Mitkä ovat korkealaatuisten sputterointitavoitteiden ominaisuudet?
1. General characteristics of sputtering targets
Sputtering target is one of the main materials for preparing thin films. It has the characteristics of high purity, high density, multi-component, and uniform grains. It is generally composed of a target blank and a backing plate. The target blank is the core part of the sputtering target and is the target material bombarded by high-speed ion beam. After the target is struck by ions, the atoms on its surface are sputtered out and deposited on the substrate to form an electronic film. Since the target needs to complete the sputtering process in a high-voltage, high-vacuum machine environment, the target blank needs to be bound and joined with the backing plate through different welding processes. The backing plate mainly plays the role of fixing the sputtering target blank. And it needs to have good electrical and thermal conductivity properties. Sputtering targets are mainly used in integrated circuits, flat panel displays, solar cells, recording media, smart glass, etc. Generally, the purity and stability of the target are very high. With the rapid development of iterative upgrades in electronic technology and thin film technology, the market demand for high-quality sputtering targets is rising rapidly at an annual rate of nearly 15%. The obvious development trend of high-quality sputtering targets is: high purity above 4N level /Ultra-high purity metal, high sputtering rate, controllable grain/crystal orientation, large size.
2. Types and classifications of sputtering targets
(1) According to the chemical composition and material of the target, sputtering targets can be divided into metal/non-metal elemental targets, alloy targets, ceramic/compound targets, etc.
(2) According to different target shapes, there are mainly long targets, square targets, round targets and tube targets.
(3) Classified by application fields, they mainly include targets for semiconductors, targets for flat panel displays, targets for solar cells, etc.
3. Main application fields and technical requirements of sputtering targets
High-purity sputtering targets are mainly used in four fields: flat panel display, information storage, solar cells, and chips, accounting for a total of 94%. Among them, the chip field, that is, the semiconductor industry, has the most stringent and demanding requirements for target materials. Copper, aluminum, molybdenum and ITO targets are the most common and widely used target materials.
1) Chip field
"Chip" is the top application field of targets. It is mainly used in the two links of "wafer manufacturing" and "chip packaging". In the wafer manufacturing link, it is mainly used for metal sputtering, and in the chip packaging link, it is often used as SMT. Coating of bonding wires. Chip target is a key raw material for manufacturing integrated circuits, and it is also the target with the highest technical requirements. It needs to ensure ultra-high purity, high-precision size and high integration, so the materials selected are mostly high-purity copper, high-purity aluminum, and high-puritytitanium.html> titanium. , high-purity tantalum, high-purity tungsten, copper-manganese alloy, etc., and integrated circuit chips usually require target purity above 5N5. The dielectric layer, conductor layer, and protective layer must also use target sputtering coating with purity above 5N. Advanced The manufacturing process requires higher purity metals.
The purpose of selecting metal sputtering targets for semiconductor chips is to make metal wires that transmit information on the chip. First, high-speed ion currents are used to bombard the surfaces of different types of metal sputtering targets under high vacuum conditions, so that atoms on the surfaces of various targets are deposited layer by layer on the surface of the semiconductor chip, and then passed through A special processing technology etches the metal film deposited on the surface of the chip into nanometer-level metal lines, which connect hundreds of millions of micro-transistors inside the chip to transmit signals.
With the rapid development of information technology, the requirements for integrated circuits are getting higher and higher. The size of unit devices in the circuit is constantly shrinking, and the size of components is from millimeter level to micron level, and then to nanometer level. The interior of each unit device is composed of a substrate, an insulating layer, a dielectric layer, a conductor layer and a protective layer.
The application of target materials in the chip production process
Among them, the dielectric layer, conductor layer, and protective layer are sputtered and coated with targets with a purity of 5N or above, which is one of the cores of preparing integrated circuits. Coating targets in the field of integrated circuits mainly include aluminum targets, copper targets, titanium targets, tantalum targets, and tungsten targets. The purity requirements are generally above 5N (99.999%). The purity of aluminum targets is often above 5N5 (99.9995%). Therefore, Chip targets are relatively the most expensive.
Chip targets have the characteristics of multiple varieties, high threshold, and customized research and development. The main types of chip targets include: (1) high-purity sputtering targets such as copper, tantalum, aluminum, titanium, cobalt, and tungsten; (2) alloy sputtering targets such as nickel-platinum, tungsten-titanium, etc. Precisely because chip targets use a wide range of metal materials, the technical threshold for actual purification, processing, and welding processes is very high, requiring customized research and development breakthroughs.
Chip target materials are mainly copper, tantalum, aluminum, and titanium to construct circuit interconnection conductors in integrated circuits. The advanced processes of "copper and tantalum" can reduce power consumption and increase computing speed. "Aluminum and titanium" above 110nm can ensure the reliability and anti-interference performance of chips, such as: flash memory chips, processor chips , power management, sensor chips. In addition to using "copper" as wires and "tantalum" as barrier layers, currently 14nm and 28nm wafer technology nodes also use a large amount of "titanium" as the main material of high dielectric constant dielectric metal gate technology, and "aluminum" As the main material for wafer bonding pad process. Overall, the use of chips is becoming more and more widespread, and the chip market demand is experiencing explosive growth, which will also drive the use of the four mainstream thin film metal materials in the industry: aluminum, titanium, tantalum, and copper.
Multiple varieties, large sizes, and 5N level high purity are the future development trends of chip target technology. With the gradual application of large-size wafers in chips, target materials are also developing in the direction of large-size. At the same time, as the size of the target increases, the difficulty of controlling the grain direction of the target increases exponentially. During the sputtering process, atoms in the sputtering target are easily sputtered out in a specific direction, and the crystal orientation of the sputtering target can affect the sputtering rate and the uniformity of the sputtered film, which ultimately determines the quality of the product. Therefore, it is crucial to obtain a target structure with a certain crystallographic orientation. However, it is very difficult to obtain a certain crystal orientation inside the sputtering target. It is necessary to use different molding methods according to the structural characteristics of the sputtering target, and to perform repeated plastic deformation and heat treatment processes to control it.
When the sputtering target is bombarded by a high-speed ion beam, the gas existing in the internal voids of the sputtering target is suddenly released, causing large-sized sputtering target particles to splash. The appearance of these particles will reduce the sputtering film. The quality may even lead to product scrapping. For example, in the extremely large-scale integrated circuit manufacturing process, the number of particles allowed per 150mm diameter silicon wafer must be less than 30. Therefore, in order to meet the demand for higher precision and smaller size nanoscale processes in semiconductors, the purity of the required sputtering target materials continues to rise, even reaching a purity of more than 99.9999% (6N).
2) Flat panel display field
Flat panel displays mainly include liquid crystal displays (LCD), plasma displays (PDP), electroluminescent displays (EL), field emission displays (FED), organic light-emitting diode displays (OLED) and touch screens (TP) developed on the basis of LCD. ) to display products. Among them, the market application is mainly liquid crystal display. The raw materials of flat panel display targets include high-purity aluminum, copper, molybdenum, etc., as well as tin-doped indium oxide (ITO target). The technical requirements for flat-panel display targets are also relatively high. They require high material purity, large area, and good tissue uniformity. Aluminum targets with a purity of more than 5N are usually used. Coating is the basic link in the modern flat panel display industry. In order to ensure the uniformity of large-area film layers, improve productivity and reduce costs, almost all types of flat panel display devices use a large amount of coating materials to form various functional films. PVD coating materials are mainly sputtering targets. Many properties of flat panel displays, such as resolution and light transmittance, are closely related to the properties of sputtered films.
The flat panel display industry mainly uses PVD coating materials in the production of display panels and touch screen panels. Among them, in the production process of flat panel display panels, the glass substrate needs to be sputtered and coated multiple times to form ITO glass, which is then coated, processed and assembled to produce LCD panels, PDP panels, OLED panels, etc. The production of touch screens also requires ITO glass to be processed, coated to form electrodes, and then assembled with protective screens and other components. In addition, in order to achieve anti-reflection, shadow elimination and other functions of flat-panel display products, the coating of corresponding film layers can also be added to the coating process.
4. Sputtering target industry chain distribution and demand trends for high-quality sputtering targets
The sputtering target industry chain is basically distributed in a pyramid, mainly including four links: metal purification, target manufacturing, sputtering coating and terminal application. Among them, metal purification and target manufacturing are the most important basic raw material links in the electronics industry, while sputtering coating is the most technically demanding link in the entire industry chain, because the quality of sputtered films has an important impact on the quality of downstream products. The terminal application link is the largest area in the entire industry chain, such as semiconductor chips, flat panel displays, solar cells and other fields mentioned above.
Upstream metal purification mainly starts from ordinary industrial-grade raw materials. Generally, industrial-grade metals can reach 99.8% purity. Sputtering targets need to reach at least 99.95% purity. Semiconductor-grade high-quality materials used for manufacturing chips Sputtering targets even require a purity of 99.99~99.9999% (4N~6N). The target manufacturing process first requires process design based on the performance requirements of downstream application fields, and then undergoes repeated plastic deformation and heat treatment to control key indicators such as grains and crystal orientations, and then undergoes water cutting, mechanical processing, metallization, ultrasonic testing, Ultrasonic cleaning and other processes. The processes involved in the manufacturing of sputtering targets are delicate and numerous. The process management and manufacturing process level will directly affect the quality and yield rate of the sputtering targets. This link is the link with the highest requirements for production equipment and technical processes in the sputtering target industry chain. The quality of sputtered films has an important impact on the quality of downstream film products.
