The cooling water temperature used in production is different from the actual water temperature of the coating line, resulting in cracking of the target material during use. In general, a slight crack will not have a great impact on coating production. However, when the target has obvious cracks, the charge is easily concentrated at the crack edge, resulting in abnormal discharge on the surface of the target. Discharge will lead to slag dropping, abnormal film formation and increased product obsolescence.
Influencing factors of target cracking
Crack formation usually occurs in ceramic sputtering targets (such as oxides, carbides, nitrides, etc.) and brittle materials sputtering targets (such as chromium, antimony, bismuth, etc.).
Ceramic or brittle material targets always contain inherent stresses. These internal stresses are generated during the manufacturing of the target material. In addition, these stresses cannot be completely eliminated through the annealing process, as it is an inherent property of these materials. During sputtering, the bombarded gas ions transfer their momentum to the target atoms, providing them with enough energy to detach from the lattice. This exothermic momentum transfer increases the temperature of the target, which may reach 1,000,000 degrees Celsius at the atomic level. These thermal shocks increase the internal stress already present in the target to many times. In this case, the target may crack if proper heat dissipation is not taken care of.
Target cracking prevention measures
In order to prevent cracking of the target, an important consideration is heat dissipation. On the one hand, the water cooling mechanism is used to remove the unwanted heat energy in the target, and on the other hand, increasing the power in a very short time will also bring thermal shock to the target. In addition, it is recommended to bind these targets to a backplane, which not only provides support for the target, but also promotes better heat exchange between the target and the water. If the target is cracked and the backplane supports it, it can still be used without problems.