Takane Usui

Area-selective atomic layer deposition of lead sulfide: nanoscale patterning and DFT simulations.

Area-selective atomic layer deposition (ALD) of lead sulfide (PbS) was achieved on octadecyltrichlorosilane (ODTS)-patterned silicon substrates. We investigated the capability of ODTS self-assembled monolayers (SAMs) to deactivate the ALD PbS surface reactions as a function of dipping time in ODTS solution. The reaction mechanism was investigated using density functional theory (DFT), which showed that the initial ALD half-reaction is energetically unfavorable on a methyl-terminated SAM surface. Conventional photolithography was used to create oxide patterns on which ODTS SAMs were selectively grown. Consequently, PbS thin films were grown selectively only where ODTS was not present, whereas deposition was blocked in regions where ODTS was grown. The resulting fabricated patterns were characterized by scanning electron microscopy and Auger electron spectroscopy, which demonstrated that ALD PbS was well confined to defined patterns with high selectivity by ODTS SAMs. In addition, AFM lithography was employed to create nanoscale PbS patterns. Our results show that this method can be applied to various device-fabrication processes, presenting new opportunities for various nanofabrication schemes and manifesting the benefits of self-assembly.

Plasma processing for crystallization and densification of atomic layer deposition BaTiO3 thin films.

High-k, low leakage thin films are crucial components for dynamic random access memory (DRAM) capacitors with high storage density and a long storage lifetime. In this work, we demonstrate a method to increase the dielectric constant and decrease the leakage current density of atomic layer deposited BaTiO3 thin films at low process temperature (250 °C) using postdeposition remote oxygen plasma treatment. The dielectric constant increased from 51 (as-deposited) to 122 (plasma-treated), and the leakage current density decreased by 1 order of magnitude. We ascribe such improvements to the crystallization and densification of the film induced by high-energy ion bombardments on the film surface during the plasma treatment. Plasma-induced crystallization presented in this work may have an immediate impact on fabricating and manufacturing DRAM capacitors due to its simplicity and compatibility with industrial standard thin film processes.

High aspect ratio and high breakdown strength metal-oxide capacitors

Thin film capacitors of HfO2 with high energy storage were fabricated using plasma-enhanced atomic layer deposition on a relatively large platform with a lateral area of 0.8-7.1 mm2. An untreated film of 10-nm HfO2 showed a breakdown strength of 0.47 V/nm. Annealing of HfO2 formed a large crystalline phase, which creates electron paths and increases defect-induced currents. Laminate structures of Al2O3 and HfO2 were also fabricated to relate crystallinity, current leakage path, and breakdown behavior. A 7-layer laminate structure exhibited a breakdown strength of 0.58 V/nm with an aspect ratio of 1:300 000 due to suppressed crystallinity.

Self-limiting atomic layer deposition of barium oxide and barium titanate thin films using a novel pyrrole based precursor

Barium oxide (BaO) is a critical component for a number of materials offering high dielectric constants, high proton conductivity as well as potential applicability in superconductivity. For these properties to keep pace with continuous device miniaturization, it is necessary to study thin film deposition of BaO. Atomic layer deposition (ALD) enables single atomic layer thickness control, conformality on complex shaped substrates, and the ability to precisely tune stoichiometry. Depositing multicomponent BaO containing ALD films in a self-limiting manner at low temperatures may extend the favorable bulk properties of these materials into the ultrathin film regime. Here we report the first temperature and dose independent thermal BaO deposition using a novel pyrrole based Ba precursor (py-Ba) and water (H2O) as the co-reactant. The growth per cycle (GPC) is constant at 0.45 A with excellent self-terminating behavior. The films are smooth (root mean squared (RMS) roughness 2.1 A) and contain minimal impurities at the lowest reported deposition temperatures for Ba containing films (180–210 °C). We further show conformal coating of non-planar substrates (aspect ratio ∼ 1:2.5) at step coverages above 90%. Intermixing TiO2 ALD layers, we deposited amorphous barium titanate with a dielectric constant of 35. The presented approach for infusing self-terminating BaO in multicomponent oxide films may facilitate tuning electrical and ionic properties in next-generation ultrathin devices.

Mechanical masking of films deposited by atomic layer deposition

In this work a new method to selectively deposit films by atomic layer deposition (ALD) is presented. It was found that polished silicon masks pressed against silicon substrates were able to mask ALD deposition with submicron diffusion under the mask. Static and dynamic assemblies were fabricated to realize the benefits of mechanical masking. The static assemblies demonstrated the ability to block deposition on the back sides of transmission electron microscopy grids, as well as the back sides of 100 mm silicon wafers. The dynamic masking assembly was able to selectively deposit platinum, and then passivate the metal region with zirconium oxide in situ, resulting in a fully embedded metal in dielectric structure.

Synthesis of Microscale Lead Sulfide Disks by Patterned Self-Assembled Monolayer

This work explores an approach to utilize nanosphere lithography (NSL) and atomic layer deposition (ALD) to fabricate an array of microscale disks of lead sulfide (PbS). In this approach, a mold to fabricate polymer stamps was produced by NSL. Using these stamps a patterned self-assembled monolayer (SAM) of octadecyltrichlorosilane (ODTS) was deposited using microcontact printing. The ODTS SAM functioned as a resist to block the growth of ALD PbS. The resulting PbS disks were characterized by scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) to confirm the morphology and stoichiometry. Regular arrays of microscale PbS disks were successfully fabricated. This is a potentially attractive methodology for fabrication of multi-layer devices.

Exploring Cellular Tensegrity: Physical Modeling and Computational Simulation

The term tensegrity was first coined by Buckminster Fuller to describe a structure in which continuous tension in its members forms the basis for structural integrity. Fuller most famously demonstrated the concept of tensegrity in architecture through the design of geodesic domes while his student, artist Kenneth Snelson, applied the concept of tensegrity to create sculptures that appear to defy gravity (Figure 1). Snelson’s tensegrity sculptures have minimal components and achieve their stability through dynamic distribution of tensile and compressive forces amongst their members to create internal balance [1]. It was upon viewing Snelson’s sculptures that Donald Ingber became inspired by their structural efficiency and dynamic force balance to adopt tensegrity as a paradigm upon which to analyze cell structure and mechanics. It has been 30 years since the premier appearance of the cellular tensegrity model and although the model is still much under debate, empirical evidence suggests that the model may explain a wide variety of phenomena ranging from tumor growth to cell motility [1–4].Copyright