Jae-Sung Roh

Characteristics of n+ polycrystalline-Si/Al2O3/Si metal–oxide– semiconductor structures prepared by atomic layer chemical vapor deposition using Al(CH3)3 and H2O vapor

We report interface and dielectric reliability characteristics of n+ polycrystalline-silicon (poly-Si)/Al2O3/Si metal–oxide–semiconductor (MOS) capacitors. Al2O3 films were prepared by atomic layer chemical vapor deposition using Al(CH3)3 and H2O vapor. Interface state density (Dit) and dielectric reliability properties of n+ poly-Si/Al2O3/Si MOS structures were examined by capacitance–voltage, conductance, current–voltage, and time-dependent dielectric breakdown measurements. The Dit of the n+ poly-Si/Al2O3/Si MOS system near the Si midgap is approximately 8×1010 eV−1 cm−2 as determined by the conductance method. Frequency dispersion as small as ∼20 mV and hysteresis of ∼15 mV were attained under the electric field of ±8 MV/cm. The gate leakage current of ∼36 A effective thickness Al2O3 dielectric measured at the gate voltage of −2.5 V is ∼−5 nA/cm2, which is approximately three orders of magnitude lower than that of a controlled oxide (SiO2). Time-dependent dielectric breakdown data of Al2O3/Si MOS capa...

Robust ternary metal gate electrodes for dual gate CMOS devices

This report describes thermally stable dual metal gate electrodes for surface channel Si CMOS devices. We found that the ternary metal nitrides, i.e., Ti/sub 1-x/Al/sub x/N/sub y/ (TiAlN) and TaSi/sub x/N/sub y/ (TaSiN) films, are stable up to 1000/spl deg/C. Especially, the stoichiometric TiAlN (y/spl sim/1) exhibited highly robust p-type gate electrode (p-TiAlN) properties, demonstrating a work function (/spl Phi//sub m/) of /spl sim/5.1 eV and excellent gate oxide integrity against the thermal budget of conventional Si CMOS processing. The N-deficient TiAlN (y < 1) showed /spl Phi//sub m/ for n-type electrode (n-TiAlN) with limited thermal stability. The dual gate electrodes, p-TiAlN and TaSiN, exhibited negligible EOT (equivalent oxide thickness) variation on the high-k gate dielectrics (ZrO/sub 2/, HfO/sub 2/) up to 950/spl deg/C.

Composition and electrical properties of metallic Ru thin films deposited using Ru(C6H6)(C6H8) precursor

Metallic ruthenium films were prepared by metalorganic chemical vapor deposition (CVD) using a new precursor named (η6-benzene)(η4-1,3-cyclohexadiene)ruthenium (Ru(C6H6)(C6H8)) in Ar atmosphere, and the absolute composition and electrical properties were investigated. The absolute composition including hydrogen was determined by means of the elastic recoil detection time of flight (ERD-TOF). It was found that carbon contents in the films markedly decreased when tetrahydrofuran (THF) was supplied with the precursor during deposition. The variation in carbon content could be interpreted by the formation of hydrocarbon compounds as well as the formation of carbon oxide, resulting from the reaction between carbon and THF. In particular, Ru films contained hydrogen that originated in the hydrogen atoms in the precursor and was involved in the CVD process due to the catalytic effect of ruthenium on hydrocarbon and hydrogen. It was shown that grain size, among several other factors strongly affected the electrical properties of ruthenium films.

Effect of oxygen migration and interface engineering on resistance switching behavior of reactive metal/polycrystalline Pr 0.7 Ca 0.3 MnO 3 device for nonvolatile memory applications

An in-depth study on the resistive switching mechanism of perovskite oxide based device was performed. Compared with filament type resistive switching device, excellent switching uniformity was obtained due to controlled redox reaction at metal/oxide interface. Electromigration of oxygen ion under the bipolar electric filed can explain the switching behavior. Formation of ultrathin AlOx at the interface can guarantee excellent retention characteristics at 125 °C. Compared with the large area (50 × 50 um2) memory cell, the nanoscale device (Φ=50 nm) showed better memory performance such as faster switching speed, better uniformity, endurance, and retention characteristics.

Bipolar Resistive Switching Behavior of a Pt/NiO/TiN Device for Nonvolatile Memory Applications

Bipolar resistive switching behavior was observed in a Pt/NiO/TiN device. The device exhibited switching behavior that was stable over 100 cycles and did not degrade after 104 s. An electroforming process was required to obtain these bipolar resistive switching properties, and the conduction behavior of the low resistance state followed Ohms law, indicating that conductive filaments formed during the electroforming process. The conductive filaments consisted of oxygen vacancies and the Pt electrode behaved as an oxygen reservoir. The bipolar resistive switching of the Pt/NiO/TiN device was explained by the generation and annihilation of oxygen vacancies in the filaments.

Leakage Current Characteristics of (Ba,Sr)TiO3 Thin Films Deposited on Ru Electrodes Prepared by Metal Organic Chemical Vapor Deposition

Leakage current characteristics of (Ba,Sr)TiO3 (BST) thin films deposited by metal-organic chemical vapor deposition (MOCVD) on Ru bottom electrodes were investigated. CVD-BST thin film on an Ru electrode showed much higher leakage current density than that on the Pt electrode. In the case of the CVD-BST thin film deposited on the PVD-BST(30 A)/Ru or N2O-plasma-treated Ru electrode, the leakage current density showed a very small value of about 2×10-8 A/cm2 at ±1 V and the dielectric loss was about 0.006. It was found that oxygen atoms adsorbed on the surface of the Ru bottom electrode during the deposition of PVD-BST or N2O plasma treatment played a key role in restoring the barrier height at the bottom interface.

Properties of Ru Thin Films Fabricated on TiN by Metal-Organic Chemical Vapor Deposition

Ruthenium (Ru) thin films were fabricated on TiN, as well as on SiO2, by metal-organic chemical vapor deposition using tris(2,4-octanedionato)ruthenium. We characterized the Ru films grown on TiN, and compared them with the films prepared on SiO2. The Ru films deposited on TiN showed weak crystallinity and random grain orientation similar to the films on SiO2, but revealed notably rougher surfaces than the films on SiO2. Moreover, deposition rates on TiN were lower than those on SiO2. These properties of the Ru films grown on TiN originated from the difficulties in nucleation and growth at the initial stage of the deposition. The inferior surface flatness and deposition rate could cause structural instability and poor coverage of the Ru electrode at the bottom of a deep concave hole for a three-dimensional capacitor where the Ru film was in contact with a diffusion barrier metal TiN plug.

Oxidation Characteristics of TiN Film as a Barrier Metal for Bottom-Electrode Ru Film Fabricated from Tris-(2,4-octanedionato)ruthenium

Bottom-electrode Ru films were fabricated on barrier metal TiN films by the reaction of tris-(2,4-octanedionato)ruthenium [Ru(od)3, Ru(C8H13O2)3] precursor and O2 gas. It was observed that the film incorporated the undesirable impurity of oxygen that could oxidize the TiN underlayer during postthermal treatments. To evaluate the oxidation characteristics of barrier metal TiN by the incorporated oxygen, samples with the Ru/TiN film stack were annealed in N2 ambient up to 700°C for 60 s by rapid thermal processing (RTP). No sign of TiN oxidation was observed in analyses by X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscopy. This was also confirmed by measuring the electrical resistance of a contact hole plugged with poly-Si and connected to the Ru/TiN stack, which shows an acceptable value below 1.3×103 Ω. We also investigated the oxidation characteristics of the Ru/TiN stack by atmospheric O2 gas. The samples were annealed in O2 ambient by RTP at 500°C, 600°C, and 700°C for 60 s. The Ru film began to oxidize to RuO2 at 500°C. With increasing temperature, further oxidations of Ru and TiN occurred simultaneously. Finally, at 700°C, Ru and TiN oxidized completely to RuO2 and rutile TiO2 phases, respectively. These results demonstrate the ease of oxidation of Ru and TiN films in O2 ambient.

Requirements of bipolar switching ReRAM for 1T1R type high density memory array

ReRAM has been researched as a promising candidate for diverse NVM application [1]. Still switching mechanism and classification are not clear, there are simply two kinds of switching polarity: unipolar and bipolar. Considering distribution, operation margin and so on, bipolar switching looks much attractive than unipolar. Along with a selective device, polarity of switching could make the architecture of cell array different. The Crossbar array structure has been considered an attractive solution for unipolar switching with diode. To make the crossbar array with bipolar switching devices, research on a new selective device such as MIEC [2] is much necessary to meet the requirements of current drivability and on/off properties. In addition, self-rectifying device [3–4] could be an alternative for a high density crossbar array. Recently, several research groups have shown very fast and high reliable device. It could be a good signal that ReRAM could have speed and endurance for DRAM or embedded applications. In case of those applications, 1T1R structure could be an effective and it could be used to check the feasibility by changing ReRAM cell with capacitor or MTJ. From now on, transistor has been mainly considered as a controller for the compliance current in set process. But the bipolar 1T1R structure for a high density array, there are several things to be considered, because a transistor would be acting as a changeable resistance at a set and reset process and its resistance goes up as the technology shrinks. So in this paper, we tried to figure out the requirements of bipolar ReRAM switching for the high density 1T1R memory array by changing reset current and symmetry of ReRAM devices.

Fabrication of Highly Dense Ru Thin Films by High-Temperature Metal-Organic Chemical Vapor Deposition with NH3 Gas as Ru Oxidation Suppressing Agent

We attempted to fabricate highly dense Ru thin films by metal-organic chemical vapor deposition at an elevated temperature of 400°C, employing NH3 gas to suppress Ru oxidation. A solution of 0.2 mol/L tris(2,4-octanedionato)ruthenium [Ru(od)3, Ru(C8H13O2)3] dissolved in n-butylacetate was used as a Ru source and O2 as a reactant gas. It was revealed that NH3 gas effectively eliminated residual oxygen from the Ru films. However, at higher feeding rates of a metal-organic source, Ru films showed poor densities and high electrical resistivities mainly due to significant carbon incorporation. By optimizing Ru(od)3 flow rate to less than 0.3 g/min to reduce contaminating carbon supply, we successfully produced highly dense and conductive Ru films. The best Ru film had a density of 12.2 g/cm3 and a resistivity of 12.0 µΩcm, which were excellent values close to the bulk ones.