What is titanium target
What is titanium target?
Table of Contents
- What is titanium target?
- Main performance requirements of target material
- Main grade of titanium target
- Manufacturing and processing of titanium target
- Use of titanium target
- Application examples of titanium targets
- Structural development of titanium targets
- Requirements for qualified sputtered titanium targets
Titanium target is the target material bombarded by high-speed charged particles. Titanium target is one of the main materials for preparing thin films, which is mainly used in integrated circuits, flat panel displays, solar cells, recording media, smart glass, etc., with high requirements for material purity and stability.
Titanium target parameters
|Relative density of material||100%|
|Target shape||Circular target||Rotating target||Rectangular target||Splicing target|
Main performance requirements of target material
Purity is one of the main performance indicators of the target, because the purity of the target has a great impact on the performance of the film. However, in practical applications, the requirements for the purity of the target are also different. For example, with the rapid development of the microelectronics industry, the silicon chip size has grown from 6 “, 8” to 12 “, and the wiring width has been reduced from 0.5 um to 0.25 um, 0.18 um or even 0.13 um. Previously, 99.995% of the target purity can meet the process requirements of 0.35 um IC, while the target purity is required to be 99.999% or even 99.9999% for the preparation of 0.18 um lines.
(2) Impurity content
Impurities in the target solid and oxygen and water vapor in the pores are the main pollution sources of the deposited films. Different target materials have different requirements for different impurity content. For example, pure aluminum and aluminum alloy targets used in the semiconductor industry have special requirements for alkali metal content and radioactive element content.
In order to reduce the porosity in the target solid and improve the performance of the sputtered film, the target is usually required to have a high density. The density of the target affects not only the sputtering rate, but also the electrical and optical properties of the film. The higher the target density, the better the film performance. In addition, increasing the density and strength of the target can better withstand the thermal stress in the sputtering process. Density is also one of the key performance indicators of the target.
(4) Grain size and grain size distribution
Usually, the target is polycrystalline, and the grain size can be from micrometer to millimeter. For the same target, the sputtering rate of targets with fine grains is faster than that of targets with coarse grains; The thickness distribution of the films deposited by target sputtering is more uniform when the grain size difference is small (uniform distribution).
Main grade of titanium target
Manufacturing and processing of titanium target
Plastic deformation, heat treatment and grain orientation control: process design shall be carried out according to the performance requirements of downstream application fields, and then repeated plastic deformation and heat treatment shall be carried out. Key indicators such as grain and grain orientation shall be accurately controlled, and then welding, machining, cleaning and drying, vacuum packaging and other processes shall be carried out. Target manufacturing involves a wide range of processes, high technical threshold, large equipment investment, and relatively few enterprises with large-scale production capacity. The manufacturing methods of target materials mainly include smelting method and powder metallurgy method. The melting method mainly includes vacuum induction melting, vacuum arc melting, vacuum electron beam melting and other methods. The melted ingots are prepared into targets through mechanical processing. The targets obtained by this method have low impurity content, high density, can be large-scale, and have no internal pores. However, if the melting point and density of the two alloys differ greatly, uniform alloy targets cannot be formed. Powder metallurgy method mainly includes hot isostatic pressing method, hot pressing method and cold pressing sintering method. The target material is obtained by mixing and sintering various raw materials. The advantages of this method are that the target material composition is relatively uniform, the mechanical properties are good, and the disadvantages are that the oxygen content is high.
Classification of target manufacturing process
|Target manufacturing process||Describe||Advantage||Shortcoming|
|Hot isostatic pressing||The powder or preformed embryo is sintered under equal pressure at 800C-1400 ° C and 100kgf/cm2 – 2000kgf/cm2.||High density, good physical and mechanical properties.||High equipment investment, high production cost and high oxygen deficient rate of products.|
|Hot pressing method||After the mold made of graphite or aluminum oxide is filled with appropriate powder, the mold is pressurized in a single axial direction at a pressure of 100kgf/cm2-1000kgf/cm2, and sintered at 1000 ° C-1600’C.||The required forming pressure is small, the sintering temperature is low, and the sintering time is short.||High anoxic rate, uneven distribution of oxygen content, and can not produce large size targets.|
|Cold pressing sintering method||The raw materials are mixed with adhesives and dispersants, then pressure formed and degreased. Sintering at 1400 ° C-1600C.||Low investment, low cost, high product density, low anoxic rate and large size.||Strong selectivity to powder.|
|Vacuum induction melting||In the process of electromagnetic induction, eddy current will be generated to melt the metal.||There is no air hole in the target and the defect is small. The target gas has low impurity content, high density and can be large-scale.||If the melting point and density of the two metals differ greatly, it is difficult to obtain alloy targets with uniform composition.|
|Vacuum arc melting||Arc heat is used to melt metals and alloys in vacuum.|
|Vacuum electron beam melting||In the high vacuum chamber, the electron beam emitted by the electron gun is used to bombard the furnace charge, so that the kinetic energy of the electron is converted into heat energy and the furnace charge is melted.|
Use of titanium target
Widely used in decorative coating, wear-resistant coating, electronic industry CD, VCD and other types of optical discs and various magnetic disc coating.
Tungsten titanium (W-Ti) films and alloy films based on tungsten titanium (W-Ti) are superalloy films, which have a series of irreplaceable excellent properties. Tungsten has high melting point, high strength and low thermal expansion coefficient. W/Ti alloy has low resistance coefficient, good thermal stability and oxidation resistance. For example, all kinds of devices need metal wiring that can conduct electricity, such as Al, Cu and Ag, which have been widely used and studied. However, the wiring metal itself is easy to oxidize, react with the surrounding environment, and has poor adhesion with the dielectric layer. It is easy to diffuse into the substrate materials of devices such as Si and SiO2, and will form metal and Si compounds at low temperatures, acting as impurities, which greatly reduces the performance of devices. However, W-Ti alloy is easy to be used as a diffusion barrier layer for wiring due to its stable thermo mechanical properties, low electron mobility, high corrosion resistance and chemical stability, especially suitable for use in high current and high temperature environments.
Application examples of titanium targets
Titanium as a raw material can be made into titanium sputtering targets by several methods. They are widely used in electronics, information industry, home decoration, automobile glass manufacturing and other high-tech fields. In these industries, titanium targets are mainly used for surface panel displays of coated integrated circuits, flat panels and other components, or for decoration and glass coating.
Different industries have different requirements for titanium targets. Let’s take the titanium circuit as an example. Generally, we use the following performance evaluation indicators to determine whether the sputtering target meets the requirements:
|Titanium targets for non integrated circuits||Titanium targets for integrated circuits|
|Microstructure (crystal size)||<100 nm||<30 nm|
|Welding method||Brazing, monomer||Monomer, brazing, diffusion welding|
|Dimensional accuracy||0.1 mm||0.01 mm|
As shown in the above table, the requirements for titanium sputtering targets for non integrated circuits and integrated circuits are different. Generally speaking, integrated circuits have high requirements for coating materials, such as higher purity, smaller grain size and more accurate size accuracy. This is just an example, but it reveals that different industries have different requirements for titanium targets. When looking for titanium targets for projects, make sure you know the exact specifications of the products you need, which will help save time and money.
Titanium targets used in integrated circuits
It can be seen from the above table that the purity requirements of titanium target for integrated circuits are mainly greater than 99.995%, which is higher than the purity used in non integrated circuits.
Titanium target used in flat panel display
Flat panel display includes liquid crystal display (LCD), plasma display (PDP), electroluminescent display (EL) and field emission display (FED). Sputtering coating technology is usually used to deposit thin films of flat panel displays. Al, Cu, Ti and Mo are the main metal sputtering targets for flat panel displays. The purity of titanium target used for flat panel display usually needs to be greater than 99.9%.
Structural development of titanium targets
Early chip foundries had high profit margins. They mainly use 100-150mm magnetron sputtering machine with small power. The sputtering film is thick and the chip size is large. At that time, the titanium target materials for integrated circuits were mainly 100-150mm monomer and composite target.
In the second stage, according to Moore’s Law, the line width of the chip narrows. In order to increase profits, the chip foundry increased the sputtering power of the equipment, mainly using 150-200mm sputtering equipment. This requires increasing the size of the target while maintaining high thermal conductivity, low price and certain strength. During this period, titanium target is mainly composed of aluminum alloy back plate diffusion welding and copper alloy back plate brazing and welding.
The third stage:
In the third stage, with the development of integrated circuits, the width of chip lines is further narrowed. At this time, the chip foundry mainly uses a 200-300mm sputtering machine, which is more strict with the target. During this period, Ti target is mainly made of copper alloy back plate by diffusion welding.
Requirements for qualified sputtered titanium targets
To produce qualified titanium sputtering target, purity is one of its important performance indicators. The purity of titanium target has a great influence on the properties of sputtered coatings. The higher the purity of titanium target, the less impurity element particles in the sputtered titanium film, which leads to the better performance of PVD coating, including corrosion resistance, electrical and optical properties. However, in practical applications, titanium targets for different purposes have different purity requirements. The target is used as the cathode source in sputtering, and the impurity elements and pore inclusions in the material are the main pollution sources of the deposited films. Porous inclusions will be basically removed in the process of non-destructive testing of the ingot, and the non removed porous inclusions will discharge during the sputtering process, which will affect the quality of the film; The impurity element content can only be reflected in the total element analysis and test results. The lower the total impurity content, the higher the purity of titanium target.
Density is also an important factor to measure the quality of titanium target. In order to reduce the porosity in the target solid and improve the performance of the sputtered film, the target is usually required to have a high density. The density of the target affects not only the sputtering rate, but also the electrical and optical properties of the film. The higher the target density, the better the film performance. In addition, increasing the density and strength of the target can make the target better withstand the thermal stress in the sputtering process. Density is also one of the key performance indicators of the target.
Particle size and its distribution
Generally, the sputtering target is a polycrystalline structure with a grain size of several microns to several millimeters. For the same target, the smaller the target particle size, the faster the target sputtering speed; In addition, targets with smaller particle size differences can sputter films with more uniform thickness. It is found that if the grain size of titanium target is controlled at 100 μ The quality of the sputtered films can be greatly improved if the grain size is kept within 20% and the sputtering temperature is below m.
Metallic titanium is a closely packed hexagonal structure. Because titanium target atoms are easy to be preferentially sputtered along the tightly arranged direction of the hexagonal atoms during sputtering, in order to achieve a higher sputtering rate, the sputtering rate can be increased by changing the crystal structure of the target. The crystallization direction of titanium target also has a great influence on the thickness uniformity of the sputtered film.
The structural homogeneity is also one of the important indicators to evaluate the target quality. For titanium target, uniformity of composition, grain orientation and average grain size is required not only in the sputtering plane of the target, but also in the normal direction of the sputtering plane. Only in this way can the titanium film with uniform thickness, reliable quality and consistent grain size be obtained at the same time during the service life of the titanium target.