Woochool Jang

Resistive switching of a TaOx/TaON double layer via ionic control of carrier tunneling

Resistance random access memory (RRAM) is an attractive candidate for future non-volatile memory due to its superior features. As the oxide thickness is scaled down, the charge transport mechanism is also subject to the transition from hopping to tunneling dominant process, which is critically related to the interfacial electronic band structure. A TaOx/TaON double layer-based RRAM is fabricated and characterized in this work. Upon TaON insertion at the lower interface, the improved switching behavior is observed. The TaON at the bottom electrode interface blocks oxygen vacancy percolation due to strong N-O bonds and also modifies interfacial band alignment to lower the injected electron energy from bottom electrode due to higher tunneling barrier height than that of TaOx/Pt. This study suggested that a defect-minimized insertion layer like TaON with a proper interfacial band alignment is pivotal in RRAM for the effective ionic control of carrier tunneling resulting in non-linear I-V behavior with improved properties.

Spatially confined electric field effect for improved resistive switching behavior of a Ni/Ta-embedded TaOx/NiSi device

In this study, Ni/TaOx/NiSi and Ni/TaOx/Ta/TaOx/NiSi devices were fabricated, and the resistive switching (RS) behaviors were investigated. A 2 nm-thick Ta metal layer was deposited between two TaOx films to form a Ni/TaOx/Ta/TaOx/NiSi stack, which was analyzed using TEM. Based on a linear scale I–V curve and an R–V graph, both devices showed conventional bipolar conductive bridge random access memory (CBRAM) characteristics with formation/rupture of Ni conductive filaments (CFs). The Ta-embedded device showed lower forming/SET voltages and initial resistance due to the reduced effective thickness of TaOx films due to the inserted Ta metal layer. In addition, the Ta-embedded device exhibited improved endurance and resistance distribution due to suppression of the random formation of Ni CFs. In this study, Ni/TaOx/NiSi and Ni/TaOx/Ta/TaOx/NiSi devices were fabricated, and the resistive switching (RS) behaviors were investigated. A 2 nm-thick Ta metal layer was deposited between two TaOx films to form a Ni/TaOx/Ta/TaOx/NiSi stack, which was analyzed using TEM. Based on a linear scale I–V curve and an R–V graph, both devices showed conventional bipolar conductive bridge random access memory (CBRAM) characteristics with formation/rupture of Ni conductive filaments (CFs). The Ta-embedded device showed lower forming/SET voltages and initial resistance due to the reduced effective thickness of TaOx films due to the inserted Ta metal layer. In addition, the Ta-embedded device exhibited improved endurance and resistance distribution due to suppression of the random formation of Ni CFs.

Improvement of thermal stability of nickel silicide film using NH3 plasma treatment

In this study, the effects of NH3 plasma pre-treatment on the characteristics of NiSi films were investigated. Nickel film was deposited on a Si(100) substrate by meal-organic chemical vapor deposition (MOCVD) using Ni(iPr-DAD)2 as a Ni precursor and NH3 gas as a reactant. Before the Ni deposition, silicon substrate was treated by NH3 plasma with various flow rates to adjust the amount of inserted hydrogen and nitrogen atoms. The Ni films showed a considerable low sheet resistance around 12 Ω/, irrespective of the NH3 plasma pre-treatment conditions. The sheet resistance of the all Ni films was decreased after annealing at 500 °C due to formation of a low resistive NiSi phase. NiSi films with a high flow rate of NH3 plasma pre-treatment exhibited a lower sheet resistance and smoother interface between NiSi and the Si substrate than the low flow rate of the NH3 plasma pre-treated NiSi films because lots of nitrogen atoms incorporated at grain boundary of NiSi which result in reduce total surface/interface energy of NiSi and enhancement interface characteristics.

Nonlinear and complementary resistive switching behaviors of Au/Ti/TaOx/TiN devices dependent on Ti thicknesses

The fabricated Au/Ti/TaOx/TiN devices demonstrate nonlinear behavior at a low resistance state and a complementary resistive switching (CRS) behavior that is dependent upon the thickness of the Ti insertion layer. The nonlinear behavior can be explained by the presence of an ultrathin TiOx layer that acts as a tunnel barrier. In addition, the CRS behavior can be understood in relation to the redistribution of oxygen vacancies between the Ti/TaOx top interfaces. A thicker Ti insertion layer forms a thicker TiOx layer at the Ti/TaOx interface, which can serve as another switching layer. The Au/Ti/TaOx/TiN devices in this study are fabricated with fully complementary metal-oxide-semiconductor-compatible materials and exhibit nonlinear behavior at a low resistance state and a CRS behavior that present possible solutions for the suppression of the sneak current in the crossbar arrays.

Stabilization of Ni conductive filaments using NH3 plasma treatment for electrochemical metallization memory

In this study, NH3 plasma treatment was utilized to enhance the resistive switching (RS) properties. Au/Ni/TaOx/NiSi and Au/Ni/NH3 plasma-treated TaOx/NiSi resistance RAM (RRAM) devices were fabricated and the resistive switching (RS) properties of these devices were subsequently investigated. Both RRAM devices exhibited conventional electrochemical metallization memory (ECM) behaviors. However, the NH3 plasma-treated samples exhibited improved resistance distribution compared with that of non-treated samples due to the remaining Ni conductive filaments (CF), even following a RESET process. Additionally, superior retention properties longer than 104 s were observed due to the formation of stable Ni CFs. The formation of a defect-minimized TaON layer, observed via X-ray photoelectron spectroscopy (XPS), could be the source of stability for the Ni CFs, resulting in improved device behavior for the NH3 plasma-treated samples.

원자층증착 기술: 개요 및 응용분야

Atomic layer deposition(ALD) is a promising deposition method and has been studied and used in many different areas, such as displays, semiconductors, batteries, and solar cells. This method, which is based on a self-limiting growth mechanism, facilitates precise control of film thickness at an atomic level and enables deposition on large and three dimensionally complex surfaces. For instance, ALD technology is very useful for 3D and high aspect ratio structures such as dynamic random access memory(DRAM) and other non-volatile memories(NVMs). In addition, a variety of materials can be deposited using ALD, oxides, nitrides, sulfides, metals, and so on. In conventional ALD, the source and reactant are pulsed into the reaction chamber alternately, one at a time, separated by purging or evacuation periods. Thermal ALD and metal organic ALD are also used, but these have their own advantages and disadvantages. Furthermore, plasma-enhanced ALD has come into the spotlight because it has more freedom in processing conditions; it uses highly reactive radicals and ions and for a wider range of material properties than the conventional thermal ALD, which uses H2O and O3 as an oxygen reactant. However, the throughput is still a challenge for a current time divided ALD system. Therefore, a new concept of ALD, fast ALD or spatial ALD, which separate half-reactions spatially, has been extensively under development. In this paper, we reviewed these various kinds of ALD equipment, possible materials using ALD, and recent ALD research applications mainly focused on materials required in microelectronics.

Characteristics of a nickel thin film and formation of nickel silicide by using remote plasma atomic layer deposition with Ni( i Pr-DAD) 2

In this study, the characteristics of a thin nickel film deposited by using remote plasma atomic layer deposition (RPALD) on a p-type Si substrate and formation of nickel silicide by using rapid thermal annealing were determined. Bis(1,4-di-isopropyl-1,3-diazabutadienyl)nickel, (Ni(iPr-DAD)2) was used as the Ni precursor and an ammonia plasma was used as a reactant. This was the first attempt to deposit a thin Ni film using by Ni(iPr-DAD)2 as a precursor for the ALD process. The Ni film that was deposited by using RPALD at a growth rate of around 2.2 Å/cycle at 250°C showed a very low resistivity of 33 μΩ·cm with a total impurity concentration of around 10 at.%. The impurities in the thin film, carbon and nitrogen, were existed in the forms of C–C and C–N bonding states. The potential for removing impurities by comparing of experimental conditions, namely, the process temperature and pressure. The nitrogen impurity could be removed by using thermal desorption during each ALD cycle, and the carbon impurity could be reduced by optimizing the process pressure, which is directly related to the mean free path in the NH3 plasma. After Ni deposition, nickel silicide was formed by rapid thermal annealing (RTA) in a vacuum ambient for 1 minute. Nickel-silicide layers from obtained by used the ALD of Ni and obtained by used of the PVD Ni annealed at temperatures from 500 to 900°C. NiSi obtained by used the ALD of Ni showed better thermal stability due to the contributions of small amounts of carbon and nitrogen in the as-deposited Ni thin film. Degradation of the silicide layer was effectively suppressed by using the ALD of ALD Ni.

Characteristics of WNxCy films deposited using remote plasma atomic layer deposition with (MeCp)W(CO)2(NO) for Cu diffusion barrier

Diffusion barrier characteristics of tungsten–nitride–carbide (WNxCy) thin films interposed between Cu and SiO2 layers were studied. The WNxCy films were deposited by remote plasma atomic layer deposition (RPALD) using a metal organic source, (MeCp)W(CO)2(NO), and ammonia. Auger electron spectroscopy analysis indicated the WNxCy films consisted of tungsten, nitrogen, carbon, and oxygen. X-ray diffraction (XRD) analysis showed that the film deposited at 350 °C was nanocrystalline. The resistivity of WNxCy film deposited by RPALD was very low compared to that in previous research because of the lower nitrogen content and different crystal structures of the WNxCy. To verify the diffusion barrier characteristics of the WNxCy film, Cu films were deposited by physical vapor deposition after WNxCy film was formed by RPALD on Si substrate. The Cu/WNxCy/Si film stack was annealed in a vacuum by rapid thermal annealing at 500 °C. Cu diffusion through the barrier layer was verified by XRD. Stable film properties wer...

Effect of a Ti capping layer on thermal stability of NiSi formed from Ni thin films deposited by metal–organic chemical vapor deposition using a Ni(iPr-DAD)2 precursor

Ni films were deposited by metal–organic chemical vapor deposition (MOCVD) using a novel Ni precursor, bis(1,4-di-isopropyl-1,3-diazabutadienyl)nickel [Ni(iPr-DAD)2], and NH3 gas. To optimize process conditions, the deposition temperature and reactant partial pressure were varied from 200 to 350 °C and from 0.2 to 0.99 Torr, respectively. Ni films deposited at 300 °C with a reactant pressure of 0.8 Torr exhibited excellent quality, and had a low carbon impurity concentration of around 4%. In addition, a sacrificial Ti capping layer was deposited by an in situ e-beam evaporator on top of the Ni films to enhance the thermal stability of the subsequently formed NiSi films. Both the Ti-capped and uncapped Ni films were annealed by a two-step method, with a first annealing conducted at 500 °C, followed by wet etching and then a second annealing carried out from 500 to 900 °C. The Ti capping layer did not affect the silicidation kinetic process, but by acting as an oxygen scavenger, it did enhance the morphological stability of the NiSi films and thus improve their electrical properties.

Remote plasma atomic layer deposition of silicon nitride with bis(dimethylaminomethyl-silyl)trimethylsilyl amine and N2 plasma for gate spacer

The silicon nitride (SiNx) atomic layer deposition with bis(dimethylaminomethylsilyl)-trimethylsilyl amine precursor and N2 remote plasma was investigated. The process window ranged from 250 to 400 °C, and the growth rate was about 0.38 ± 0.02 A/cycle. The physical, chemical, and electrical characteristics of the SiNx thin films were examined as a function of deposition temperature and plasma power. Based on the results of spectroscopic ellipsometry and x-ray photoelectron spectroscopy, the growth rate and state of binding energy showed little difference depending on the plasma power. The better film properties such as leakage current density and etch resistance were obtained at higher deposition temperatures and higher plasma power. High wet etch resistance (wet etch rate of ∼2 nm/min) and low leakage current density (∼10−8 A/cm2) were obtained. The step coverage, examined by transmission electron microscopy, was about 80% on a trench with an aspect ratio of 4.5.