxidized metal surfaces. Oxygen plasma in the vacuum plasma state appears light blue, and is similar to white under partial discharge conditions. The light in the discharge environment is relatively bright, and the discharge in the vacuum chamber may not be seen when observed with the naked eye.

Argon

Argon is an inert gas. The ions generated after ionization will not react chemically with the substrate. In plasma cleaning, it is mainly used for physical cleaning and surface roughening of the substrate surface. The biggest feature is that in surface cleaning Will not cause surface oxidation of precision electronic devices. For this reason, 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 is lower than that of nitrogen and higher than that of hydrogen, which is better to distinguish.

1. Surface cleaning

In the process of removing surface particles of wafers, glass and other products, Ar plasma is usually used to bombard the surface particles to achieve the effect of the particles being scattered and loosened (detached from the surface of the substrate), and then combined with ultrasonic cleaning Or centrifugal cleaning and other processes to remove the particles on the surface. Especially in the semiconductor packaging process, argon plasma or argon-hydrogen plasma is used for surface cleaning in order to prevent wire oxidation after the wire bonding process is completed.

2. Surface roughening

The surface roughening of the plasma cleaning machine is also called surface etching. Its purpose is to improve the roughness of the material surface, so as to increase the bonding force of bonding, printing, welding and other processes. The surface tension of the plasma cleaning machine will be significantly improved. The plasma generated by the active gas can also increase the roughness of the surface, but the particles produced by ionization of argon are relatively heavy, and the kinetic energy of the argon ions under the action of the electric field will be significantly higher than that of the active gas, so the roughening effect will be more. Obviously, it is the 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 plasma cleaners, process gases are often mixed to achieve better results. Because the molecules of argon are relatively large, the particles generated after ionization are compared, and they 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 reactive gas, which can effectively chemically decompose the surface of organic pollutants or organic substrates, but its particles are relatively small, and its ability to break bonds and bombardment is limited. If a certain proportion of argon is added, the generated plasma will The ability of the body to break bonds and decompose organic pollutants or the surface of organic substrates will be stronger, and the efficiency of cleaning and activation will be accelerated. The mixture of argon and hydrogen gas is used in the wire bonding and bonding process. In addition to increasing the pad roughness, 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, similar to oxygen, is a highly reactive gas that can activate and clean surfaces. The main difference between hydrogen and oxygen is that the active groups formed after the reaction are different, and hydrogen has reducibility, which can be used to remove the microscopic oxide layer on the metal surface and is not easy to cause damage to the surface-sensitive organic layer. Therefore, it is widely used in the microelectronics, semiconductor and circuit board manufacturing industries. Because hydrogen is a dangerous gas, it will explode when combined with oxygen when it is not ionized, so it is usually forbidden to mix the two gases in plasma cleaners. In the vacuum plasma state, the hydrogen plasma is red, similar to the argon plasma, and slightly darker than the argon plasma in the same discharge environment.

nitrogen

The plasma formed by nitrogen ionization can react with some molecular structures, so it is also an active gas, but its particles are heavier than oxygen and hydrogen, and this gas is usually used in plasma cleaner applications. A gas defined between the reactive gases oxygen, hydrogen, and the inert gas argon. While cleaning and activating, it can achieve certain effects of bombardment and etching, 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 state of vacuum plasma. Under the same discharge environment, nitrogen plasma will be brighter than argon plasma and hydrogen plasma.