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Copper is one of highly elastically anisotropic materials, it is possible to acquire the films with (111) preferred orientation by sputtering and electroplating processes on Si substrate. The Cu films on Si substrate has very flat surface, and we investigated etching rates for various oriented surfaces by coupled techniques of AFM and FIB. The faceting surface appeared after etching in 10 vol% nitric acid and the etched surfaces with three kind orientations of (111), (110) and (100) had triangular flake, ridge and rectangular pyramidal shapes, respectively. The etching rates were measured quantitatively, it was found that etching rates for nanosized as-plated initial region, (111), (110) and (100) oriented regions were 383, 270, 276, and 317 ㎚/min, respectively. These faceting surfaces seemed to be built up based on the thermodynamic equilibrium state of etching reaction because most of them had (111) front surface. The difference of etching rates was owing to the planar density of kink or ledge for each recrystallized orientation grains. In other words, the etching happened by step flow mechanism maintaining the thermodynamic equilibrium state. By using this technique, we expect to robustly perform fundamental studies of etching solutions with various organic and inorganic additives, effects of stress and impurity in the Cu thin films.

3D IC integration is the latest technological breakthrough for maximizing its performance while reducing wiring lengths, interconnection latency, and power consumption. Through-silicon via (TSV) is an essential feature of the 3D IC integration. Filling high aspect ratio TSVs by the conductive materials can be a challenging task. Copper electrodepostion is often adopted due to its optimal electrical preoperties, simplicity, and cost-effectiveness. However, the coefficient of thermal expansion (CTE) of copper is much higher (16.7 ppm/℃) than that of silicon (2.3 ppm/℃). Therefore, the CTE mismatch between copper and silicon substrate can induce thermal stresses, which may lead to TSV protrusion and interfacial delamination. In previous studies, this is mostly managed via suitable heat treatment. This study however proposes a novel method for controlling TSV protrusion. Copper with JGB (Janus Green B, C30H31ClN6) concentration increases (and at the level of 0.2mM of JGB), while the sheet resistance decrease by 7% for the initial resistance. Here, the crystal growth is not observed that is due to impurity pinning or solute dragging effect at grain boundaries. This leads to the conclusion that controlling impurity contents may relieve stress of TSV overhang area. To prevent TSV protrusion, we also perform the same concentration split tests on TSV pattern wafers. Figure 1. EBSD IPF maps of Cu electrodeposit after annealing at 80 ℃ for 90 min with various JGB concentrations of (a) 0, (b) 0.01, (c) 0.03, (d) 0.1, (e) 0.2 and (f) 1 mM in the Cu plating bath. Figure 1

GaN based photoelectrode with a nanowire structure have been studied due to superior performance of water splitting ability. Self‐organized GaN nano‐rod on silicon has been demonstrated, and a direct growth via vapour–liquid–solid using metal particle as a catalyst has been reported. Nonowire structure has benefit with short minority carrier diffusion lengths and large surface-to-volume ratio. It allows minor carrier to easily reach to surface without recombination, so that water splitting ability could be increased. However, this structure has photocorrosion problem. For solving this problem, we covered graphene material on the tips of nanowires as a passivation layer. Graphene has been known to have excellent mechanical, thermal, optical, and electrical properties. For these reasons, we studied the photoelectrochemical water splitting properties of graphene coated GaN nanowire (graphene/GaN nanowire) photoelectrode. GaN nanowire sample without graphene was used for the reference. The GaN nanowire structures were grown on n-type Si(111) substrates using radio-frequency plasma-assisted molecular beam epitaxy. The graphene was grown by chemical vapor deposition method and exfoliated to surface of GaN nanowire. As a result, compared with non-coated GaN nanowire sample, the graphene/GaN nanowire phoeoelectrode showed higher photocurrent density. Also, we could know that it has much higher photocurrent stability. We will present the results and the reasons for higher efficiency and stability of this graphene coated GaN nanowire sample at this conference. Reference [1] Allon I. Hochbaum, and Peidong Yang, Chem. Rev., 110 (2010) 527–546 [2] B. AlOtaibi, M. Harati, S. Fan, S. Zhao, H. P. T. Nguyer, M. G. Kibiria, and Z. Mi, Nanotechnology, 24 (2013) 175401

Anisotropic behavior of Sn based solder during electromigration has been studied by many researchers, and it is very important to control the microstructure for more reliable bump joints[1]. Here, we prepared various SnAg bumps with different Ag concentrations including pure Sn[2]. Unary electroplating has various advantages such as easy handling bath, negligible bump composition and maintaining equipment with securing about environmental health and safety issue. Figure 1 shows our preliminary experiments for the cross-sectional EBSD and EDS measurement of Cu pillar with pure Sn bump, and it is reflowed at 235°C for 6 min. In this study, we will report comparison of Sn microstructures according to various Ag inclusions by using cross-sectional EBSD(electron backscattered diffraction) analysis and EDS(energy dispersive spectroscopy) measurement. We carried out multiple reflows at various atmosphere how this impact IMC(intermetallic compound) growth along with microstructures. Through this crystallographic aspect approach, we will present optimum condition for resistance of electro migration and void formation. [1] Yiwei Wang, Kuan H. Lu, Vikas Gupta, Leon Stiborek, Dwayne Shirley, Seung-Hyun Chae, Jay Im, Paul S. Ho, J. Mater. Res., 27, 1131 (2008) [2] Ui-Hyoung Lee, Moongi Cho, Woojin Choi, Ha-Young You, Jinho Choi and Jaihyung Won, 224th ECS meeting, San Francisco, Oct. (2013)

Electroless nickel with immersion gold (ENIG) process has been widely used as a surface finishing for PCB (Printed Circuit Board). The ENIG process provides a uniform coating on Cu layer without any complex patterning process, and so it has wide and diverse electronic industrial applications; fine pitch surface mount, ball grid array(BGA), flip chip BGA packages and so on. However, there is a reliability issue in the ENIG process. Many researchers have pointed out that severe corrosion of electroless Ni surface is the one of the major factors to reliability failure. In the extreme case, it is known as the black pad which caused a failure of solder joint. A content of phosphorous higher than Ni-P deposits was detected on the failed pad surface, and galvanic cell formation resulted into the corrosion due to the difference of P concentration. The Ni surface has a mud-cracked appearance and the phosphorous content is abnormally higher (exceeding 10 wt%). Another similar issue related to ENIG process is pad discoloration due to Ni oxidation on the top of ENIG pad. Such discoloration pad is regarded as a failure due to cosmetic reason and a lack of clear standards. Sometimes, it actually leads to high contact resistance due to Ni oxides on the top of ENIG layer. Excessive oxidation of Ni layer may result in the non-wetting of solder to the ENIG layer during the reflow process for solder ball attachment because it is difficult for the flux to remove such excessive oxides. The Ni oxidation may be owing to Ni cation diffusion passing through Au immersion during wet process such as rinsing steps in the downstream process after ENIG treatment, which is an electrochemical phenomenon as well. Here, the pad discoloration of Ni corrosion during Electroless nickel with immersion gold (ENIG) treatment was investigated by SEM, XPS and cross-sectional EDS analysis. The Ni corrosion happened at the nodule boundary for relatively thinner layer whereas the corrosion pits were generated in the thick Ni deposits. The electroless Ni was amorphous structure, which meant that the domain boundary energy between two Ni nodules did not change during Ni growth. However, the cusp stress at the surface intersection of two nodules gradually decreased during Ni growth, and hence the corrosion mode changed from nodule boundary corrosion to pit corrosion. It can be surmised that the nodule boundary corrosion can be suppressed by increasing Ni nucleation as well as Ni thickness.

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