Target poisoning means that the target has reacted and the composition has changed. For example, in the process of TiN, the Ti target reacts with N2 to generate TiN. After the process is completed, there is a layer of TiN on the surface of the Ti target. We call this phenomenon target poisoning.
The phenomenon of target poisoning
Phenomenon 1: The target voltage cannot reach normal for a long time, and it has been in a low-voltage operation state, accompanied by arc discharge; in general, the sputtering voltage of magnetron sputtering is between 400V-600V. When target poisoning occurs, the sputtering voltage will drop significantly. The sputtering rate of metal target and compound target is different. In general, the sputtering coefficient of metal is higher than that of compound, so the sputtering rate is low after the target is poisoned.
Phenomenon 2: The surface of the target appears white attachments or densely covered with needle-like gray discharge traces. Oxide or nitride may be formed on the surface of the target.
The root cause of target material poisoning
The poisoning of the target material is mainly due to the loss of conductivity of the conductive target material caused by the medium synthesis speed greater than the sputtering speed. A layer of insulating film is formed on the target surface. When the positive ions reach the cathode target surface, due to the barrier of the insulating layer, they cannot directly enter the cathode target surface, which is easy to produce arc discharge caused by cold field, and the sputtering cannot go on. In actual use, only by effectively increasing the strength of the breakdown voltage can it operate normally.
The direct cause of target poisoning
1. The target material is placed in the air for a long time, resulting in the formation of oxides on the surface, such as Al;
2. The sputtering power supply is unsuitable, such as DC sputtering, which can cause ZrN easily poisoned;
3. For example, improper handling. The target material is not sufficiently cooled and inflated just after sputtering, which may lead to target poisoning;
4. The failure of the cooling water of the target causes the target to react with other gases at a higher temperature to produce thicker compounds. This is the case with almost common metal targets;
5. The vacuum chamber leaks or leaks water. There are volatile components in the vacuum chamber. If argon is not filled, air or other gases may be filled, which may cause poisoning. These components react with the target material and become black matter covering the surface of the target material, affecting film formation speed.
summarizes the solutions for target poisoning
1. To prevent target material poisoning, first ensure that the vacuum chamber does not leak, clean the interior, and remove volatile components, etc.
2. Intermediate frequency power supply or radio frequency power supply must be used instead of DC power supply;
3. Methods such as reducing the amount of reactant gas, increasing the sputtering power, cleaning up pollutants (especially oil) on the target, and selecting a dust-proof arc hood with good vacuum performance can effectively prevent the occurrence of target poisoning;
4. Maintain a clean target surface and maintain a high pumping speed, the poisoning problem can be solved;
5. The target material can be recovered by hitting it with a medium-grade source or a radio frequency source for one or two hours. Remove the target material and polish it with sandpaper.
