The role and classification of bias voltage
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Bias Effect in the coating process:
1. Increase the energy of charged particles in the vacuum plasma, bombarding and cleaning the surface of the workpiece (anti-sputtering/etching), so that the surface of the workpiece can be exposed to high-energy particles and get a brand new surface layer, thus improving the adhesion of subsequent deposition film layer.
2. Improve and control the energy of charged particles in the vacuum plasma, increase the probability of ionization in collision, attract charged particles to accelerate, and improve the adhesion between the film layer and the workpiece matrix.
3, depending on different voltage output polarity or way to change the deposition rules to adjust the color of the film.
4. Change the crystal structure of the film to improve its quality.
Bias Classification in the coating process :
1.DC negative bias
The negative bias voltage of direct current is loaded on the workpiece, so that the positive ions in the plasma can obtain more energy, and the positive ions can be accelerated to bombard the workpiece, which can also conduct some degree of guiding deposition on the charged ions splashed from the surface of the target material. Dc negative bias has no interruption, so it has heating effect on the substrate.
2. DC positive bias
In ion-plating gas discharge, the gas-phase nucleating particles will present a certain negative potential, in which case the workpiece is loaded with a certain positive bias, which is conducive to film deposition.
3. Pulse bias
It produces oscillating plasma. The density and temperature of plasma can be increased by increasing the intensity of pulse power supply while decreasing pulse duty ratio. Bombardment effect on all types of substrates (conductive & non-conductive) is enhanced. The lifetime of the secondary electron increases and the probability of collision increases, which increases the plasma density. Deposition rate can be controlled by adjusting pulse frequency and duty cycle. The temperature rise can be controlled by adjusting pulse frequency and duty ratio, and the film can be formed at low temperature to avoid damaging the original structure of the substrate. For multiple arcs, due to the rapid deposition rate, it is not suitable for film deposition of electronic devices and other precision workpieces. The introduction of pulse bias can be effectively improved.
4. Zero bias and suspension bias
Zero bias/suspension bias can be used in coating processes where no charged particles are involved (such as simple evaporation, etc.).
When the workpiece (such as plastic parts) with low temperature tolerance coating, in order to prevent the workpiece deformation, can choose zero bias/suspension bias or choose small duty ratio low amplitude bias voltage.