Guide to Sputtering Targets: Key Materials for Integrated Circuits
High-purity sputtering targets primarily refer to metallic or non-metallic targets with a purity of 99.9% to 99.9999% (3N to 6N), used in the physical vapor deposition (PVD) process for the manufacturing of electronic components. They are essential materials for the fabrication of integrated circuit chips, flat panel displays, photovoltaic solar cells, and other electronic films.
Physical Vapor Deposition (PVD) is a technique that utilizes ions generated from an ion source, which are accelerated in a vacuum to form a high-speed ion beam that bombards the surface of a target material. The energetic exchange between the incoming ions and the atoms on the target surface causes the atoms to be ejected from the solid and deposited onto a substrate surface, making this one of the primary technologies for the preparation of thin film materials.
The manufacturing process of integrated circuits imposes stringent requirements on the purity of the target materials, the control of impurities and defects, the uniformity of grain size and orientation, as well as the precision of processing; it ranks as the highest in technical demands among all applications of target materials.The development of target material technology is closely related to advancements in integrated circuit film technology.
As integrated circuit fabrication technology continues to advance, the improvement of chip performance increasingly depends on the development of material technology and system integration technology, leading to the continuous development of various high-purity metals, novel alloys, and functional films of compounds.
The application of these new materials plays a crucial role in manufacturing integrated circuit devices with higher operating speeds, stronger performance characteristics, and lower power consumption. Currently, the target materials used for integrated circuit manufacturing primarily include aluminum targets, titanium targets, copper targets, tantalum targets and their alloys, as well as cobalt targets, nickel and Alloy targets, and precious metal targets, among others.
- Aluminum (Al) and its alloy target materials
High-purity aluminum (Al) and its alloy target materials have the following main applications: In processes at technology nodes greater than 0.13µm, they are primarily used in the backend metal interconnection processes of integrated circuit manufacturing; in the two planar CMOS processes at 45nm and 28nm technology nodes, they serve as work function materials in high-k metal gate processes, adjusting the threshold voltage of devices; at all technology nodes, they can be applied as aluminum pads (Al Pad) in the top layer of metal, forming metal connections with external circuits through aluminum pads.Based on different application requirements, aluminum and its alloy target materials mainly include varieties such as 5N to 5N5 (99.999% to 99.9995%) pure Al, Al-0.5%Cu, Al-1%Si, and Al-1%Si-0.5%Cu.Additionally, aluminum and its alloy target materials are also utilized in chip packaging processes, including 5N and 5N5 pure Al, Al-0.5%Cu, and Al-4%Cu.
- Titanium (Ti) target material
High purity titanium (Ti) target materials are used for PVD sputtering of high purity titanium metal thin films. In processes at technology nodes above 0.25µm, titanium is generally sputtered using SIP (Self Ionized Plasma) PVD technology. With the advancement of semiconductor technology, IMP (Ionized Metal Plasma) PVD technology is predominantly employed in processes at technology nodes of 0.18µm and below. Titanium, due to its favorable step coverage and deposition rate, is primarily utilized in the backend global interconnects which mainly involve aluminum metal interconnects at technology nodes above 0.13µm, as well as the local interconnects for contact holes across various technology nodes. Titanium and its nitride films are combined to serve as metal interconnect barrier layers. In technology nodes of 45nm and below, titanium metal nitrides can also function as hard mask materials in backend copper metal interconnect processes, allowing for well-controlled interconnect via and trench fine structures. In processes above 0.25µm, titanium can form silicides (TiSi) through PVD technology for self-aligned applications in the source-drain and gate regions, effectively reducing contact resistance. Furthermore, titanium target materials are utilized in chip packaging processes.The purity of titanium target materials typically ranges from 4N5 to 5N (99.995% to 99.999%).
- Copper (Cu) and its alloy target materials
In the interconnection process of large-scale integrated circuits, as technology nodes continue to shrink, the weak electromigration resistance and stress migration capability of aluminum wires easily lead to the formation of wire void defects, resulting in circuit failure.To improve the conductivity and reliability of aluminum metal interconnections, copper has gradually been adopted as a substitute for aluminum as the metal interconnect material starting from the 0.13µm technology node. This change allows devices to be made smaller and denser, and copper wiring can also be made thinner to reduce impedance interference between interconnections. However, due to the difficulties in etching copper, embedded processes are used for copper interconnects, specifically the Damascene Technology.This process involves sputtering a diffusion barrier layer and a copper seed layer within the etched grooves, followed by filling the grooves with copper through electroplating, and finally achieving planarization through CMP polishing.The sputtering of the copper seed layer requires high-purity copper metal targets. As the linewidth of integrated circuits becomes finer, in order to reduce metal contamination caused by copper atom diffusion, copper alloy targets containing trace amounts of aluminum (0.11% wt Al) and manganese (0.5-10% wt Mn) are selectively chosen based on product design and process requirements. Additionally, phosphorus-containing copper (CuP) is needed as the anode for electro-deposited copper.Typically, the purity requirement for high-purity Cu targets is 6N (99.9999%) or above, while the phosphorus content in CuP anodes is required to be within the range of 400 to 650 ppm.
- Tungsten (W) and alloy target materials.
High-purity tungsten (W) metal is primarily used in the contact hole processes of logic devices and memory chips. When the line width is relatively large, the PVD sputtering process can be employed for preparation. With the rapid technological advancements, since the 0.25µm technology node, the processes for logic devices have fully adopted CVD technology with higher fill capabilities for manufacturing. However, in some memory applications, the requirements for operational speed are not as critical as those for logic devices, and the line width of the contact holes tends to be larger, thus still utilizing the PVD sputtering technique with high-purity W target materials for filling contact hole films.However, as three-dimensional memory continues to demand higher requirements for interconnections, the contact hole filling technology may also transition to CVD deposition methods in the future. Tungsten-titanium (W-10wt%Ti) alloy target materials can be used for subsequent packaging barrier layers. Tungsten-silicon (WSi) alloys can serve as gate barrier layers in the stacked structures of memory gates.The purity of W and W alloy target materials is generally above 5N (99.999%).
