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As the device scaling of dynamic random access memory continues, the demand for the development of new dielectric film with high permittivity and low leakage current that may replace the currently used ZrO2/Al2O3-based dielectric film has increased drastically. In this aspect, MgO thin film has been spotlighted due to its high band gap (7-8 eV) and moderate dielectric constant (9-10). In this study, we investigated the growth behavior and film properties of the MgO ALD film using Mg(EtCp)2 precursor and the different reactants of H2O and O2 plasma. MgO thin films were deposited at the temperature range of 200-400°C, and the self-limited surface reaction was observed to secure optimal growth conditions. Glancing angle X-ray diffraction and X-ray photoelectron spectroscopy were used to examine crystalline structure and chemical properties, respectively. To evaluate the electrical characteristics of the MgO films, the Pt/MgO/TiN capacitor was fabricated with different MgO thicknesses at various deposition temperatures. The electrical characteristics such as dielectric constant and leakage current density of the MgO film were examined depending on the reactants, and the leakage current conduction mechanism of the MgO thin films was elucidated. Figure 1

Ruthenium (Ru) has attractive material properties due to its promising characteristics such as a low resistivity (7.1 μΩ·cm in the bulk), a high work function (4.7 eV), and feasibility for the dry etch process. These properties make Ru films appropriate for various applications in the state-of-art semiconductor device technologies. Thus, it has been widely investigated as an electrode for capacitor in the dynamic random access memory (DRAM), a metal gate for metal-oxide semiconductor field effect transistor (MOSFET), and a seed layer for Cu metallization. Due to the continuous shrinkage of microelectronic devices, better deposition processes for Ru thin films are critically required with excellent step coverages in high aspect ratio (AR) structures. In these respects, atomic layer deposition (ALD) is a viable solution for preparing Ru thin films because it enables atomic-scale control of the film thickness with excellent conformality. A recent investigation reported that the nucleation of ALD-Ru film was enhanced considerably by using a zero-valent metallorganic precursor, compared to the utilization of precursors with higher metal valences. In this presentation study, we will display our research results on the synthesis and characterization of novel ruthenium complexes. The ruthenium compounds were easy synthesized by the reaction of ruthenium halide with appropriate organic ligands in protic solvent, and characterized by NMR, elemental analysis and thermogravimetric analysis. ALD of Ru film was demonstrated using the new (zero-valent) Ru metallorganic precursor and O2 as the Ru source and reactant, respectively, at the deposition temperatures of 300-350oC. Self-limited reaction behavior was observed as increasing Ru precursor and O2 pulse time, suggesting that newly developed Ru precursor is applicable for ALD process. Detailed discussions on the chemical and structural properties of Ru thin films as well as its growth behavior using new Ru precursor will be also presented.

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Dynamic random access memory (DRAM) is used as the main memory of every modern computer, due to its high density, high speed and efficient memory function. For successful operation of DRAM, a large cell capacitance (~ 25 fF) and low leakage current (10 A/cm or 1 fA/cell) are required. In a traditional Si-based capacitor, the target cell capacitance has been achieved by increasing the surface area of the capacitor. More recently, innovations have been made in the component materials. A metal electrode, TiN or Ru, and a dielectric material with a higher-k value (k is the relative dielectric constant), such as HfO2 (k ~ 25) and ZrO2 (k ~ 40), are being explored in giga-bit scale DRAMs. The minimum achievable tox is ~ 0.7 nm for ZrO2 which are currently being used in the DRAM industry. However, the technology road map for memory devices states that tox less than 0.5 nm is necessary for the DRAMs with a design rule of < 40 nm. Perovskite-based dielectric films such as SrTiO3 and (Ba,Sr)TiO3 were reported to exhibit k values of several hundreds. However, growth of these films is extremely difficult with the atomic-layerdeposition (ALD) which is a method of choice for the growth of the dielectric films in microelectronic devices. In this presentation, the authors will report rutile TiO2 (k value ~100) based capacitor technology. The possible leakage current by the small energy gap of 3.1 eV rutile TiO2 was tweaked by the elaborate doping of TiO2 films with Al atoms. A minimum tox ~ 0.4 nm was achieved with the safe leakage current density. A crucial problem related with the high cost of Ru material was alleviated by adopting ultra-thin Ru/TiN electrode. Some specific Ru electrode material that offers a superior dielectric performance of the capacitor was also introduced. The merit of oxide electrode (ex. RuO2) over its metal counterpart is also discussed. Figure 1 shows the summary of the leakage current vs. tox data from the TiO2 and Al-doped TiO2 thin films on Ru (30 nm) and Ru (3 nm)/TiN electrode. The growth of thinner Ru films on TiN electrode are influenced by the TiN layer and show a even improved dielectric performance of TiO2 film grown on top.

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TiO2 thin films with high dielectric constants (83 - 100) were grown on sputtered and atomic-layer-deposited (ALD) Ru electrode at a growth temperature of 250oC using the atomic- layer-deposition method. The as-deposited films were crystallized with rutile structure. Further improvements in the leakage current characteristics are achieved by proper doping of Al and Hf, thereby an equivalent oxide thickness (tox) ~ 0.6 nm with small enough leakage current density (1 x 10-7 A/cm2 at 0.8V) was achieved. These good properties are also realized from 3D structured hole-type capacitors. The rutile structured TiO2 films were also obtained from Ru electrode which is deposited by an ALD process using a newly developed noble precursor. In addition, it was confirmed that the Ru metal film step coverage on the capacitor hole structure with an aspect ratio of 17 is > 90 %. The thermal stability of the Ru electrode on severe 3D holes was improved with the adoption of hydrogen plasma process.