High Purity Tungsten Powder and Ultrapure Tungsten Powder

High-purity tungsten and its silicide are mainly used in very large-scale integrated circuits as a resistance layer, a diffusion barrier, etc., and as gate materials and connecting materials in metal oxide semiconductor transistors, which are expensive on the market.

High purity tungsten powder or ultra pure tungsten powder is widely used as gate electrode material, wiring material and shielding metal material for semiconductor large scale integrated circuit because of its high electron migration resistance, high temperature stability and high electron emission coefficient. High purity tungsten metal targets are one of the basic materials for the manufacture of integrated circuits, and their market prospects are closely related to the development of integrated circuits. If the purity of the tungsten target is not high, the operation reliability of the large-scale integrated circuit will be reduced, and even the electric discharge phenomenon will be produced. The use of high purity tungsten can reduce or even eliminate the effects of harmful impurities, and improve the performance of the terminal products.

The main raw material for the preparation of high-purity tungsten powder and ultra-pure tungsten powder is high-purity ammonium paratungstate (APT). The general procedure is APT → tungsten powder → high-purity tungsten powder, ultrapure tungsten powder, it often takes two or three cycles to purify, so the cost is very high. Secondary purification methods commonly used are vacuum melting and chemical vapor deposition.

Hydrogen reduction of WO₃ is currently the most widely used industrial W powder preparation process, the tungsten oxide reduction process, we should pay attention to keep building highly clean, to avoid the introduction of impurities, the main parameters affecting the rate of reduction is the reduction temperature, powder loading, boat moving speed, H₂ velocity and H₂ humidity. In the process of high temperature reduction, APT completes the densification process by material migration, and finally gets high-purity tungsten billets, which has fewer processes and lower cost.

Chemical vapor deposition is six tungsten hexafluoride (WF₆) as the tungsten source, using tungsten fluoride low melting point and boiling point (melting point of 2.3 ℃), the boiling point of 19.9 ℃), purified by distillation or distillation, and at a certain temperature by H₂ reduction, the tungsten deposited in specific substrate after removal of the substrate material, the deposition of high purity tungsten, this procedure is simple, has been widely used.

The purity of tungsten powder produced by hydrogen reduction or chemical vapor deposition is limited. If we want to produce tungsten powder with higher purity (5N or 6N), we must further purify it. The methods used in tungsten metal refining are vacuum melting and vacuum degassing. The vacuum melting method uses the high energy electron beam emitted by the electron beam generation system to bombardment the smelting metal, and realizes the smelting, purifying and impurity removing technology of metallic materials.

At present, China's industrial development by leaps and bounds, the development of microelectronics and nuclear technology overwhelming, China is a large tungsten resource should give full play to its industrial advantages, to high-tech industries, high-purity tungsten is an important raw material for its application; How to improve the purification process to prepare more excellent high purity tungsten and its related products, to achieve its industrialization is the future direction of development.

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