The Effect of Magnetic Field on the Combustion Stability of Multi-arc Coating Machine's Target Arc(multi-arc ion sputtering coating machine)
The vacuum arc discharge of the target source of the vacuum multiple-arc coating machine is supplemented by thermionic emission, and field emission is the main. Field emission relies on the space charge in front of the target to generate the required strong electric field. The ionization rate of this arc discharge is quite high, generally 60%-90% ionization rate. In the vacuum coating chamber, especially near the target surface, it is basically a complete plasma. Since the magnetic field has a great influence on the movement of the charged particles, the vacuum arc will be controlled by the magnetic field.
In the case of pvd vacuum multi-arc coating machinewithout an external magnetic field, the pile-like cathode arc spots move randomly on the target surface. At this time, the arc combustion is extremely unstable, and the target surface is etched very rough and the arc is often extinguished.
When a non-axisymmetric magnetic field is applied near the target surface and the magnetic field lines are parallel to the target surface, the arc spot is also in a pile shape, and its movement is in one direction (related to the direction of the magnetic field), and finally stays outside the target surface along a point to Extinguish the arc.
When a magnetic field symmetrical to the target surface is applied to the target surface, the cluster-shaped arc spots disappear, and the arc spots rotate around the target axis on the target surface, forming several fine arc rings. In this case, the discharge stability is better. On the cathode target surface of the multi-arc coating machine, the position of the arc spot is controlled by the magnetic field, and the place where the arc combustion is relatively stable on the target surface is the place where the magnetic field is strongest.
In the case of the pvd vacuum multi-arc coating machine without an external magnetic field, the cathodic arc is in the shape of a pile. There are two reasons for the formation of this pile-shaped arc spot: One is the self-magnetic compression produced by the arc itself, which is similar to the fact that two parallel wires pass through current in the same direction, and the interaction forces attract each other. The second is that the concentration of the arc spot makes the temperature of the cathode target surface under the arc spot extremely high, which produces a large amount of thermionic emission, which leads to the re-concentration of the arc spot. In this case, the arc spot causes local melting of the target surface, a large amount of evaporation, and even splashing of metal droplets, a large number of arc craters are generated on the target surface, and the film quality is affected at the same time. Such irregularly moving arc spots can easily move to the non-evaporating surface and cause the arc to extinguish.
When a magnetic field parallel to the target surface is added near the target surface of the multi-arc coating machine, the charged particles are only subjected to one direction force under the action of the magnetic field, causing the arc spot to move in one direction and quickly stay at a point on the edge of the target, and finally extinguish.
The situation of applying an axisymmetric magnetic field near the target surface of the multi-arc coating machine is different. Because the magnetic field has both an axial component and a radial component at this time, the charged particles near the target surface (evaporated and ionized from the target surface) ) Generally, the initial velocity direction is perpendicular to the target surface. Under the action of the radial component of the magnetic field and the collision between particles, the charged particles produce radial and circumferential motions, which increases the movement distance of the charged particles in space and makes them There are more opportunities for collision and ionization, and at the same time, the distribution of space charges in front of the target is changed so that it is distributed according to the distribution of the magnetic field. In the first two cases, the cluster-shaped arc spots are dispersed into uniform circular arc spots. On the other hand, the circumferential component of the arc current and the radial component of the magnetic field act to form an arc stabilizing force. As a result, the space charge in front of the accumulation target is closer to the target surface, forming a strong electric field, and maintaining the normal combustion of the arc.
Whether the magnetic field setting of the pvd vacuum multi-arc coating machine is reasonable or not directly affects the working characteristics of the multi-arc target inside the equipment. Not only that, the magnetic field of the coater can also increase the potential between the cathode and the anode, increasing the number of atoms released from the cathode target source and the particle beam flux density, resulting in an increase in the deposition rate of the multi-arc target source, and the magnetic field can also improve the vacuum. The direction of the ion beam generated by the multi-arc target source.