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The purity is one of the essential factors of the materials for preparing well controlled materials and devices, because the existence of ppm or sub-ppm level impurities leads to a significant and sometimes critical influence on the material properties and devise performance. Since the development of high technology depends strongly on the availability of high purity metals required for fabricating a new functional device, and furthermore, the purity of commercial pure materials for exploratory material researches is insufficient, the purification process that meets any requirements should be developed. In this article, based on our experience, we will describe how to construct the purification process, purification methods, and the purification of iron as an example.

The long-term native oxidation of Cu films has been investigated at the nanoscale by angle resolved X-ray photoelectron spectroscopy, spectroscopic ellipsometry, and high-resolution transmission electron microscopy. Cu films with different microstructures and crystallographic textures were deposited by with or without a negative substrate bias voltage of − 50 V. The oxidation rate of the Cu films deposited at − 50 V is much lower than that of the Cu films deposited at 0 V. The electron microscopy observation showed that the Cu films deposited at 0 V have two oxide layers, namely, an outer CuO and an inner Cu2O, whereas the oxide layer of the Cu films deposited at − 50 V consists of only Cu2O layer. The difference of texture between the Cu films deposited at 0 V and − 50 V is found to affect native oxidation behavior. It is also considered that many defects in the Cu films deposited at 0 V provide preferential nucleation sites and subsequent growth, which promotes Cu oxidation. The difference in the oxidation behavior of the two Cu films and high-purity bulk Cu can be mainly explained by the difference in texture and microstructure.

Indium zinc oxide (IZO) films were deposited as a function of the deposition temperature using a sintered indium zinc oxide target (In 2 O 3 :ZnO = 90:10 wt.%) by direct current (DC) magnetron reactive sputtering method. The influence of the substrate temperature on the microstructure, surface roughness and electrical properties was studied. With increasing the temperature up to 200 °C, the characteristic properties of amorphous IZO films were improved and the specific resistivity was about 3.4 × 10 − 4 Ω cm. Change of structural properties according to the deposition temperature was also observed with X-ray diffraction patterns, transmission electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. IZO films deposited above 300 °C showed polycrystalline phases evolved on the amorphous IZO layer. Very flat surface roughness could be obtained at lower than 200 °C of the substrate temperature, while surface roughness of the films was increased due to the formation of grains over 300 °C. Consequently, high quality IZO films could be prepared by DC magnetron sputtering with O 2 /Ar of 0.03 and deposition temperature in range of 150–200 °C; a specific resistivity of 3.4 × 10 − 4 Ω cm, and the values of peak to valley roughness and root-mean-square roughness are less than 4 nm and 0.5 nm, respectively.

We have investigated the effect of FeSi 2 source purity on the electrical property of β-FeSi 2 grown from solution. A high-purity FeSi 2 source avoided a contamination of Cu and W metals was synthesized by melting a high-purity Fe (5N) and Si (5N-up) in a quartz ampoule. Glow discharge mass spectrometry revealed that the purity of the FeSi 2 source synthesized using 5N-Fe and a quartz-ampoule-melting process is one order of magnitude higher than that of the conventional arc-melted FeSi 2 source using 4N-Fe. The β-FeSi 2 crystals grown using the high-purity FeSi 2 and Zn solvent showed n-type conduction, whereas those grown using the arc-melted FeSi 2 showed p-type. The carrier concentration of the n-type crystals was (4.9–6.3) × 10 18 cm − 3 , which was more than 10 times higher than that of the p-type crystals (5.2 × 10 17 cm − 3 ). From the ICP-MS and SIMS analysis of the grown crystals, we found that dominant impurity concentrations (Cr, Mn, Co, Ni, Cu, Zn and W) in the p-type crystals were higher than those in the n-type ones. Therefore, the p-type conductivity of undoped crystals grown using Zn solvent results from unintentional doping by the high impurity level of the used FeSi 2 source.

Ta thin films were deposited on Si (100) substrates by an ion beam deposition method at various substrate bias voltages under Ar + N 2 atmosphere with different pressure ratios of Ar and N 2 . The effects of nitrogen pressure in the plasma gas and the substrate bias voltage on the surface morphology, crystalline microstructure, electrical resistivity and diffusion barrier property were investigated. It was found that the fraction of a metastable β -phase in the Ta film deposited at the substrate bias voltage of − 50 V films decreased by adding nitrogen gas, while the α -Ta phase became dominant. As a result, the Ta films deposited at the substrate bias voltage of − 50 V under Ar (9 Pa) + N 2 (3 Pa) atmosphere showed a dominant α -phase with good surface morphology, low resistivity, and superior thermal stability as a diffusion barrier.

Semiconductor grade high-purity Fe will be required in practical use of β-FeSi2. However, high-purity Fe with more than 99.9999% in purity has not been produced commercially. Then, a process consisting of anion exchange in a HCl solution, hydrogen reduction and plasma arc melting has been developed for the production of high-purity Fe. All metallic impurities can be virtually removed from Fe by the two anion-exchange steps, in which some elements such as Cu and Mo are separated efficiently under reducing conditions by the addition of Fe powder at the 1st step, and the rest of impurities are surely separated under oxidizing conditions at the 2nd step. Non-metallic impurities such as oxygen, carbon and nitrogen also can be eliminated to very low levels by the hydrogen reduction and the hydrogen plasma arc melting steps.

Cu films were deposited on Si (1 0 0) substrates at room temperature by a non-mass separated ion beam deposition method. The effect of the negative substrate bias voltage on the property of the Cu films was investigated by using field emission scanning electron microscopy and secondary ion mass spectroscopy. The Cu film deposited at the negative bias voltage of −50 V showed an extremely fine and homogeneous morphology without a columnar structure. The purity of the Cu film deposited at the bias voltage of −50 V was much improved in comparison with the 6N Cu target, while the Cu film deposited without applying substrate bias voltage contained more impurities than the 6N Cu target.

Cu thin films as a seed layer were deposited on Si (1 0 0) substrates by applying a negative substrate bias voltage using a non-mass separated ion beam deposition method. Using resistivity measurement, X-ray diffraction analysis, atomic force microscopy, secondary ion mass spectroscopy, and scanning electron microscopy, the Cu films were characterized. The Cu films deposited at the substrate bias voltage of −50 V showed higher purity, strong (1 1 1) preferred orientation, smoother surface and better step coverage in comparison with the Cu films deposited without the substrate bias voltage. The thickness dependence of the resistivity showed clear size effects with decreasing the film thickness. In the case of Cu (100 nm)/Ta (50 nm)/Si structures, the Cu films deposited on Ta/Si substrates by applied the substrate bias voltage maintained a completely (1 1 1) preferred orientation without (2 0 0) texture even after thermal annealing at 450 °C for 60 min.