Browsing by Subject "Chemical vapor deposition"

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Characterization of growth and thermal behaviors of thin films for the advanced gate stack grown by chemical vapor deposition
(2002-05) Taek Soo, Jeon; Kwong, Dim-Lee
Abstract – Studies have been done on the materials for alternative gate dielectrics (high-k) and a metal gate electrode, which will replace conventional SiO2 gate dielectric and poly silicon gate electrode, for the sub100 nm CMOS technologies. Ultrathin HfO2 films prepared by chemical vapor deposition on Si(100) were annealed in high vacuum or N2 ambient at high temperature and their thermal stability was measured. Based on in-situ XPS, annealing HfO2 films grown by CVD on clean Si(100) leads to silicide formation at 950 o C for ultrahigh vacuum but not 4 Torr of N2. For an HfO2 film capped with amorphous Si, silicide does form upon annealing in 4 torr, but not 760 torr, of N2. TEM shows when hafnium silicide forms, it forms discontinuous islands. HfON thin film prepared by chemical vapor deposition on silicon substrate showed superior thermal stability compared to HfO2 thin film. X-ray photoelectron spectroscopy studies shows that HfON thin film is chemically stable in contact with silicon up to 1000 o C under high vacuum. Excellent resistance to crystallization of HfON thin film during high temperature process is proven by a glancing angle XRD. MOS devices using HfON dielectric thin film showed better electrical properties than HfO2. CVD TaN film exhibited excellent thermal stability in terms of chemical, structural, and electrical aspects. PMOS compatible work function (~5.0 eV) and the excellent electrical performance of CVD TaN gate electrode suggest that it is a promising candidate to replace p+ poly silicon for sub-100 nm CMOS technology.
Chemical vapor deposition of MoS₂ on distributed Bragg reflector for room temperature polariton condensation
(2022-12-02) Bodemann, Isaac Michael; Banerjee, Sanjay; Akinwande, Deji
The creation of a room temperature Bose Einstein Condensate has been the goal of much research since the phenomenon was first experimentally realized in 1995. Currently, polaritons stand out as a particularly viable option to achieve this goal as their low effective mass should in theory allow for a high condensation temperature. One proposed system to realize such a condensate is a semiconductor optical microcavity. In a semiconductor microcavity distributed Bragg reflectors (DBR) are used to trap photons in the cavity, while a direct band gap semiconductor placed in the cavity would allow for the creation of excitons for those photons to couple with. In this work we explore the growth of crystalline monolayer Molybdenum Disulfide (MoS₂) directly onto the DBR to create such a microcavity. Growth of MoS₂ is well studied, however the DBR substrate presents unique challenges as the surface is inconducive for crystalline growth and the substrate itself warps and deteriorates at high temperatures. We then present techniques to overcome these challenges and recipes by which large area growth of monolayer MoS₂ growth on DBR can be attained.
Cold wall reactor for ultra-high vacuum high temperature chemical vapor deposition
(2013-05) Points, Micah Shane; Tutuc, Emanuel, 1974-
Chemical vapor deposition is a process that enables the deposition of thin films material with a high degree of thickness control, composition and film quality. In an ultra-high vacuum environment (UHV), films of high purity and controlled crystal structure can be achieved. The control of the crystal structure is achieved thanks to reduced contamination, e.g. oxygen, which allows the grown film to align itself with the underlying substrate. The film purity is also ensured by the reduced amount of contaminants present in the UHV environment. This master’s thesis discusses the design and construction of a cold wall reactor using a pyrolytic graphite heater encased in a thin layer of pyrolytic boron nitride, and an Oerlikon-Leybold Turbovac 361 turbomolecular pump. This heater is shown to achieve temperatures greater than 1200°C, as well as reach pressures in the 10-10 Torr range. Graphene growth on copper is discussed as well as the ultra-high vacuum annealing of graphene devices on boron nitride substrates. The graphene growth experiments coupled with this system’s annealing capabilities demonstrate the functionality and versatility of this type of chemical vapor deposition system.
Controlling nucleation and growth of ultra-thin ruthenium films in chemical vapor deposition
(2016-05) Liao, Wen; Ekerdt, John G.; Korgel, Brian A; Hwang, Gyeong S; Hildebrandt Ruiz, Lea; Ferreira, Paulo
As feature sizes in microelectronic devices decrease, ultra-thin (< 3 nm) and smooth diffusion barriers are required to prevent copper from diffusing into the surrounding dielectric layers and to limit electron scattering at the copper-liner surface. Chemical vapor deposition (CVD) is one route to these barriers. The inhibitor gas adsorbs on metal nanoparticles, forces additional nucleation and enhances nucleation density. Island growth combined with a sparse nucleation density leads to film roughness and the deposition of more metal mass than is needed to form a film of sufficient thickness to function as a copper diffusion barrier when compared to a uniformly-thick metal film. In the first study, a higher nucleation density and smoother Ru film is achieved in CVD with CO addition during growth. CO competes with Ru3(CO)12 for free hydroxyl adsorption. The CO addition to Ru3(CO)12 deposition at proper timing and effective partial pressure reduces the film growth rate, surface roughness and nanocrystalline grain size by chemical vapor deposition. The second study reports the use of ammonia to inhibit the growth of previously-nucleated ruthenium islands and force the nucleation of additional islands such that thinner films form as the islands coalesce with continued growth using Ru3(CO)12. The ammonia addition reduces the film nanocrystallinity and the films appear X-ray amorphous with the highest ammonia partial pressure during film deposition. In the third study, films grown from Ru(tBu-Me-amd)2(CO)2 form a 2D wetting layer before 3D particle growth is observed. CO and ammonia addition to the gas phase during film growth from Ru(tBu-Me-amd)2(CO)2 leads to smoother films by inducing surface reconstructions during the film growth; these gases also lead to films with lower resistivity and lower crystalline character. Overall, this research is to understand how blocking adsorbed moieties effect the nucleation of metals on a silica substrate, and to discover the principles leading to ultra-thin and smooth metallic films in CVD.
Deposition and properties of Co- and Ru-based ultra-thin films
(2009-12) Henderson, Lucas Benjamin; Ekerdt, John G.
Future copper interconnect systems will require replacement of the materials that currently comprise both the liner layer(s) and the capping layer. Ruthenium has previously been considered as a material that could function as a single material liner, however its poor ability to prevent copper diffusion makes it incompatible with liner requirements. A recently described chemical vapor deposition route to amorphous ruthenium-phosphorus alloy films could correct this problem by eliminating the grain boundaries found in pure ruthenium films. Bias-temperature stressing of capacitor structures using 5 nm ruthenium-phosphorus film as a barrier to copper diffusion and analysis of the times-to-failure at accelerated temperature and field conditions implies that ruthenium-phosphorus performs acceptably as a diffusion barrier for temperatures above 165 °C. The future problems associated with the copper capping layer are primarily due to the poor adhesion between copper and the current Si-based capping layers. Cobalt, which adheres well to copper, has been widely proposed to replace the Si-based materials, but its ability to prevent copper diffusion must be improved if it is to be successfully implemented in the interconnect. Using a dual-source chemistry of dicobaltoctacarbonyl and trimethylphosphine at temperatures from 250-350 °C, amorphous cobalt-phosphorus can be deposited by chemical vapor deposition. The films contain elemental cobalt and phosphorus, plus some carbon impurity, which is incorporated in the film as both graphitic and carbidic (bonded to cobalt) carbon. When deposited on copper, the adhesion between the two materials remains strong despite the presence of phosphorus and carbon at the interface, but the selectivity for growth on copper compared to silicon dioxide is poor and must be improved prior to consideration for application in interconnect systems. A single molecule precursor containing both cobalt and phosphorus atoms, tetrakis(trimethylphosphine)cobalt(0), yields cobalt-phosphorus films without any co-reactant. However, the molecule does not contain sufficient amounts of amorphizing agents to fully eliminate grain boundaries, and the resulting film is nanocrystalline.
Growth and characterization of CVD Ru and amorphous Ru-P alloy films for liner application in Cu interconnect
(2007-12) Shin, Jinhong, 1972-; Ekerdt, John G.
Copper interconnect requires liner materials that function as a diffusion barrier, a seed layer for electroplating, and an adhesion promoting layer. Ruthenium has been considered as a promising liner material, however it has been reported that Ru itself is not an effective Cu diffusion barrier due to its microstructure, which is polycrystalline with columnar grains. The screening study of Ru precursors revealed that all Ru films were polycrystalline with columnar structure, and, due to its strong 3D growth mode, a conformal and ultrathin Ru film was difficult to form, especially on high aspect ratio features. The microstructure of Ru films can be modified by incorporating P. Amorphous Ru(P) films are formed by chemical vapor deposition at 575 K using a single source precursor, cis-RuH₂(P(CH₃)₃)₄, or dual sources, Ru₃(CO)₁₂ and P(CH₃)₃ or P(C6H5)₃ The films contain Ru and P, which are in zero-valent states, and C as an impurity. Phosphorus dominantly affects the film microstructure, and incorporating > 13% P resulted in amorphous Ru(P) films. Metastable Ru(P) remains amorphous after annealing at 675 K for 3 hr, and starts recrystallization at ~775 K. The density of states analysis of the amorphous Ru(P) alloy illustrates metallic character of the films, and hybridization between Ru 4d and P 3p orbitals, which contributes to stabilizing the amorphous structure. Co-dosing P(CH)₃ with Ru₃(CO)₁₂ improves film step coverage, and the most conformal Ru(P) film is obtained with cis-RuH2(P(CH₃)₃)₄; a fully continuous 5 nm Ru(P) film is formed within 1 µm deep, 8:1 aspect ratio trenches. First principles density functional theory calculations illustrate degraded Cu/Ru adhesion by the presence of P at the interface, however, due to the strong Ru-Cu bonds, amorphous Ru(P) forms a stronger interface with Cu than Ta and TaN do. Cu diffusion studies at 575 K suggests improved barrier property of amorphous Ru(P) films over polycrystalline PVD Ru.
Growth and characterization of Ru films deposited by chemical vapor deposition : towards enhanced nucleation and film properties
(2009-12) Thom, Kelly Marriott; Ekerdt, John G.
As device dimensions in integrated circuits scale down, there is an increasing need to deposit ultra-thin, smooth, continuous films for use in applications such as the liner in back end processing. The liner must have good adhesion to both Cu and the dielectric, act as a Cu diffusion barrier, and be conductive enough to allow the electroplating of Cu. Ruthenium (Ru) has been considered as a possible material to be implemented into the liner due to its low electrical resistivity, high thermal and chemical stability, and negligible solubility with copper. Chemical vapor deposition (CVD) is an attractive growth technique for Ru films because it allows conformal deposition in high-aspect ratio features. However, there are some limitations that must be overcome in the deposition of Ru films. CVD Ru films suffer from poor nucleation on oxide and nitride substrates. Poor nucleation leads to rough, large-grained polycrystalline columnar films, which may not coalesce into a continuous film until the thickness greatly exceeds the requirements for the liner. This dissertation presents surface chemistry and film growth studies involving Ru CVD and focuses on improving the nucleation and properties of Ru films. In situ surface analysis techniques including X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) were used to study the fundamental adsorption behavior of the Ru precursor, (2,4- dimethylpentadienyl)(ethylcyclopentadienyl)Ru or DER, on polycrystalline Ta, both with and without iodine adsorbed on the Ta. Based upon these results, CVD films were grown using DER/O₂, and it was shown that nucleation and film properties can be improved by the addition of methyl iodide. Ru films grown using DER/O₂ show sparse nucleation, which leads to very rough surface topography and large polycrystalline columnar grains. The addition of methyl iodide during growth significantly improves nucleation and results in smoother, smaller-grained films. Iodine adsorbs on the initially-formed Ru islands and continuously segregates through the film to the surface during the entire deposition. In addition, CVD films grown with Ru₃(CO)₁₂ were studied. Use of the Ru₃(CO)₁₂ precursor results in thin, ultra-smooth films that show little to no columnar grain structure.
I-V transport measurements of a single unsupported MWCNT under various bending deformations
(2008-05) Kim, Suenne; de Lozanne, Alejandro L.
The first part of this dissertation is an introduction describing a brief historical background of carbon nanotubes (CNTs) and their pseudo 1D structure responsible for many exotic electronic properties. The second part describes our experimental setup. The third part is about the growing of Multi-Walled Carbon Nanotubes (MWCNTs) by the chemical vapor deposition (CVD) method. Then the fourth part demonstrates a simple but reliable method to make firm contact junctions between MWCNTs and metals such as tungsten (W). The novel point of our method consists, after making a mechanical preliminary contact at a selected MWCNT, in applying a series of voltage pulses across the contact. Thin oxide layers that may form between the MWCNT and the W wire, are removed in steps by the resistive heating and electron impact during the application of each voltage pulse. Furthermore, this simple process of contact welding in steps does not bring about any permanent change in the electronic transport properties of the MWCNTs. The fifth part discusses our bending experiments. We apply a uniform and continuous bending to a selected MWCNT at room and liquid nitrogen temperatures to study the strain effect on the electrical transport in the MWCNT. There are a few published experimental works related to the bending deformation; however, this is the first study of electronic transport properties in continuous bending and releasing deformations. We observed a saturation behavior with the MWCNT and also found the bending deformation causing an anomalous change in the saturation behavior. In the sixth part we depict some interesting phenomena due to the stretching deformation of MWCNT, where we were able to propose a simple model for electron localization induced by the deformation. The last part deals with the formation of the "X-junction" between two MWCNTs. A strong X-junction can be formed simply by means of the e-beam inside the Scanning Electron Microscope (SEM). The X-junctions may form the basic elements of nano-electronic circuits such as various metal-insulator junctions, quantum dots, and similar devices.
Metal-oxide-semiconductor devices based on epitaxial germanium-carbon layers grown directly on silicon substrates by ultra-high-vacuum chemical vapor deposition
(2006) Kelly, David Quest; Banerjee, Sanjay
After the integrated circuit was invented in 1959, complementary metal-oxidesemiconductor (CMOS) technology soon became the mainstay of the semiconductor industry. Silicon-based CMOS has dominated logic technologies for decades. During this time, chip performance has grown at an exponential rate at the cost of higher power consumption and increased process complexity. The performance gains have been made possible through scaling down circuit dimensions by improvements in lithography capabilities. Since scaling cannot continue forever, researchers have vigorously pursued new ways of improving the performance of metal-oxide-semiconductor field-effect transistors (MOSFETs) without having to shrink gate lengths and reduce the gate insulator thickness. Strained silicon, with its ability to boost transistor current by improving the channel mobility, is one of the methods that has already found its way into production. viii Although not yet in production, high-κ dielectrics have also drawn wide interest in industry since they allow for the reduction of the electrical oxide thickness of the gate stack without having to reduce the physical thickness of the dielectric. Further out on the horizon is the incorporation of high-mobility materials such as germanium (Ge), silicongermanium (Si1-xGex), and the III-V semiconductors. Among the high-mobility materials, Ge has drawn the most attention because it has been shown to be compatible with high-κ dielectrics and to produce high drive currents compared to Si. Among the most difficult challenges for integrating Ge on Si is finding a suitable method for reducing the number of crystal defects. The use of strainrelaxed Si1-xGex buffers has proven successful for reducing the threading dislocation density in Ge epitaxial layers, but questions remain as to the viability of this method in terms of cost and process complexity. This dissertation presents research on thin germanium-carbon (Ge1-yCy) layers on Si for the fabrication of MOS transistors with improved drive currents. By incorporating a small amount of C in Ge, the crystal quality of Ge epitaxial layers grown directly on Si can be dramatically improved. The Ge1-yCy layers have been used to fabricate high-drivecurrent p-MOSFETs with high-κ dielectrics and metal gates. In addition to the electrical results, materials-related experimental data was acquired and analyzed to provide insights on the surface morphology, crystal quality, strain, C incorporation, and growth kinetics of the Ge1-yCy layers. This work describes an exciting new possibility for the ultimate goal of incorporating high-mobility semiconductor materials in CMOS technology.
Selective silicon and germanium nanoparticle deposition on amorphous surfaces
(2007-08) Coffee, Shawn Stephen, 1978-; Ekerdt, John G.
This dissertation describes the development of a process for the precise positioning of semiconductor nanoparticles grown by hot wire chemical vapor deposition and thermal chemical vapor deposition on amorphous dielectrics, and it presents two studies that demonstrate the process. The studies entailed growth and characterization using surface science techniques and scanning electron microscopy. The two systems, Ge nanoparticles on HfO₂ and Si nanoparticles on Si₃N₄, are of interest because their electronic properties show potential in flash memory devices. The positioning technique resulted in nanoparticles deposited within 20 nm diameter feature arrays having a 6x10¹⁰ cm⁻² feature density. Self-assembling diblock copolymer poly(styrene-b-methyl methacrylate) thin films served as the patterning soft mask. The diblock copolymer features were transferred using a CHF₃/O₂ reactive ion etch chemistry into a thin film SiO₂ hard mask to expose the desired HfO₂ or Si₃N₄ deposition surface underneath. Selective deposition upon exposed pore bottoms was performed at conditions where adatom accumulation occurred on the HfO₂ or Si₃N₄ surfaces and not upon the SiO₂ mask template. The selective deposition temperatures for the Ge/HfO₂ and Si/Si₃N₄ systems were 700 to 800 K and 900 to 1025 K, respectively. Germanium nucleation on HfO₂ is limited from hot wire chemical vapor deposition by depositing nanoparticles within 67% of the available features. Unity filling of features with Ge nanoparticles was achieved using room temperature adatom seeding before deposition. Nanoparticle shape and size are regulated through the Ge interactions with the SiO₂ feature sidewalls with the adatom removal rate from the features being a function of temperature. The SiO₂ mask limited Ge nanoparticle growth laterally to within ~5 nm of the hard mask at 800 K. Silicon deposition on patterned Si₃N₄ has multiple nanoparticles, up to four, within individual 20 nm features resulting from the highly reactive Si₃N₄ deposition surface. Silicon nucleation and continued nanoparticle growth is a linear function of deposition flux and an inverse function of sample temperature. Diblock copolymer organization can be directed into continuous crystalline domains having ordered minority phases in a process known as graphoepitaxy. In graphoepitaxy forced alignment within microscopic features occurs provided certain dimensional constraints are satisfied. Graphoepitaxy was attempted to precisely locate 20 nm diameter features for selective Ge or Si deposition and initial studies are presented. In addition to precise nanoparticle positioning studies, kinetic studies were performed using the Ge/HfO₂ material system. Germanium hot wire chemical vapor deposition on unpatterned HfO₂ surfaces was interpreted within the mathematical framework of mean-field nucleation theory. A critical cluster size of zero and critical cluster activation energy of 0.4 to 0.6 eV were estimated. Restricting HfO₂ deposition area to a 200 nm to 100 [mu]m feature-width range using SiO₂ decreases nanoparticle density compared to unpatterned surfaces. The studies reveal the activation energies for surface diffusion, nucleation, and Ge etching of SiO₂ are similar in magnitude. Comparable activation energies for Ge desorption, surface diffusion and cluster formation obscure the change with temperature an individual process rate has on nanoparticle growth characteristics as the feature size changes.
Synthesis and Raman spectroscopy characterization of long Carbon Nanotubes
(2023-08) Cantu, Rodolfo, Jr.; Shi, Li, Ph. D.
Carbon Nanotubes (CNTs) are promising nanomaterials with outstanding thermal, electrical, and mechanical properties. Composed of carbon atoms arranged in thin cylindrical walls, these nanostructures have promising applications in nanoelectronics, ultra-strong fibers, and thermal management solutions. Chemical Vapor Deposition (CVD) has been used to grow CNTs from catalytical nanoparticles at low pressure and high temperatures. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterization of the structures of CNTs can potentially induce defects due to the high electron beam energy. This thesis reports an effort to establish Raman spectroscopy mapping as a relatively non-invasive technique for locating individual suspended and long single-walled carbon nanotubes (SWCNTs) grown by catalytic CVD before they are transferred for subsequent measurements of their thermal transport and other properties. The g-band and radial breathing mode in the Raman spectrum is used to identify SWCNTs and determine their diameters.
Synthesis of high-quality graphene via chemical vapor deposition
(2020-08-14) Lee, Byoungdo; Li, Wei (Of University of Texas at Austin); Cullinan, Michael; Ho, Paul S.; Koo, Joseph; Liu, Yuanyue
Due to its extraordinary properties, graphene has been attracting enormous interest for large-scale applications. Among preparation methods of graphene, low-pressure chemical vapor deposition (LPCVD) remains the most efficient and scalable method to produce high quality and cost-effective graphene in large size. Control over the high quality of graphene is indispensable to synthesize graphene by LPCVD. This research investigates a factor analysis affecting the graphene quality under five key LPCVD process parameters. These parameters are responsible for the graphene quality ranging from the number of graphene layers to the number of graphene grains. The statistical analysis on both the main process parameters and second-order interaction effects of experiment is conducted to review the interplay of LPCVD process parameters. Furthermore, cooling rate study discovers that fast cooling rate and temperature dependent gas feeding time are required to obtain monolayer graphene with high quality. Copper (Cu) wire is used in many electrical devices because of their inherent beneficial properties, but it is easily oxidized in air. Graphene is a good candidate for anti-corrosion and anti-oxidation due to its impermeability to oxygen or etchants and its atomically thin thickness. The following study characterizes the anti-oxidation and anti-corrosion performances of Cu wire with different numbers of graphene layers and grains. Monolayer, bilayer, and multilayer graphene are synthesized on bare Cu wire by adjusting growth parameters of LPCVD process. The higher number of graphene layers leads to low resistivity values at high temperatures due to the delay of the oxidation process of the Cu wire. The resistivity of twisted bare Cu wire pair is considerably higher than the twisted pair one covered with multilayer graphene. The lower cooling rate, the better protection effects against oxidation, leading to a small number of larger graphene grains. The etching time of Cu wire with multilayer-graphene protection doubles comparing to their bare Cu wire counterparts. This research provides not only guidelines to control the quality of graphene for large scale fabrication, but also baseline data for research on the temperature dependent anti-oxidation and anti-corrosion performances of multilayered graphene for Cu and Cu wires.
Synthesis, characterization, and electrical transport in 2-D transition metal dichalcogenides grown by chemical vapor deposition
(2022-08-11) Chowdhury, Sayema; Banerjee, Sanjay; Akinwande, Deji; Register, Leonard F; Dodabalapur, Ananth; Wang, Yaguo
Transition metal dichalcogenides (TMDs), possessing a multitude of interesting properties, have emerged as an interesting choice for various types of electronic, optoelectronic and beyond CMOS device applications. Chemical vapor deposition (CVD) has been used extensively as an efficient, fast, reliable, and scalable route to grow uniform, high quality, large area TMDs. In this work, we report atmospheric pressure CVD (APCVD) and metal-organic CVD (MOCVD) growth of TMDs and study the effects of growth temperature, metal/chalcogen flux, reaction environment, etc. in modulating the shape, size, crystal structure, and uniformity of the grown film. To control the morphology more efficiently, we established a process for transition from compact two-dimensional (2D) domain to branched domain morphologies by varying the growth temperature and transition metal flux. Two different types of branched domains, fractals and dendrites, are observed which follow different growth mechanisms. In addition to the experimental investigations, we used a phase field simulation method for a better understanding of the dependence of the domain morphologies on the growth parameters. To control the 2D/3D growth mode, crucial role of chalcogen flux is investigated. While multilayer islands form in a chalcogen-deficient condition, a chalcogen-rich condition promotes lateral growth by restricting transition metal-rich nuclei formation. Study of APCVD growth with different carrier gases show that a reducing environment under hydrogen gas is more favorable to achieve uniform 2D growth. Based on the experimental observations, we propose an optimized CVD growth condition to achieve large-area high quality 2D TMD domains. Beside the APCVD growth of TMDs, an alternative approach via MOCVD growth under low pressure followed by a high-temperature sulfurization process under atmospheric pressure has also been explored. This two-step process can substantially heal chalcogen vacancies, suppress carbon/oxygen contamination, and produce more homogeneously distributed triangular monolayer domains with the electrical performance comparable to APCVD-grown domains.