Technical requirements of titanium target material

In order to ensure the quality of the deposited film, the quality of the target must be strictly controlled. Through a lot of practice, the main factors affecting the quality of the titanium target include purity, average grain size, crystal orientation and structure uniformity, geometric shape and size, etc.

(1) Purity
The purity of titanium target has great influence on the properties of sputtering films. The higher the purity of titanium target, the less impurity element particles in sputtering titanium film, resulting in better film performance, including better corrosion resistance and electrical and optical properties. But in practice, different titanium targets have different purity requirements. For example, the purity of titanium targets for decorative coating is not demanding, but the purity of titanium targets for integrated circuits, display bodies and other fields is much higher. As the cathode source of sputtering, the impurity elements and pore inclusion in the target are the main pollution sources. The blowhole inclusions can be basically removed in the process of nondestructive testing of ingots. The blowhole inclusions that are not removed will cause Arcing in the process of sputtering, which will affect the quality of thin films. However, the content of impurity elements can only be reflected in the test results of total element analysis. The lower the total content of impurities, the higher the purity of titanium target.

(2) Average grain size
The sputtering rate of fine grain targets is faster than that of coarse-grain targets, and the thickness distribution of sputtering films is more uniform for targets with smaller grain size difference on the sputtering plane. It is found that if the grain size of titanium target is controlled below 100μm and the change of grain size is kept within 20%, the quality of the films prepared by sputtering can be greatly improved. The average grain size of Ti targets used in integrated circuits is generally required to be less than 30μm, and the average grain size of ultra-fine Ti targets is less than 10μm.

(3) Crystal orientation
Titanium metal is a dense hexagonal structure, because in sputtering titanium target atoms tend to sputter preferently along the direction of the most compact atomic hexagonal arrangement, therefore, in order to achieve the highest sputtering rate, the method of changing the crystal structure of the target can increase the sputtering rate. At present, most of the titanium target of integrated circuit sputtering plane {1013} crystal plane group is more than 60%. The target grain orientation produced by different manufacturers is slightly different, and the crystal direction of titanium target has a great influence on the thickness uniformity of sputtering film layer. The thin film size of planar display and decorative coating is relatively thick, so the corresponding titanium target has low requirements on grain orientation.

(4) Uniformity of structure
The uniformity of structure is also one of the important indexes to evaluate the quality of target material. For titanium target, the uniformity of composition, grain orientation and average grain size is required not only in the sputtering plane but also in the normal direction of the target. Only in this way, titanium films with uniform thickness, reliable quality and consistent grain size can be obtained at the same time during the service life of titanium target.

(5) Geometry and size
Mainly reflected in the processing precision and processing quality, such as processing size, surface flatness, roughness, etc. If the mounting hole Angle deviation is too large, it cannot be installed correctly; Small thickness will affect the service life of the target; The size of sealing surface and sealing groove is too rough, which will lead to vacuum problems after the installation of target material, leading to water leakage seriously; The target sputtering surface roughness treatment can make the target surface full of rich convex tip, under the action of tip effect, the potential of these convex tip will be greatly improved, so as to breakdown dielectric discharge, but too large convex for the amount of sputtering and stability is not good.

(6) Welding bonding
Generally, the diffusion welding of high melting point titanium and low melting point aluminum is mainly based on unidirectional or bidirectional pressure vacuum diffusion.