Jaegab Lee

The effect of the internal capacitance of InGaN-light emitting diode on the electrostatic discharge properties

The electrostatic discharge (ESD) properties of the InGaN-light emitting diode (LED) were investigated in terms of the internal capacitance of the InGaN-LED. The LEDs with higher internal capacitance were found to be more resistant to external ESD impulses. The internal capacitance of the InGaN-LED was controlled by the silicon doping level of the n-GaN layer bordering the active layer. The human body model ESD yield at −500 V was increased from 27% to 94% by increasing the internal capacitance. Moreover, the high ESD pass yield was maintained up to −7000 V.

Factors Affecting Passivation of Cu(Mg) Alloy Films

Variables affecting the passivation capability of Cu(Mg) alloy films, which were sputter deposited from a Cu (4.5 atom %) target, have been investigated. As-deposited Cu(Mg)/SiO 2 /Si multilayer samples were annealed for 30 min in various oxygen ambients at pressures ranging from 10 mTorr to 30 Torr and at various temperatures in the 200-800°C range. The results show that the passivation capability of a Cu(Mg) alloy film is a function of annealing temperature, O 2 pressure, and Mg content in the film. Increasing the annealing temperature favors formation of a dense MgO layer on the surface. Decreasing the O 2 pressure enhances the preferential oxidation of Mg over Cu. Furthermore, increasing the Mg content in the Cu(Mg) film promotes formation of a dense MgO layer. Vacuum preannealing before taking the as-deposited samples to O 2 annealings was found to be very effective in segregating Mg to the surface, facilitating the passivation capability of the Cu(Mg) alloy film even when the Mg content is low. In the current study, self-aligned MgO layers with low resistivity and an effective passivation capability over the Cu surface have been obtained by manipulating these factors when Cu(Mg) thin films are annealed.

Highly efficient phosphor-converted white organic light-emitting diodes with moderate microcavity and light-recycling filters

We demonstrate the combined effects of a microcavity structure and light-recycling filters (LRFs) on the forward electrical efficiency of phosphor-converted white organic light-emitting diodes (pc-WOLEDs). The introduction of a single pair of low- and high-index layers (SiO(2)/TiO(2)) improves the blue emission from blue OLED and the insertion of blue-passing and yellow-reflecting LRFs enhances the forward yellow emission from the YAG:Ce(3+) phosphors layers. The enhancement of the luminous efficacy of the forward white emission is 1.92 times that of a conventional pc-WOLED with color coordinates of (0.34, 0.34) and a correlated color temperature of about 4800 K.

Nonvolatile nanocrystal charge trap flash memory devices using a micellar route to ordered arrays of cobalt nanocrystals

This study demonstrates that self-assembled diblock copolymer micelles can be used as a template to assemble cobalt (Co) nanocrystal (NC) arrays for use as charge storage layers in charge trap flash memory devices. Diblock copolymer micelles embedded with Co were synthesized on p-Si substrates having a thin tunneling oxide of HfO2. The micelle templates were completely removed by oxygen plasma treatment and reduction procedures, resulting in ordered arrays of Co NCs. The nonvolatile memory devices exhibit program/erase characteristics, as confirmed by their capacitance-voltage responses, current-voltage responses, endurance characterization, and nanoscale device measurement using scanning nonlinear dielectric microscopy.

Plasma pretreatment of the Cu seed layer surface in Cu electroplating

Effects of plasma pretreatment to the Cu seed layer on copper (Cu) electroplating were investigated. Copper seed layers were deposited by magnetron sputtering onto tantalum nitride barrier layers before electroplating copper in the forward pulsed mode. The Cu seed layer was cleaned by plasma H2 or N2 prior to electroplating a copper film. Cu films electroplated on the copper seed layer with plasma pretreatment have shown better electrical and physical properties such as electrical resistivities, surface morphologies, levels of impurities, adhesion and surface roughness than those without plasma pretreatment. It is shown that carbon and metal oxide contaminants at the sputtered Cu seed/TaN surface can be effectively removed by plasma H2 cleaning. The degree of the (1 1 1) preferred orientation of the pulsed plated Cu film with plasma H2 pretreatment is as high as that without plasma pretreatment. Also, plasma H2 precleaning is more effective in enhancing the Cu electroplating properties onto the Cu seed layer than plasma N2 precleaning.

Mobility enhanced photoactivity in sol-gel grown epitaxial anatase TiO2 films.

Epitaxial anatase thin films were grown on single-crystal LaAlO3 substrates by a sol-gel process. The epitaxial relationship between TiO2 and LaAlO3 was found to be [100]TiO2||[100]LaAlO3 and (001)TiO2||(001)LaAlO3 based on X-ray diffraction and a high-resolution transmission electron microscopy. The epitaxial anatase films show significantly improved photocatalytic properties, compared with polycrystalline anatase film on fused silica substrate. The increase in the photocatalytic activity of epitaxial anatase films is explained by enhanced charge carrier mobility, which is traced to the decreased grain boundary density in the epitaxial anatase film.

Effect of Mg content in Cu(Mg)/SiO2/Si multilayers on the resistivity after annealing in an oxygen ambient

The formation mechanism of self-aligned MgO layers obtained from Cu(Mg) alloys has been investigated. Self-aligned surface and interfacial MgO layers were formed upon annealing Cu(Mg)/SiO2/Si multilayer films in an oxygen ambient, resulting in a structure of MgO/Cu/MgO/SiO2/Si. Upon annealing at 300 °C or higher in an oxygen ambient, Mg segregates preferentially to the Cu surface until a dense, uniform MgO layer is formed. A growth limited thickness of the surface MgO was found to be about 150 A , providing substantial passivation of the exposed Cu surface. After a dense MgO layer forms, substantial Mg segregation to the SiO2 surface takes place. However, the formation of the interfacial MgO caused a sudden increase in resistivity after annealing for about 20 min, which can be due to the release of free Si being diffused into the Cu film by the reaction of Mg with Si in the SiO2. The optimum Mg contents in Cu(Mg) alloy films with various thickness were thus estimated to obtain the Cu(Mg) alloy multilayer film with substantially lower resistivity while retaining the beneficial properties of Cu passivation in an oxygen ambient.The formation mechanism of self-aligned MgO layers obtained from Cu(Mg) alloys has been investigated. Self-aligned surface and interfacial MgO layers were formed upon annealing Cu(Mg)/SiO2/Si multilayer films in an oxygen ambient, resulting in a structure of MgO/Cu/MgO/SiO2/Si. Upon annealing at 300 °C or higher in an oxygen ambient, Mg segregates preferentially to the Cu surface until a dense, uniform MgO layer is formed. A growth limited thickness of the surface MgO was found to be about 150 A , providing substantial passivation of the exposed Cu surface. After a dense MgO layer forms, substantial Mg segregation to the SiO2 surface takes place. However, the formation of the interfacial MgO caused a sudden increase in resistivity after annealing for about 20 min, which can be due to the release of free Si being diffused into the Cu film by the reaction of Mg with Si in the SiO2. The optimum Mg contents in Cu(Mg) alloy films with various thickness were thus estimated to obtain the Cu(Mg) alloy multilayer ...

Effects of processing variables on the mechanical properties of Ta/TaN multilayer coatings

Abstract The Ta/TaN multilayer structure with repeated layers of a poly-crystalline Ta layer of high ductility and a TaN layer of high hardness is expected to exhibit toughness. This paper reports the results on the hardnesses and the adhesion strengths of the Ta/TaN multilayer and the compositionally gradient Ta/TaN layer deposited on the high speed steel substrate by reactive sputtering as a function of annealing temperature. The TaN film deposited with the N 2 /Ar ratio of 0.4 in the reactive sputtering process exhibits the highest crystallinity leading to the highest hardness and adhesion strength of the Ta/TaN multilayer. The hardness and adhesion strength of the Ta/TaN multilayer becomes deteriorated with increasing the annealing temperature in the heat treatment conducted right after the deposition of the layer. Therefore, the post-annealing treatment is not desirable in the case of the Ta/TaN multilayer from the standpoint of mechanical properties. Also the hardness of the Ta/TaN multilayer increases with decreasing the compositional modulation wavelength, but the adhesion property of the layers is nearly independent of the wavelength. On the other hand, the compositionally gradient Ta/TaN film exhibits the highest hardness and adhesion strength for the post-annealing temperatures of 200 and 400°C, respectively. This result for the compositionally gradient Ta/TaN film differs from that of the Ta/TaN multilayer.

MOCVD of TiN and/or Ti from new precursors

Abstract Titanium nitride films were prepared by means of metal organic chemical vapor deposition (MOCVD) technique, using a new TiN precursor tetrakis (ethylmethyl-amido) titanium (TEMAT). Deposition of TiN films at the low temperature of 250–350°C yielded growth rates of 70 to 1050 A/min with the excellent bottom coverage of ∼90% over 0.35 μm contacts. The addition of ammonia to a TEMAT chemistry lowered the resistivity of as-deposited TiN film to ∼1000 μΩ cm from 3500–6000 μΩ cm and reduced the resistivity variation in TiN film upon air-exposure. Examination of the films by Auger electron spectroscopy (AES) showed that the oxygen and carbon contents decreased significantly with the addition of ammonia. Based on the byproduct gases detected by quadrupole mass spectrometer (QMS), the transamination reaction, similar to that of TDMAT with NH3, was proposed to be responsible for TiN deposition. Since steric interactions determines the extent of the gas phase reaction, the reactivity of TEMAT with NH3 in gas phase must be less than that of TDMAT with NH3, and thus, facilitating the control of the gas phase reaction. Finally, we examined MOCVD Ti using a new compound, (acac)2TiNEt2 to find out the possibility of the sequential process for MOCVD TiN/Ti. No thermal decomposition of the chemistry occurred up to 380°C, but the use of plasma enabled the dissociation of (acac)2TiNEt2, resulting in gold-colored films. However, the films mainly consisted of carbon.

Dry patterning of copper films using an O2 plasma and hexafluoroacetylacetone

Abstract Dry etching of copper films using O2 plasmas and H(hfac) has been investigated. A one-step process consisting of copper film oxidation with an O2 plasma and removal of surface copper oxide by reaction with H(hfac) to form volatile Cu(hfac)2 and H2O was carried out. The etching rate of Cu was in the 50–700 A/min range at the substrate temperature from 150 to 300°C and depended on the H(hfac)/O2 flow rate ratio and the plasma power. The copper film etch rate increased with increasing radio frequency (RF) power at temperatures higher than 215°C. The optimum H(hfac)/O2 flow rate ratio was 1:1, suggesting that the oxidation process and the reaction with H(hfac) should be in balance. Cu patterning using a Ti mask was performed at a flow rate ratio of 1:1 at 250°C and an isotropic etching profile with a taper slope of 30° was obtained. Cu dry patterning with a taper angle necessary for high-resolution large-area thin film transistor liquid-crystal displays was thus successfully obtained from the one-step process by manipulating the substrate temperature, RF power and flow rate ratio.