The bias voltage refers to the negative voltage applied to the substrate during the coating process. The positive terminal of the bias power supply is connected to the vacuum chamber, while the vacuum chamber is grounded. The negative terminal of the bias voltage is connected to the workpiece. Because the voltage of the earth is generally considered to be zero potential, the voltage on the workpiece that negative bias, referred to as bias.
1. Function of the negative bias
◆Provide particle energy;
◆Heating effect on the substrate;
◆Removing the gas and greasy dirt adsorbed on the substrate is beneficial to improve the bonding strength of the film;
◆Activate the substrate surface;
◆For the large particles in arc ion plating have purification effect.
2. Classification of bias voltage
(1) According to the waveform can be divided into:
DC bias DC pulsed bias
DC superimposed pulse bias Bipolar pulse bias
(2) According to the need to switch the high voltage and low voltage when the power is used, it can be divided into:
Power output diagram of switching high voltage and low voltage
No need to switch high and low voltage stepless continuous regulation output
Adjustable parameters of bias power supply: bias amplitude, duty ratio, frequency, and waveform.
3. Characteristic of bias power supply
◆The number of arc extinguishing per minute.
◆Detection of the sensitivity of large arcs (mJ/kW detectable arc energy).
4. Load characteristic of bias
The working load of the bias is plasma, and the plasma exhibits resistive when the DC bias is used. For another, when pulsed bias is applied, the plasma exhibits resistive + capacitive, which can be considered as a series connection of resistors and capacitors. The essence of capacitance is caused by plasma sheath on the substrate.
