The phenomenon of bombarding the surface of the target with ions so that the atoms of the sputtering target are knocked out is called sputtering. The atoms generated by sputtering deposit on the surface of the substrate to form a film. This process is called sputter coating.
Sputter coating usually uses the gas discharge to generate gas ionization. Its positive ions bombard the cathode sputter target at high speed under the action of the electric field, and hit the cathode target atoms or molecules, and fly to the surface of the substrate to be deposited into a thin film. At present, RF sputtering, three-pole sputtering and magnetron sputtering techniques have been developed.
RF sputtering is using a high-frequency alternating electric field with a frequency of 13.56 MHz to discharge gas to generate the plasma. For insulating sputter coater targets, RF sputtering is the most advantageous sputtering method. In 1966, BM Company of the United States used RF sputtering to deposit SiO2 film on Silicon substrate.
Three-pole sputtering is the use of hot wire arc discharge to enhance the glow discharge to generate the plasma. However, it is difficult to achieve a uniform coating of a large area by this method, and thus it has not been widely used in the industry.
To increase the rate of sputter coating, the key is to increase the sputtering rate of the target, which means increasing the ionization degree of the plasma, that is, obtaining more ions at the same discharge power. From the point of view of the sputtering product of the ion bombardment target surface, in addition to the sputtered atoms or molecules, secondary electrons are also sputtered. These electrons are accelerated by an electric field and collide with gas atoms or molecules to cause gas ionization. Making full use of the energy of secondary electrons is an effective way to improve plasma ionization.
Magnetron sputtering takes advantage of the secondary electrons. It establishes the runway magnetic field on the cathode target surface, uses it to control the secondary electron motion, prolongs its stay near the target surface, increases the collision probability with the gas, and thus increases the plasma density. In this way, the sputtering rate of the target can be greatly increased, ultimately increasing the deposition rate. (Related: An Overview of Magnetron Sputtering)
Magnetron sputtering has a higher coating rate than other sputtering techniques. Generally, the coating rate of two-pole sputtering and RF sputtering is 20~250nm/min, and the sputtering of three-pole is 50~500m/min. Magnetron sputtering can achieve a sputtering rate as high as 200~2000mm/min. Magnetron sputtering coatings have been industrialized in the 1970s.
Today, magnetron sputtering has become one of the mainstream technologies for coating. People have been working hard to improve the efficiency of magnetron sputtering technology and explore its application range.
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