Growth Of Aluminum Research Articles

The Appearance of Pitting on Thermally Grown Aluminum Oxide caused by Surface Segregation of Fe Impurities from the Bulk

Abstract The oxidation of 99 wt.-% purity (low purity – main impurities were Fe and Si) and 99.999 wt.-% purity (high purity) Al foil was studied using a thermo-gravimetric method. The Al oxide was characterized with several techniques such as scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS) and x-ray photoelectron spectroscopy (XPS). The Al foils were oxidized in a 50 % O2 – 50 % Ar mixture between 773 and 843 K. Microscopic examination (SEM) of the oxide revealed that “pitting” occurred on the low purity Al. High Si and Fe concentration were found on the surface or near-surface of the oxide. The presence of Fe, as precipitates, on the surface of the oxide accounts for the pitting of the oxide. XPS inspection revealed the formation of γ-Al2O3 with the presence of some Al hydroxide.

Graphene tunnel junctions with aluminum oxide barrier

We report a development of graphene tunnel junctions made by chemical vapor deposition grown graphene and sputtered aluminum insulating by an in-situ grown aluminum oxide. The thin oxide layer formed in between the metal layer and the two-dimensional material is a crucial part of a tunnel junction. We characterized surface morphology of oxide layers and studied tunneling spectra of lead and silver tunnel junctions to estimate the quality of the aluminum oxide. The Brinkman-Rowell-Dynes model was applied to fit the conductance-voltage plots to calculate the thickness of oxide layers. Junctions with graphene both on bottom and on top were fabricated and their tunneling properties were characterized after exposure to air for weeks to test time stability. Furthermore, the resistances of graphene tunnel junctions with aluminum oxide formed naturally and in an oxygen atmosphere were studied. Our results demonstrate that in-situ aluminum oxide is an effective barrier for graphene tunnel junctions. The methods of barrier formation enable the realization of more tunnel devices and circuits based on graphene.

Hybrid cavity-coupled plasmonic biosensors for low concentration, label-free and selective biomolecular detection.

Simple optical techniques that can accurately and selectively identify organic and inorganic material in a reproducible manner are of paramount importance in biological sensing applications. In this work, we demonstrate that a nanoimprinted plasmonic pattern with locked-in dimensions supports sharp deterministic hybrid resonances when coupled with an optical cavity suitable for high sensitive surface detection. The surface sensing property of this hybrid system is quantified by precise atomic layer growth of aluminum oxide using the atomic layer deposition technique. The analyte specific sensing ability is demonstrated in the detection of two dissimilar analytes, inorganic amine-coated iron oxide nanoparticles and organic streptavidin protein. Femto to nanomolar detection limits were achieved with the proposed coupled plasmonic system based on the versatile and robust soft nanoimprinting technique, which promises practical low cost biosensors.

Aluminum bond pad corrosion of wirebond packages

Abstract Corrosion of aluminum bond pads in wirebonded packages can lead to device reliability issues under the harsh conditions in automotive applications. Corroded Al (aluminum) surface forms a mud-crack type appearance with a relatively very thick aluminum oxide/hydroxide (> 0.1μm) compared to thin protective native aluminum oxide (< 7nm). Various factors contributing to the formation of mud-crack type corrosion are identified. In all cases of mud-crack corrosion observed for packaged devices, Cl (chlorine) was detected on the corroded Al pad. The corrosive impact of high levels of Cl on the Al pad resulting in thick aluminum oxide growth will be discussed. The concentration levels of Cl to form mud-crack corrosion is far beyond the level of ionizable Cl typically present in packaging materials (such as mold compound or organic die attach) so the source of high levels of Cl is due to foreign contamination. The effect of Cl on mud-crack corrosion depends on other factors including pH and applied bias voltage. Corrosion susceptibility is found to be significantly reduced, even in the presence of high levels of Cl, when the pH > 6 and close to the neutral value of a pH of 7. It was also found that Cl is not essential to form mud-crack corrosion. Conditions leading to the corrosion in the absence of Cl are presented. F (fluorine) is a known contaminant in semiconductor processing and its influence on Al pad corrosion is examined. The differences on the impact of F vs. Cl on mud-crack corrosion will be discussed. Corrosion was observed irrespective of the wirebonds in the package (gold (Au) or copper (Cu)). However, the type of bi-metallic contact influences the extent of corrosion. The impact of bi-metallic contact on the mud-crack corrosion will be presented.

Modelling the growth of porous alumina matrix for creating hyperbolic media

Porous aluminum oxide is a regular self-assembled structure. During anodization it is possible to control nano-parameters of the structure using macroscopic parameters of anodization. Porous alumina films can be used as a template for the creation of hyperbolic media. In this work we consider the anodization process, our model takes into account the influence of layers of aluminum and electrolyte on the rate of growth of aluminum oxide, as well as the effect of surface diffusion. As a result of our model we obtain the minimum distance between centers of alumina pores in the beginning of anodizing process. We also present the results obtained by numerical modelling of hyperbolic media based on porous alumina film.

Effect of Anionic Surfactant on the Growth of Anodic Nanoporous Aluminum Oxide

Nanoporous aluminum oxide film was prepared by anodizing Aluminum in a mixture of 0.3 M H3PO4 with the addition of varying concentration of Sodium Dodecyl Sulfate (SDS), which is an anionic surfactant. We found that addition of anionic surfactant during anodization of aluminum leads to the delay in dissolution of the formed pores as compared to those prepared without SDS surfactant. The results show that sufficient addition of SDS during anodization of aluminum oxide facilitates pore channel length, pore density and progress in chemical resistance. Morphology of nanoporous oxide with surfactant was confirmed by FE-SEM and EDS. Evaluation of pore diameter, interpore distance, pore density and porosity and uniformity of pores was done with the help of image-J software. Surface dissolution was observed when the concentration of SDS is more than 3.4 × 10−3 M (1g) after 2 hrs in one step anodization at 170 V which means that the optimum tolerance concentration against surface dissolution is less than 3.4 × 10−3 M (1g).

Interconnected mesoporous V2O5 electrode: impact on lithium ion insertion rate.

Here we introduce a strategy for creating nanotube array electrodes which feature periodic regions of porous interconnections providing open pathways between adjacent nanotubes within the array, utilizing a combination of anodized aluminum oxide growth modification (AAO) and atomic layer deposition. These porous interconnected structures can then be used as testbed electrodes to explore the influence of mesoscale structure on the electrochemical properties of the interconnected mesoporous electrodes. Critically, these unique structures allow the solid state lithium diffusion pathways to be held essentially constant, while the larger structure is modified. While it was anticipated that this strategy would simply provide increased mass loading, the kinetics of the Li+ ion insertion reaction in the porous interconnected electrodes are dramatically improved, demonstrating significantly better capacity retention at high rates than their aligned counterparts. We utilize a charge deconvolution method to explore the kinetics of the charge storage reactions. We are able to trace the origin of the structural influence on rate performance to electronic effects within the electrodes.

Modelling the growth process of porous aluminum oxide film during anodization

Currently it has become important for the development of metamaterials and nanotechnology to obtain regular self-assembled structures. One such structure is porous anodic alumina film that consists of hexagonally packed cylindrical pores. In this work we consider the anodization process, our model takes into account the influence of layers of aluminum and electrolyte on the rate of growth of aluminum oxide, as well as the effect of surface diffusion. In present work we consider those effects. And as a result of our model we obtain the minimum distance between centers of alumina pores in the beginning of anodizing process.

Corrosion reliability of copper wirebond (CuWB) packages-Impact of voltage and corrosive ions from packaging materials

Reliability of electronic devices used in extreme and harsh conditions such as in automotive applications is often associated with prevention of corrosion at the interfaces of dissimilar interconnect metals and of metal (Al or Cu) bonding pads. Packaging materials, especially molding compounds, contain several ionic components and can uptake certain level of moisture to provide electrolytic conditions to initiate corrosion processes. Probability of occurrence of corrosion in devices with high voltage applications is of special interest as many analog devices operates at higher voltages and with new CuWB packages there is a higher susceptibility of corrosive failures. This paper examines the impact of voltage on the mold compound compatibility with CuWB packages up to 65 V. Bias HAST reliability evaluation of various mold compounds at different voltages will be described. Corrosion of bonding pad (Al) and at the Al-Cu intermetallic compound interface was observed in the presence of certain ions present in mold compounds. Even though current mold compounds are “green”, the allowable amounts of halide ions can far exceed the ppm limit to prevent CuWB corrosive failures. Bromide ions are known to be very corrosive to metals. Br ions are still present in some mold compounds. The impact of the Br ion on CuWB reliability will be described. Additive impact of Br ions in presence of Cl will be examined. Another corrosive component present in many mold compounds, sulfur compounds, also can be corrosive under certain reliability stress conditions. Difference in corrosion behavior of Cu and Pd –Cu wirebonded packages due to sulfur compounds will be presented. Corrosive impact of high levels of Cl on the Al pad corrosion leading thick aluminum oxide growth and reliability failures will be discussed.

Role of Oxide Stress in the Initial Growth of Self-Organized Porous Aluminum Oxide

Porous anodic oxide films are formed by electrochemical oxidation of aluminum, titanium and other metals in solutions in which the oxide is soluble. Anodic films produced at particular process conditions contain spontaneously ordered hexagonal arrangements of submicron-diameter cylindrical pores. These self-organized porous anodic oxides have been studied extensively as templates for nanostructured devices and as functional materials.1-2 For example, much recent work has explored the use of TiO2 nanotubes in dye-sensitized solar cells, photocatalysis and sensors. Understanding of the oxide growth and metal dissolution processes that control the porous oxide morphology has enabled the improvement of these devices. Further advancements in the design and processing of anodic oxides will be possible by development in models based on mathematical descriptions of these processes.3,4Ultimately, models should be able to predict the bath compositions and anodizing voltages in which self-organized oxides are produced, and the scaling relations relating processing conditions to porous layer geometry. The experiments reported here focus on identifying the critical factors that govern pore initiation, so as to guide the development of anodizing models. Recent work has introduced pore formation mechanisms in which oxide stress plays an important role. Compressive stress is considered to be elevated near the pore base, where the current density is high. Stress-driven transport of oxide toward the pore walls is thought to assist pore formation. In the reported work, the role of oxide stress in the initiation in anodic aluminum oxide was investigated, for constant current anodizing of aluminum in phosphoric acid.5-8 Using phase-shifting curvature interferometry, through-thickness profiles of the in-plane stress in the oxide were measured by in-situ monitoring of stress change during both oxide growth, open circuit dissolution following anodizing. During barrier oxide growth prior to pore formation, compressive stress accumulated to several GPa within a 3-5 nm thick layer at the oxide surface, while stress in the interior of the oxide was relaxed. Oxide composition measurements revealed elevated concentrations of incorporated phosphate ions in the same region, indicating that stress is generated by field-driven anion incorporation. Pore initiation occurs when surface stress reaches a maximum, and is accompanied by oxide flow establishing the pore shape. It is suggested that pores are created by a flow instability caused by spatially nonuniform near-surface compressive stress caused by anion incorporation. Anion-induced stress can explain why the acid anion type determines the length scales of self-organized porous anodic films.1 ACKNOWLEDGMENT This work was supported by the National Science Foundation through NSF-CMMI-100748. REFERENCES 1. W. Lee, S.-J. Park, Chem. Rev. 114,7487 (2014). 2. K. Lee, A. Mazare, P. Schmuki, Chem. Rev. 114,9385 (2014). 3. V. P. Parkhutik, V. I. Shershulsky, J. Phys. D Appl. Phys., 25,1258 (1992). 4. J. E. Houser and K. R. Hebert, Nature Mater., 8, 415 (2009). 5. O. O. Capraz, P. Shrotriya, K. R. Hebert, J. Electrochem. Soc. 160, D501 (2013). 6. O. O. Capraz, P. Shrotriya, K. R. Hebert, J. Electrochem. Soc. 161, D256 (2014). 7. O. O. Capraz, P. Shrotriya, P. Skeldon, G. E. Thompson, K. R. Hebert, Electrochim. Acta, 159,16 (2015). 8. O. O. Capraz, P. Shrotriya, P. Skeldon, G. E. Thompson, K. R. Hebert, Electrochim. Acta, 167,404 (2015). Figure 1. Residual stress profiles in oxides formed to various voltages at 5 mA/cm2 in 0.4 M H3PO4.8 The range of voltages corresponds to the initial stage of barrier oxide growth prior to pore initiation, which occurs at about 100 V. Figure 1

Investigations of nanodimensional Al2O3 films deposited by ion-plasma sputtering onto porous silicon

The purpose of this study is the deposition of nanodimensional Al2O3 films on the surface of nanoporous silicon and also fundamental investigations of the structural, optical, and morphological properties of these materials. Analyzing the results obtained here, it is possible to state that ultrathin nanostructured Al2O3 films can be obtained in the form of threads oriented in one direction and located at a distance of 300–500 nm from each other using ion-plasma sputtering on a layer of porous silicon. Such a mechanism of aluminum-oxide growth is conditioned by the crystallographic orientation of the initial single-crystalline silicon wafer used to fabricate the porous layer. The results of optical spectroscopy show that the Al2O3/por-Si/Si(111) heterophase structure perfectly transmits electromagnetic radiation in the range of 190–900 nm. The maximum in the dispersion of the refractive index obtained for the Al2O3 film grown on por-Si coincides with the optical-absorption edge for aluminum oxide and is located in the region of ~5.60 eV. This fact is confirmed by the results of calculations of the optical-absorption spectrum of the Al2O3/por-Si/Si(lll) heterophase structure. The Al2O3 films formed on the heterophase-structure surface in the form of nanodimensional structured threads can serve as channels of optical conduction and can be rather efficiently introduced into conventional technologies, which are of great importance in microelectronics and optoelectronics.

Composition Effects on TBC/Silicate Melt (CMAS) Interaction Dynamics

Thermal barrier coatings (TBC) employed in the hot section of modern gas turbine engines are susceptible to degradation by molten deposits formed when siliceous debris is ingested into the engine [1]. These deposits, generically known as CMAS, may contain SiO2, CaO, MgO, AlO1.5, FeOx, and minor fractions of other oxides; the compositions can vary widely based on the geological source and engine service history [2]. Regardless of the specific deposit composition, the melt wicks into the open features in the TBC microstructure and solidifies under the imposed thermal gradient, leading to stiffening of the coating material and, upon cycling, elevated thermal stresses in the infiltrated region may produce cracking and/or spallation. Thermochemical attack may compound the damage, especially if the CMAS interacts with the thermally grown aluminum oxide that protects the alloy from oxidation. These degradation mechanisms can be mitigated, in part, with coatings designed to minimize the depth of melt penetration for a given exposure condition. In this context, the most effective coatings react readily with the deposit, converting the penetrating melt to a combination of stable crystalline phases that block the open porosity near the coating surface. The desired behavior is most clearly demonstrated by rare earth (RE) zirconate TBCs, notably Gd2Zr2O7, which react with CMAS to form a combination of fluorite and apatite (~Ca2Gd8Si6O26)[3]. Work with one model CMAS composition (33CaO-9MgO-13AlO1.5-45SiO2 in mol%, or Ca33Mg9Al13Si45) has shown that related RE zirconate and hafnate phases also form fluorite and apatite, among other reaction products. The efficacy of the crystallization reactions, however, varies with the RE cation radius, with the larger RE’s (i.e. La) acting as more potent apatite formers [4]. Efforts to design new TBC compositions would benefit from improved understanding of the role of the silicate deposit composition on the reaction processes. Elucidating these effects is the focus of this study. This work examined the effect of melt composition on the phase equilibria between the melts and candidate TBC materials such yttria stabilized zirconia (YSZ) and yttrium zirconate (Y4Zr3O12, YZO). The silicate melts were selected to span a relevant range of compositions while leveraging existing knowledge about the intrinsic melting and crystallization behaviors [5]. Initial experiments were performed in the simple, well-characterized CaO-AlO1.5-SiO2 (CAS) system with additional work in more complex silicate melts. Pre-reacted crystalline silicate powders were mixed with thermal barrier oxide (TBO) particles and annealed to identify the equilibrium crystalline phases and determine how the solubility limit of the TBO constituents in the melt changes with the melt composition. The results reveal that the melt composition plays a significant role in determining the crystallization product identity and volume fraction. Figure 1 highlights the effect of systematic changes in melt composition on the phase equilibria with YZO at 1300ºC. Figure 1(a,b) show melt compositions in the CAS system. Both systems form apatite while the primary ZrO2-bearing phase changes from zircon (ZrSiO4) to fluorite with a moderate shift in the SiO2 concentration. Meanwhile Ca33Mg9Al13Si45, the CMAS composition used in many past laboratory studies and shown in Figure 1(c), forms only fluorite. The latter behavior is related to the relatively high solubility of YO1.5 in both the melt and precipitated fluorite so the melt is not sufficiently saturated in YO1.5 to promote apatite crystallization. The findings shed new light on observations from ex-service TBCs that exhibit a range of deposit compositions and corresponding crystallization products and offer guidance for improved laboratory tests. The conclusions underscore the importance of considering a variety of factors related to melt chemistry when assessing the CMAS degradation of existing TBC materials and designing novel TBCs for improved CMAS resistance. Figure 1: Reaction between Y4Zr3O12 TBC material and selected silicate melt compositions (initially 25mol% YZO in the melt) produced a variety of crystallization products after 50h/1300ºC equilibration. Compositions (a) and (b) represent changes in the Ca:Si ratio but similar AlO1.5 concentration in the CAS system; (a) has sufficient SiO2 activity to form zircon (ZS) while (b) forms fluorite (F) as the only ZrO2-containing reaction product. Melt composition (c) has lower SiO2 activity and higher YO1.5 solubility; as such, no apatite (Ap) crystallization is observed even with the higher CaO concentration than (a) or (b). [1] M.P. Borom, C.A. Johnson, L.A. Peluso, Surf. Coat. Technol, 86 (1996) 116-126. [2] C.G. Levi, J.W. Hutchinson, M.-H. Vidal-Sétif, C.A. Johnson, MRS Bulletin, 37 (2012) 932-941. [3] S. Krämer, J. Yang, C.G. Levi, J.Am. Ceram. Soc., 91 (2008) 576-583. [4] D.L. Poerschke, C.G. Levi, J.Eur. Ceram. Soc., 35 (2015) 681-691. [5] E.M. Zaleski, C. Ensslen, C.G. Levi, Submitted (2014) Figure 1

Chemical Nature and Control of High-k Dielectric/III-V Interfaces

III-V semiconductor surfaces are notoriously difficult to control as their native oxides are not stable. For the growth of high-k dielectric, interface passivation layers have recently been incorporated into InP/high-k dielectric stacks using different approaches, including atomic layer deposition (ALD) to grow thin aluminum silicate layers and deposition of a buffer silicon layer prior to aluminum oxide growth. While beneficial effects have been observed on the interface electrical properties, little is known about the chemical composition and formation mechanisms of these interfacial layers. Futhermore, there is growing evidence that elemental diffusion from the substrate or its oxide may impair electrical properties. There is therefore a need for chemical characterization of surfaces and interfaces under typical processing conditions. Combined in-situ IR measurements and ab initio calculations of InP(100) surfaces reveal that a mild annealing (~300oC) typically needed for atomic layer deposition leads to marked chemical changes at the surface, with the formation of surface InPO4-species (P=O and P-OH species). The initial interaction of trimethylaluminum with this hydrophosphonated surface is characterized by the formation of P-O-Al and dative bonding between Al and the oxygen atom of neighboring P=O moiety, requiring several cycles to complete this interfacial layer. This chemical interface transformation and subsequent impact on the quality of an ALD-grown Al2O3 layer can be substantially altered by silicon deposition using trisilane exposure. Comparison of several silicon precursors [SiCl4, Si(OCH3)4 and Si3H6] by in-situ spectroscopy reveals that Si3H6 best reacts with the hydrophosphonate-terminated surface and reduces the native oxide by forming a SiOx layer that prevents interaction of TMA with the native oxide, leading to a denser Al2O3 layer. Deposition of a thin aluminum silicate barrier layer by ALD is also investigated, and Al from TMA found to play a key role in activating silicon precursors. However, TMA reaction with Si-modified surfaces leads to efficient methyl transfer to Si, a source of interfacial carbon contamination. Finally, mass transport is examined in HfO2/In0.53Ga0.47As stacks. Diffusion of indium through HfO2 is observed after post deposition annealing in N2 or forming gas environments by low energy ion scattering and X-ray photo electron spectroscopy, and found to be consistent with changes in interface layer thickness observed by transmission electron microscopy. Prior to post processing, elemental arsenic is detected in the form of arsenic oxide at the surface of ALD-grown HfO2 and is desorbed upon annealing at 350oC. Indium diffusion occurring upon annealing, resulting in a reduction of the interfacial layer thickness and a potential densification of HfO2, is confirmed by an increase in capacitance.

Role of Oxide Stress in the Initial Growth of Self-Organized Porous Aluminum Oxide

Self-organized porous anodic oxide films are produced when reactive metals such as aluminum and titanium are electrochemically oxidized in baths that dissolve the oxide. The role of oxide stress in the initiation of pores in anodic aluminum oxide was investigated, for constant current anodizing in phosphoric acid. Through-thickness profiles of the in-plane stress in the oxide were measured by in-situ monitoring of stress change during open circuit dissolution following anodizing. During barrier oxide growth prior to pore formation, compressive stress accumulated to several GPa within a 3–5nm thick layer at the oxide surface, while stress in the interior of the oxide was relaxed. Oxide composition measurements revealed elevated concentrations of incorporated phosphate ions in the same region, indicating that stress is generated by field-driven anion incorporation. Pores initiate when surface stress reaches a maximum, and is accompanied by oxide flow establishing the pore shape. It is suggested that pores are created by a flow instability caused by spatially nonuniform near-surface compressive stress.

Factors Controlling Stress Generation during the Initial Growth of Porous Anodic Aluminum Oxide

Anodic oxidation of reactive metals such as Al and Ti produces oxide films with self-organized arrangements of nanoscale pores. Stress-driven mass transport of oxide is considered to play an important role in pore formation and self-ordering. Using in situ stress monitoring during both anodizing and subsequent open-circuit oxide dissolution, distributions of in-plane residual stress were measured in anodic alumina films formed by galvanostatic anodizing in phosphoric acid. Anodizing produced significant stress both in the oxide and at the metal-oxide interface. For oxides grown to 20nm thickness, the oxide stress was tensile below 3mA/cm2 and compressive above this current density, while the interface stress exhibited the opposite dependence. Stress generation correlated with interfacial volume change due to reactions and transport processes: oxide or interface stress was compressive when interfacial volume was created, and vice versa. Compressive stress buildup in the oxide is apparently required for self-ordered pore formation by flow-assisted mechanisms. From the present results, a simple criterion was derived specifying the conditions for compressive stress and pore formation in terms of parameters governing film composition, ionic transport and interfacial reaction kinetics.

Dispersion fraction enhances cellular growth of carbon nanotube and aluminum oxide reinforced ultrahigh molecular weight polyethylene biocomposites.

Ultrahigh molecular weight polyethylene (UHMWPE) is widely used as bone-replacement material for articulating surfaces due to its excellent wear resistance and low coefficient of friction. But, the wear debris, generated during abrasion between mating surfaces, leads to aseptic loosening of implants. Thus, various reinforcing agents are generally utilized, which may alter the surface and biological properties of UHMWPE. In the current work, the cellular response of compression molded UHMWPE upon reinforcement of bioactive multiwalled carbon nanotubes (MWCNTs) and bioinert aluminum oxide (Al2O3) is investigated. The phase retention and stability were observed using X-ray diffraction, Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The reinforcement of MWCNTs and Al2O3 has shown to alter the wettability (from contact angle of ~88°±2° to ~118°±4°) and surface energy (from ~23.20 to ~17.75 mN/m) of composites with respect to UHMWPE, without eliciting any adverse effect on cytocompatibility for the L929 mouse fibroblast cell line. Interestingly, the cellular growth of the L929 mouse fibroblast cell line is observed to be dominated by the dispersion fraction of surface free energy (SFE). After 48 h of incubation period, a decrease in metabolic activity of MWCNT-Al2O3 reinforced composites is attributed to apatite formation that reduces the dispersion fraction of surface energy. The mineralized apatite during incubation was confirmed and quantified by energy dispersive spectroscopy and X-ray diffraction respectively. Thus, the dispersion fraction of surface free energy can be engineered to play an important role in achieving enhanced metabolic activity of the MWCNT-Al2O3 reinforced UHMWPE biopolymer composites.

Role of Interfacial Aluminum Silicate and Silicon as Barrier Layers for Atomic Layer Deposition of Al2O3 Films on Chemically Cleaned InP(100) Surfaces

Interface passivation layers have recently been incorporated into InP/high-k dielectric stacks using different approaches, including atomic layer deposition (ALD) to grow thin aluminum silicate layers and deposition of a buffer silicon layer prior to aluminum oxide growth. While beneficial effects have been observed on the interface electrical properties, little is known about the chemical composition and formation mechanisms of these interfacial layers. In this work, in situ infrared measurements are complemented by first-principles calculations to investigate (i) the ALD growth of aluminum silicate layers, using two different silicon precursors [silicon tetrachloride (SiCl4) and tetramethyl orthosilicate (Si(OCH3)4)], and (ii) the dependence on the specific order of the precursor sequence involving trimethylaluminum (TMA), water, and the Si precursors. Aluminum is found to foster silicate deposition by enhancing the reaction of silicon precursors (reaction with Al–OH). TMA readily transfers CH3 to surfa...

Growth of aluminum oxide nanorods using sandwich structures composed of Al and SiO x layers

In this work, we report a simple method for growing aluminum oxide nanorods based on low-temperature annealing of a sandwich structure composed of a thin Al film sandwiched between two silicon-rich oxide (SiOx: 0 < x < 2) layers produced by plasma-enhanced chemical vapor deposition. Aluminum oxide nanorods produced using a typical sandwich structure of SiO1.4(20 nm)/Al(2 nm)/SiO1.4(20 nm)/Si substrate exhibited the features of the mean diameter and length of the nanorods of about 0.3 and 1.7 μm, respectively. A possible growth mechanism is discussed on the basis of the vapor–solid process. The nanorod growth is proposed to be mediated by a vapor–solid mechanism in which the dominant vapor-phase source of reactants is Al2O/AlO produced by a phase separation of SiOx.

Ordered Growth of Anodic Aluminum Oxide in Galvanostatic and Galvanostatic-Potentiostatic Modes

The results are presented of obtaining anodic aluminum oxide with an ordered pore arrangement by employing two anodizing modes - galvanostatic mode and combined (galvanostatic + potentiostatic) mode, at high values of the current density and voltage. Use has been made of an oxalate electrolyte and a complex electrolyte comprising oxalic acid and phosphoric acid.

Simultaneous Ellipsometric and Potentiostatic Study of Aluminum Oxide Growth and Dissolution in Acetate Buffer

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