There are many types of magnetron sputtering. Each has different working principles and application objects. However, they have one thing in common: the interaction between magnetic field and electric field is used to make electrons run in spiral shape near the target surface, thus increasing the probability of electrons striking argon to produce ions. The generated ions will collide with the target surface under the action of electric field and then sputter out the target material.
Magnetron target classification:
Target source is divided into balanced and non-balanced, balanced target source coating is uniform, non-balanced target source coating film and substrate bonding force is strong. Balanced target source is mostly used in semiconductor optical film and non-balanced target is mostly used in wear decorative film. Magnetic controlled cathodes can be roughly divided into equilibrium and non-equilibrium magnetic controlled cathodes according to different magnetic field configuration distribution. Equilibrium magnetron cathode magnetic flux is roughly equal, both inside and outside the lines of magnetic force between closed in target surface, a good electronic/plasma constraint near the target surface, increase the collision probability, improve the efficiency of the ionization, and therefore under low working pressure and voltage can be bright and maintain glow discharge, the target material utilization rate is relatively high, but because the main moving along the lines of magnetic force close to the target surface, the substrate region is less bombarded by ions. Unbalanced magnetron sputtering technology concept, that is, let the magnetron cathode magnetic flux is greater than the magnetic pole, the magnetic field lines between the target surface is not closed completely, part of the magnetic field lines can extend along the edge of the target to the substrate region, thus part of the electron can be extended along the lines of magnetic force to the substrate, increasing substrate region of the plasma density and gas ionization rate. Regardless of equilibrium or non-equilibrium, 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 target material, rotating magnetic fields can be used. However, rotating magnetic field requires rotating mechanism, and the sputtering rate should be reduced. Rotating magnetic fields are often used for large or expensive targets, such as semiconductor film sputtering. For small equipment and general industrial equipment, magnetic stationary target sources are used.
Magnetron target source for sputtering metals and alloys:
It is easy to sputter metals and alloys with magnetron target source, and easy to ignite and sputter. This is because the target (cathode), plasma, and splashed part/vacuum chamber can form a loop. But if the sputtering insulator is ceramic, the circuit is broken. So they use high-frequency power, and they put very strong capacitors in the loop. Thus the target becomes a capacitor in the insulating loop. However, high frequency magnetron sputtering power supply is expensive, the sputtering rate is very small, and the grounding technology is very complex, so it is difficult to adopt large-scale. To solve this problem, magnetron reactive sputtering was invented. You take a metal target; you add argon and reaction gases like nitrogen or oxygen. When the metal target hits the part, it combines with the reaction gas to form nitrides or oxides due to energy conversion. Magnetron reactive sputtering insulator looks easy, but the actual operation is difficult. The main problem is that the reactions occur not only on the surface of the parts, but also on the anode, the vacuum cavity, and the target source. And that causes fire extinguishing, target source and workpiece surface arc.
Cooling is necessary for all sources (magnetically controlled, multi-arc, ionic) because a large part of the energy is converted to heat, which, without or without cooling, will melt the entire target source to a temperature of more than 1,000 degrees.
