How do sputtering targets work?

Working principle of sputtering target

Sputtering is one of the main techniques to prepare thin film materials, it uses ions generated by ion source, after accelerated aggregation in vacuum, and form a high-velocity energy ion beam, bombard the solid surface, ions and solid surface atoms kinetic energy exchange, so that the solid surface atoms leave the solid and deposited on the substrate surface, the bombarded solid is the sputtering target.

Components of sputtering target

The target material is made of "target blank" and "back plate" welded together.  

(1) The target blank is the target material bombarded by the high-speed ion beam, which is the core part of the sputtering target, involving high-purity metal and grain orientation control. In the sputtering coating process, the target blank is hit by ions, its surface atoms are sputtered out and deposited on the substrate to make electronic films.

(2) The backplane plays the role of mainly fixing the sputtering target, involving the welding process. Due to the low strength of high-purity metals, the sputtering target needs to be installed in a special machine to complete the sputtering process. The inside of the machine is a high-voltage, high-vacuum environment, so the sputtering target blanks of ultra-high-purity metals need to be joined with the backplane through different welding processes, and the backplane needs to have good electrical and thermal conductivity.

Processes for sputtering target coating

The main processes of coating are physical vapor deposition (PVD) and chemical vapor deposition (CVD).

(1) PVD technology is currently the mainstream coating method, of which the sputtering process is widely used in semiconductors and display panels. pvd technology is divided into vacuum vapor deposition method, sputtering method and ion plating method. Each of the three methods has its own advantages and disadvantages: vacuum vapor deposition method has no restriction on substrate material; sputtering method has better film properties and uniformity than vapor deposition film; ion plating method has strong winding ability and simplified cleaning process, but it affects the coating quality under high power. The choice of different methods mainly depends on the product usage and application scenarios.  

(2) CVD technology generates thin films mainly through chemical reactions. One or several gas-phase compounds or monomers containing thin film elements are introduced into the reaction chamber at high temperature, and chemical reactions are carried out on the substrate surface to generate thin films.

Classification of sputtering targets

There are many types of sputtering targets, and even the sputtering targets of the same material have different specifications. According to different classification methods, sputtering targets can be divided into different categories, the main classification is as follows.  

Classification by shape: long target, square target, round target  

Classification by chemical composition: metal targets (pure metal aluminum, titanium, copper, tantalum, etc.), alloy targets (nickel-chromium alloy, nickel-cobalt alloy, etc.), ceramic compound targets (oxide, silicide, carbide, sulfide, etc.)  

Classification by application: semiconductor chip targets, flat panel display targets, solar cell targets, information storage targets, tool modification targets, electronic device targets, other targets

Applications of sputtering targets

1) Microelectronics Among all application industries, the semiconductor industry is quite demanding on the quality of target sputtering films. Nowadays, 12-inch (300 epithelial) silicon wafers have been manufactured. And the width of interconnects is decreasing. The requirements of silicon wafer manufacturers for targets are large size, high purity, low bias and fine grains, which require better microstructure of the manufactured targets.  

2) Flat panel displays (FPD) for monitors have significantly impacted the computer monitor and TV market over the years, mainly cathode ray tube (CRT), which will also drive the technology and market demand for ITO targets. Nowadays, there are two kinds of iTO targets. One is the use of nano-state indium oxide and tin oxide powder mixed and sintered, and one is the use of indium-tin alloy target.

3) For storage In storage technology, the development of high-density and high-capacity hard disk requires a large number of giant magnetoresistive film materials, and CoF~Cu multilayer composite film is a widely used giant magnetoresistive film structure today. TbFeCo alloy targets needed for magnetic discs are still being further developed, and the magnetic discs made from them have high storage capacity, long life, and can be repeatedly erased without contact.