1. Magnetron Sputtering
Magnetron sputtering is a two-pole sputtering in a magnetron operating mode. The differences between diode sputtering and quadrupole sputtering are as follows:
The permanent magnet or electromagnet is placed behind the sputtered cathode target. A magnetic field of a horizontal component or a magnetic field of a vertical component (for example, an opposite target) is generated on the target surface, and the electrons generated by the gas discharge are bound to operate in a specific orbit within the plasma region near the target surface. And it rounds in circles along a certain runway under the complex action of the electric field force and the magnetic field force. The target surface magnetic field has a restraining effect on the charged particles, and the stronger the magnetic field, the tighter the binding force. Because of the binding and acceleration of electromagnetic field for electrons, the path of motion is also greatly extended before the electrons reach the substrate and the anode, so that the probability of collision ionization of the local Ar gas is greatly increased. The argon ion Ar+ accelerates under the action of the electric field, and then bombards the targets that served as a cathode. The molecules, atoms, ions and electrons on the surface of the target are all sputtered out to increase the spatter extraction rate of the target. The sputtered particles carry a certain amount of kinetic energy, they strike the substrate in a certain direction, and finally deposit on the substrate to form a film. After many collisions, the energy of the electrons gradually decreases, frees from the constraints of the magnetic flux, and ultimately falls on the substrate, the vacuum chamber wall, and the target power anode.
The increase in the probability of ionization of the working gas and the increase in the ionization rate of the target reduce the internal resistance of the vacuum gas discharge. Therefore, the working voltage for sputtering deposition of the magnetron target is low (mostly between 4-600 V). Sometimes operating voltage is slightly higher (eg, >700V) and some operating voltages are lower (eg, about 300V). When the magnetron sputtering occurs, the sputtering operation voltage mainly falls on the cathode landing zone of the magnetron target.
Because the magnetron sputtered film is uniform and dense with small pinholes, high purity and strong adhesion, it can realize high-speed deposition of various material films under low temperature and low damage conditions. Magnetron sputtering has become a kind of mature technology and industrialized production methods in vacuum coating nowadays. Magnetron sputtering technology has been rapidly developed and widely used in scientific research and industrialization of various industries.
In short, magnetron sputtering technology is the process of sputtering coating that uses the electromagnetic field to control the trajectory and distribution of ions and electrons of the gas “abnormal glow discharge” in the vacuum chamber.
2. Three Generation Conditions for Magnetron Sputtering
Magnetron gas discharges, which in turn cause sputtering, must meet three necessary and sufficient conditions:
(1) Having a suitable discharge gas pressure P: DC or pulsed medium frequency magnetron discharge, about 0. 1 Pa ~ 10Pa), typical value is 5 × 10-1Pa; RF magnetron discharge is about 10-1~10-2Pa.
(2) The magnetron target surface has a certain horizontal (or equivalent) magnetic field strength B (about 10mT~100mT), typical value is 30~50mT, and minimum 10~20mT (100~200 Gauss).
(3) The vacuum chamber has an electric field V that is orthogonal (or equivalently orthogonal) to the magnetic field, typical value is 500 to 700V.
We generally refer to the above three conditions as P-B-V conditions.