Types of magnetron sputtering (1)
Magnetron sputtering includes many types. Each has different working principles and application objects. But there is one thing in common: the interaction between the magnetic field and the electric field causes the electrons to spiral around the target surface, thereby increasing the probability of electrons hitting the argon gas to produce ions. The generated ions collide with the target surface under the action of the electric field to sputter the target material.
The target source is divided into balanced and unbalanced types. The balanced target source has a uniform coating, and the unbalanced target source has a strong bonding force between the coating film and the substrate. Balanced target sources are mostly used for semiconductor optical films, and unbalanced sources are mostly used for wearing decorative films.
According to the different magnetic field configuration, magnetron cathodes can be roughly divided into equilibrium magnetron cathodes and non-equilibrium magnetron cathodes. The magnetic flux of the magnetic steel inside and outside the equilibrium magnetron cathode is approximately equal. The two poles of magnetic field lines are closed on the target surface, which confines the electrons/plasma near the target surface well, increases the collision probability and improves the ionization efficiency. Under the working pressure and voltage, it can start and maintain the glow discharge, and the utilization rate of the target material is relatively high. However, since the electrons move along the magnetic field lines are mainly closed to the target surface, the area of the substrate is less bombarded by ions.
Unbalanced magnetron sputtering technology, that is, the magnetic flux of the outer magnetic pole of the magnetron cathode is greater than the inner magnetic pole. The two-pole magnetic field lines are not completely closed on the target surface. Part of the magnetic field lines can extend to the substrate area along the edge of the target, so that part of the electrons can follow the magnetic field lines. Extend to the substrate to increase the plasma density and gas ionization rate in the substrate area.
Regardless of balanced or unbalanced, if the magnet is stationary, its magnetic field characteristics determine the general target utilization rate is less than 30%. In order to increase the utilization rate of the target material, a rotating magnetic field can be used. However, a rotating magnetic field requires a rotating mechanism, and the sputtering rate must be reduced. Rotating magnetic fields are mostly used for large or valuable targets, such as semiconductor film sputtering. For small equipment and general industrial equipment, a stationary target source with a magnetic field is often used.