What is the principle of colorful PVD vacuum coating?
Molecular beam epitaxy is widely used to fabricate various optical integrated devices and various super-lattice films. When the solid surface is bombarded with high-energy particles, the particles on the solid surface can obtain energy and escape from the surface to deposit on the substrate. Sputtering began to be used in coating technology in 1870, and was gradually used in industry after 1930 due to the increasing deposition rate. The material to be deposited is usually made into a plate, a target, which is fixed on the cathode. The substrate is placed on the anode facing the target surface, several centimeters from the target. After being pumped to a high vacuum, the system is filled with 10 ~ 1 pa of gas (usually argon), and a few kilovolts are applied between the cathode and anode, producing a glow discharge between the electrodes. The positive ions generated by the discharge fly to the cathode under the action of electric field and collide with the atoms on the target surface. The target atoms escaping from the target surface by the collision are called sputtering atoms, whose energy ranges from 1 to dozens of electron volts. The sputtering atoms are deposited on the substrate surface to form electroplating. Different from evaporative electroplating, sputtering electroplating is not limited by the melting point of film material and can sputter refractory substances such as W, Ta, C, Mo, WC and TiC. Sputtering compound films can be prepared by reactive sputtering, in which reaction gases (O, N, HS, CH, etc.) are added into Ar gas, and the reaction gases and their ions react with target atoms or sputtering atoms to produce compounds (such as oxides, nitride, etc.) and deposited on the substrate. The insulation film can be deposited by high frequency sputtering method. The substrate is mounted on the earthing electrode, and the insulation target is mounted on the opposite electrode. The hf power supply is earthed at one end and connected to an electrode with an insulating target via a matching network and isolated DC capacity. After switching on the hf power supply, the HF voltage continuously changes the polarity. The electrons and positive ions in the plasma hit the insulation target at the positive and negative half cycles of the voltage. Since the electron mobility is higher than the positive ion, the surface of the insulating target is negatively charged. When the dynamic equilibrium is reached, the target is at a negative bias potential, so that the sputtering of the positive ion to the target continues.
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