Can be divided into DC magnetron sputtering and RF magnetron sputtering.

The DC sputtering method requires the target to transfer the positive charge obtained from the ion bombardment process to the cathode that is in close contact with it, so that this method can only sputter the conductor material, and is not suitable for the insulating material because the surface of the insulating target is bombarded with ions. The charge cannot be neutralized. This will cause the potential of the target surface to rise. The applied voltage will be almost applied to the target. The chance of ion acceleration and ionization between the two electrodes will become smaller, and it will not even be ionized, resulting in the inability to discharge continuously or even stop the discharge. stop. Therefore, radio frequency sputtering (RF) is required for insulating targets or non-conductive targets with poor conductivity.

The sputtering process involves a complex scattering process and a variety of energy transfer processes: First, the incident particles and the target atoms elastically collide, and part of the incident particle kinetic energy is transmitted to the target atoms, and the kinetic energy of some target atoms exceeds that of the target atoms. The barriers formed by other atoms around it (5-10 eV for metals) are collided out of lattice lattices to generate off-site atoms, which in turn repeatedly collide with nearby atoms to produce an impact cascade. . When this collision cascade reaches the surface of the target, if the kinetic energy of the atoms near the surface of the target is greater than the surface binding energy (1-6 eV for the metal), these atoms will detach from the target surface and enter the vacuum.

Sputtering is the technique of bombarding the surface of a target with energetic particles in a vacuum to deposit the bombarded particles on the substrate. Typically, incident ions are generated using a low pressure inert gas glow discharge. The cathode target is made of a coating material, the substrate is used as an anode, and 0.1 to 10 Pa of argon or other inert gas is introduced into the vacuum chamber to generate a glow at a cathode (target) of 1-3 kV DC high voltage or a radio frequency voltage of 13.56 MHz. Light discharge. The ionized argon ions bombard the target surface, causing the target atoms to be sputtered and deposited on the substrate to form a thin film. At present, there are many sputtering methods, including two-stage sputtering, three- or four-stage sputtering, magnetron sputtering, target sputtering, radio frequency sputtering, bias sputtering, asymmetrical alternating-current RF sputtering, and ion beam sputtering. Shooting and reactive sputtering.

Since the sputtered atoms are sputtered out after exchanging kinetic energy with positive ions having energy of several tens of electron volts, the atomized energy of the sputtered atoms is high, which is favorable for increasing the atomic diffusion ability during deposition and improving the density of the deposited structure. The resulting film has a strong adhesion to the substrate.

During sputtering, after the gas is ionized, the gas ions fly under the electric field toward the target that is connected to the cathode, while the electrons fly toward the grounded wall cavity and the substrate. In this way, at low voltage and low pressure, the number of generated ions is small, and the sputtering efficiency of the target is low; while at high voltage and high pressure, although more ions can be generated, electrons flying to the substrate carry high energy. , It is easy to make the substrate generate heat or even secondary sputtering, affecting the quality of the film. In addition, the probability of collision of the target atoms with the gas molecules during the flying toward the substrate is also greatly increased. Therefore, scattering of the target atoms into the entire cavity will not only cause waste of the target but also cause layers when the multilayer film is prepared. Pollution.

In order to solve the above defects, DC magnetron sputtering technology was developed in the 1970s. It effectively overcomes the weaknesses of the low cathode sputtering rate and the increase of the temperature of the substrate due to the electrons, and has been rapidly developed and widely used. .

The principle is that in magnetron sputtering, since the moving electrons are subjected to Lorentz force in the magnetic field, their trajectories will bend or even generate spiral motions, and their motion paths will become longer, thus increasing the collision with the working gas molecules. The number of times increases the plasma density, so that the magnetron sputtering rate is greatly improved, and it can work at a lower sputtering voltage and pressure to reduce the tendency of the film to contaminate; on the other hand, it also improves the incidence of lining. The energy of the atoms on the bottom surface can thus greatly improve the quality of the film. At the same time, electrons that have lost energy after multiple collisions reach the anode, have become low-energy electrons, and do not overheat the substrate. Therefore, the magnetron sputtering method has the advantages of "high speed" and "low temperature". The disadvantage of this method is that the insulator film can not be prepared, and the non-uniform magnetic field used in the magnetron electrode will cause the target material to produce a significant uneven etching, resulting in a low utilization of the target material, generally only 20% -30%.