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Refractory metal tungsten and tungsten alloys have the advantages of good high temperature stability, high electron migration resistance and high electron emission coefficient. High-purity tungsten and tungsten alloy targets are mainly used to manufacture gate electrodes, connection wiring, and diffusion barriers of semiconductor integrated circuits. There are extremely high requirements on the purity of materials, content of impurity elements, density, grain size and uniformity of grain structure. The following will take you to see what are the influencing factors in the preparation process of high-purity tungsten targets.
1. The influence of sintering temperature
The molding process of the tungsten target body is generally produced by cold isostatic pressing. The tungsten grains will grow up during the sintering process. The growth of the tungsten grains will fill the gaps between the grain boundaries, thereby improving the quality of the tungsten target. Density. As the number of sintering increases, the density increase of the tungsten target gradually slows down. The main reason is that the quality of the tungsten target has not changed much after multiple sinterings. Since most of the gaps in the grain boundaries are filled by tungsten crystals, the overall size change rate of the tungsten target has been reduced after each sintering. It is very small, which leads to limited space for increasing the density of tungsten targets. As the sintering proceeds, the grown tungsten grains fill the voids, resulting in higher density of the target material with smaller grain size.
2. The influence of holding time
Keeping at the same sintering temperature, as the sintering holding time prolongs, the compactness of the tungsten target is correspondingly improved. The growth multiple of the particle size gradually slows down, which means that increasing the holding time can also improve the performance of the tungsten target.
3. The effect of rolling on target performance
In order to improve the density of the tungsten target material and obtain the processed structure of the tungsten target material, the medium temperature rolling of the tungsten target material must be carried out below the recrystallization temperature. If the rolling temperature of the target blank is high, the fibrous structure of the target blank will be thicker, otherwise the fibrous structure of the target material will be finer. When the warm rolling processing rate is above 95%. Although the sintered original grains are different or the difference in fiber structure caused by different rolling temperatures will be eliminated, the internal structure of the target will form a relatively uniform fiber structure, so the higher the processing rate of warm rolling, the better the performance of the target. good.
Tungsten target, also known as tungsten sputtering target, is a product made of pure tungsten powder, with a silver-white appearance, and is popular in many fields because of its excellent physical and chemical properties.
Tungsten sputtering target characteristics
1) High purity, the purity of the target material after sintering and forging can usually be higher than 99.95%. Generally speaking, when other conditions remain unchanged, the higher the purity of the target material, the better the electrical properties of the resulting coating, and the less likely the corresponding circuit will be short-circuited or damaged.
2) The cost is relatively reasonable, and the speed of direct compression molding by powder metallurgy is faster, which can effectively shorten the production cycle and thus reduce the cost.
3) The density is high, and the target density after sintering and forging can reach more than 19.1g/cm³.
4) The deflection force is high, and the composition and structure of the finished target produced by ultra-fine tungsten powder are relatively uniform and consistent.
5) Good thermal and chemical stability, not prone to volume expansion or shrinkage, chemical reactions with other substances, etc.
6) The resistance is low and will not cause the circuit to generate unnecessary energy.
In addition, it has high melting point, high elasticity, low expansion coefficient, low vapor pressure, non-toxic, non-radioactive and other characteristics
Tungsten sputtering target production process
It is generally prepared by powder metallurgy method.
First, put tungsten powder in a vacuum heat treatment furnace for pre-degassing, then introduce hydrogen, and continue heating for degassing;
Second, the degassed tungsten powder is sintered by vacuum hot pressing;
Thirdly, the product after the primary sintering is passed through a hot isostatic press to complete the secondary sintering;
Fourth, the product after secondary sintering is machined to grind the entire surface to obtain the product.
Note: 1) The purity of tungsten powder should be more than 99.999%, and the particle size should be between 3.2-4.2μm.
Tungsten target application
Widely used in flat panel displays, solar cells, integrated circuits, automotive glass, microelectronics, memory, X-ray tubes, medical equipment, smelting equipment and other products.
Note: The purity, density, microstructure, internal quality, welding quality, appearance quality and geometric size of the target material have an important impact on the quality of the coating.
The main uses of tungsten targets include:
1. Preparation of electronic devices: Tungsten targets are widely used in the preparation of electronic devices, such as integrated circuits (Integrated Circuits, IC), flat panel displays (Flat Panel Displays, FPD) and solar cells. During the preparation process, the tungsten target is placed in the target gun in the vacuum chamber, tungsten atoms or ions are released by ion bombardment or electron beam, and deposited on the surface of the substrate to form the required tungsten film.
2. Conductive material: Because tungsten has good electrical conductivity and high melting point, tungsten target is often used as the preparation of conductive material. It can be used to prepare high-temperature resistors, electrode materials, high-power electronic devices, etc.
3. Metal evaporation source: Tungsten target can be used as a metal evaporation source to carry out metal evaporation process in vacuum. In the evaporation process, the tungsten target is heated to a high temperature, which evaporates into a metal vapor, which is then deposited on the substrate to form a metal film.
Users of tungsten targets include semiconductor manufacturers, display manufacturers, photovoltaic industry, electronic device manufacturers, scientific research institutions, etc. These industries and units widely use tungsten targets in the fields of thin film preparation, material research and electronic device production.
