Young-Do Kim

Study on the characteristics of TiN thin film deposited by the atomic layer chemical vapor deposition method

TiN film was deposited on Si substrate by using an atomic layer chemical vapor deposition (CVD) system. In this system, the TiCl4 and NH3 gases were supplied, separately and Ar purge gas was added between the source and reactant gases to suppress the direct reaction. The microstructure of TiN was observed to be the columnar grain structure. The chemical species was analized by Auger electron spectroscopy (AES) and the Cl content in TiN film was detected below the detection limit of AES which was below 0.5%. The density of film grown at 450 °C measured by Rutherford backscattering spectroscopy was 4.85 g/cm3 and decreased as the process temperature decreased. The resistivity of this TiN was about 75 μΩ cm, which was very low compared to TiN film grown by other CVD methods. The step coverage of TiN film showed almost 100% conformality at 450 °C.

Study on the characteristics of TiAlN thin film deposited by atomic layer deposition method

The microstructural characteristics and electrical and chemical properties of TiAlN films deposited by the atomic layer deposition (ALD) method were investigated. The growth rate of TiAlN film was measured to be 1.67 A/cycle. TiAlN film deposited by ALD has a B1(NaCl) structure with a lattice parameter of 4.20 A. The chlorine content in TiAlN film was below the detection limit of Auger electron spectroscopy. TiAlN film showed the columnar structure with a resistivity of about 400 μΩ cm. The sheet resistance increased abruptly after annealing at 650 °C due to the formation of a high resistivity Cu-silicide phase at the interface between the TiAlN and Si substrate. The failure of the ALD TiAlN barrier layer was observed by an etch-pit test after annealing at 600 °C for 1 h. TiAlN films deposited by the ALD method exhibited excellent film properties and improved barrier characteristics compared to other chemical vapor deposition methods.

Crystallographic model for bcc-to-9R martensitic transformation of Cu precipitates in ferritic steel

A crystallographic model, which can calculate lattice invariant shear, habit plane and orientation relationship for bcc-to-9R martensitic transformation of Cu precipitates in low-alloyed transformation-induced plasticity (TRIP) steel, is suggested. At the early stage of ageing at 500°C, coherent bcc Cu clusters were formed and characterized by a periodic array of distinguished striations perpendicular to [001]α direction. On prolonged ageing for 10 h, spherical precipitates with banded contrast formed within ferrite matrix and high-resolution transmission electron microscopy (HRTEM) observations confirmed that these bands corresponded to the intervariant boundary of twinned 9R Cu precipitates lying parallel to the {110}α planes and showed an orientation relationship with α: , . Analytical equations for lattice invariant shear and habit plane were derived, and calculated to be 0.09669 and , respectively. The orientation relationship between 9R Cu precipitates and ferrite matrix, calculated using transformation matrix, was and . The deviation angles between the calculated and measured by HRTEM were approximately 0.1° in direction and 3.7° in plane, respectively. The present model successfully described the crystallographic features of bcc-to-9R martensitic transformation of Cu precipitates in ferritic steel.

Electron-emission from nano- and micro-crystalline diamond films: the effects of nitrogen and oxygen additives

Abstract Diamond films are grown on Si substrate by microwave plasma CVD using CH 4 +H 2 (for undoped) and additive N 2 (for nitrogen-incorporated) with/without O 2 as precursors. Crystal structures for grown films, such as micro- and nano-crystalline and surface morphologies are characterized in terms of growth condition by Raman and field-emission SEM, respectively. Cathodoluminescence (CL) spectra are monitored to identify the nitrogen-incorporation in grown diamond films. Relative intensity ratios of nitrogen-related band to band-A (denoted by I N / I A ) are also estimated from the CL characteristics and the influence of additive N 2 and O 2 precursors on the I N / I A ratio is analyzed. For all-grown films, electron-emission characteristics are measured, from which threshold fields for the emission are also estimated. Observed emission properties are correlated with crystal structures and morphologies obtained from grown films by considering the structural transformation from micro- to nano-crystalline as well as the nitrogen-induced defect states.

Micro metal powder injection molding of W-Cu nanocomposite powder

Increasing attention is being paid to micro metal injection molding as a manufacturing technology for miniature part. W-Cu nanocomposites have been used as heat sink and packaging materials in microelectronic devices. A micro injection molding technique will provide and appropriate tool to fabricate W-Cu nanocomposite materials for microcomponents. In the present study, a fundamental investigation of micro metal injection molding using W-Cu nanocomposite powder is reported. The densification behavior of W-Cu nanocomposite was examined in order to confirm the shape stability of microcomponents.

Cooling rate effect on phase transformation of plasma sprayed partially stabilized zirconia

Insulating ceramic coatings known as thermal barrier coatings (TBCs) are of great interest because of their ability to improve performance and efficiency of turbine engines by allowing a higher turbine inlet temperature or reduced cooling air flow [1, 2]. Zirconia (ZrO2) is an attractive material for a thermal barrier coating because, compared with other ceramics, it has superior mechanical properties such as high strength and fracture toughness combined with good wear resistance and, above all, a thermal expansion coefficient close to that of metallic substrates [3]. However, ZrO2 exists in three crystallographic phases: a low temperature monoclinic, an intermediate-temperature tetragonal phase and a high temperature cubic phase. In particular, the phase transformation of tetragonal phase to monoclinic phase accompanies a significant volume expansion (approximately 3–5 vol%), so this transition generally results in cracking and contributes to the failure TBC system. Therefore the amount of monoclinic phase is one of the important indicators of coating quality. The addition of several oxides (Y2O3, CeO2, MgO etc.) can stabilize the cubic phase in zirconia, so the occurrence of the monoclinic phase can be repressed. In case of yttria-partially-stabilized zirconia (YSZ), the rapid solidification during the plasma spray process can drive diffusionless transformation from high temperature cubic phase to non-transformable tetragonal phase without composition change [4].However,during isothermal aging stage the non-transformable tetragonal phase separate into two phases—a cubic phase (high stabilizer) and a transformable tetragonal phase (low stabilizer). If the system is cooled, the transformable tetragonal phase can transform to monoclinic phase and the phase transformation is affected by cooling rate. Commercial powders of partially stabilized zirconia, ZrO2-8Y2O3 (YSZ) and ZrO2-25CeO2-Y2O3 (CYSZ), were used as spray materials. Both YSZ (−125 + 11μm) and CYSZ (−90 + 16μm) have spherical shape because these powders were manufactured by homogeneous oven spherical powder (HOSP) method. Two powders were coated on a SS41 substrate (50 × 50 × 5 mm) by atmospheric plasma spraying and the thickness of the coating was about 1 mm. After cutting specimens in 10 × 10 mm, the SS41 substrate was removed by soaking in a 60% HNO3 dilute solution for several hours. The specimens were isothermally heated at 1300 ◦C and 1500 ◦C for 100 h, and then cooled to room temperature through four different cooling rates: water quenching, air cooling, open furnace cooling (a furnace door is open during cooling stage) and furnace cooling. An evaluation of the changes in phase fraction in the PSZ coat due to thermal cycle (heat treatment and cooling rate) was performed using X-ray diffractometer (XRD).The monoclinic fraction at each specimen was calculated from the following equation [5]:

Effect of DC Bias on the Plasma Properties in Remote Plasma Atomic Layer Deposition and Its Application to HfO2 Thin Films

This work was supported by the National Program for Tera-Level Nanodevices of the Ministry of Science and Technology of Korea as one of the 21st Century Frontier Programs.

Micropatterns of W-Cu Composites Fabricated by Metal Powder Injection Molding

The metal powder injection molding (MIM) process has been applied to fabricate micropatterns of W-Cu composites. A 150μm×150μm×300 μm column array patterned lost plastic mold was used as the mold insert. Several parameters were examined to overcome limitations of lost plastic molding such as low plastic strength, unvented blind hole structure and parting line. Molding temperature was a more dominant factor than molding pressure for the complete filling of feedstock into the micro patterns. The intrinsic defects originating from the lost plastic mold could be eliminated by the re-injection molding of the disc-shaped green part in a vacuum. The final micropatterns of W-Cu composite were fabricated by sintering at 1100°C and 1300°C for 1 h.

Characteristics of probe current harmonics based on various applied voltage waveforms in low temperature plasmas

The characteristics of probe currents induced by applying various probe voltage waveforms, such as sinusoidal, sawtooth, square, and triangular, were investigated at a floating potential. It was found that the measured probe currents have many harmonics depending on the voltage waveforms. This was mainly due to the nonlinearity of the sheath in the plasma and was analyzed using the fast Fourier transform and a circuit model. By applying a triangular voltage waveform to a probe, plasma parameters such as electron temperature and plasma density could be obtained and compared to those of a single Langmuir probe and a floating harmonic method.

Transition of electron kinetics in weakly magnetized inductively coupled plasmas

Transition of the electron kinetics from nonlocal to local regime was studied in weakly magnetized solenoidal inductively coupled plasma from the measurement of the electron energy probability function (EEPF). Without DC magnetic field, the discharge property was governed by nonlocal electron kinetics at low gas pressure. The electron temperatures were almost same in radial position, and the EEPFs in total electron energy scale were radially coincided. However, when the DC magnetic field was applied, radial non-coincidence of the EEPFs in total electron energy scale was observed. The electrons were cooled at the discharge center where the electron heating is absent, while the electron temperature was rarely changed at the discharge boundary with the magnetic field. These changes show the transition from nonlocal to local electron kinetics and the transition is occurred when the electron gyration diameter was smaller than the skin depth. The nonlocal to local transition point almost coincided with the calculation results by using nonlocal parameter and collision parameter.