1. Target poisoning
◆ Accumulation of positive ion
When the target is poisoned, an insulating film is formed on the target surface. When the positive ions reach the cathode target surface, they cannot be directly entered into it due to the barrier of the insulating layer, but accumulate on the target surface. So, the cold field is easily generated as well as the arc discharge – arc lighting. So that cathode sputtering cannot proceed.
◆ Anode disappears
When the target is poisoned, an insulating film is also deposited on the wall of the grounded vacuum chamber. Electrons that reach the anode cannot enter the anode and disappear.
2. Influencing factors of target poisoning
The factors that affect the target poisoning are mainly the ratio of reactive gas and sputtering gas. Excessive reaction gas will cause target poisoning. In the process of the reactive sputtering process, the sputtering channel region on the target surface is covered by the reaction product, or the reaction product is peeled off to re-expose the metal surface, which trading off and taking turns.
If the rate of formation of the compound is greater than the rate that the compound is stripped, the area covered by the compound increases. At a certain power, the amount of reactant gas involved in the formation of compounds increases, and the rate of compound formation increases. If the amount of reactant gas increases excessively, the area covered by the compound increases.
If the flow of the reactant gas cannot be adjusted in time, the rate of increase of the compound coverage area cannot be suppressed, and the sputtering channel will be further covered by the compound, when the sputtering target is completely covered by the compound, the target is completely poisoned.
3. Solution of target poisoning
◆ Adopt medium frequency power or RF power.
◆ Adopt a closed loop to control the amount of reactant gas.
◆ Use twin targets
◆ Control the transformation of coating mode: Before coating, collect the hysteresis effect curve of target poisoning, make the inlet flow be controlled at the front of target poisoning, and ensure that the process is always in the mode that before deposition rate drops sharply.