High-Purity Nickel Prepared by Electron Beam Melting: Purification Mechanism
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NICKEL and its alloys possess a useful combination of properties, including good oxidation and corrosion resistance, good strength, and high ductility, even at extremely low temperatures. They also possess useful electronic properties and special magnetic properties.[1,2] These unique properties allow them to be used in a variety of specialized applications. For example, lots of critical components used in aircrafts, radars, nuclear reactors, aerospace equipment, and other industries were largely manufactured using nickel and nickel alloys.[3–6] More especially, high-purity (4N5 to 5N) nickel and nickel alloys have been used particularly as a certain sputtering target and evaporation materials to fabricate ultra large-scale integration (ULSI) gate electrodes and wiring, or magnetic thin films in semiconductors.[7–13] To the best of our knowledge, the application of high-purity metals (Ni, Cu Al, and Ta, etc.) in ULSI chips requires virtually complete elimination of: (1) Alkali metal elements (e.g., Na, K, and Li, especially for Na+) can easily migrate into the gate insulation film and cause deterioration of MOS-LSI interface characteristics, (2) heavy metal elements (e.g., TAO ZHANG, Research Engineer, ZAIYAN SHANG, Supervisor, MING CHEN and JINJIANG HE, Associate Supervisors, BAOGUO LV and XIAODONG XIONG, Vice Presidents, and XINGQUAN WANG, President, are with the Division of PVD Thin Film and the Grikin Advanced Materials Co., Ltd., Beijing, P.R. China. Contact e-mail: [email protected] Manuscript submitted January 15, 2013. Article published online December 17, 2013. 164—VOLUME 45B, FEBRUARY 2014
Fe, Co, Cu, and Cr) cause impairment of interface junctions, (3) radioactive impurities (e.g., U and Th) cause microprocessor soft errors by a-rays emission, and (4) gaseous components (e.g., C and O) cause the generation of particles during sputtering.[14–17] With the influences and harms of impurities on the properties of ULSI, we are focusing on a certain method to prepare high-purity nickel used in such field, with purity of more than 5N (99.999 wt pct) in this article. In the past, various processes like impurity (e.g., As, Fe, Co, Cu, Pb, Zn, and Cd) removal using an extractive agent (i.e., alkyl phosphate),[18] oxidation-reduction reaction (i.e., reaction between nickel oxide and reductive gas), sodium reduction,[19] and a complicated combination of high-pressure acid leach (HPAL) and matte chlorine leach electro-winning (MCLE) were employed to manufacture nickel,[20–23] and nickel with much lower purity (3N5 to 4N) was obtained. Other patents[24,25] have been publicized showing that highpurity nickel with 5N can be obtained through a combination of initial elimination of impurities (e.g., Fe, Co, and Cu) contained in anolyte and consequent electrolysis by using the anolyte as the catholyte. The methods aforementioned are the technologies based on chemistry and electrochemistry, and most have obtained the lower purity of nickel based on the complicated technology and energy consumptions. In addition, Liu et al.
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