Titanium target is a product of high-purity titanium after processing. It is made into a thin film by physical vapor deposition. It is used as a barrier layer for aluminum wires in semiconductor chips.

1. Main performance requirements of titanium target

(1) Appearance quality: Before leaving the factory, the titanium target should be cleaned without dust and the surface should be clean. The surface of the titanium target is finely processed and the surface roughness should meet the customer's requirements.

(2) Internal defects: There should be no defects such as inclusions, pores, cracks, etc. inside the titanium target.

(3) Composition: Titanium targets are divided into pure titanium targets and alloy targets. Alloy targets include titanium aluminum alloy targets, titanium nitride alloy targets, titanium boride alloy targets, etc. The target material purity is 99.9%-99.999%.

(4) Grain size: The titanium target grains are uniform and fine, and the average grain size is generally controlled to be ≤50μm.

(5) Texture: The crystal orientation <002> of the titanium target is preferred and ≥35%.

(6) Geometric dimensions: The size of titanium targets varies according to the requirements of use, and the diameter is generally 200-460mm.

 

Titanium targets are divided into single titanium targets and welded titanium targets according to the structure. Single titanium targets do not require welding, and the blanks are processed into one piece. Welded titanium targets are welded to the titanium target blanks and the backing plate. Common welding methods include brazing and diffusion welding. Welded backing plate materials include copper and copper alloy backing plates, aluminum and aluminum alloy backing plates, etc. After welding, ultrasonic testing is performed to ensure that the connection between the target material and the backing plate has a certain bonding strength to avoid problems such as falling off and brittle cracking during sputtering. The quality requirements for titanium target welding are shown in Table 9-23.

 

2. Preparation of titanium targets

The preparation of pure titanium targets generally adopts the hot pressing method of smelting ingots. The preparation of titanium alloy targets adopts the powder metallurgy method.

 

The hot pressing method of smelting ingots uses high-purity titanium ingots obtained by smelting as raw materials, and controls the microstructure and shape and size of the billet through plastic processing processes such as forging, rolling, and annealing, and then mechanically processes the billet to obtain a titanium target. The titanium target that has undergone forging, rolling, and annealing has fine and uniform grains and a dominant texture, which can meet the use requirements of titanium targets in the sputtering process. The loss during the smelting ingot processing is large, including the loss during the casting process, the need to turn the oxide scale during the forging and rolling process, and the loss during the cutting process, so its final utilization rate is about 80%.

 

For alloy targets such as TiB2 and TIAI, they are prone to cracking during forging, and are more suitable for powder metallurgy processing, that is, titanium powder and additives are used as raw materials, and after a powder mixing process, the billet is processed by hot pressing or hot isostatic pressing to obtain a titanium alloy target. Powder metallurgy can form a blank in one go, with high material utilization, and alloy elements can be easily added. It is the preferred method for preparing titanium alloy targets. The problem with powder metallurgy is that it has high requirements for the control of material purity, alloy composition uniformity, density, and internal defects of materials.