Initiated Chemical Vapor Deposition: A Versatile Tool for Various Device Applications

Advances in device technology have been accompanied by the development of new types of materials and device fabrication methods. Considering device design, initiated chemical vapor deposition (iCVD) inspires innovation as a platform technology that extends the application range of a material or device. iCVD serves as a versatile tool for surface modification using functional thin film. The building of polymeric thin films from vapor phase monomers is highly desirable for the surface modification of thermally sensitive substrates. The precise control of thin film thicknesses can be achieved using iCVD, creating a conformal coating on nano‐, and micro‐structured substrates such as membranes and microfluidics. iCVD allows for the deposition of polymer thin films of high chemical functionality, and thus, substrate surfaces can be functionalized directly from the iCVD polymer film or can selectively gain functionality through chemical reactions between functional groups on the substrate and other reactive molecules. These beneficial aspects of iCVD can spur breakthroughs in device fabrication based on the deposition of robust and functional polymer thin films. This review describes significant implications of and recent progress made in iCVD‐based technologies in three fields: electronic devices, surface engineering, and biomedical applications.

     

利用原子层沉积技术制备柔性超高阻隔膜研究进展

在柔性产业的引领下,柔性超高阻隔膜由于可以使器件免受水汽侵蚀,延长使用寿命,广泛应用于有机发光二极管(OLED)柔性面板、量子点显示、柔性光伏等行业.原子层沉积(ALD)技术是一种原子尺度的薄膜制备技术,沉积的薄膜均匀性好、纯度高、而且厚度精确可控,是超高阻隔膜的理想制备方法.本文总结了ALD的基本原理,技术特点和沉积...     

原子层沉积生长速率的控制研究进展

原子层沉积生长技术(ALD)是以表面自限制化学反应为机制的薄膜沉积技术, 可以一层一层地生长薄膜。该技术具有生长温度低、沉积厚度精确可控、保形性好和均匀性高等优点, 逐渐成为制备薄膜材料最具发展潜力的薄膜生长技术。作为ALD技术中一个关键的指标--生长速率, 不仅对沉积所得薄膜的晶体质量、致密度起重要作用, 更重要的是影响集成电路的生产效率。本文综述了近年来ALD生长机制和生长速率方面的研究结果, 以及ALD技术生长速率的影响因素, 并分析探讨了提高和改善ALD生长速率的方法以及研究趋势。     

Characteristics of Al-doped ZnO films grown by atomic layer deposition for silicon nanowire photovoltaic device

We report the structural, electrical, and optical characteristics of Al-doped ZnO (ZnO:Al) films deposited on glass by atomic layer deposition (ALD) with various Al2O3 film contents for use as transparent electrodes. Unlike films fabricated by a sputtering method, the diffraction peak position of the films deposited by ALD progressively moved to a higher angle with increasing Al2O3 film content. This indicates that Zn sites were effectively replaced by Al, due to layer-by-layer growth mechanism of ALD process which is based on alternate self-limiting surface chemical reactions. By adjusting the Al2O3 film content, a ZnO:Al film with low electrical resistivity (9.84 x 10(-4) Omega cm) was obtained at an Al2O3 film content of 3.17%, where the Al concentration, carrier mobility, optical transmittance, and bandgap energy were 2.8 wt%, 11.20 cm2 V(-1) s(-1), 94.23%, and 3.6 eV, respectively. Moreover, the estimated figure of merit value of our best sample was 8.2 m7Omega(-1). These results suggest that ZnO:Al films deposited by ALD could be useful for electronic devices in which especially require 3-dimensional conformal deposition of the transparent electrode and surface passivation.     

柔性高阻隔薄膜材料的研究现状

目的为柔性高阻隔薄膜的应用提供理论指导。方法综述柔性高阻隔膜的应用现状及存在问题,总结热蒸发、化学气相沉积、原子层沉积等制备柔性高阻隔薄膜的方法、原理、特点及应用,展望高阻隔膜包装材料的发展前景。结果高阻隔薄膜制备工艺趋向于单次制备,采用等离子体辅助原子层沉积技术是制备超高阻隔薄膜的首选,原子层沉积(ALD)和分子层沉积(MLD)结合也是获得超高阻隔薄膜的未来发展方向。结论快速、高效地制备柔性高阻隔薄膜是包装工业的发展趋势。     

Ultrathin oxide films by atomic layer deposition on graphene

In this paper, a method is presented to create and characterize mechanically robust, free-standing, ultrathin, oxide films with controlled, nanometer-scale thickness using atomic layer deposition (ALD) on graphene. Aluminum oxide films were deposited onto suspended graphene membranes using ALD. Subsequent etching of the graphene left pure aluminum oxide films only a few atoms in thickness. A pressurized blister test was used to determine that these ultrathin films have a Young's modulus of 154 ± 13 GPa. This Young's modulus is comparable to much thicker alumina ALD films. This behavior indicates that these ultrathin two-dimensional films have excellent mechanical integrity. The films are also impermeable to standard gases suggesting they are pinhole-free. These continuous ultrathin films are expected to enable new applications in fields such as thin film coatings, membranes, and flexible electronics.     

Synthesis and Surface Engineering of Complex Nanostructures by Atomic Layer Deposition

Atomic layer deposition (ALD) has recently become the method of choice for the semiconductor industry to conformally process extremely thin insulating layers (high‐k oxides) onto large‐area silicon substrates. ALD is also a key technology for the surface modification of complex nanostructured materials. After briefly introducing ALD, this Review will focus on the various aspects of nanomaterials and their processing by ALD, including nanopores, nanowires and ‐tubes, nanopatterning and nanolaminates as well as low‐temperature ALD for organic nanostructures and biomaterials. Finally, selected examples will be given of device applications, illustrating recent innovative approaches of how ALD can be used in nanotechnology.     

Chemical vapor phase polymerization deposition of layer-ordered conducting polymer nanostructure for hole injection layer

Layer-ordered and ultrathin films of conducting polymer poly(3,4-ethylene dioxythiophene) (PEDOT) was prepared through a chemical vapor phase polymerization method. The chemical polymerization of 3, 4-ethylenedioxythiophene monomer was initiated in as-prepared oxidant LB films,and PEDOT nanofilms with layer-ordered structure was constructed. UV-Vis absorption spectrum and Fourier transform infrared spectroscopy was used to confirm an interface polymerization of PEDOT in as-prepared LB films. The results of X-ray diffraction and secondary ion mass spectrometry revealed that conductive PEDOT ultrathin layers were well located at different planes of LB films. The film deposition surface pressure and chemical polymerization time of PEDOT monomer in as-prepared LB films showed distinct influence on surface morphology and conductive performance of the polymerized PEDOT LB films. This layer-ordered conducting polymer ultrathin films was deposited on ITO surface as hole injection layer for organic light-emitting diodes, and the luminescence performance of devices was improved as well.     

Atomic layer deposition of transition metals

Atomic layer deposition (ALD) is a process for depositing highly uniform and conformal thin films by alternating exposures of a surface to vapours of two chemical reactants. ALD processes have been successfully demonstrated for many metal compounds, but for only very few pure metals. Here we demonstrate processes for the ALD of transition metals including copper, cobalt, iron and nickel. Homoleptic N,N'-dialkylacetamidinato metal compounds and molecular hydrogen gas were used as the reactants. Their surface reactions were found to be complementary and self-limiting, thus providing highly uniform thicknesses and conformal coating of long, narrow holes. We propose that these ALD layers grow by a hydrogenation mechanism that should also operate during the ALD of many other metals. The use of water vapour in place of hydrogen gas gives highly uniform, conformal films of metal oxides, including lanthanum oxide. These processes should permit the improved production of many devices for which the ALD process has previously not been applicable.     

CHEMICAL VAPOR DEPOSITION OF SEVERAL SILICON-BASED DIELECTRIC FILMS

Thin films of dielectric materials are used extensively in the semiconductor and microelectronics industries, and a number of techniques are used to prepare them. Both conventional chemical vapor deposition and plasma-enhanced chemical vapor deposition of silicon dioxide, silicon nitride, and silicon oxynitride are discussed in this review. The effect of process parameters on the properties of these films is discussed.     

Opportunities for new materials synthesis by hot wire chemical vapor process

Over the last 20 years the hot wire chemical vapor deposition (HWCVD) technique is being explored as an effective alternative to the conventional plasma enhanced chemical vapor deposition (PECVD) for silicon based thin film devices and is claimed to have various advantages. An important point to be appreciated is the mixed nature of the HWCVD process. On one hand it offers all the benefits of being a chemical vapor process and on the other it has the flavor of physical vapor deposition due to the generation of precursors at a line/plane like source (wire array) far away from the substrate albeit with subsequent transport accompanied by secondary gas phase reactions. The possible control over the secondary gas phase reactions gives a unique feature to the HWCVD process. Apart from employing HWCVD for the preparation of a-Si:H and μc-Si:H with high deposition rates we have extended the applicability of the HWCVD to the synthesis of piezoresistive microcrystalline silicon, diffusion barriers of a-SiC:H, silicon nanowires, boron carbide for thermal neutron detectors, stress free a-SiN:H thin films for MEMS devices and metal nano-templates for semiconductor nanowire synthesis. We also established the applicability of HWCVD in surface nano-engineering to incorporate different functionalities (without actually depositing any film) i.e. nano-engineering or nano-modification of the surface to avoid electromigration on low-k dielectric layers and reduce surface defects in crystalline silicon and also bring about nano-crystallization of metallic thin films. Hence I would like to coin a more general nomenclature for this technique and refer to it as hot wire chemical vapor process (HWCVP). This paper discusses the results and outcomes of some of the case studies that we have carried out employing the HWCVP.     

Large-area vapor-phase growth and characterization of MoS(2) atomic layers on a SiO(2) substrate

Atomic-layered MoS(2) is synthesized directly on SiO(2) substrates by a scalable chemical vapor deposition method. The large-scale synthesis of an atomic-layered semiconductor directly on a dielectric layer paves the way for many facile device fabrication possibilities, expanding the important family of useful mono- or few-layer materials that possess exceptional properties, such as graphene and hexagonal boron nitride (h-BN).     

Electrical and thermal conduction in atomic layer deposition nanobridges down to 7 nm thickness

While the literature is rich with data for the electrical behavior of nanotransistors based on semiconductor nanowires and carbon nanotubes, few data are available for ultrascaled metal interconnects that will be demanded by these devices. Atomic layer deposition (ALD), which uses a sequence of self-limiting surface reactions to achieve high-quality nanolayers, provides an unique opportunity to study the limits of electrical and thermal conduction in metal interconnects. This work measures and interprets the electrical and thermal conductivities of free-standing platinum films of thickness 7.3, 9.8, and 12.1 nm in the temperature range from 50 to 320 K. Conductivity data for the 7.3 nm bridge are reduced by 77.8% (electrical) and 66.3% (thermal) compared to bulk values due to electron scattering at material and grain boundaries. The measurement results indicate that the contribution of phonon conduction is significant in the total thermal conductivity of the ALD films.     

Synchrotron X-ray reflectivity study of high dielectric constant alumina thin films prepared by atomic layer deposition

High dielectric constant (high-k) gate dielectric alumina films were prepared with nanoscale thicknesses on p-type silicon substrates by atomic layer deposition (ALD) with alternating pulses of trimethyl aluminum, nitrogen, ozone and nitrogen, and some of them were further thermally annealed. These high-k gate dielectric films were characterized by synchrotron X-ray reflectivity (XR), and the XR data were quantitatively analyzed, providing the following structural parameters of each gate dielectric film: the surface roughness and interfacial roughness, the electron density profile, the number of layers, and the thickness of individual layers. These structural characteristics were then analyzed in detail by considering the ALD processing conditions and post-thermal annealing history.     

Effect of substrate on the nucleation and growth of aluminum films deposited from methylpyrrolidine alane

Methylpyrrolidine alane complex was used to deposit aluminum films on various types of substrates in a low pressure chemical vapor deposition reactor. The films grow easily on metallic and transition metal oxide surfaces, but not on any other tested semiconductor and dielectric substrates below 200 °C, showing strong substrate dependency. The free energies of precursor adsorption, surface dissociation reaction and product desorption, as well as the film wettability to substrate are among the key factors which affect the energy barrier for nucleation or deposition selectivity. In general, a metal substrate can enhance nucleation because it catalyzes the surface reactions and bonds strongly with aluminum. The oxidation-reduction reaction may occur between the precursor and substrate on a metal oxide surface. The reduced metal sites can be the seed nuclei and are possibly responsible for Al growth on the surfaces of transition metal oxides.     

PROCESSING ASPECTS OF CHEMICAL VAPOUR DEPOSITION (CVD) FOR ADVANCED MATERIALS

Chemical vapor deposition (CVD) is an established process used to deposit thin films of advanced materials, based on chemical reactions. Three recent developments in CVD materials processing are described. Low pressure CVD is used extensively in the semiconductor, microelectronics, and optoelectronics industries for depositing stabilized oxides to protect graphite composites, and hard coatings of titanium compounds for cutting tools. Metallorganic CVD is the primary process for depositing the III-V group elements for advanced epitaxial semiconductor designs. Plasma-enhanced CVD is based on the ionization of chemical species and is growing rapidly in importance in areas such as the deposition of diamond films in a microwave plasma.     

Parallel core-shell metal-dielectric-semiconductor germanium nanowires for high-current surround-gate field-effect transistors

Core-shell germanium nanowires (GeNW) are formed with a single-crystalline Ge core and concentric shells of nitride and silicon passivation layer by chemical vapor deposition (CVD), an Al2O3 gate dielectric layer by atomic layer deposition (ALD), and an Al metal surround-gate (SG) shell by isotropic magnetron sputter deposition. Surround-gate nanowire field-effect transistors (FETs) are then constructed using a novel self-aligned fabrication approach. Individual SG GeNW FETs show improved switching over GeNW FETs with planar gate stacks owing to improved electrostatics. FET devices comprised of multiple quasi-aligned SG GeNWs in parallel are also constructed. Collectively, tens of SG GeNWs afford on-currents exceeding 0.1 mA at low source-drain bias voltages. The self-aligned surround-gate scheme can be generalized to various semiconductor nanowire materials.     

Atomic Layer Deposition on Dispersed Materials in Liquid Phase by Stoichiometrically Limited Injections

Atomic layer deposition (ALD) is a well‐established vapor‐phase technique for depositing thin films with high conformality and atomically precise control over thickness. Its industrial development has been largely confined to wafers and low‐surface‐area materials because deposition on high‐surface‐area materials and powders remains extremely challenging. Challenges with such materials include long deposition times, extensive purging cycles, and requirements for large excesses of precursors and expensive low‐pressure equipment. Here, a simple solution‐phase deposition process based on subsequent injections of stoichiometric quantities of precursor is performed using common laboratory synthesis equipment. Precisely measured precursor stoichiometries avoid any unwanted reactions in solution and ensure layer‐by‐layer growth with the same precision as gas‐phase ALD, without any excess precursor or purging required. Identical coating qualities are achieved when comparing this technique to Al₂O₃ deposition by fluidized‐bed reactor ALD (FBR‐ALD). The process is easily scaled up to coat >150 g of material using the same inexpensive laboratory glassware without any loss in coating quality. This technique is extended to sulfides and phosphates and can achieve coatings that are not possible using classic gas‐phase ALD, including the deposition of phosphates with inexpensive but nonvolatile phosphoric acid.     

A Single‐Chamber System of Initiated Chemical Vapor Deposition and Atomic Layer Deposition for Fabrication of Organic/Inorganic Multilayer Films

A single‐chamber system capable of depositing both organic and inorganic layers by initiated chemical vapor deposition (iCVD) and atomic layer deposition (ALD) is demonstrated to facilitate the fabrication of organic/inorganic hybrid thin film encapsulation (TFE). The chamber geometry and the process conditions of iCVD and ALD are similar to each other, which enabled the design of the single‐chamber system. Both organic and inorganic films deposited via the single‐chamber system produces films with their properties equivalent to those deposited in separate iCVD and ALD reactors. Alternating the deposition mode between iCVD and ALD produces organic/inorganic multilayers with outstanding barrier properties as well as optical transparency mechanical flexibility.     

原子层沉积技术及其在半导体中的应用

首先简述原子层沉积（ALD）技术的发展背景，通过分析ALD的互补性和自限制性等工艺基础，介绍了它在膜层的均匀性、保形性以及膜厚控制能力等方面的优势，着重列举ALD在半导体互连技术、高k电介质等方面的应用。同时指出了目前ALD工艺中存在的主要问题。