Eco-Materials Processing and Design IX

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Authors: Ya Jie Guo, Jian Ping Lin, Guan Jun Qiao, Hai Yun Jin
Abstract: Copper and aluminium laminates are alternately stacked and sintered by PAS at T=743K under different pressures. Microstructure of the cross section of the samples are characterized and analyzed by means of Optical Microscope (OM), Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscope (EDS). The results show that the initial Al layers melted and produced Al-rich liquid phase during sintering at T=743K, and the Al-rich liquid phase ultimately formed complicated L layer consisting of the saturated solid solution phase Al(Cu) and the two-phase Al2Cu-Al(Cu) eutectic when the laminates was cooled to room-temperature. The interface between the Cu layer the L layer consists of solid solution(α), Al2Cu3(δ)and Al2Cu(θ) layer. Voids and cracks are not found at or near the interfaces of the polished samples. The most important effect of the pressure is to change the shapes of interfaces, which almost smooth at 10MPa but flexual at 50MPa.
Authors: Suk Hoon Jeong, Suk Bae Joo, Ho Jun Lee, Boum Young Park, Hyoung Jae Kim, Hae Do Jeong
Abstract: Chemical mechanical polishing (CMP) has been used as planarization process in the fabrication of semiconductor devices. The CMP process is required to planarize the overburden film in an interconnect process by high relative velocity between head and platen, high pressure of head and chemical effects of an aqueous slurry. But, a variety of defects such as dishing, delamination and metal layer peering are caused by CMP factors such as high pressure, pad bending and strong chemical effect. The electrical energy of the electro-chemical mechanical planarization (ECMP) dissolves copper (Cu) solid into copper ions electrochemically in an aqueous electrolyte. The dissolved copper complex layer or passivation layer is removed by the mechanical abrasions of polishing pad and abrasive. Therefore the ECMP process realizes low pressure processing of soft metals to reduce defects comparing to traditional CMP process. But, if projected metal patterns were removed and not remained on whole wafer surface in final processing stage, Cu layer could not be removed by ECMP process. The two-step process consists of the ECMP and the conventional CMP used in micro patterned Cu wafers. First, the ECMP process removed several tens 'm of bulk copper on Cu patterned wafer within shorter process time than the Cu CMP. Next, residual Cu layer was completely removed by the Cu CMP under low pressure. Total time and process defects are extremely reduced by the two-step process.
Authors: Joo Hyoung Choi, Jin Rae Cho
Abstract: In this paper, an efficient optimum material design technique is introduced for hybrid designing of dual-phase heat-resisting functionally graded composites. The graded region is divided into a finite number of homogeneous material layers in order to reduce the total design variables. The discrete optimum volume fractions are sought by making use of the interior penalty method and the finite difference sensitivity scheme. A linear interpolation technique is adopted to make the final optimum volume fraction distribution be continuous. The validity of the proposed optimization technique is examined through the illustrative numerical experiment.
Authors: Peng Xiao, Zhi Kang Fan
Abstract: The Cu20W70Cr10 composites were fabricated by two methods which are the conventional powder metallurgy, and mechanical alloying to prepare WCr compound powders, followed by sintering and infiltration. The erosion behavior of CuWCr composites under breakdown was investigated. The surfaces of the composites before and after erosion and the mechanism of arc erosion were studied by scanning electron microscopy. The results show that the CuWCr composites prepared by mechanical alloying have superfine microstructure, uniform composition and high density, thus result in good characteristics of diffusing arcs and arc eroding endurance. Arc erosion zones are dispersive and uniform on the surfaces with some flat eroding pits. The Cu20W70Cr10 composites have excellent electrical properties such as high breakdown voltage, low chopping current and long arc life.
Authors: Han Chul Cho, Suk Hoon Jeong, Jae Hong Park, Ho Jun Lee, Ji Heon Oh, Hyoung Jae Kim, Hae Do Jeong
Abstract: Lithium niobate (LN, LiNbO3) is a kind of artificial crystal with piezoelectricity, pyroelectricity and ferroelectricity, which has been widely used in electron components. The large difference in thermal expansion coefficients between Si and LN causes a serious thermal stress during the thermal-pressure bonding process. Therefore room temperature bonding would be the best candidate to make strong and stress-free interface between Si and LN. However, room temperature bonding requires lower surface roughness (Ra<2nm) and lower defects on the LN wafer surface than those of thermal bonding. Chemical mechanical polishing (CMP) process helps LN to obtain the high quality surface and thin wafer suited in room temperature bonding. The LN wafer was polished using colloidal silica slurry, resulting in high material removal rate (MRR) and fine surface quality under the condition of low pH, high abrasive concentration and low flow rate. The polishing mechanism of LN was discussed by mechanical, chemical and thermal analysis.
Authors: Ho Jun Lee, Boum Young Park, Hyun Seop Lee, Suk Hoon Jeong, Heon Deok Seo, Suk Bae Joo, Hae Do Jeong, Hyoung Jae Kim
Abstract: Silicon carbide (SiC) is a wide band gap semiconductor being developed for high temperature, high power, and high frequency device applications. For the manufacturing of SiC to semiconductor substrate, many researchers have studied on the subject of SiC polishing. However, SiC faces many challenges for wafer preparation prior to epitaxial growth due to its high hardness and remarkable chemical inertness. A smooth and defect free substrate surface is important for obtaining good epitaxial layers. Therefore, hybrid process, chemical mechanical polishing (CMP) has been proposed to achieve epi-ready surface. In this paper, the material removal rate (MRR) is investigated to recognize how long the CMP process continues to remove a damaged layer by mechanical polishing using 100 nm sized diamond, and the authors tried to find the dependency of mechanical factors such as pressure, velocity and abrasive concentration using single abrasive slurry (SAS). Especially, the authors tried to get an epi-ready surface with mixed abrasive slurry (MAS). The addition of the 25nm sized diamond in MAS provided strong synergy between mechanical and chemical effects resulting in low subsurface damage. Through experiments with SAS and MAS, it was found that chemical effect (KOH based) was essential and atomic-bit mechanical removal was efficient to remove residual scratches in MAS. This paper concluded that SiC CMP mechanism was quite different from that of relatively soft material to achieve both of high quality surface and MRR.
Authors: Ji Eon Yoon, Won Hyo Cha, Dong Hyun Hwang, Chul Su Lee, In Seok Lee, Young Gook Son
Abstract: The SBT(SrBi2Ta2O9) thin films with Bi2O3 buffer layer were deposited on Pt/Ti/SiO2/Si substrate by R.F. magnetron sputtering method in order to improve the ferroelectric characteristics. In SBT thin films, the deficiency of bismuth due to its volatility during the process results in an obvious non stoichiometry of the films and the presence of secondary phases. Bi2O3 buffer layer was found to be effective to achieve lower temperature crystallization and improve ferroelectric properties of SBT thin films. Ferroelectric properties and crystallinities of SBT thin films with various substrate temperature of Bi2O3 buffer layer were observed, using X-Ray Diffraction (XRD), Precision LC (Radient Technologies. Inc.) and GDS (glow discharge spectrometer).
Authors: Suk Hoon Shin, Chul Kim, Dong Gyu Ahn, Kwang Ho Kim, Myung Chang Kang
Abstract: Ti-Al-Si-N and Ti-Al-N coatings were deposited on WC-Co substrates by a DC magnetron sputtering method. The oxidation behavior of two kinds of Ti0.75Al0.25N and Ti0.69Al0.23Si0.08N coatings were comparatively investigated by XRD patterns and GDOES depth profiles. Si addition of 8 at.% into Ti-Al-N film modified its microstructure to a fine composite comprising, Ti-Al-N crystallites and amorphous Si3N4, and to a smoother surface morphology. While the solid solution Ti0.75Al0.25N film had superior oxidation resistance up to around 700°C, the composite Ti-Al-Si-N film showed further enhanced oxidation resistance. Both Al2O3 and SiO2 layers played roles as a barrier against oxygen diffusion for the quaternary Ti-Al-Si-N film, whereas only the Al2O3 oxide layer formed at surface did a role for the Ti-Al-N film. The cutting performances of two coated carbide ball-end mills were evaluated by cutting of AISI D2 cold-worked die steel (60 HRC) under high-speed cutting condition. The tool wear and cutting temperature are discussed along with coating characteristics.
Authors: Han Sol Kim, Won Yong Kim
Abstract: Pseudoelastic behavior of Ti-xNb-yGe alloys, where x=22~28at.% and y=0.5~2.0at.%, was investigated by controlling martensite start temperature and phase stability of β phase. Cyclic tensile test was carried out to display a pseudoelastic behavior at room temperature. Determination of the martensitic transformation temperature (Ms and Mf) and reverse transformation temperature (As and Af) of the alloys were carried out using differential scanning calorimetry (DSC). Optical microscopy, X-ray diffraction (XRD) and DSC results revealed that Ge is stronger stabilizer of β-phase than Nb. XRD spectra of the deformed specimens confirmed that the crystal structure of stress-induced martensite phase is orthorhombic structured α″. It is concluded that pseudoelasticity of the present Ti-Nb-Ge alloy is closely associated with phase stability, and metastable β-phase is better to increase pseudoelasticity than stable one.
Authors: Sun Ki Kim, Han Sol Kim, Won Yong Kim
Abstract: This study is to examine wear properties of Ti-Nb-Si alloys under dry condition and to investigate its wear mechanism. A ball-on-disc type wear testing machine was used to evaluate the wear factor. Optical microstructure observation revealed that the microstructure appeared to mixture appearance consisting of β phase and small amount of α″ martensite phase. Yield strength increased with increasing Nb and Si content. Wear resistance of the present alloy are strongly dependent upon yield strength and elastic modulus. Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis confirmed the tribo-chemical reaction between the alumina ball and the present alloy occurs due to decomposition of alumina to aluminum.

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