Thermal Oxide Layer Research Articles

Silicon nanowire growth on Si and SiO2 substrates by rf magnetron sputtering in Ar/H2

Silicon nanowires (SiNWs) have been grown on Si(100) substrates with and without a thermal oxide layer by rf magnetron sputtering of Si in Ar/H2. In the experiments, thin Au layers were employed as catalysts, resulting in a significant and substantial growth of randomly oriented, polycrystalline SiNWs, typically 20 µm long and 350 nm in diameter after 60 min of growth on both Si and SiO2 substrates at 700 °C. These indicate the possibility of providing an alternative method of SiNW growth that does not require toxic feed gases and high-temperature tube furnaces, and hence is suitable for growth on large-diameter substrates in industry.

Formation of stable charge regions in an array of germanium nanocrystallites inside SiO2 using electrostatic force microscopy

The objects of investigations are germanium nanocrystallites formed inside a SiO2 layer by ion implantation followed by high-temperature annealing. Germanium nanocrystallites inside a thin (30 nm) layer of thermal SiO2 oxide are charged by means of scanning probe microscopy, and the resulting charged zones are visualized and analyzed. It is shown that stable charge regions up to 30 nm in diameter that consist of several charged germanium nanocrystallites can be formed under the probe of an atomic-force microscope. It turns out that the ability of the germanium nanocrystallites to keep the induced charge is extremely sensitive to the intercrystallite distance and the presence of defect centers in the SiO2 layer. This is explained by the fact that the charge escapes from the germanium nanocrystallites by tunneling either between adjacent crystallites or through defect centers in the SiO2.

Electrochemical Reduction of CO2 Using Bi-Layer Cu2O Electrodes

Unmodified Cu foil electrodes are prepared by etching briefly in 1.0M HCl, followed by ultrasonic cleaning in sequential baths of 2-propanol, acetone and de-ionized H2O. The single-layer Cu2O electrode is prepared by electrodepositing a Cu2O layer onto Cu foil using a mixed CuSO4/ lactic acid bath, adjusted to pH = 9 using NaOH and held at 65̊C for a deposition time of 30 minutes. The bi-layer electrode is prepared by first thermally oxidizing a Cu foil in air at 400̊C for 4 hours, followed by a subsequent 10 minute electrodeposition step. The CO2 reduction measurements are performed using a two compartment cell with a Nafion membrane separator, a Pt wire counterelectrode, and Ag/AgCl reference electrode. The working electrolyte is aqueous 0.5M KHCO3 that is bubbled continuously with CO2. Product concentrations are determined using gas chromatography. Gas phase products (H2, CO, CH4, and C2H4) are sampled directly from the CO2 purge gas leaving the reactor. Liquid products (mainly CH2H5OH) are measured by taking syringe samples of the electrolyte at 15 minute intervals. X-ray diffraction measurements confirm that the layers grown either thermally or by electrodeposition consist mainly of Cu2O. After being exposed to CO2 electroreduction conditions, the XRD peaks for Cu2O on the single-layer electrode appear to be completely removed, suggesting the electrode may have become fully reduced to Cu metal. In contrast, the bi-layer electrode still exhibits XRD peaks for Cu2O and CuO following CO2electroreduction, suggesting the inclusion of the thermal oxide layer has increased the electrochemical stability of the bi-layer electrode. SEM images of the initially deposited single-layer electrode show cubic morphology characteristic of Cu2O crystallites with a relatively large particle dimension (ca. 1μm). Following CO2 electroreduction, the primary morphology remains intact, although many of original crystallites have broken apart, and the particle surfaces show a modest degree of roughening. For the bi-layer electrode, the initial thermal oxide layer shows a more random crystallite morphology with a some what smaller length scale (500 nm). The subsequent electrodeposited Cu2O overlayer reflects the same smaller length scale but with a more sharply define cubic habit. Following CO2electroreduction, the surface of the bilayer sample undergoes restructuring in a manner similar to the single-layer electrode, but with a more sharply defined morphology (i.e., well-resolved cubes with length scale about 100 nm). The CO2 electroreduction measurements are performed at −1.745 VSCE. As expected, the control experiment using an unmodified Cu foil produces CO and CH4 as the greatest CO2 reduction products (formation rates of 8.3 μmole CO /cm2/hr and 2.8 μmole CH4/cm2/hr, respectively). In addition, the C2H4 formation rate was much lower (0.3 μmole C2H4/cm2/hr), such that the C2H4/CH4 ratio was only 0.1 . By comparison, the single-layer electrode produces CO and C2H4 as the largest CO2 reduction products (formation rates of 4.3 μmole CO/cm2/hr and 2.5 μmole C2H4/cm2/hr, respectively). The CH4 formation rate is reduced to 0.06 μmole CH4/cm2/hr, so that the C2H4/CH4 ratio is reversed to a value of 42. This effect becomes even more pronounced for the bilayer electrode. The CO and C2H4 formation rates increase to 15.6 μmole CO/cm2/hr and 9.1 μmole C2H4/cm2/hr, while the CH4 formation rate decreases slightly, to 0.04 μmole CH4/cm2/hr. The increased CO and C2H4 formation rates may be partially the result of higher electrode surface area, as suggested by a higher current density observed with the bilayer electrode. However, the C2H4/CH4ratio has clearly increased to over 200, indicating that the bilayer electrode provides a higher selectivity for carbon-carbon coupling than for single carbon species hydrogenation. Our present results support a model in which the Cu2O particles are converted to metallic Cu during CO2 reduction. The morphological evolution of the starting Cu2O nanoparticles during this reduction leads to the formation of more highly dispersed Cu clusters on the surface of the converted particles. The dispersed Cu clusters are expected to contain a higher concentration of more open crystal faces and lower co-ordination surface atoms, which leads to the observation of a higher C2H4/CH4ratio, relative to low-index planar Cu surfaces. Additional work is underway to further characterize these dispersed Cu clusters, and to explore methods to improve their stability during prolonged electrochemical operation. This material is based upon work supported as part of the Center for Atomic Level Catalyst Design, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001058.

Fabrication and properties of thermal sprayed stainless steel-based nanocomposite coatings

Stainless steel-based feedstock powders with nano-iron oxide particles (from direct addition and thermal oxidation) were prepared by ball milling and oxidation process, respectively. It was found that iron oxide nanoparticles were on the surface of stainless steel powders in the form of particulates (deliberate addition of magnetite and hematite) or nanoplatelets (thermal oxidation). The powders were thermal sprayed by low velocity oxy-fuel (LVOF) technique. The stainless steel-based coatings had the typical thermal spray microstructure, including splats, oxide layers, unmelted particles and pores. There were no nanoparticles seen in the microstructure due to complete oxide melting at the flame spray temperature and iron oxide in all coatings was in the form of hematite. Considering physical properties, porosity was decreased when there were second phase nanoparticles and thickness was very similar except the coating with hematite addition. Hardness of the coatings was slightly increased when incorporating with iron oxide nanoparticles. Sliding wear rate and friction coefficient of the nanocomposite coatings were lower than that of the pure stainless steel. Iron oxide nanoparticles could improve hardness and sliding wear resistance in the stainless steel-based coatings due to an increasing amount of iron oxide in the coatings.

Reduction of Surface Roughness in Epitaxially Grown Germanium by Controlled Thermal Oxidation

Obtaining a smooth substrate with surface roughness of 2 A is essential for semiconductor device fabrication. In this letter, we characterize the effect of thermal oxidation of epitaxially grown Ge on its surface roughness. First, the effect of oxidation on root-mean-square roughness is investigated for epi-Ge surface that is bombarded with phosphorous ions. Next, the effect of oxidation is investigated with the presence of low thermal oxide layer on the epi-Ge. Finally, examination of the effect of temperature on surface roughness for capped epi-Ge is conducted. By making the Ge oxidation diffusion limited, surface roughness can be reduced to $\sim 2$ A.

Surface Structure of Hydrogenated Diamond-like Carbon: Origin of Run-In Behavior Prior to Superlubricious Interfacial Shear

The oxidized layers at the surface of hydrogenated diamond-like carbon (H-DLC) were studied with X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure, and Raman spectroscopy. The structure of these layers was correlated with the friction and wear behavior observed on H-DLC. H-DLC is well-known for its ultralow friction in inert environments, but the steady superlubricious state is always preceded by a run-in period with a high friction. It was hypothesized that the run-in period is related to the surface oxide layer formed naturally upon exposure of the sample to air. To test this hypothesis, thermal oxide layers were grown, and their structures were analyzed and compared with the native oxide layer on a pristine sample. It was found that the Raman spectra of the surface oxide layers of H-DLC have higher D/G band ratio than the bulk, indicating a larger amount of aromatic clusters compared to the bulk film. Thick oxide layers grown at 300 °C showed a run-in friction behavior that resembled the friction of graphite. The run-in periods were found to become longer when the thickness of the oxide layers increased, indicating that the run-in behavior of H-DLC is attributed to the removal of the surface oxide layers.

ハイブリッド接合のための表面活性化法を用いた常温によるCu/Cu接合及びSiO<sub>2</sub>/SiO<sub>2</sub>接合

It has been said that the end of Moore’s law will be reached in 10 to 20 years. Three dimensional integration technology is expected to be a possible solution in the post-Moore era. The bonding of the metal electrode and insulator hybrid interfaces is one of key technique in three dimensional technology. The hybrid bonding technique is highly challenging issue. Surface activated bonding (SAB), which is a bonding method carried out at room or low temperatures, is expected to solve various problems which caused by heating process. Metal materials such as Cu or Al are easy to directly bond by SAB method at room temperature, but insulator materials such as SiO2 or SiN is very difficult. First, we investigated the bonding interface of Cu/Cu by transmission electron microscopy (TEM) observations. No intermediate layers or voids were visible at the bonding interface. The bonded specimen fractured not at the interface of the bonded Cu/Cu, but at the interface between the thermal oxide layer and Ti film by tensile test. The current-voltage characteristic of the bonding interface was linear. Secondly, we proposed a new bonding technique for bonding of SiO2/SiO2 using Si ultra-thin films by applying the SAB method. The amorphous Si layer with the thickness of about 7 nm was observed at the bonding interface by TEM observation. The bonded specimen fractured at the glue interface and not the bonded interface by tensile test. The bonding strength is estimated to be higher than the adhesive glue for tensile test. We have shown that the SAB method at room temperature is a bonding technique that can fulfill requirements for hybrid bonding, which serves as both mechanical bonding and electrical connection, in 3D integration technology.

Investigation of the Copper Gettering Mechanism of Oxide Precipitates in Silicon

One of the reasons why the principal gettering mechanism of copper at oxide precipitates is not yet clarified is that it was not possible to identify the presence and measure the copper concentration in the vicinity of oxide precipitates. To overcome the problem we used a 14.5 nm thick thermal oxide layer as a model system for an oxide precipitate to localize the place where the copper is collected. We also analyzed a plate-like oxide precipitate by EDX and EELS and compared the results with the analysis carried out on the oxide layer. It is demonstrated that both the interface between the oxide precipitate being SiO2 and the silicon matrix and the interface between the thermal oxide and silicon consist of a 2–3 nm thick SiO layer. As the results of these experiments also show that copper segregates at the SiO interface layer of the thermal oxide it is concluded that gettering of copper by oxide precipitates is based on segregation of copper to the SiO interface layer.

The influence of interface morphology on the stress distribution in double-ceramic-layer thermal barrier coatings

The influences of the interface morphologies upon the stress distribution in the double-ceramic-layer thermal barrier coating (DCL-TBC) have been mainly studied in our present article using the finite element method. The two important interfaces in the DCL-TBC, which are interface #1 (the interface between two ceramic layers) and interface #2 (the interface between the inside ceramic layer and the bond coat (BC)), are modeled as a sinusoidal wave with considering different values of the amplitude.Results show that the interface #1 has important influence upon the stress of the top ceramic layer. Especially, in the edge of the model, the rougher interface can relief the high stress level of the top ceramic layer caused by the edge stress concentration. Similarly, the influence of the interface #2 upon the stress of different parts of the thermal growth oxide layer has also been studied.

Determination of Residual Stress Fields in a Thermally Grown Oxide under Thermal Cycling Loadings, Using XRD and Raman Spectroscopy — Correlations with Microstructural States

The presence of residual stresses in thermal oxide layers has been recognized for a long time. In the present work, the mechanical fields for chromia oxide are determined either by XRD or Raman spectroscopy. In addition, the microstructure of the chromia films is investigated ant its influence on the evolution of the stress release processes is analyzed.

Determination of Stress Fields and Identification of Thermomechanical Parameters in a Thermally Grown Oxide under Thermal Cycling Loadings, Using Advanced Models

The presence of residual stresses in thermal oxide layers has been recognized for a long time. In the present work, the mechanical fields for chromium oxide are investigated. An extended model is established to take into account the effects of temperature and thermal cycling for the calculation of oxide stress. Numerical results are given in order to predict the influence of different parameters, especially the dependence of some material parameters with temperature. This enables to make comparison with experimental results.

Fabrication and characterization of gridded Pt/SiO2/Si MOS structure for hydrogen and hydrogen sulphide sensing

A gridded gate Pt/SiO2/Si MOS capacitor has been fabricated for detection of Hydrogen (H2) and Hydrogen Sulphide (H2S) gases. The MOS device was fabricated on P-type Si <100> (1–6 Ω cm) wafer with thermal oxide layer of thickness about 100 Å, whereas, Platinum (Pt) gate of ∼350 Å was deposited by thermal evaporation technique. The C–V (capacitance vs voltage) and G–V (conductance vs voltage) measurements have been performed for the evaluation of gas sensing behavior of fabricated MOS capacitor structure in H2 (250–4000 ppm) and H2S (1000–6000 ppm) gases at both room and 120 °C temperatures, in a closed chamber in air atmosphere. It has been observed that the value of capacitance decreases with increase in gas concentration. The fabricated MOS capacitor sensor has shown better sensitivity towards H2 (88.6%) at room temperature (∼25 °C) as compared to (∼45%) at 120 °C. Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) studies have revealed the porous nature of the deposited metal film. The side wall diffusion, spillover of Hydrogen into oxide layer, increase in fixed oxide charge density, increase in surface area caused by gridded structure, the formation of dipole layer and change in interface state density on gas exposure, may be the mechanisms of gas sensing for improved sensitivity of the fabricated MOS device.

Novel double-ceramic-layer (La0.8Eu0.2)2Zr2O7/YSZ thermal barrier coatings deposited by plasma spraying

Pyrochlore-type (La0.8Eu0.2)2Zr2O7 feedstocks prepared by spray drying have been used to produce ceramic thermal barrier coatings. Double-ceramic-layer thermal barrier coatings with a first layer of 8wt% yttria-stabilized zirconia (YSZ) and a top layer of (La0.8Eu0.2)2Zr2O7 were deposited by plasma spraying. Plasma sprayed (La0.8Eu0.2)2Zr2O7 coatings are composed of a defect fluorite-type phase and a t-ZrO2 phase. However, after thermal shock tests at 1250°C for 32 cycles, (La0.8Eu0.2)2Zr2O7 coatings exhibit a pyrochlore-type structure. The thermal shock failure of double-ceramic-layer (La0.8Eu0.2)2Zr2O7/YSZ coatings mainly occurs at the interface between the (La0.8Eu0.2)2Zr2O7 and YSZ layers, and is not caused by thermal grown oxide layer from the bond coat.

Study of HKMG Stack Interface Engineer Applicable to 22nm/16nm Finfet Mosfet

Since Intel announced that they had made a great breakthrough in 22nm node[1][2]on May 4, 2011, FinFET Transistor structures had almost controlled CMOS technology beyond 22nm node. In this node, with the development of lithography, silicide process was switched to the back end. This huge change bring benefit to the formation of HKMG stack interface engineer. Before the silicide step switched, limited by the already formed silicide, the growth temperature of interfacial oxide layer couldn’t be higher than 600°C for NiSi unstability at high temperature, but now 800°C or 850°C will also be allowed. So we could adopt thermal oxide as HKMG stack interface layer. In this paper, as interface layer of HKMG stack, chemical and thermal oxide were all studied. In 32nm/22nm node Bulk Planar CMOS technology, chemical oxide was grown through spraying DI water diluted Ozone on bare silicon substrate which was generally used in industry. It’s advantage was low thermal budget and the disadvantage was thermal unstability of Chemical ox during ALD HfOX growth. ChemOX would diffuse into HK dielectric, referred to Fig 1(b). It could also be observed very clearly at Si/ChemOX/RTCVD SIN structure , referred to Fig 2(b). From Fig 1(a) and Fig 2(a) , we had no doubt about the stability of thermal oxide interface layer. In this article, We chose three different thermal oxidation methods which were RTO, ISSG alone, ISSG with plasma nitridation[3][4]respectively. Considering the state of silicon substrate surface would severely affect the quality of ultrathin interface oxide layer, we also chose two different cleaning process which were HF 100:1 and BOE 100:1 last.In conclusion, in order to improve HKMG stack characteristic in FinFET Transistor structures, different interface layer and cleaning process had been studied. Considering the thermal unstability of Chemical oxidation method currently used in industry, we plan to take high quality thermal ultrathin interface oxide into 22nm node and beyond.

(Invited) Inhomogeneous Strain in Silicon Photonics

The lack of a dipolar second order susceptibility (χ(2)) in silicon due to its centrosymmetric diamond lattice usually inhibits efficient second order nonlinear optical processes in the silicon bulk. Depositing stressed silicon nitride layers or growing a thermal oxide layer introduces an inhomogeneous strain into the silicon lattice and breaks the centrosymmetry of its crystal structure thereby creating a χ(2). This causes enhanced second harmonic generation and was observed in reflection and transmission measurements for wavelengths in the infrared. However strain is not the only means to break the structures symmetry. Fixed charges at the silicon nitride/silicon interface cause a high electric field close to the silicon interface which causes electric-field-induced-second-harmonic (EFISH) contributions too. The combination of both effects leads to χ(2) values which are estimated to be of the order as classic χ(2) materials like KDP or LiNiO3. This paves the way for the exploitation of other second order nonlinear processes in the area of silicon photonics and is an example how fundamental optical properties of materials can be formed by strain.

Thickness influence of thermal oxide layers on the formation of self-catalyzed InAs nanowires on Si(111) by MOCVD

The thickness influence of thermal oxide layers on Si(111) substrates on the formation of self-catalyzed InAs nanowires (NWs) grown by metal-organic chemical vapor deposition (MOCVD) has been investigated. It is found that the thickness of the thermal oxide layer has a strong effect on the morphological characteristics of InAs NWs formed on the Si substrates. In particular, within a suitable thickness range, it is possible to achieve vertical InAs NWs with a uniform distribution of their positions, lengths and diameters. In addition, growth on the thermal oxide layer both improves the morphology of the NWs, and suppresses the frequently observed parasitic islands compared to growth on bare Si. A growth model, which is based on the diffusion length of adatoms, the growth temperature, the thickness of thermal oxide layer, the size and the density of thermal oxide holes, has been developed to explain the formation of the self-catalyzed InAs NWs on the Si substrate with a thermal oxide layer.

A Novel Method to Fabricate Silicon-Beam with Polygon Section Based on Thermal Oxidation Layer Protection Technique

Simplex wet etching method to fabricate silicon-beam has limited the categories of silicon-beam, it has confined the design and fabrication of silicon-beam with polygon section. Moreover, due to the side-etching of sidewalls and arris during the process of wet etching, the sections of the fabricated silicon-beam are not identical, which will induce the mechanics characters of silicon-beam to be altered, depressing the quality of silicon-beam; In order to avoid the shortages above, a novel method to fabricate silicon-beam with polygon section based on thermal oxidation layer technique is proposed, thermal oxidation SiO2 layer is utilized as the protection layer of the sidewalls of the silicon-beam instead of the mask layer as usual for the first time. Combining the wet etching technique with the thermal oxidation technique innovatively, several varieties of silicon-beam with polygon section, which can hardly be obtained only by the use of wet etching technique, can be manufactured, respectively. Based on such an innovative method, this paper proposes and develops five varieties of silicon-beam with novel structure by means of adjustable mask layer, extending the application field of wet etching. The subsequent fabrication experiment of silicon-beam with hexagonal section has been taken as an example to validate the technique principle. The dimension parameters of silicon-beam have been tested precisely and the arris angle error between the theoretic value and the experimental measurement is less than 1.5%; The SEM photos with the amplifier of 100 and 250 have been obtained through HITACHI S-4800 field emission scanning electron microscope (FE-SEM), the SEM results have demonstrated the clear sidewall arris without undercut. Through this fabrication method, the sidewall arris of silicon-beam can be maintained due to the protection layer of thermal oxidation SiO2. In this manner, the arris disfigurement of the silicon-beam decreases dramatically, the process of etching can be controlled precisely, and the quality of the silicon-beam has been improved greatly.

Optical studies of the effect of oxidation on GaN

Optical studies are reported of GaN following oxide layer growth using thermal oxidation and atomic layer deposition (ALD). The low-temperature photoluminescence (PL) probes the topmost GaN layer (&amp;lt;100 nm) where any influence from the oxide is expected. Thermal oxidation results in a 6 meV blue shift of the main PL band (3.478 eV) that is attributed to stress due to formation of GaON/β-Ga2O3 upon the GaN surface. A weak PL feature at ∼3.38 eV is due to diffusion of oxygen into the GaN. The Al2O3 deposited by ALD does not result in the 3.38 eV band following deposition and subsequent annealing. In contrast, HfO2 deposited by ALD results in sub-band gap features, which strengthen upon annealing. No appreciable stress is observed for either oxide deposited using ALD, which are not expected to produce GaON/β-Ga2O3 layer.

21%-efficient PERL Solar Cells with Plated Front Contacts on Industrial 156 mm p-type Crystalline Silicon Wafers

We have achieved 21% large-area conversion efficiency with PERL (passivated emitter, rear locally diffused) solar cells featuring plated front contacts. Industrial 156mm p-type Czochralski single-crystalline silicon wafers were used as substrates. Our cells employ a single-side texture, a single-side emitter, and a double-layer anti-reflective coating composed of PECVD silicon nitride and thermal silicon oxide layers. The rear side is passivated with a dielectric stack (Al2O3–SiOxNy), and the rear contacts are formed through laser-ablated openings by screen-printing and firing an aluminum electrode. The nickel–silver or nickel–copper–silver contacts are plated on the front side by light-induced plating (LIP). The champion batch shows average values of 669mV open-circuit voltage, 40.0mA/cm2 short-circuit current density, and 77.3% fill factor. The efficiency of our PERL cell is currently limited by the series resistance. Implementing small (1–2μm) and uniform pyramids and thermally annealing the cells after plating show promising results for future improvements.

Formation Hybrid Method of Multilayer Biocoatings, Based on PVD Technology

Hybrid method of obtaining calcium-phosphate coatings is presented in this article. Physical and chemical, mechanical and tribological hybrid coatings research makes it possible to determine the coatings formation modes satisfying medical and technical requirements. This multilayer coating consists of an oxide underlayer formed by gas thermal oxidation and calcium phosphate layer formed by RF magnetron sputtering at a frequency of 13.56 MHz. Experiments were carried out in different modes. Calcium-phosphate coatings formed in mixture of argon and oxygen at 1:1 ratio pressure of 0.3 Pa have the best physical and chemical, mechanical and tribological properties.