Application Of Atomic Layer Deposition Research Articles

Trends in Copper Precursor Development for CVD and ALD Applications

The continued dominance of copper in microelectronic manufacturing is due in part to the techniques that have kept pace with the relentless trend towards smaller feature sizes. Pure and defect-free copper features can be created at these and smaller scales using gas phase deposition methods such as chemical vapor deposition (CVD) and atomic layer deposition (ALD). Here we review the deposition processes and in particular surface chemistry for depositing copper metal by CVD and ALD. A summary of known processes is given, and new trends in copper film deposition research are discussed. As well, process parameters and properties of copper films deposited from precursors using key ligand systems such as aminoalkoxides, amidinates, guanidinates, betadiketonates and betaketoiminates are presented. Surface chemistry is examined from the point of view of the similarities of CVD and ALD, considering precursors that can be used in both types of processes. This serves to highlight trends in decomposition mechanisms and illuminates some interesting similarities in process temperature and other parameters.

Selective-Area Atomic Layer Deposition of Copper Nanostructures for Direct Electro-Optical Solar Energy Conversion

Nanoantennas combined with rectifying diodes have been proposed as new devices for light harvesting in the visible and infrared. Metallic nanostructures act as antennae to concentrate electric fields at nanogaps and enable the conversion of light into an electrical signal through asymmetric tunneling across metal-vacuum-metal junctions. Electro-optical conversion occurs when surface-plasmon induced charge oscillations are converted into unidirectional electrical current flow. The proposed devices would accomplish the electro-optical conversion without the need for semiconductor materials. The nanofabrication of antenna-coupled tunnel diodes is extremely challenging, and requires sub-nm precision for tuning tunnel junction resistance. Atomic layer deposition is one of the few methods available with the necessary precision to accomplish this. In this work, we investigate selective-area atomic layer deposition of copper to modify lithographically-defined antenna structures and form arrays of geometrically-asymmetric tunnel diodes. Finite-difference time-domain simulations and optical characterization measurements are used to guide antenna design, including shape, polarization dependence, and wavelength response. Simulations show the electric-field enhancement in the gap to increase significantly with decreasing gap distance; moreover, antenna size and morphology allows for tuning of the peak wavelength response over the infrared to visible range. Nucleation is found to be a critical factor for tuning the electrical and geometric properties of the tunnel junctions. Whereas conformal, epitaxial growth is desired, actual growth is sensitive to surface preparation and seed-layer properties. Analysis of copper growth on palladium seed layers using in-situ spectroscopic ellipsometry reveals a surface chemistry mechanism different than previously understood. Contrary to expectations, palladium-hydrogen complexes are found to be the stable intermediates during growth cycles, and their sensitivity to surface structure may explain non-epitaxial growth. The discussion underscores the link between fundamental surface chemistry and advanced applications of atomic layer deposition.

Modification and Resonance Tuning of Optical Microcavities by Atomic Layer Deposition

AbstractRecently, enormous interest has been focused on the nanofabrication of optical micro‐ and nanocavities for applications in lab‐on‐a‐chip and quantum optics. At the same time, the atomic layer deposition (ALD) process presents several advantages for the fabrication and modification of micro‐ and nanostructures because of its atomic level thickness fine‐tuning and perfect coating conformability in three‐dimensional (3D) structures. Hence, ALD technology has been directed into the field of optical microcavities for the tracking and tuning of their properties. In this short review, we will summarize recent progress in the application of ALD on optical microcavities. Firstly, we will briefly introduce ALD technology and emphasize its distinctive features when applied to optical microcavities. Then, various microcavities such as photonic crystals, opals, and tubular microcavities will be illustrated to demonstrate their development with the assistance of ALD technology. Such an influential manufacturing tool for optical devices could inspire numerous interesting applications, as concluded in the final part.

Atomic layer deposition, a unique method for the preparation of energy conversion devices.

Keywords: atomic layer deposition; batteries; energy conversion; electrochemistry; electrolysis; fuel cells; photovoltaics; solar cells; thin films

Controllable fabrication of nanostructured materials for photoelectrochemical water splitting via atomic layer deposition

Photoelectrochemical (PEC) water splitting is an attractive approach to generate hydrogen as a clean chemical fuel from solar energy. But there remain many fundamental issues to be solved, including inadequate photon absorption, short carrier diffusion length, surface recombination, vulnerability to photo-corrosion, and unfavorable reaction kinetics. Owing to its self-limiting surface reaction mechanism, atomic layer deposition (ALD) is capable of depositing thin films in a highly controllable manner, which makes it an enabling technique to overcome some of the key challenges confronted by PEC water splitting. This tutorial review describes some unique and representative applications of ALD in fabricating high performance PEC electrodes with various nanostructures, including (i) coating conformal thin films on three-dimensional scaffolds to facilitate the separation and migration of photocarriers and enhance light trapping, as well as realizing controllable doping for bandgap engineering and forming homojunctions for carrier separation; (ii) achieving surface modification through deposition of anti-corrosion layers, surface state passivation layers, and surface catalytic layers; and (iii) identifying the main rate limiting steps with model electrodes with highly defined thickness, composition, and interfacial structure.

Evolution of microstructure and related optical properties of ZnO grown by atomic layer deposition

A study of transmittance and photoluminescence spectra on the growth of oxygen-rich ultra-thin ZnO films prepared by atomic layer deposition is reported. The structural transition from an amorphous to a polycrystalline state is observed upon increasing the thickness. The unusual behavior of the energy gap with thickness reflected by optical properties is attributed to the improvement of the crystalline structure resulting from a decreasing concentration of point defects at the growth of grains. The spectra of UV and visible photoluminescence emissions correspond to transitions near the band-edge and defect-related transitions. Additional emissions were observed from band-tail states near the edge. A high oxygen ratio and variable optical properties could be attractive for an application of atomic layer deposition (ALD) deposited ultrathin ZnO films in optical sensors and biosensors.

0.2-$\mu{\rm m}$ AlGaN/GaN High Electron-Mobility Transistors With Atomic Layer Deposition ${\rm Al}_{2}{\rm O}_{3}$ Passivation

We report a successful application of atomic layer deposition (ALD) aluminum oxide as a passivation layer to gallium nitride high electron-mobility transistors (HEMTs). This new passivation process results in 8%-10% higher dc maximum drain current and maximum extrinsic transconductance, about one order of magnitude lower drain current in the sub-threshold region, 10%-20% higher pulsed- IV drain current, and 27%-30% higher RF power with simultaneously 5-8 percentage point higher power-added efficiency. The achieved improvement in device performance is attributed to the outstanding quality of the interface between III-N and the ALD aluminum oxide resulting from the uniqueness of the adopted ALD process, featuring a wet-chemical-based wafer preparation as well as a pregrowth self-cleaning procedure in the growth chamber. This technology can be readily integrated into the HEMT-based integrated circuit fabrication process, making the ALD aluminum oxide-passivated GaN HEMTs excellent candidates for multiple microwave and millimeter-wave power applications.

Towards broad-bandwidth polarization-independent nanostrip waveguide ring resonators

We demonstrate a new method for accessing the broad-bandwidth polarization-independent operation of a microring resonator based on the standard photonic nanostrip waveguides. The method employs the selective application of atomic layer deposition to form highly uniform TiO(2) overlayers with the specific dispersion properties. The wide operation window is achieved by matching the wavelength dependencies of the free spectral ranges of the two orthogonal polarizations.

Characterization of atomic layer deposition HfO2, Al2O3, and plasma-enhanced chemical vapor deposition Si3N4 as metal–insulator–metal capacitor dielectric for GaAs HBT technology

Characterization was performed on the application of atomic layer deposition (ALD) of hafnium dioxide (HfO2) and aluminum oxide (Al2O3), and plasma-enhanced chemical vapor deposition (PECVD) of silicon nitride (Si3N4) as metal–insulator–metal (MIM) capacitor dielectric for GaAs heterojunction bipolar transistor (HBT) technology. The results show that the MIM capacitor with 62 nm of ALD HfO2 resulted in the highest capacitance density (2.67 fF/μm2), followed by capacitor with 59 nm of ALD Al2O3 (1.55 fF/μm2) and 63 nm of PECVD Si3N4 (0.92 fF/μm2). The breakdown voltage of the PECVD Si3N4 was measured to be 73 V, as compared to 34 V for ALD HfO2 and 41 V for Al2O3. The capacitor with Si3N4 dielectric was observed to have lower leakage current than both with Al2O3 and HfO2. As the temperature was increased from 25 to 150 °C, the breakdown voltage decreased and the leakage current increased for all three films, while the capacitance increased for the Al2O3 and HfO2. Additionally, the capacitance of the ALD Al2O3 and HfO2 films was observed to change, when the applied voltage was varied from −5 to +5 V, while no significant change was observed on the capacitance of the PECVD Si3N4. Furhermore, no significant change in capacitance was seen for these silicon nitride, aluminum oxide, and hafnium dioxide films, as the frequency was increased from 1 kHz to 1 MHz. These results show that the ALD films of Al2O3 and HfO2 have good electrical characteristics and can be used to fabricate high density capacitor. As a result, these ALD Al2O3 and HfO2 films, in addition to PECVD Si3N4, are suitable as MIM capacitor dielectric for GaAs HBT technology, depending on the specific electrical characteristics requirements and application of the GaAs devices.

Ultra-thin atomic-layer deposited alumina incorporating silica sol makes ultra-durable antireflection coatings

We propose a strategy to make soda-lime glass maintain both high transparency and long-term durability in stringent high temperature and humid environments. Experiments reveal that the double-layered coatings with 110-nm-thick SiO2 and ultra-thin 25-nm- or 50-nm-thick Al2O3 layers, prepared by sol-gel dip coating and atomic layer deposition (ALD), respectively, exhibit the improvement of 5.88–6.32% in Tave (the average transmittance from the wavelength of 400–700 nm), as compared with that of the bare glass. On the other hand, the highly accelerated temperature and humidity stress test (HAST) confirms that both samples can sustain the 180 h test without any proven transmittance degradation, while the normalized Tave of the bare glass drastically drops to 43.1% of the initial value after the 108 h HAST. It implies that the ultra-thin Al2O3 films prepared by ALD, followed by dip-coated low-index layers such as SiO2 or nanostructured layer, can achieve both higher average transmittance and better durability, which would be of significance for the applications of ALD and dip coating techniques in the fields of consumer electronics, architecture with glass facades, and photovoltaics.

Emerging Applications of Atomic Layer Deposition for Lithium‐Ion Battery Studies

Lithium-ion batteries (LIBs) are used widely in today's consumer electronics and offer great potential for hybrid electric vehicles (HEVs), plug-in HEVs, pure EVs, and also in smart grids as future energy-storage devices. However, many challenges must be addressed before these future applications of LIBs are realized, such as the energy and power density of LIBs, their cycle and calendar life, safety characteristics, and costs. Recently, a technique called atomic layer deposition (ALD) attracted great interest as a novel tool and approach for resolving these issues. In this article, recent advances in using ALD for LIB studies are thoroughly reviewed, covering two technical routes: 1) ALD for designing and synthesizing new LIB components, i.e., anodes, cathodes, and solid electrolytes, and; 2) ALD used in modifying electrode properties via surface coating. This review will hopefully stimulate more extensive and insightful studies on using ALD for developing high-performance LIBs.

Atomic layer deposition for nanofabrication and interface engineering

Atomic layer deposition (ALD) provides a tool for conformal coating on high aspect-ratio nanostructures with excellent uniformity. It has become a technique for both template-directed nanofabrications and engineering of surface properties. This Feature Article highlights the application of ALD in selected fields including photonics, SERS and energy materials. Specifically, the topics include fabrication of plasmonic nanostructures for the SERS applications, fabrication of 3-D nanoarchitectured photoanodes for solar energy conversions (dye-sensitized solar cells and photoelectrochemical cells), and coating of electrodes to enhance the cyclic stability and thus device life span of batteries. Dielectric coating for tailoring optical properties of semiconductor nanostructures is also discussed as exemplified by ZnO nanowires. Future direction of ALD in these applications is discussed at the end.

ChemInform Abstract: Tailoring Nanoporous Materials by Atomic Layer Deposition

AbstractReview: 90 refs.

Effect of pulsed deposition of Al2O3 for native oxides reduction of GaAs by atomic layer deposition technique

The reduction of native oxides on GaAs substrates is studied by predeposition cleaning as well as by short time pulsing of the metal precursor for the self-cleaning mechanism using atomic layer deposition (ALD) of trimethyl aluminum (TMA). The role of the predeposition cleaning followed by ALD application has significant effects in restraining the regrowth of native oxides. The short time pulsing of the TMA is effective for the self-cleaning mechanism to reduce the intensity of GaAs native oxides. The reduction in native oxides on GaAs surface during ALD of TMA was investigated using x-ray photoelectron spectroscopy. X-ray photoelectron studies demonstrated that the pulsed deposition of TMA in the range of 2 to 4 s is the most effective way of cleaning the GaAs native oxides. Our studies demonstrate a full proof self-cleaning process for GaAs wafers for any potential applications.

Advanced process technologies: Plasma, direct-write, atmospheric pressure, and roll-to-roll ALD

Abstract

(Invited) Current and Future Applications of ALD in Micro-Electronics

This paper describes the status of current and future applications of Atomic Layer Deposition (ALD) and Plasma Enhanced ALD (PEALD) in the field of Micro-electronics. Substantial expansion of the ALD market is expected in the coming decade, both in IC manufacturing, but also in adjacent non-IC applications. Several techniques will be described that work around the relatively slow deposition rate of ALD.

(Invited) ALD of Thin Films for Lithium-Ion Batteries

Atomic layer deposition (ALD) technique is a thin film deposition method that provides highly conformal films on 3D structured supports, including powder materials. The technique relies on sequential self-limiting gas-to-surface reactions which enable control of thin film depositions even down to the atomic level on complex surface geometries. Even if ALD technique has been used in the semiconductor industry in production scale for several years now, there are rather few reports on ALD of battery materials. However, the recent development in processes for lithium containing films clearly opens up new possibilities. Promising applications of ALD include 3D structured all-solid-state batteries and surface modification of electrode powders. The present paper presents an overview of the present status in application of ALD in the field of lithium ion batteries.

Plasma-Assisted Atomic Layer Deposition: Basics, Opportunities, and Challenges

Plasma-assisted atomic layer deposition (ALD) is an energy-enhanced method for the synthesis of ultra-thin films with Å-level resolution in which a plasma is employed during one step of the cyclic deposition process. The use of plasma species as reactants allows for more freedom in processing conditions and for a wider range of material properties compared with the conventional thermally-driven ALD method. Due to the continuous miniaturization in the microelectronics industry and the increasing relevance of ultra-thin films in many other applications, the deposition method has rapidly gained popularity in recent years, as is apparent from the increased number of articles published on the topic and plasma-assisted ALD reactors installed. To address the main differences between plasma-assisted ALD and thermal ALD, some basic aspects related to processing plasmas are presented in this review article. The plasma species and their role in the surface chemistry are addressed and different equipment configurations, including radical-enhanced ALD, direct plasma ALD, and remote plasma ALD, are described. The benefits and challenges provided by the use of a plasma step are presented and it is shown that the use of a plasma leads to a wider choice in material properties, substrate temperature, choice of precursors, and processing conditions, but that the processing can also be compromised by reduced film conformality and plasma damage. Finally, several reported emerging applications of plasma-assisted ALD are reviewed. It is expected that the merits offered by plasma-assisted ALD will further increase the interest of equipment manufacturers for developing industrial-scale deposition configurations such that the method will find its use in several manufacturing applications.

Curauá Fiber Microimaging, Atomic Layer Deposition of Metal Oxide Films, and Obtaining of Nanowalled Microtubes

AbstractCurauá (Ananas erectifolius) is a new lignocellulosic material possessing valuable properties. Scanning electron microscopy (SEM) studies of natural and delignified fibers reveal their dense structure and nanoveinlets of cellulose agglomerates. Thin Al2O3 and Ta2O5 coatings of various thicknesses (30 − 130 nm) are grown on the fiber surface by atomic layer deposition (ALD). Nanowalled microtubes of Al2O3 and Ta2O5 are prepared by annealing the coated fibers in an oxidative atmosphere to verify compactness, homogeneity, and continuity of the coatings obtained. The suitability of curauá fiber for ALD applications is shown. Both ALD coatings and the nanowalled microtubes replicate well the irregular fiber relief, they are resistant and homogeneous.

Atomic layer deposition: state-of-the-art and research/industrial perspectives

Interest on nanometric conformal coatings is currently growing across a wide range of applications, from electronic components to corrosion protection, chemical barriers or even wear decrease. Currently, atomic layer deposition (ALD) is one of the most promising nanometric deposition technologies: it offers the possibility to obtain conformal coatings even on very complex tridimensional substrates, with a strict thickness tolerance. During an ALD cycle, only one molecular layer is deposited on the substrate surface, enabling the theoretical possibility to tailor the composition of the deposit up to molecular resolution. In the first part of this review, a brief history of ALD is presented to better understand the evolution of the technique during the past five decades; in the second part, a short description of the main ALD techniques is given, considering their main advantages and drawbacks. In the third part, a short review about ALD applications is presented, and in the fourth part the most useful and used instruments for the analysis and characterization of ALD are listed; some results are discussed and particular emphasis on the corrosion protection of different metallic alloys of common industrial interest is given.