In the wave of development in high-tech industries such as semiconductors, flat panel displays, and new energy, targets, as core foundational materials, directly influence the quality and technical level of end products. Due to significant differences in the demand for targets across various industries, a complex and refined classification system has been established. This article will delve into the classification logic and application scenarios of targets from four dimensions: material, application field, preparation process, and shape.
1. Classification by Material
1. Metal Targets
Metal targets are based on single metal elements and, due to their excellent electrical conductivity, thermal conductivity, and ductility, have become the main materials in semiconductor manufacturing and flat panel display fields. For example, aluminum targets are commonly used for interconnect wiring in chips due to their low cost and strong conductivity; copper targets replace aluminum in advanced processes to reduce resistance and electromigration risks; titanium targets serve as transition layer materials between metal films and substrates due to their good adhesion.
2. Alloy Targets
Alloy targets achieve properties that a single metal cannot possess by mixing two or more metals in specific proportions. For instance, nickel-chromium alloy targets combine high resistivity and good oxidation resistance, commonly used for fabricating thin-film resistors; copper-aluminum alloy targets can optimize hardness and conductivity by adjusting composition, suitable for electrode materials in high-density storage chips. The precise control of alloy composition allows them to meet the customized material performance requirements of electronic devices.
3. Ceramic Targets
Ceramic targets are primarily composed of metal oxides, nitrides, and other compounds, characterized by high hardness, high melting points, strong chemical stability, and unique optical properties. Among them, indium tin oxide (ITO) targets are core materials in the flat panel display field, with excellent transparent conductivity used for fabricating touch screens and liquid crystal display electrodes; zinc oxide targets are widely used in transparent conductive films for solar cells due to their outstanding optoelectronic properties.
2. Classification by Application Field
1. Semiconductor Chip Manufacturing Targets
The purity and precision requirements for targets in semiconductor chip manufacturing are nearly stringent, typically needing to reach above 6N (99.9999%) purity to avoid impurities affecting chip performance. For example, copper targets are used in advanced processes for damask technology to achieve multilayer interconnections; tantalum targets serve as diffusion barrier layers to prevent copper atoms from diffusing into silicon substrates; tungsten targets are used for contact hole filling, constructing vertical connections within chips.
2. Flat Panel Display Targets
The flat panel display industry pursues large-area, high-uniformity thin film deposition, requiring extremely high standards for target size and stability. ITO targets are key materials for liquid crystal displays (LCD) and organic light-emitting diode (OLED) panels, used for fabricating transparent conductive electrodes; aluminum targets are used for forming backplane circuits; additionally, molybdenum targets are used as materials for OLED vapor deposition masks due to their high melting point and low resistance characteristics.
3. Solar Cell Targets
The solar cell field emphasizes the efficiency of optoelectronic conversion and cost control. Aluminum zinc oxide (AZO) targets, with high conductivity, high transparency, and low cost advantages, have become the preferred transparent conductive electrodes for thin-film solar cells; copper indium gallium selenide (CIGS) targets are used to fabricate high-performance copper indium gallium selenide thin-film batteries, driving technological upgrades in the photovoltaic industry.
3. Classification by Preparation Process
1. Melting Targets
The melting method involves melting raw materials at high temperatures and casting them into shape, suitable for metals and alloy targets with lower melting points and easy processing. The targets produced by this process have dense structures and uniform compositions, effectively reducing porosity and impurities, making them suitable for semiconductor targets with high purity requirements. For example, high-purity aluminum and copper targets are often produced using vacuum arc melting or vacuum induction melting technologies.
2. Powder Metallurgy Targets
For high melting point and difficult-to-melt metals (such as tungsten and molybdenum) and ceramic materials, powder metallurgy methods are more advantageous. This process shapes materials through powder mixing, pressing, and sintering steps, allowing precise control of material composition and microstructure. For instance, zirconia ceramic targets need to be formed through isostatic pressing and high-temperature sintering to ensure their hardness and density meet usage requirements.
3. Sputtering Targets
Sputtering targets are core consumables in physical vapor deposition (PVD) processes, where ion beams bombard the target surface, causing atoms or molecules to deposit onto the substrate to form thin films. Their performance depends not only on the material itself but also closely relates to the target’s density, grain size, and surface smoothness. Depending on the sputtering process, they can be classified into direct current sputtering targets, radio frequency sputtering targets, and others.
4. Classification by Shape
1. Circular Targets
Circular targets are widely used in small sputtering equipment and laboratory research due to their symmetrical structure and easy installation. Their design facilitates uniform sputtering deposition, suitable for thin film preparation on small substrates, such as localized coating processes for semiconductor wafers.
2. Rectangular Targets
Rectangular targets are more suitable for large-area, continuous thin film deposition, such as production lines for flat panel displays. By increasing the target area, deposition efficiency can be enhanced, and costs reduced, while meeting the strict requirements for film uniformity in panel manufacturing.
3. Special-shaped Targets
Special-shaped targets are customized according to specific equipment or process requirements, such as ring targets used for the design of circular magnetic fields in magnetron sputtering equipment, and columnar targets suitable for coating three-dimensional structures. These targets require a combination of simulation design and precision processing technology to achieve efficient deposition in specific scenarios.
The classification system of targets not only embodies the concentration of material science and engineering technology but also serves as an important support for technological advancement in various industrial fields. With the continuous iteration of semiconductor, display, and new energy technologies, the demands for target performance and customization will continue to rise, driving the industry towards higher purity and precision. In the future, the classification and innovation of targets may become a key breakthrough to overcome technological bottlenecks and achieve industrial upgrades.