Native Si Oxide Research Articles

Growth of Pd4S, PdS and PdS2 films by controlled sulfurization of sputtered Pd on native oxide of Si

Thin films of different Pd–S phase, namely Pd4S, PdS and PdS2, have been reproducibly grown by the sulfurization of Pd films deposited on native oxide of (111) Si substrates by radio frequency sputtering method. In order to achieve controlled sulfurization, a three-stage sulfurization setup consisting of evaporation chamber, activation chamber and sulfurization chamber has been developed. The sulfurization of Pd films (kept at a constant temperature of 500°C) was carried out using sulfur vapors activated to different temperature between 550 and 700°C. The results of X-ray diffraction and X-ray photoelectron spectroscopy measurements show that formation of Pd4S, PdS and PdS2 phases takes place for the activation temperatures of 550, 600 and 700°C, respectively. The room temperature resistivity of Pd, Pd4S, PdS and PdS2 were found to be respectively 0.1, 15.9, 15,000 and 20,000μΩ cm. The temperature-dependent electrical resistivity measurements showed metallic conduction for Pd and Pd4S films. The Seebeck coefficient measured at 300K for these Pd–S phases showed their n-type conducting behavior.

The surface morphology of thin Au films deposited on Si(001) substrates by sputter deposition

Thin (100nm) gold films were deposited on the native oxide of Si(001) substrates by direct current magnetron sputtering. The effects of the deposition rate, the target/substrate distance, the substrate orientation, substrate bias, and substrate temperature on the surface morphology of the gold film have been studied using atomic force microscopy. It was observed that the deposition of Au on Si(001) is characterized, in most cases, by hemi-spherical particles distributed uniformly on the surface. Decreasing the target/substrate distance caused both the average particle diameter and the height to increase. However, at a target/substrate distance of 5cm using a deposition rate of 0.1Å/s, samples with different morphologies were produced characterized by the coalescence of the surface Au particles. Increasing the relative angle from 0° to 90° between the substrate and the sputtering target caused the average particle diameter to decrease by approximately 8.7% and the average particle height to increase by approximately 52.3%. Applying a high negative voltage to the substrate during the deposition caused a small decrease of approximately 10.2% in the average particle size and a change of 26.2% to the average particle height. Lowering the substrate temperature from 12 to −11°C during the deposition process caused a decrease of 21.6% in the average grain size and an increase of 44.7% in the average grain height. By adjusting the above parameters it was possible to obtain samples with an average particle size ranging from 25.8 to 180nm with root-mean-square roughness values ranging from 0.8 to 21nm. The results of this work provide an understanding on how to produce a wide range of surface morphologies of thin Au films on Si(001+native oxide) for applications such as cantilever sensing and for producing bio-functionalized tips for atomic-force microscopy.

Mechanism of selective area growth of InP on Si(001) substrates using SiO2 mask by gas-source molecular beam epitaxy

X-ray photoemission spectroscopy (XPS) and reflection high-energy electron diffraction (RHEED) have been used to investigate the initial stages of InP growth on H-terminated Si and native Si oxide surfaces. By annealing at 800°C, the H-terminated Si surface exhibits a (2×1) RHEED pattern while the native oxide surface just shows a halo RHEED pattern. After exposing them to P2 flux, the Si(2×1) clean surface exhibits a (2×1) RHEED pattern while the native Si oxide layer always shows the halo RHEED pattern. XPS measurement reveals that while P atoms adsorb on the Si(2×1) surface, the adsorption of P atoms does not take place on the native Si oxide surfaces. In consequence of the difference in the adsorption of P atoms between the clean Si and Si oxide surfaces, InP does not grow on the Si oxides at temperatures above 450°C while InP grows on the clean Si substrates. Based on the findings, we will discuss the mechanism of the selective area growth of InP on patterned Si substrates with Si oxide mask in terms of desorption of In and P.

I-V Characteristics of PtxCo1−x (x = 0.2, 0.5, and 0.7) Thin Films

Three different chemical ratios of PtxCo1−x thin films were grown on p‐type native oxide Si (100) by Magneto Sputtering System with cosputtering technique at 350°C temperature to investigate electrical prosperities. X‐ray photoelectron spectroscopy analysis technique was used to specify chemical ratios of these films. The current‐voltage (I-V) measurements of metal‐semiconductor (MS) Schottky diodes were carried out at room temperature. From the I-V analysis of the samples, ideality factor (n), barrier height (ϕ), and contact resistance values were determined by using thermionic emission (TE) theory. Some important parameters such as barrier height, ideality factor, and serial resistance were calculated from the I-V characteristics based on thermionic emission mechanism. The ideality factors of the samples were not much greater than unity, and the serial resistances of the samples were also very low.

Thermal chemistry of Mn2(CO)10 during deposition of thin manganese films on silicon oxide and on copper surfaces

The surface chemistry of dimanganese decacarbonyl on the native oxide of Si(100) wafers was characterized with the aid of x-ray photoelectron spectroscopy. Initial experiments in a small stainless-steel reactor identified a narrow range of temperatures, between approximately 445 and 465 K, in which the deposition of manganese could be achieved in a self-limiting fashion, as is desirable for atomic layer deposition. Deposition at higher temperatures leads to multilayer growth, but the extent of this Mn deposition reverses at even higher temperatures (about 625 K), and also ifhydrogen is added to the reaction mixture. Extensive decarbonylation takes place below room temperature, but limited C–O bond dissociation and carbon deposition are still seen after high exposures at 625 K. The films deposited at low (∼450 K) temperatures are mostly in the form of MnO, but at 625 K that converts to a manganese silicate, and upon higher doses a manganese silicide forms at the SiO2/Si(100) interface as well. No metallic manganese could be deposited with this precursor on either silicon dioxide or copper surfaces.

Surface and Interface Modifications of Aluminum Thin Films on Silica Glass Substrate Using 157 nm F2 Laser for Selective Metallization

A 157 nm F2 laser induced strong oxidation of an Al thin film surface, allowing it to show chemical resistance to KOH aqueous solution used for selective metallization on silica glass or native oxide Si substrate. The strong oxidation reactions on the surface and in the depth direction were confirmed by X-ray photoelectron spectroscopy. A high adhesion strength of 663 kgf/cm2 between Al and silica glass was also obtained for the F2-laser-irradiated sample, compared with that of the nonirradiated sample, 16 kgf/cm2. The suitable thickness of Al thin films for the F2-laser-irradiated surface and interface modifications was examined to be approximately 20 nm. The mechanism of the F2-laser-induced interface modification was discussed regarding the dependence of substrate material and the analyses of the chemical bonding state of silica glass underneath Al thin films.

The Charge of Solid–Liquid Interfaces Measured by X‐Ray Standing Waves and Streaming Current

Measurements of ion distributions at a charged solid-liquid interface using X-ray standing waves (XSW) are presented. High energy synchrotron radiation (17.48 keV) is used to produce an XSW pattern inside a thin water film on a silicon wafer. The liquid phase is an aqueous solution containing Br and Rb ions. The surface charge is adjusted by titration. Measurements are performed over a pH range from 2.2-9, using the native Si oxide layer and functional (amine) groups as surface charge. The Debye length, indicating the extension of the diffuse layer, could be measured with values varying between 1-4 nm. For functionalized wafers, the pH dependent change from attraction to repulsion of an ion species could be detected, indicating the isoelectric point. In combination with the measurement of the streaming current, the surface charge of the sample could be quantified.

Metal‐Insulator Transition‐Induced Adsorption‐Resistant Behavior of Small Au Nanoparticles

Smaller nonmetallic nanoparticles are more inert: Metal-insulator transition of Au nanoparticles on silica is closely related to the metal-support charge transfer, which has a strong influence on chemisorption reactivity of Au. Smaller nonmetallic Au nanoparticles are more resistant towards butanethiol chemisorption [picture and graph: see text].The size-dependent variation of the electronic and chemical properties of Au nanoparticles formed on native Si oxide surfaces is investigated using synchrotron radiation photoemission spectroscopy and ultraviolet photoelectron spectroscopy. The adsorption reactivity toward butanethiol adsorption initially increases with decreasing particle size; however, the reactivity of Au nanoparticles becomes gradually lower below a size of approximately 0.8 nm. The photoemission spectral changes suggest a metal-insulator transition, accompanied by negative charge transfer from the nanoparticles to the support, which may be the source of the chemical inertness of small Au nanoparticles.

Polarity Effect near the Surface and Interface of Thin Supported Polymer Films: X-ray Reflectivity Study

Four homopolymer films (poly(methyl methacrylate) (PMMA), poly(4-vinylpyridine) (P4VP), polystyrene (PS), and poly(alpha-methyl styrene) (PAMS)) with different interactions with native Si oxide on Si wafers and three random copolymer films (PS-ran-PMMA) with different mole fractions were investigated with the X-ray reflectivity (XRR) method. The electron density profile of each film was obtained by fitting the results of the XRR measurements. A new data correction technique that uses the vertical real beam profile and a fitting method that uses the distorted wave Born approximation were combined to overcome the sensitivity limitations of XRR analysis. The results show that the chemical structures of polymer pendant groups and the interactions between the polymer films and the native Si oxide layer are strongly correlated with the density profiles of the films near the surfaces and interfaces. Two general types of electron density profiles were found that are characterized by the polarity of the pendant group of the polymer. The reproducibility and credibility of the fitting technique were also thoroughly tested.

Study on Solid-Electrolyte-Interphase of Si and C-Coated Si Electrodes in Lithium Cells

The solid-electrolyte-interphase (SEI) layers formed on the electrodes of pristine Si and carbon-coated Si (C-Si) particles in Li cells have been studied. The counter electrode is Li, and the electrolyte is in the mixture of ethylene carbonate and ethyl methyl carbonate. Other than those, such as Li carbonates and fluoride, already known to the SEI of graphite electrode, there were detected significant amounts of SEI species unique to each of the Si electrodes. On the pristine Si electrode, there was concurrence of abundance of C and Si fluorides after long cycles. Coating the Si particles with a graphitized carbon layer has significant effects on the SEI formation. It helps to keep the Si particles remaining integrated after cycling, resulting in a smooth superficial SEI layer. It removes the native oxide layer not only to reduce humidity contamination but also to significantly change the SEI compositions. The SEI of the C–Si electrode shows the absence of Si and C fluorides but the presence of siloxane species. Reaction mechanisms leading to the formation of the fluoride and siloxane species have been proposed, elucidating an important role played by the native Si oxide layer.

Degenerate Si as an Electrode Material for Electrochemical Biosensors

The use of degenerate (heavily doped) Si as an electrode material for electrochemical biosensors is demonstrated by a series of voltammetry and impedance studies. Cyclic voltammetry in solutions of and exhibits reversible electrochemistry without illumination, which to the best of the authors’ knowledge has not been previously reported for Si electrodes in an aqueous environment. The presence of prevents formation of the Si native oxide, while the use of a degenerate Si substrate makes its electrochemistry more like that of a metal. In addition, impedance detection of peanut protein Ara h 1 is demonstrated on a degenerate Si electrode following immobilization of the monoclonal mouse antibody to this protein. The variation in charge-transfer resistance with protein concentration is employed to estimate the dissociation constant of the surface-immobilized antibody-antigen complex as . The advantages of degenerate Si relative to n- and p-type Si include the lack of photoeffects, a simpler equivalent circuit, easier electrical connection to the working electrode, and knowledge that the applied potential applied is dropped within the electrical double layer, not within the semiconductor space-charge layer. Most important, degenerate Si electrodes are easily incorporated into Si-based semiconductor devices.

Formation of Aromatic Siloxane Self-Assembled Monolayers

We describe reproducible protocols for the chemisorption of self-assembled monolayers (SAMs), useful as imaging layers for nanolithography applications, from p-chloromethylphenyltrichlorosilane (CMPS) and 1-(dimethylchlorosilyl)-2-(p,m-chloromethylphenyl)ethane on native oxide Si wafers. Film chemisorption was monitored and characterized using water contact angle, X-ray photoelectron spectroscopy, and ellipsometry measurements. Atomic force microscopy was used to monitor the onset of multilayer deposition for CMPS films, ultimately allowing film macroscopic properties to be correlated with their surface coverage and nanoscale morphologies. Although our results indicate the deposition of moderate coverage, disordered SAMs under our conditions, their quality is sufficient for the fabrication of sub-100-nm-resolution metal features. The significance of our observations on the design of future imaging layers capable of molecular scale resolution in nanolithography applications is briefly discussed.

Study of graded Ni-Ti shape memory alloy film growth on Si(100) substrate

In-situ X-ray diffraction (XRD) was employed to study the effect of the deliberate change of the Ti/Ni ratio during the deposition of Ni-Ti films. Thus, graded films were deposited exhibiting distinctive composition and crystalline structure along the growth direction. The as-sputtered films were ex-situ characterized by Auger electron spectroscopy (AES), cross-sectional transmission electron microscopy (XTEM), and electrical resistivity (ER) measurements (during thermal cycling). In this paper results are presented concerning a film (thickness of ≈ 420 nm) with a Ti-rich composition in the central part (ranging from 50 to ≈60 at. %) and near-equiatomic composition in the extremities, following four distinct deposition periods (different Ti target powers). During the initial deposition step (near-equiatomic composition) the Ni-Ti B2 phase starts by stacking onto (h00) planes on the naturally oxidized Si(100) substrate due to the presence of the native Si oxide (2–3 nm). The increase of the power of the Ti target in the second and third steps induced the precipitation of Ti2Ni. When stopping the Ti co-sputtering, Ti2Ni dissolves and, thus, plays the role of a Ti reservoir for the formation of B2 phase now preferentially stacking onto (110) with the system approaching again the equiatomic composition. The ex-situ study of the morphology of the interface has shown the presence of NiSi2 silicides (A-NiSi2 and B-NiSi2), Ti4Ni4Si7, Ti2Ni and a non-identified phase constituted by Ni, Ti and Si, most likely amorphous. During thermal cycling, ER measurements revealed phase transitions associated with the B2, R-phase and B19′ phases. These type of studies allow the identification of intermediate states during deposition and annealing, and the correlation with the final structure of the film, being useful for the optimisation of the deposition parameters in order to fabricate films with a two-way reversible actuation.

Deposition of yttrium oxide thin films in supercritical carbon dioxide

A synthetic avenue for the formation of yttrium oxide thin films on Si native oxide surfaces is demonstrated by the reaction of Tris(2,2,6,6-tetramethyl-3,5-heptanedionato) yttrium(III) with inorganic (H 2O 2) and organic (tert-butyl and di-tert-amyl) peroxides in supercritical carbon dioxide. The reactions are carried out in a hot wall reactor at temperatures below 130 °C and pressures ranging from 13.10 to 22.75 MPa. Spectroscopic Ellipsometry verifies thin film formation and X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy measurements confirm formation of yttrium oxide films and the presence of carbonate and hydroxide species which are removed after high temperature anneals.

Spectroellipsometric analysis of CHF3 plasma-polymerized fluorocarbon films

Optical and morphological properties of fluorocarbon films (CFx) deposited on Si substrates from CHF3 in a reactive ion etcher were studied by spectroscopic ellipsometry (SE). The study has led for 0.3–1.5μm thick films to a thickness-independent, roughnessless, apparently nongraded two-layer model that requires the Cauchy dispersion and the Gaussian absorption for the film refractive index and extinction coefficient, and to an interface mixture of CFx, Si, and voids. The Si native oxide removal was ascertained from films formed on SiO2-sputtered Si substrate. The sample SE results were further verified by x-ray diffraction, atomic force microscopy, Fourier transform infrared, x-ray photoelectron and Auger electron spectroscopies, and capacitance studies. The film microstructure may thus be considered isotropic and homogeneous resulting from a random addition of CFx fragments including cross-links along the film depth. The films have low-dielectric constant(k≈2.2) quality index of 1.38(615nm) and are noticeably absorbent in UV while exhibiting strong transparency in visible. These films growing at a rate of 0.033μm∕min have 2%–3% thickness nonuniformity. The SE model decision making steps are described and the degree of confidence on the SE results are discussed with the support of literature results and those from and the above studies.

Formation of body-centered-cubic tantalum via sputtering on low-κ dielectrics at low temperatures

Sputtered Ta films (60 nm) were deposited at room temperature onto selected substrates, including silicon, SiO2, porous methyl silsesquioxane (porous MSQ), parylene-N (Pa-N) caulked porous MSQ, benzocyclobutene (BCB), and SiLK layers. It was observed that the Ta structure after deposition mainly depends on the underlayer surface chemistry. β-Ta with a resistivity of ∼130–160μΩcm and an average grain size of ∼20nm was observed after sputter depositing 60-nm-thick Ta films onto the oxygen-rich materials of native oxide of Si, SiO2, and porous MSQ. α-Ta with a much lower resistivity (∼35μΩcm) and an average grain size of ∼16nm was observed after sputter deposition of Ta onto a substrate with a 4-nm-thick hydrocarbon Pa-N film on porous MSQ. α-Ta was also formed when sputter depositing on the hydrocarbon BCB and SiLK low-κ dielectrics. The lattice constants of the α-Ta films were slightly larger (3.310–3.351 Å) than those of the bulk Ta (3.305 Å).

Molecular Orientation and Film Morphology of Pentacene on Native Silicon Oxide Surface

The growth morphology and mechanism of pentacene films on native Si oxide surface have been studied by using high-resolution electron energy loss spectroscopy (HREELS), X-ray diffraction (XRD), and atomic force microscopy (AFM). Despite the good agreement between our own and the reported XRD results, the previous XRD interpretation that the pentacene molecules are tilt-standing on the substrate cannot explain our HREELS data. The HREELS results show that a substantial portion of the first two layers of pentacene molecules are tilted-standing or randomly oriented, whereas the upper-layer molecules are mostly lying flat to the substrate. AFM reveals that the first two layers of molecules form a flat and smooth surface, but the upper layers show a rough terrace structure with a mean-square roughness equal to the average thickness (without counting the first two layers). This relationship is explained by a theoretical model which assumes the pentacene molecules to remain on a particular molecule layer after arrival. The observed film growth morphology may have significant implication on the performance of electronic devices based on pentacene thin films. A plausible explanation was proposed for the discrepancy between the HREELS-indicated and the XRD-derived molecular orientations.

Critical height and growth mode in epitaxial copper nanowire arrays fabricated using glancing angle deposition

The growth and resulting crystallography of Cu nanowire arrays fabricated using glancing angle deposition are studied. On native oxide Si(100), the nanowires exhibited a strong (110) texture for a deposition angle θ=75° with rotational symmetry of the low energy Cu[111] about the long axis. On hydrogen-terminated Si(110), the wires are epitaxial with the substrate. The critical height for epitaxial growth is maximal at θ=35°, and decreases rapidly with increasing deposition angle. Based on the growth mechanisms in glancing-angle-deposited materials, the theory of growth mode in epitaxial thin films, and the observations about texture formation in epitaxial and nonepitaxial Cu nanowires; we discuss the observed growth modes in epitaxial nanowire arrays.

Influence of thickness of Hf buffer layer on the interfacial structures of sputtered HfO 2 on SiO 2/Si

The influence of thickness of Hf–metal buffer layer on the interfacial diffusion and reaction was investigated using in situ X-ray photoelectron spectroscopy, scanning Auger microscope and grazing incident X-ray reflectivity. Hf–metal firstly reacted with native Si oxide forming Hf silicates, and all Si–O was further reduced to be Si 0 after 1 nm Hf–metal deposition. The Hf–metal and Hf-suboxide in Hf(1 nm)/SiO 2/Si structure were further oxidized to be Hf 4+ during HfO 2 sputtering deposition and post-deposition annealing. Si diffused out and reacted with HfO 2 during annealing. The Hf(1 nm) buffer layer exhibited a better performance than the Hf(0.3 nm) buffer layer in suppressing the diffusion of Si and the reaction between diffused Si and HfO 2.

Texture orientation of glancing angle deposited copper nanowire arrays

Self-assembled copper nanowires were deposited on native oxide Si(100) substrates using glancing angle deposition with and without substrate rotation. Wire morphology, texture and crystallographic orientation are strongly dependent on the deposition parameters. A method for determining the preferred crystal orientation is described. This orientation is found to be different from what is expected from the geometric orientation of the wires. For wires deposited without substrate rotation, the face-centered-cubic (fcc)(111) crystal orientation, which corresponds to the close-packed, low surface energy (111) plane of copper, lies between the long axis of the wire and that normal to the substrate. X-ray diffraction data show that the wires exhibit bundling behavior perpendicular to the plane of incidence. For samples deposited with azimuthal rotation of the substrate, the fcc(111) directions in the wires are evenly distributed in a cone around the long axis of the wires, which point normal to the substrate. When the substrate is rotated during deposition at an angle of 75°, the wires exhibit a strong fcc(220) texture. These observations show that wires deposited with substrate rotation are highly textured and have random orientations in the plane of the substrate.