Thin Silicon Dioxide Research Articles

Silicon wafer wettability and aging behaviors: Impact on gold thin-film morphology

This paper reports on the wettability and aging behaviors of the silicon wafers that had been cleaned using a piranha (3:1 mixture of sulfuric acid (H2SO4, 96%) and hydrogen peroxide (H2O2, 30%), 120°C), SC1 (1:1:5 mixture of NH4OH, H2O2 and H2O, at 80°C) or HF solution (6 parts of 40% NH4F and 1 part of 49% HF, at room temperature) solution, and treated with gaseous plasma. The silicon wafers cleaned using the piranha or SC1 solution were hydrophilic, and the water contact angles on the surfaces would increase along with aging time, until they reached the saturated points of around 70°. The contact angle increase rate of these wafers in a vacuum was much faster than that in the open air, because of loss of water, which was physically adsorbed on the wafer surfaces. The silicon wafers cleaned with the HF solution were hydrophobic. Their contact angle decreased in the atmosphere, while it increased in the vacuum up to 95°. Gold thin films deposited on the hydrophilic wafers were smoother than that deposited on the hydrophobic wafers, because the numerous oxygen groups formed on the hydrophilic surfaces would react with gold adatoms in the sputtering process to form a continuous thin film at the nucleation stage. The argon, nitrogen, oxygen gas plasma treatments could change the silicon wafer surfaces from hydrophobic to hydrophilic by creating a thin (around 2.5nm) silicon dioxide film, which could be utilized to improve the roughness and adhesion of the gold thin film.

Green Emission of Terbium Doped Silicon Rich Silicon Oxide Films Obtained By Chemical Vapor Deposition

The effect of silicon concentration, annealing temperature and influence of post-growth hydrogen incorporation on terbium (Tb3+) luminescence was investigated for thin silicon rich silicon oxide films (SRSO). The structures were deposited by means of plasma enhanced chemical vapor deposition (ECR-PECVD). The structural properties of these films were investigated by Rutherford backscattering spectrometry, transmission electron microscopy, FTIR and Raman scattering. The optical properties were investigated by means of photoluminescence, cathodoluminescence and photoluminescence decay spectroscopy.In this poster, we present a detailed discussion of these issues and determine the optimal conditions of the SRSO films from the point of view of Tb3+ emission properties.An increase in the Si concentration in SRSO influences the emission properties in two ways. First of all, the refractive index of the film increases which enhances the oscillator strength of the optical transitions. On the other hand, the non-radiative recombination also increases, limiting the PL intensity. Therefore, from the point of view of emission efficiency, the optimal Si concentration in the film is about 35 at.% Si. Besides the Si concentration, another effect investigated in this work was the influence of the annealing temperature on Tb3+ emission. It was found that the PL intensity increases as a function of the annealing temperature. This effect was ascribed to the structural changes of the SRSO matrix. At early stages of the annealing (up to annealing temperature equal to 900oC) the most important factor enhancing the Tb3 emission intensity is a reduction in the number of non-radiative recombination centers. However, as shown by Raman measurements, starting from Ta =1100oC structural changes occur in the matrix (crystallization and formation of the Si nanocrystals) and the Tb environment significantly changes. Therefore, the further increase in the PL intensity obtained for high annealing temperatures (temperatures in the 1100–1200 oC range) can be ascribed to the increasing oscillator strength of the intra-4f transitions, induced by the change of the crystal field around the ions.

Infrared ellipsometry for improved laterally resolved analysis of thin films

In the present article we discuss developments towards increasing the spatial resolution of infrared ellipsometry and ellipsometric microscopy for the study of thin films. Relevant aspects in the interpretation of observed peaks in the infrared (ellipsometric) spectra are discussed. In particular anisotropic effects in dependence of molecular orientations in organic films and the excitation of a macroscopic wave, the Berreman mode, in thin silicon oxide films are addressed. For correct interpretation of measured data optical simulations are essential to avoid incorrect conclusions on band frequency and assignments.

Strong and broadband terahertz absorber using SiO2-based metamaterial structure

We design and experimentally demonstrate a broadband metamaterial absorber in the terahertz (THz) band based on a periodic array of aluminum (Al) squares with two different sizes. A thin silicon dioxide (SiO2) film rather than a conventional polyimide (PI) layer is used as a dielectric spacer to separate Al squares from the platinum (Pt) ground plane in our design, which significantly improves the design precision and the feasibility of the device fabrication. The combination of different sizes of Al squares gives rise to an absorption bandwidth of over 210 GHz with an absorption of over 90%. Our results also show that our device is almost polarization-insensitive. It works very well for all azimuthal angles with an absorption of beyond 80%.

Investigations on the Passivation Mechanism of AlN:H and AlN:H-SiN:H Stacks

In this paper, the properties of hydrogenated aluminum nitride layers (AlN:H) as an excellent passivation layer of silicon surfaces are examined. The structural and chemical properties of the AlN:H bulk are analyzed using a great variety of measurements techniques such as GI-XRD, FTIR, SEM, HR-TEM, corona charging and a thickness dependent measurements of the surface passivation. A model for the formation of negative fixed charges at the interface to silicon is presented based on the charge state of ionized point defects in AlN.Additionally, stacks of AlN:H and SiNx:H are introduced into silicon photovoltaics and their combination with two different types of thin low temperature silicon oxide layers is studied. Excellent passivation results are presented for highly doped p-type silicon and highly doped n-type silicon using the previous described stacks. Emitter saturation current densities of textured samples show, that 75 Ω/sq. phosphorous emitter can be passivated as efficient as with the typically used SiNx:H allowing maximum open circuit voltages of 657 mV. This is supported by measurement of cell parameters of p-type solar cells using these stacks as a combined anti-reflective coating and passivation layer. Furthermore, the passivation level reached for high efficiency 70 Ω/sq. boron emitters is nearly as high as with excellent passivating PECVD Al2O3/SiNx stacks. Emitter saturation current densities down to 61 fA/cm2 are presented corresponding to a maximum open circuit voltage of 696 mV. This indicates that the invented stacks containing AlN:H can also be applied as combined anti-reflective coating and passivation layers in n-type cells.

Passivation Properties of Subnanometer Thin Interfacial Silicon Oxide Films

Subnanometer thin silicon oxide films, applied as interlayer between crystalline silicon absorbers and functional layers, have demonstrated to improve interface passivation properties. Here we compare the interface defect density as well as the fixed charge of simple native air oxides to wet-chemical oxides on silicon substrates of different doping type, with different crystal orientations and after different chemical pre-treatment processes. We show that optimized wet-chemical pre-treatment and wet-chemical oxidation leads to strong improvement in terms of interface defect density as compared to simple oxidation in air. Furthermore we show that such subnanometer thin layers can contain large positive fixed charges of up to 1011 cm-2. Due to excellently low defect densities for thin layers <0.5nm, tunneling transport and thus application for solar cells with passivated contacts should be possible. While on p-type substrates such layers feature a high positive charge and would thus support an emitter band bending, on n-type substrates the charge is smaller and can even be negative due to electrons trapped in mid gap defects.

Stress control of plasma enhanced chemical vapor deposited silicon oxide film from tetraethoxysilane

Thin silicon dioxide films have been studied as a function of deposition parameters and annealing temperatures. Films were deposited by tetraethoxysilane (TEOS) dual-frequency plasma enhanced chemical vapor deposition with different time interval fractions of high-frequency and low-frequency plasma depositions. The samples were subsequently annealed up to 930 °C to investigate their stress behavior. Films that were deposited in high-frequency dominated plasma were found to have tensile residual stress after annealing at temperatures higher than 800 °C. The residual stress can be controlled to slightly tensile by changing the annealing temperature. High tensile stress was observed during the annealing of high-frequency plasma-deposited films, leading to film cracks that limit the film thickness, as predicted by the strain energy release rate equation. Thick films without cracks were obtained by iterating deposition and annealing to stack multiple layers. A series of wet cleaning experiments were conducted, and we discovered that water absorption in high-frequency plasma-deposited films causes the residual stress to decrease. A ∼40 nm thick low-frequency deposited oxide cap is sufficient to prevent water from diffusing through the film. Large-area free-standing tensile stressed oxide membranes without risk of buckling were successfully fabricated.

An Ultraviolent-Enhanced Response Solar Cell and Tunneling Effect

A sort of ITO/SiO2/n+p configuration of solar grade silicon - based SINP device has been successfully fabricated by coupling high quality of indium tin oxide (ITO) thin film and ultra-thin silicon dioxide buffer layer on the p-n junction, which showed a potential to improve the short-circuit current density (JSC) as well as the conversion efficiency. The progress to avoid the use of last two processes with PECVD and high temperature firing in the normal production for the crystal silicon solar cell may be a way toward the low cost and the high efficiency. In addition, the tunneling hypostasis of carriers is present in the device.

Influence of layer type and order on barrier properties of multilayer PECVD barrier coatings

Due to their macromolecular structure, plastics are limited in their scope of application whenever high barrier functionality against oxygen and water vapour permeation is required. One solution is the deposition of thin silicon oxide coatings in plasma-enhanced chemical vapour deposition (PECVD) processes. A way to improve performance of barrier coatings is the use of multilayer structures built from dyad layers, which combine an inorganic barrier layer and an organic intermediate layer. In order to investigate the influence of type and number of dyads on the barrier performance of coated 23 µm PET films, different dyad setups are chosen. The setups include SiOCH interlayers and SiOx-barrier layers deposited using the precursor hexamethyldisiloxane (HMDSO). A single reactor setup driven in pulsed microwave plasma (MW) mode as well as capacitively coupled plasma (CCP) mode is chosen. In this paper the effects of a variation in intermediate layer recipe and stacking order using dyad setups on the oxygen barrier properties of multilayer coatings are discussed with regard to the chemical structure, morphology and activation energy of the permeation process.Changes in surface nano-morphology of intermediate layers have a strong impact on the barrier properties of subsequent glass-like coatings. Even a complete failure of the barrier is observed. Therefore, when depositing multilayer barrier coatings, stacking order has to be considered.

Self-catalyzed VLS grown InAs nanowires with twinning superlattices

We report on the self-catalyzed growth of InAs nanowires by molecular beam epitaxy on GaAs substrates covered by a thin silicon oxide layer. Clear evidence is presented to demonstrate that, under our experimental conditions, the growth takes place by the vapor–liquid–solid (VLS) mechanism via an In droplet. The nanowire growth rate is controlled by the arsenic pressure while the diameter depends mainly on the In rate. The contact angle of the In droplet is smaller than that of the Ga droplet involved in the growth of GaAs nanowires, resulting in much lower growth rates. The crystal structure of the VLS grown InAs nanowires is zinc blende with regularly spaced rotational twins forming a twinning superlattice.

Enhanced Light Absorption and Minority Carrier Lifetime for Pn&lt;sup&gt;+&lt;/sup&gt; Multicrystalline Silicon by Treatment with HF/H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt;-Based Solutions

A novel method was proposed to form porous silicon (PS) antireflection layers and thin SiO2 films at the same time by HF/H2O2 treatment of acid-textured pn+ multicrystalline silicon. Porous silicon structures formed inside the cavities and the porosity became large with an increase of the treated time resulting in a dramatical decrease of reflectance. The reflectance decreased to less than 5% within the wavelength range of 420-970 nm after 5 min HF/H2O2 treatment. Furthermore, the minority-carrier lifetime showed an increase of about 42% for a short treated time because of the formation of a thin silicon oxide layer resulting the reduction of dangling silicon bonds in the interface between PS/Si.

Polarization-Dependent and Ellipsometric Infrared Microscopy for Analysis of Anisotropic Thin Films

Dielectric functions and anisotropic thin film properties such as electronic conductivity or molecular orientations are of high technological importance for engineering efficient optical, electronic, and sensing devices. This work demonstrates for the first time how full-scale polarization-dependent Fourier-transform infrared (FTIR) microscopy may be used for quantitative determination of polarized reflection coefficients of thin film samples with thicknesses down to a few nanometers. Out-of-plane and in-plane optical properties of thin silicon oxide, indium tin oxide (ITO), and polyimide films are measured and characterized quantitatively with respect to anisotropy and thickness. Sample homogeneity is accessed using FTIR microscopic mapping. By performing measurements at multiple polarizer azimuths we demonstrate the technique of ellipsometric microscopy. Exemplarily ellipsometric measurements of a polyimide film are presented and discussed. We describe how introducing a retarder into the optical path wo...

결맞음길이보다 두꺼운 두 개의 막에 덮여있는 시료의 타원식

회전검광자 방식의 타원계 구조에 기초하여 두꺼운 막들 내부에서 일어나는 다중반사에 인한 빛의 세기를 결맞지 않도록 중첩함으로써 결맞음길이보다 두꺼운 막 두 개가 다층박막시료 위에 있을 때 적용되는 타원상수 표현들을 유도하였다. 유도된 표현들을 커버유리와 공기층 아래에 있는 산화규소 박막이 코팅되어 있는 시료의 타원법 분석에 적용하여 그 유용성을 확인하였다. The expressions for ellipsometric constants of a sample covered with two thick films are derived, where incoherent superposition of multiply reflected lights inside thick films is properly considered in the frame of the rotating analyzer ellipsometry. The derived expressions are successfully applied to the analysis of a silicon wafer with a thin silicon dioxide film on it, which is placed beneath a cover glass and an air gap.

Aluminum-Induced Crystallization of p&lt;sup&gt;+&lt;/sup&gt; Silicon Pinholes for the Formation of Rear Passivation Contact in Solar Cell

Formation of nano-crystalline p+ silicon (Si) in pinholes through a silicon dioxide layer was achieved by pinning of aluminum through the thin silicon dioxide (SiO2) layer. In addition to opening holes of SiO2 layer by aluminum (Al) pining, amorphous silicon (a-Si) was subsequent deposited on the Al layer and another heated at low temperature (500°C) to allow solid- phase epitaxial growth of p+ Si in the pinholes due to the Al induced layer exchange process. The poly-crystalline p+ Si obtains lower effective surface recombination than the Al back surface field (BSF). The technique demonstrated to result in ohmic contacts with low contact resistance. The evaluation of Al-induced crystallization of a-Si in a-Si/Al bilayer was studied by X-ray diffraction. In this paper, the influence of a-Si/Al thickness ratio on the specific conductivity value and crystalline grain size of the p+ Si thin film is discussed. The obtained results are helpful for a further design of the rear passivation contact in solar cell.

Time-Dependent Determination of HF Formation in LiPF6 -Containing Electrolytes in Different Cell Types by Spectroscopic Ellipsometry

A novel experimental technique was developed to investigate HF formation in organic carbonate based electrolytes containing LiPF6. Using spectroscopic ellipsometry, aging and thermal decomposition of the electrolyte were monitored in a standard glass cell and in a polypropylene vessel. The amount of HF generated was determined by following the etching rate of a thin silicon dioxide layer on a silicon wafer in contact with the electrolyte. The material of cell construction clearly influenced the etching rate of the SiO2 sensor and affected the rate of degradation.

Local Charge Storage in Thin Silicon Oxide Films: Mechanisms and Possible Applications

We report on charge storage in silicon oxide below the micrometer scale as needed for the controlled attachment of charged particles. Thin silicon oxide films were locally charged using conductive atomic force microscopy. The charge was investigated using Kelvin probe force microscopy. We found that charges are stored in different traps in the silicon oxide matrix. We also discovered two different decay pathways: one parallel and one perpendicular to the surface. The parallel path, which is mediated by water adsorbed on the surface, was suppressed by a hydrophobic monolayer. This led to a stabilization of the stored charges in the oxide, which enabled the targeted attachment of ionic species from solution. As proof of concept, we deposited dye molecules selectively to previously written charge patterns on silicon oxide for the first time.

Antireflection coatings produced on silicate glass from silicon dioxide sols with addition of poly(propylene glycols) at gel annealing temperature of 200°C

Thin transparent nanoporous silicon dioxide films with low refractive index (1.26–1.30) were formed on a glass substrate by deposition of a formulation that is based on silicon dioxide sol with addition of poly(propylene glycols) at a low gel annealing temperature of 200°C. The maximum optical transmission of glass with these antireflection coatings is 97.5–98.7%.

Monitoring Apnea in the Elderly by an Electromechanical System with a Carbon Nanotube-based Sensor

Summary Background Breathing, a part of respiration, is one of the vital functions. Breathing disorders are common in the elderly. An effective breathing sensor for real-time detection of apnea is important in clinical critical care. We aimed to construct a real-time warning platform with a combination of carbon nanotubes (CNTs) and related nano-electromechanical system (NEMS) for elderly care. Methods Through a specific acid-treated procedure, multiwalled carbon nanotubes (MWCNTs) were immobilized on a thin silicon dioxide (SiO 2 ) film, coated on a heated silicon wafer. Techniques of photolithography and sputtering with chromium and gold were then implemented on the MWCNT film to develop micro-interdigitated electrodes as a base for the breathing sensor. The sensor was equipped with a programmed microchip processor to become a warning detector for abnormal human breathing, namely less than six breaths per minute. Elderly volunteers were enrolled for examining the effective sensitivity of this novel electromechanical device. Results There were 15 elderly volunteers (9 males and 6 females) tested in this experiment. The dynamic analyses of the MWCNT sensor to exhaled breath showed that it had characteristics of rapid response, high aspect ratio, small tip ratio, and high electrical conductivity. Responses of the MWCNT sensor to exhaled breath was recorded according to different performance parameters, i.e., strength, frequency, flow rate, and breath components. In this study, variable pattern-simulated tests showed that a MWCNT sensor combined with a processor could accurately evoke warning signals (100% of sensitivity rate), indicating its effectiveness and usefulness for detecting abnormal breathing rates, especially apnea. Conclusion Our results showed that a new device composed of an NEMS by combining an MWCNT sensor and complementary metal-oxide semiconductor (CMOS) circuits could be integrated to effectively detect apnea in the elderly. This novel device may improve the pattern of safe respiratory care for the elderly in the future.

Surface pre-treatment for barrier coatings on polyethylene terephthalate

Polymers have favourable properties such as light weight, flexibility and transparency. Consequently, this makes them suitable for food packaging, organic light-emitting diodes and flexible solar cells. Nonetheless, raw plastics do not possess sufficient barrier functionality against oxygen and water vapour, which is of paramount importance for most applications. A widespread solution is to deposit thin silicon oxide layers using plasma processes. However, silicon oxide layers do not always fulfil the requirements concerning adhesion and barrier performance when deposited on films. Thus, plasma pre-treatment is often necessary. To analyse the influence of a plasma-based pre-treatment on barrier performance, different plasma pre-treatments on three reactor setups were applied to a very smooth polyethylene terephthalate film before depositing a silicon oxide barrier layer. In this paper, the influence of oxygen and argon plasma pre-treatments towards the barrier performance is discussed examining the chemical and topological change of the film.It was observed that a short one-to-ten-second plasma treatment can reduce the oxygen transmission rate by a factor of five. The surface chemistry and the surface topography change significantly for these short treatment times, leading to an increased surface energy. The surface roughness rises slowly due to the development of small spots in the nanometre range. For very long treatment times, surface roughness of the order of the barrier layer's thickness results in a complete loss of barrier properties. During plasma pre-treatment, the trade-off between surface activation and roughening of the surface has to be carefully considered.

Al/SiOx/Al single and multiband metamaterial absorbers for terahertz sensor applications

To increase the sensitivity of uncooled thermal sensors in the terahertz (THz) spectral range (1 to 10 THz), we investigated thin metamaterial layers exhibiting resonant absorption in this region. These metamaterial films are comprised of periodic arrays of aluminum (Al) squares and an Al ground plane separated by a thin silicon-rich silicon oxide (SiOx) dielectric film. These standard MEMS materials are also suitable for fabrication of bi-material and microbolometer thermal sensors. Using SiOx instead of SiO2 reduced the residual stress of the metamaterial film. Finite element simulations were performed to establish the design criteria for very thin films with high absorption and spectral tunability. Single-band structures with varying SiOx thicknesses, square size, and periodicity were fabricated and found to absorb nearly 100% at the designed frequencies between three and eight THz. Multiband absorbing structures were fabricated with two or three distinct peaks or a single-broad absorption band. Experimental results indicate that is possible to design very efficient thin THz absorbing films to match specific applications.