Vor dem Hintergrund der in der Mikroelektronik-Fertigung heute verbreiteten Kupfertechnologie werden in der vorliegenden Arbeit drei neuartige metallorganische Verbindungen, nämlich phosphitstabilisierte Kupfer(I)-Trifluoracetat-Komplexe vorgestellt und hinsichtlich ihrer Anwendbarkeit für die chemische Gasphasenabscheidung (CVD) von Kupfer untersucht. Im einzelnen handelt es ich um die Substanzen Tris(trimethylphosphit)kupfer(I)trifluoracetat (METFA), Tris(triethylphosphit)kupfer(I)trifluoracetat (ETTFA) und Tri(tris(trifluorethyl)phosphit)kupfer(I)trifluoracetat (CFTFA). Mit den Substanzen erfolgen CVD-Experimente auf TiN und Cu bei Temperaturen <400°C. Die Precursoren werden dabei mittels eines Flüssigdosiersystems mit Verdampfereinheit der Reaktionskammer zugeführt. Während METFA wegen seiner ausreichend geringen Viskosität unverdünnt verwendet werden kann, kommen für ETTFA und CFTFA jeweils Precursor-Acetonitril-Gemische zum Einsatz. Mit keinem der Neustoffe können auf TiN geschlossene Kupferschichten erzeugt werden, während dies auf Kupferunterlagen in Verbindung mit Wasserstoff als Reduktionsmittel gelingt. Die Abscheiderate beträgt hierbei 2-3nm/min; der spezifische Widerstand der Schichten bewegt sich zwischen 4μΩcm und 5μΩcm. Mit allen Substanzen werden besonders an dünnen, gesputterten Kupferschichten Agglomerationserscheinungen und Lochbildung beobachtet. Im Fall von CFTFA treten zusätzlich Schäden am darunterliegenden TiN/SiO₂-Schichtstapel auf. Vergleichende Untersuchungen mit der für die Cu-CVD etablierten Substanz (TMVS)Cu(hfac) ergeben sowohl auf Cu als auch auf TiN geschlossene Kupferschichten. Dabei liegen die Abscheideraten bei Temperaturen zwischen 180°C und 200°C im allgemeinen deutlich über 100nm/min. Ein Vergleich dieser Resultate mit den Ergebnissen für die Neustoffe legt nahe, dass den untersuchten Kupfer(I)-Trifluoracetaten keine ausreichende Tauglichkeit für Cu-CVD-Prozesse in der Mikroelektronik-Technologie bescheinigt werden kann. Die im Vergleich zu (TMVS)Cu(hfac) höhere thermische Stabilität der Precursoren und ihre Fähigkeit, mit Wasserstoff als Reaktionspartner auf Cu geschlossene Kupferschichten erzeugen zu können, deutet jedoch auf ihre eventuelle Eignung für ALD-Prozesse hin. Daher widmet sich die Arbeit in einem abschließenden Kapitel dem Thema der Atomic Layer Deposition (ALD), wobei nach einem allgemeinen Überblick besonders auf für die Mikroelektronik relevante ALD-Prozesse eingegangen wird.

Thin film solar cells, such as Cu(In,Ga)Se2, have a large potential for cost reductions, due to their reduced material consumption. However, the lack in commercial success of thin film solar cells can be explained by lower efficiency compared to wafer-based solar cells. In this work, we have investigated the aluminum oxide as a passivation layer to reduce recombination losses in Cu(In,Ga)Se2 solar cells to increase their efficiency. Aluminum oxides have been deposited using spatial atomic layer deposition. Blistering caused by post-deposition annealing of thick enough alumina layer was suggested to make randomly arranged point contacts to provide an electrical conduction path through the device. Techniques such as current-voltage measurement, photoluminescence and external quantum efficiency were performed to measure the effectiveness of aluminum oxide as a passivation layer. Very high photoluminescence intensity was obtained for alumina layer between Cu(In,Ga)Se2/CdS hetero-junction after a heat treatment, which shows a reduction of defects at the absorber/buffer layers of the device.

One of the keys to successful commercialization of photonic devices is compatibility with complementary metal-oxide-semiconductor technology (CMOS), the major platform of the microelectronics industry. Silicon photonics, with plasmonic materials are promising candidates for next generation chip-scale technology. The majority of plasmonics research has focused on noble metals, which are not CMOS compatible. Transition metal nitrides are an emerging class of alternative plasmonic materials that are complementary metal-oxide-semiconductor compatible and have shown promising results when compared to devices utilizing noble metals. This dissertation highlights, a CMOS compatible method to produce such alternative plasmonic materials using atomic layer deposition (ALD), specifically ultrathin plasmonic titanium nitride, aluminum metal and zirconium nitride. A post-deposition hydrogen plasma treatment is also introduced to improve the metallic properties of the ultrathin films. Additionally, this dissertation proposes a core-multishell (CMS) nanowire (NW) device structure that utilizes these materials to enable the creation of photonic devices, specifically detailing designs for cloaking and photoelectrochemical (PEC) water splitting applications. It is shown theoretically that zirconium nitride cloaks a silicon nanowire without substantially compromising the absorption of light, resulting in a less-intrusive, better performing silicon nanowire photosensor, and outperforms a gold cloak in the wavelength region of 400-500 nm. It is demonstrated theoretically that emerging plasmonic materials TiN and ZrN are promising candidates to improve the ideal photocurrent density hematite photoanodes in core-multishell nanowire devices, allowing hematite to remain electrically thin enough to effectively transport charge carriers while absorbing light similar to thick hematite features.

Tin dioxide (SnO2) is considered one of the most promising anode materials for Lithium ion batteries (LIBs), due to its large theoretical capacity and natural abundance. However, its low electronic/ionic conductivities, large volume change during lithiation/delithiation and agglomeration prevent it from further commercial applications. In this thesis, we investigate modified SnO2 as a high energy density anode material for LIBs. Specifically two approaches are presented to improve battery performances. Firstly, SnO2 electrochemical performances were improved by surface modification using Atomic Layer Deposition (ALD). Ultrathin Al2O3 or HfO2 were coated on SnO2 electrodes. It was found that electrochemical performances had been enhanced after ALD deposition. In a second approach, we implemented a layer-by-layer (LBL) assembled graphene/carbon-coated hollow SnO2 spheres as anode material for LIBs. Our results indicated that the LBL assembled electrodes had high reversible lithium storage capacities even at high current densities. These superior electrochemical performances are attributed to the enhanced electronic conductivity and effective lithium diffusion, because of the interconnected graphene/carbon networks among nanoparticles of the hollow SnO2 spheres.

No description available.

No description available.

Atomic layer deposition (ALD) is a technique by which surface-based reactions between a precursor molecule (often metal-containing) and a co-reactant (e.g. H2O, O2 or H2) yield highly uniform and conformal (ultra-)thin films. The precursor and co-reactant are each delivered in the gas phase, separated from one another by inert gas purge steps. The self-limiting nature of these surface-based reactions allows the thickness of the film to be controlled solely by the number of ‘precursor – purge – co-reactant – purge’ cycles. This nano-scale control of film thickness allows for a large number of applications such as in flat panel displays, fuel and solar cells, and microelectronic devices. The first goal of this project was the pursuit of new low-temperature methods for main group elemental ALD using silyl-substituted precursor molecules. The second goal of the project was the development of alternative methods for thin film deposition of group 4 (M = Hf, Zr) oxides that would encourage effective (ie. void-free) filling of narrow (<20 nm) trenches in high-aspect-ratio (HAR) substrates. This thesis includes the development of new precursor molecules and reaction pathways, evaluation of precursor molecular structures, thermal stability, volatility and solution reactivity, identification of appropriate experimental conditions for ALD, and characterization of the resulting thin films. ALD of elemental antimony was achieved on hydrogen-terminated silicon (H-Si) and SiO2/Si substrates using Sb(SiMe3)3 (2-1) and SbCl3 in the temperature range 23- 65 °C. The mirror-like films were confirmed to be composed of crystalline antimony by XPS (for the film deposited at 35 °C) and XRD, with low impurity levels and strong preferential orientation of crystal growth relative to the substrate surface. To the best ofour knowledge, this is the first example of room temperature thermal ALD (with demonstrated self-limiting growth) of a pure element. Film growth at 35 °C exhibited a substrate-enhanced mechanism, characterized by faster film growth for the first ~125 ALD cycles, where substantial deposition is occurring on the original substrate surface (GPC (growth-per-cycle) = 1.3 Å on SiO2/Si, and 1.0 Å on H-Si), and slower film growth (GPC = 0.40 Å on SiO2/Si, and 0.27 Å on H-Si) after ~125 cycles, once much of the initial substrate surface has been covered. Films deposited using 500-2000 ALD cycles were shown to be continuous by SEM. The use of less than 250 cycles afforded discontinuous films. However, in this initial growth phase, when deposition is occurring primarily on the original substrate surface, in-situ surface pre-treatment by Sb(SiMe3)3 or SbCl3 (50 x 0.4 or 0.8 s pulses), followed by the use of longer precursor pulses (0.4 or 0.8 s) during the first 50 ALD cycles resulted in improved nucleation. For example, on H-Si, a continuous 6.7 nm thick film was produced after initial pre-treatment with 50 x 0.8 s pulses of SbCl3, followed by 50 ALD cycles using 0.8 s pulses. The use of longer ALD pulses in the first 50 ALD cycles following surface pre-treatment is likely required in order to achieve complete reactivity with an increased density of reactive surface sites. Boranes featuring bulky silyl or sterically unencumbered trimethylgermyl groups, in combination with a stabilizing dimethylamido group, were pursued as potential precursors for ALD of elemental boron. This ALD process would employ a boron trihalide (BX3; X = F, Cl, Br, I) co-reactant, exploiting the thermodynamically favourable formation of tetrel-halide bonds as a driving force. This work required multistep syntheses of alkali metal silyl reagents, {(Me3Si)3Si}Li(THF)2 (3-1) and tBu3SiNa(THF)n (3-2), and previously un-isolated [Me3GeLi(THF)2]2 (3-3), and their reactions with B(NMe2)Cl2 (3-4). The boranes {(Me3Si)3Si}2B(NMe2) (3-8) and (tBu3Si)(Me3Ge)B(NMe2) (3-12) were successfully synthesized, spectroscopically and crystallographically characterized, and assessed for their suitability as precursor molecules for boron ALD. Unfortunately, deposition attempts on SiO2/Si using 3-8 and BCl3 led to minor film growth (GPC = 0.01 Å). However, the enhanced volatility and solution-state reactivity of 3-12 in comparison to 3-8 makes it a promising precursor candidate for future ALD reactor studies. Attempts to synthesize bis(trimethylgermyl)(dimethylamido)borane from the 2:1 reaction of 3-3 with 3-4 resulted in the formation of a lithium trigermylamidoborate, {(Me3Ge)3B(NMe2)}Li(THF)2 (3-13). ALD can give rise to uniquely uniform and conformal ultra-thin films, but voids often remain after attempted filling of narrow high-aspect-ratio trenches. To achieve void-free trench-filling, ALD (or CVD; chemical vapour deposition) methods which deposit a flowable material are desirable, and this initially-deposited material can be converted to the target material (e.g. a metal oxide) by post-deposition annealing, or potentially at the deposition temperature on a longer timescale than flowable behaviour. In this work, a new HfO2 ALD process was developed using [Hf(NMeEt)4] in combination with β- hydroxyisovaleric acid (IVA; CMe2(OH)CH2CO2H) that introduces the potential for flowability. Self-limiting growth was observed at 100, 250, and 300 °C, with a GPC of 1.5- 2.2 Å on planar SiO2 substrates. Films deposited at 100 °C consisted of amorphous HfO2 with significant carbon content (~22 at%) and <1 at% nitrogen. After annealing at 400 °C in vacuo for 1 hour, the films were composed of amorphous HfO2 with low (<1 at%) carbon content. The co-reactant in this work, β-hydroxyisovaleric acid, was chosen with the following criteria in mind: Firstly, the carboxylic acid group may be sufficiently acidic to cleave linkages between chemisorbed hafnium species and the surface, generating flowable non-surface-tethered hafnium carboxylate species (with low volatility, so that they are not lost from the surface). Secondly, the hydroxyl groups of the ligands can potentially serve as reactive sites for the hafnium precursor delivered in the next pulse. Thirdly, fairly low-energy pathways should exist for deprotonated IVA ligands to decompose to generate oxide or hydroxide ligands with release of volatile by-products, such as CO2 and isobutene, or acetone and ketene. Experiments to gain insight into the nature of reactivity between [Hf(NMeEt)4] and IVA and a structurally similar carboxylic acid are described. These include (a) solution-state reactions between [Hf(NMeEt)4] and IVA or pivalic acid (tBuCO2H), with formation of [H2NMeEt]2[Hf(κ2-O2CCH2CMe2OH)2(κ2- OC(O)CH2CMe2O)2] (4-1) and [Hf5(μ3-O)4(κ2-O2CtBu)4(μ-O2CtBu)8] (4-2), (b) attempted ALD using pivalic acid (which lacks a hydroxyl group) in place of IVA, and (c) roomtemperature solution reactions between [Hf(NMeEt)4] and 4 equiv. of IVA to form 4-1, followed by removal of volatiles, heating at 200 °C, and volatile/soluble product analysis by NMR spectroscopy and GC-MS headspace analysis. Compounds 4-1 and 4-2 were isolated and crystallographically characterized. Heteroleptic zirconium(IV) complexes were designed, synthesized, spectroscopically and crystallographically characterized, and assessed as potential precursor molecules to enable flowable ZrO2 ALD. The envisaged process would operate via the deposition of oligomeric, one-dimensional chains that, if grown untethered on a functionalized substrate, could potentially flow to the bottoms of trenches. Reaction of one equivalent of H2(acen), H2(cis-Cyacen) or H2(trans-Cyacen) with [Zr(CH2SiMe3)4] at room temperature afforded [Zr(acen)(CH2SiMe3)2] (5-1), [Zr(cis-Cyacen)(CH2SiMe3)2] (5-2) or [Zr(trans-Cyacen)(CH2SiMe3)2] (5-3), respectively (acen = C2H4(NCMeCHC(O)Me)2; Cyacen = 1,2-C6H10(NCMeCHC(O)Me)2). These alkyl compounds are trigonal prismatic in the solid state, and whereas 5-1 and 5-3 decomposed without sublimation above 120 °C (5-10 mTorr), 5-2 sublimed in >95% yield at 85 °C (5-10 mTorr). However, heating solid 5-2 at 88 °C under static argon for 24 hours resulted in extensive decomposition to afford H2(cis-Cyacen) and SiMe4 as the soluble products. Compound 5-2 reacted cleanly with two equivalents of tBuOH to afford [Zr(cis-Cyacen)(OtBu)2] (5-4), but excess tBuOH caused both SiMe4 and H2(cis-Cyacen) elimination. The 1:1 reaction of H2(acen) with [Zr(NMeEt)4] did not proceed cleanly, and 8-coordinate [Zr(acen)2] (5-5) was identified as a by-product; this complex was isolated from the 2:1 reaction. A zirconium amido complex, [Zr(acen)(NMeEt)2] (5-6) was accessed via the reaction of 1 with two equiv. or excess HNMeEt, but decomposed readily in solution at room temperature. More sterically hindered [Zr(acen){N(SiMe3)2}2] (5-7) was synthesized via the reaction of [Zr(acen)Cl2] with two equivalents of Li{N(SiMe3)2}, but was also thermally unstable as a solid and in solution at room temperature. Compounds 5-1 to 5-3, 5-5 and 5-7 were crystallographically characterized. / Dissertation / Doctor of Science (PhD) / The focus of this work is the development of new processes to deposit ultra-thin films of main group elements and transition metal oxides. The deposition method utilized in this work is atomic layer deposition (ALD), which involves the use of a precursor molecule (which contains the target element) and a co-reactant. These chemical species must be appropriately reactive towards one another, and display adequate volatility and thermal stability. The feasibility of a precursor/co-reactant combination can be assessed using solution-state reactivity studies. For main group element ALD, silyl-containing compounds (E(SiR3)3, E = Sb, B) have been investigated as precursors in combination with EX3 (X = F, Cl, Br, I) coreactants, due to the potential for thermodynamically favourable Si-X bond formation to drive the required surface-based reactions. For metal oxide ALD (MO2; M = Hf, Zr), new ALD methods have been proposed to enable gap-free filling of narrow trenches on the surface of a silicon wafer. This work involved the design, synthesis, and evaluation of new ALD precursor molecules and reactions, ALD reactor studies for thin film deposition, and characterization of the resulting films.

<p>As a scalable and CMOS compatible novel ferroelectric material, the ferroelectric HZO thin film has been the promising material for various applications and continues to attract the attention of researchers. Achieving strong ferroelectricity and fast switching speed in ultrathin FE HZO film are crucial challenges for its applications towards scaled devices.</p> <p>The ferroelectric and anti-ferroelectric properties of HZO are investigated systematically down to 3 nm. The ferroelectric polarization, switching speed and the impact of ALD tungsten nitride electrodes are studied. Record high Pr on FE HZO and record high PS on AFE HZO are achieved with WN electrodes, especially in ultrathin sub-10 nm regime. The polarization switching speed of FE and AFE HZO, associated with C-V frequency dispersion, are also qualitatively studied. On the other side of the scaling limit, ferroelectric/dielectric stack superlattice structure is found to enhance the ferroelectricity in thick films which would have severely degraded.</p> <p>Ultrafast direct measurement on the transient ferroelectric polarization switching is used to study the switching speed in FE HZO with a crossbar MFM structure. Sub-nanosecond characteristic switching time of 925 ps was achieved, supported by the nucleation limited switching model. The impact of electric field, film thickness and device area on the polarization switching speed is systematically studied. The ferroelectric switching speed is significantly improved compared to previous reports and more importantly is approaching GHz regime, suggesting FE HZO to be competitive in high-speed non-volatile memory technology. Record fast polarization switch speed of 360 ps is obtained in sub-μm crossbar array FE HZO MFM devices. It also unveils that domain wall propagation speed in HZO is the limiting factor for switch speed and more aggressively scaled devices will offer much faster switch speed.</p> <p>The first experimental determination of nucleation time and domain wall (DW) velocity by studying switching dynamics of ferroelectric (FE) hafnium zirconium oxide (HZO) was performed. Experimental data and simulation results were used to quantitatively study the switching dynamics. The switching speed is degraded in high aspect ratio devices due to the longer DW propagation time or with dielectric interfacial layer due to the required additional tunneling and trapping time by the leakage current assist switch mechanism.</p>

No description available.

<p>As the miniaturization of the transistors in integrated circuits approaches the atomic scale limit, novel materials with exceptional performance are desired. Moreover, to conduct enough current with an ultrathin and small-scale body, high drain current density is preferably required. Nevertheless, devices may suffer seriously from self-heating effect (SHE) with high drain bias and current if the generated heat cannot be dissipated efficiently. In this thesis, we introduce two material systems and several techniques to accomplish the demand without SHE. Tellurium, as a van der Waals material composed by atomic helical chains, is able to realize its one-dimensional structure. We illustrate that the cross-sectional current density of 150 MA/cm2 is achieved through boron nitride nanotube (BNNT) encapsulation without SHE due to the superior thermal conductivity of BN. With the nanotube encapsulation technique applied, one-dimensional tellurium nanowire transistors with diameter down to 2 nm are realized as well, and single tellurium atomic chain is isolated. Furthermore, atomic-layer-deposited indium oxide (In2O3) as thin-film transistors exhibit even better current carrying capacity. Through co-optimization of their electrical and thermal performance, drain current up to 4.3 mA/μm is achieved with a 1.9-nm-thick body without SHE. The alleviation of SHE is due to a) the high thermal conductivity of the substrate assisting on efficiently dissipating the generated thermal energy, b) SHE avoidance with short-pulse measurement, and c) interface engineering between the channel stack and the substrate. These two material systems may be the solid solution to the desire of high current density transistors in the post-Moore era.</p>