Jee-Hwan Bae

Microstructural evolution of nickel-germanide in the Ni1−xTax/Ge systems during in situ annealing

The formation and morphological evolution of the germanides formed in the Ni1−xTax/Ge (x=0 and 0.1) systems were examined using ex situ and in situ annealing experiments. It was observed that the Ni-germanide in the Ni0.9Ta0.1/Ge system remained stable at temperatures up to 550 °C whereas the Ni-germanide in the Ni/Ge system agglomerated and was unstable. Microstructural and chemical analyses of the Ni0.9Ta0.1/Ge system during and after in situ annealing in a transmission electron microscope confirmed that the Ta-rich layer was formed by the accumulation of Ta atoms on the interface between the Ni0.9Ta0.1 alloy film and the Ge substrate during the diffusion reaction, and a small amount of residual Ta was found in the Ni-germanide grains. Ultimately, the Ta-rich layer helps reduce the level of agglomeration in the Ni-germanide film and improves the thermal stability of Ni-germanide.

Development of High-Temperature Solders: Contribution of Transmission Electron Microscopy

This article briefly reviews the results of recently reported research on high-temperature Pb-free solder alloys and the research trend for characterization of the interfacial reaction layer. To improve the product reliability of high-temperature Pb-free solder alloys, thorough research is necessary not only to enhance the alloy properties but also to characterize and understand the interfacial reaction occurring during and after the bonding process. Transmission electron microscopy analysis is expected to play an important role in the development of high-temperature solders by providing accurate and reliable data with a high spatial resolution and facilitating understanding of the interfacial reaction at the solder joint.

Temperature Calibration of a Specimen-heating Holder for Transmission Electron Microscopy

The in-situ heating transmission electron microscopy experiment allows us to observe the time- and temperature-dependent dynamic processes in nanoscale materials by examining the same specimen. The temperature, which is a major experimental parameter, must be measured accurately during in-situ heating experiments. Therefore, calibrating the thermocouple readout of the heating holder prior to the experiment is essential. The calibration can be performed using reference materials whose phase-transformation (melting, oxidation, reduction, etc.) temperatures are well-established. In this study, the calibration experiment was performed with four reference materials, i.e., pure Sn, Al-95 wt%Zn eutectic alloy, NiO/carbon nanotube composite, and pure Al, and the calibration curve and formula were obtained. The thermocouple readout of the holder used in this study provided a reliable temperature value with a relative error of

Formation of an oxygen vacancy-dinitrogen complex in nitrogen-doped hafnium oxide

Nitrogen in a thin HfO2−xNx layer was observed in the form of dinitrogen molecules by atom probe microscope measurements. To evaluate the chemical state, an ab initio calculation based on monoclinic HfO2 was performed with using oxygen vacancy models combined with interstitial or substitutional nitrogen. The formation of a hafnium dinitrogen complex near the oxygen vacancy was found to considerably lower the system energy. This result contrasts the substitutional nitrogen complex passivating the oxygen vacancy level in the cubic structure and suggests that the structural stability enhanced by the oxygen vacancy-dinitrogen complex restrains the formation of grain boundaries in amorphous HfO2, which are responsible for the large leakage current.

Enhanced morphological and thermal stabilities of nickel germanide with an ultrathin tantalum layer studied by ex situ and in situ transmission electron microscopy.

The formation and morphological evolution of germanides formed in a ternary Ni/Ta-interlayer/Ge system were examined by ex situ and in situ annealing experiments. The Ni germanide film formed in the Ni/Ta-interlayer/Ge system maintained continuity up to 550°C, whereas agglomeration of the Ni germanide occurred in the Ni/Ge system without Ta-interlayer. Through microstructural and chemical analysis of the Ni/Ta-interlayer/Ge system during and after in situ annealing in a transmission electron microscope, it was confirmed that the Ta atoms remained uniformly on the top of the newly formed Ni germanide layer during the diffusion reaction. Consequently, the agglomeration of the Ni germanide film was retarded and the thermal stability was improved by the Ta incorporation.

Synthesis and Characterization of a Pt/NiO/Pt Heterostructure for Resistance Random Access Memory

We examined the electrical properties and microstructure of NiO produced using a sol-gel method and Ni nitrate hexahydrate () to investigate if this NiO thin film can be used as an insulator layer for resistance random access memory (ReRAM) devices. It was found that as-prepared NiO film was polycrystalline and presented as the nonstoichiometric compound with Ni interstitials (oxygen vacancies). Resistances-witching behavior was observed in the range of 0~2 V, and the low-resistance state and high-resistance state were clearly distinguishable ( orders). It was also demonstrated that NiO could be patterned directly by KrF eximer laser irradiation using a shadow mask. NiO thin film fabricated by the sol-gel method does not require any photoresist or vacuum processes, and therefore has potential for application as an insulating layer in low-cost ReRAM devices.

Control of chemical residue on photomasks using thermal treatment

We choose thermal treatment as part of a methodology to remove chemical residue on the surface of a mask. This new step of thermal treatment is inserted into our standard cleaning process for embedded attenuate phase shift masks (EAPSMs). The treatment is carried out in a modified hot plate system at various temperatures and times. After thermal treatment, ion chromatography measures the residual ions on a given surface. The thermal treatment is found to considerably reduce residual sulfate ions on the mask surface. The remaining sulfate ions on the mask are <0.18 ng/cm2 using thermal treatment.

Cross-Sectional Transmission Electron Microscopy Sample Preparation of Soldering Joint Using Ultramicrotomy

Many studies have reported the interfacial reaction of Sn-Ag/ electroless nickel immersion gold (ENIG). Various analysis techniques, such as scanning electron microscopy, electron probe microanalyzer, and transmission electron microscopy (TEM), have been used to examine interfacial reaction. Among them, TEM equipped with analytical attachments offers the most complete tool for characterizing the formation of intermetallic compounds (IMCs) at the interface. However, solders are typically soft and ductile, while IMCs tend to be quite hard and brittle, which has limited the level of success in preparing TEM samples. We utilized ultramicrotomy since it might offer a reasonable and relatively quick alternative in this case. Ultramicrotomy has been used for the preparation of TEM specimens from biological materials and extending a range of materials including polymers, coating layer, particles, and even metals (Becker & Bange, 1993; Glanvill, 1995; Howell et al., 1995). TEM sample making to section hard materials by ultramicrotomy are not new. Besides, it has been traditionally considered that the mechanical damage during sectioning by diamond knife might hinder unambiguous specimen characterization. However, this technique also has many advantages such as no ion beam irradiation damage, no chemical mixing, no differential thinning rate and the ease of preparation of many serial sections with large, thin areas of uniform thickness in a relatively short time (Quintana, 1997). The increasing acceptability of ultramicrotomy in materials science is evidenced by a number of recent paper giving results for different hard materials (Hwang & Suganuma, 2003).