Sputtering in physics is called to the process in which a plasma of high energy particles/ions knock out the species on the surface layer of a solid target. This phenomenon naturally happens in the outer space, constantly forming the universe and causes spacecraft’s corrosion. Here, on Earth, the science and industry make use of sputtering process to generate or eradicate thin films of nano/micrometer thickness for various applications in optics, electronics, etc.
What is Sputtering?
Due to the collision of high-energy ions with the target material atoms, momentum transfer occurs between them. These ions, called incident ions, cause a series of collision cascades on the surface of the target. Sometimes these successive collisions cause the ions to travel long distances and lose their energy. If the ion energy at the time of reaching the target surface is greater than the bonding energy between the atoms of the target material, the collided atom separates from the target material. This phenomenon is called Sputtering.
Sputter Yield
The energy of sputtered atoms varies widely, and usually the kinetic energy of these atoms is more than tens of electron volts (typically 600 eV). Approximately one percent of the ions that hit the surface of the target material have a ballistic impact and return to the substrate, causing Re-sputtering. The average number of atoms ejected from the surface of the target material by the collision of each ion is called the Sputter Yield.
The sputter yield depends on many factors, such as:
- The angle at which the ions strike the surface of the target material
- The amount of ion energy during the collision
- The weight of the ions
- The weight of the atoms of the target material
- The binding energy between the atoms of the target material
- Magnetic field strength and design factors (in magnetron cathodes)
- Plasma gas pressure
A table of sputtering yields of several material is displayed in Table 1. The numbers vary under different deposition conditions as mentioned earlier, but are useful for comparison purposes.
If the structure of the target material is crystalline, the orientation of the crystal axis relative to the surface is also an important factor in the sputtering yield.
Deposition
One of the applications of sputtering phenomenon is Deposition. Sputtering deposition is a method of creating thin films of a few nanometers to a few micrometers on the desired substrate. In this process, the atoms separated from the surface of the target material are gaseous. These thermodynamically unstable atoms tend to be on a surface in a vacuum chamber. The atoms on the substrate which form a layer with a few nanometers to a few micrometers thick, is called a Thin Film.
Physical Vacuum Deposition Method
This type of deposition is a physical vacuum deposition method (Physical Vapor Deposition). PVD is a set of deposition methods in which the material enters the vapor phase from the dense state and returns to the dense phase as a thin film.
