Magnetron sputtering is currently the most widely used method of sputtering coating, because it has the advantages of high deposition rate, excellent film quality, simple equipment and easy operation, less radiation damage to the substrate and easy continuous production. It can make use of magnetic control to ignition, discharge, and sputter at very low voltage. And the electron bombardment damage to the deposited film is greatly reduced. Low pressure (0.1 Pa) sputtering can be achieved due to the effect of magnetic control.
In general DC glow discharge, ion bombardment target surface generated by the secondary electron (also known as the primary electron, which discharge and discharge of high-energy electrons and gas molecules ionized collision electrons generated) in the cathode dark area to obtain energy, In addition to ionospheric collision with the gas molecules on the way to the outside, basically from the cathode line to reach the anode. In magnetron discharge, due to the magnetic field parallel to the cathode surface and the interaction of the orthogonal electric field, the trajectory of the primary electron is a circular roll. The motion of a circular roll line is a synthetic motion of the drift motion of the gyratory movement and the center of the cyclotron. The direction of the drift motion is E × B, indicating that most of the primary electrons always move against the cathode surface regardless of whether they collide with gas molecules or not. The magnetic field distribution of magnetron discharge in space so that the trajectory of its end to end, into a closed track.
In principle, if the primary electron does not lose energy, it will always move against the cathode surface without falling onto the anode and this orthogonal electromagnetic field structure, also known as electronic trap. Only after the collision ionization, losing most of the energy, and the eventual transformation into a disorderly motion electron, the primary electrons will fall to the anode. It can be seen, magnetron discharge is a very effective method of generating plasma. This is due to the increase of the ionization efficiency of the electrons in magnetic field, and on the other hand, the probability of sputtering is reduced under the condition of low working pressure.
In addition, since the magnetic field can effectively improve the probability of collision with the electron gas molecules, which can significantly reduce the working pressure, can be reduced from 1 Pa to 10-1 Pa, it also reduces the tendency of film pollution, and also increases the incidence of incident light onto the substrate the energy of the surface atoms will therefore greatly improve the quality of the film.
Due to the different of target shape and structure, magnetron sputtering can be divided into plane, cylinder, concave plate and cone and other types. The schematic diagram of the magnetron sputtering is shown in the figure below. In the cathode sputtering target, a cylindrical magnetic pole is added in the middle and a circular magnetic pole is added in the periphery so as to form a closed runway area where the electric field and the magnetic field are orthogonal to the target surface, and using the orthogonal electromagnetic field runway bound electron motion. Under the action of the orthogonal electromagnetic field, the electron in the magnetic field moves around the magnetic line of force, increasing the probability that it participates in the process of atomic collision and ionization. Therefore, the sputtering rate and deposition rate can be significantly improved under the same current and air pressure.
The difference between the AC planar magnetron sputtering and the traditional planar magnetron sputtering is that the original DC power supply is replaced by the medium frequency AC power supply. Compared with the DC sputtering, the target potential of the AC sputtering is not a constant negative voltage, but a certain period of alternating pulse voltage, which can not only effectively eliminate the abnormal discharge sputtering phenomenon, the plasma density near the substrate was enhanced without changing the cooling measures of the target. This is because the average power of the target surface is certain, and the pulse power can be applied to the target during the negative pulse.
The advantages of ac planar magnetron sputtering:
◆ It can sputter ZAO targets and other semiconductor targets, the frequencies used are not as harmful to the health of the operator as RF sputtering.
◆ It can eliminate the problem of the target material poisoning that can be produced in the reaction sputtering medium film, and stabilize the deposition process.
◆ The process parameters can be controlled and the film thickness is easy to be uniform.
◆ The adhesion of film and matrix is large, and the film is compact and without pinhole.
◆ Consumption of less material, especially for expensive materials coating.
◆ Compared with the general sputtering, which has high speed, low temperature and low loss characteristics.