Grown Silicon Dioxide Research Articles

Photoluminescence enhancement of porous silicon particles by microwave‐assisted activation

AbstractPhotoluminescence (PL) of porous silicon (PSi) particles can be significantly enhanced in some organic solvents (i.e., ethanol or dimethyl sulfoxide) under microwave irradiation. Fourier transform infrared spectra, dynamic‐light‐scattering measurements, and scanning electron microscopy had been adopted to explore the mechanism of PL enhancement of PSi particles under microwave irradiation, which is attributed to the formation of higher porosity and the growth of silicon oxide by microwave‐assisted wet etching. Compared with that fabricated by ultrasonication, smaller luminescent PSi nanoparticles (average size ∼60 nm) with stronger orange‐red fluorescence (PL quantum yield ∼14.8%) and higher dispersibility can be large‐scale prepared for cellular imaging and drug delivery in biomedical applications.

Detection of a piezoelectric effect in thin films of thermally grown SiO2 via lock-in ellipsometry

We report the observation of structural piezoelectricity in partially ordered thin films of thermally grown silicon dioxide (SiO2). The piezoelectric coefficient was determined to be 0.14-0.26 pm/V, and the piezoelectricity was found to originate in a layer with thickness at least 3.5 nm. This value is consistent with literature descriptions of SiO2 residual ordering based on structural measurements and modeling. Our observation demonstrates that the residual ordering in thermally grown silicon SiO2 is non-centrosymmetric and provides a rare example of diffusion controlled uniaxial growth producing macroscopic piezoelectricity.

Thin-film transistors with a channel composed of semiconducting metal oxide nanoparticles deposited from the gas phase

The fabrication of semiconducting functional layers using low-temperature processes is of high interest for flexible printable electronics applications. Here, the one-step deposition of semiconducting nanoparticles from the gas phase for an active layer within a thin-film transistor is described. Layers of semiconducting nanoparticles with a particle size between 10 and 25 nm were prepared by the use of a simple aerosol deposition system, excluding potentially unwanted technological procedures like substrate heating or the use of solvents. The nanoparticles were deposited directly onto standard thin-film transistor test devices, using thermally grown silicon oxide as gate dielectric. Proof-of-principle experiments were done deploying two different wide-band gap semiconducting oxides, tin oxide, SnO x , and indium oxide, In2O3. The tin oxide spots prepared from the gas phase were too conducting to be used as channel material in thin-film transistors, most probably due to a high concentration of oxygen defects. Using indium oxide nanoparticles, thin-film transistor devices with significant field effect were obtained. Even though the electron mobility of the investigated devices was only in the range of 10−6 cm2 V−1 s−1, the operability of this method for the fabrication of transistors was demonstrated. With respect to the possibilities to control the particle size and layer morphology in situ during deposition, improvements are expected.

Role of plastic deformation mechanisms in the formation of nanostructured silicon and its photoluminescent properties

The role of plastic deformation mechanisms in the process of obtaining nanostructured silicon layers is demonstrated. The process of obtaining nanostructured silicon consists in growing of silicon oxide layers of various thicknesses on the silicon wafer surface, their subsequent removal, and treatment by selective chemical etchants (SE) before the formation of defectless silicon islands possessing the photoluminescent properties typical of nanostructured silicon. Based on analysis of the photoluminescence intensity spectra of nanostructured silicon islands, the conclusion is drawn on different plastic deformation mechanisms at different thicknesses of thermally grown silicon oxide. Possible mechanisms of displacement of the intensity maximum in the photoluminescence (PL) spectrum toward shorter wavelengths with decreasing nanostructured silicon island sizes are discussed.

Analysis of structural transformations and fluctuation effects in the nanosized nickel films in the vicinity of the melting point

The effect of heating temperature on the structure of the nickel films with an original thickness of 20 nm that are deposited on silicon-oxide substrate (the thickness of the thermally grown silicon oxide SiO2 is about 1 μm) is studied using the scanning probe microscopy. An increase in the temperature causes a decrease in the mean thickness of the Ni film from the original thickness h = 20 nm to 18 ± 2 nm at a temperature of 737 K and 15 ± 2 nm at a temperature of 752 K. The thickening of the film is interpreted with allowance for the heterogeneous melting. The voltage jumps across the film sample in the vicinity of the melting point under slow heating and constant current flow through the sample are interpreted. In particular, the primary fluctuations lead to a decrease in the nickel film thickness due to the formation of drops from the liquid layer on the film surface and, hence, significant positive fluctuations of the resistance (or voltage jumps across the sample). Irreversible variations in the properties of thin metal films upon heating below the melting point are interpreted.

Effects of Thermal Annealing on the Structural and Optical Properties of Carbon-Implanted SiO2

Amorphous carbon (a-C) nanoclusters were synthesized by the implantation of carbon ions (C-) into thermally grown silicon dioxide film (-500 nm thick) on a Si (100) wafer and processed by high temperature thermal annealing. The carbon ions were implanted with an energy of 70 keV at a fluence of 5 x 10(17) atoms/cm2. The implanted samples were annealed at 1100 degrees C for different time periods in a gas mixture of 96% Ar+4% H2. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and High Resolution Transmission Electron Microscopy (HRTEM) were used to study the structural properties of both the as-implanted and annealed samples. HRTEM reveals the formation of nanostructures in the annealed samples. The Raman spectroscopy also confirms the formation of carbon nano-clusters in the samples annealed for 10 min, 30 min, 60 min and 90 min. No Raman features originating from the carbon-clusters are observed for the sample annealed further to 120 min, indicating a complete loss of implanted carbon from the SiO2 layer. The loss of the implanted carbon in the 120 min annealed sample from the SiO2 layer was also observed in the XPS depth profile measurements. Room temperature photoluminescence (PL) spectroscopy revealed visible emissions from the samples pointing to carbon ion induced defects as the origin of a broad 2.0-2.4 eV band, and the intrinsic defects in SiO2 as the possible origin of the -2.9 eV bands. In low temperature photoluminescence spectra, two sharp and intense photoluminescence lines at -3.31 eV and -3.34 eV appear for the samples annealed for 90 min and 120 min, whereas no such bands are observed in the samples annealed for 10 min, 30 min, and 60 min. The Si nano-clusters forming at the Si-SiO2 interface could be the origin of these intense peaks.

Morphology of inkjet printed 6,13 bis(tri-isopropylsilylethynyl) pentacene on surface-treated silica

The soluble small molecule organic semiconductor, 6,13 bis(tri-isopropylsilylethynyl) pentacene, is inkjet printed on thermally grown silicon dioxide via an orthodichlorobenzene solvent. This paper studies the effect of surface treatment on the size and geometry of sessile drops, as well as the film growth and crystallization behavior on the substrate. The mechanism of morphology control of inkjet-printed arrayed isolating dots or thin film involves the interaction at the interface between the solute molecules and solid substrate. The size and geometry of microscale isolating dots depend on the substrate’s surface uniformity, while the thin film morphology is less affected by this uniformity. Crystallization of the semiconductor requires a relatively high solute concentration at the contact line and is usually accompanied by solute diffusion driven under a concentration gradient. The polar contribution of the surface energy enhances pinning interaction between the substrate and solute molecules and favors the formation of a continuous film.

Patterned gold-assisted growth of GaP nanowires on Si

The patterning of metal seed particles for the vapor–liquid–solid (VLS) growth of semiconductor nanowires is examined. We report the challenges of obtaining GaP nanowires grown by molecular beam epitaxy (MBE) from a patterned array of Au seed particles created by electron beam lithography. Transmission electron microscopy studies revealed the presence of a thin silicon oxide layer over the patterned Au seed particles. Au acted as a catalyst for silicon oxide growth at even moderate temperatures. In particular, the annealing of Au-patterned Si (1 1 1) substrates at low temperatures required for indium mounting (200–300 °C) was responsible for the formation of an oxide layer that was detrimental to Au-assisted growth. Removal of the oxide layer by a buffered HF etch prior to MBE sample loading enabled patterned VLS growth.

O3-TEOS CVD Film Formation on Thermal SiO2 Pre-Coated with Ethanol

We previously reported that organic solvent (ethanol) treatment of a film formed by plasma enhanced chemical vapor deposition (PE-CVD) remarkably improved the gap-filling property of O3-tetraethylorthosilicate (O3-TEOS) atmospheric pressure chemical vapor deposition (AP-CVD) film. Based on these results, we concluded that alkoxy (ethoxy) groups, which are generated by ethanol treatment, reduced the adsorptive activities of the sites distributed on the surface, causing a decrease in the sticking probability of vapor-phase species responsible for the deposition. However, an opposite hypothesis has been reported, which proposes that ethoxy groups become adsorption sites. In this study, we offer a counterargument and clarify that ethoxy groups, which were generated by ethanol treatment following light etching using dilute hydrofluoric acid (HF), do not become adsorption sites on the surface of thermally grown silicon dioxide (thermal SiO2) during O3-TEOS film deposition, since the O3-TEOS film was formed at a low deposition rate (DR). A smooth surface and excellent gap-filling into the patterns covered with thermal SiO2 were observed on the O3-TEOS film formation by ethanol treatment. We propose that a degasification step during O3-TEOS film formation or during annealing after the deposition could be closely related to improved surface roughness and gap-filling.

Surface Passivation Studies on n+pp+ Bifacial Solar Cell

Bifacial solar cell is a specially designed solar cell for the production of electricity from both sides of the solar cell. It is an active field of research to make photovoltaics (PV) more competitive by increasing its efficiency and lowering its costs. We developed an n+pp+ structure for the bifacial solar cell. The fabrication used phosphorus-oxy-trichloride (POCl3) diffusion to form the emitter and Al diffusion using conventional screen printing to produce the back surface field (BSF). The n+pp+ bifacial solar cell was a sandwiched structure of antireflective coatings on both sides, Argentum (Ag) as a front contact and Argentum/Aluminum (Ag/Al) as a back contact. This paper reports the solar cell performance with different surface passivation or antireflecting coatings (ARC). Silicon nitride (SiN) deposited by Plasma-Enhanced Chemical Vapor Deposition (PECVD), thermally grown silicon dioxide (SiO2), PECVD-SiO2, and SiO2/SiN stack were used as ARC. The efficiency obtained for the best bifacial solar cell having SiN as the ARC is 8.32% for front surface illumination and 3.21% for back surface illumination.

Color-encoded microcarriers based on nano-silicon dioxide film for multiplexed immunoassays

Multiplexed analysis allows researchers to obtain high-density information with minimal assay time, sample volume and cost. Currently, microcarrier or particle-based approaches for multiplexed analysis involve complicated or expensive encoding and decoding processes. In this paper, a novel optical encoding technique based on nano-silicon dioxide film is presented. Microcarriers composed of thermally grown silicon dioxide (SiO(2)) film and monocrystalline silicon (Si) substrate were fabricated. The nano-silicon dioxide film exhibited unique surface color by low-coherence interference. Hence the colors can be used for encoding at least 100 microcarriers loaded with films of different thickness. We demonstrated that color-encoded microcarriers loaded with antigens could be used for multiplexed immunoassays to detect goat anti-human IgG, goat anti-mouse IgG and goat anti-rabbit IgG, with fluorescent detection as the interrogating approach. This microcarrier-based method also exhibited improved analytical performance compared with a microarray technique. This approach will provide new opportunities for multiplexed target assay development.

Light Induced Curing (LIC) of Passivation Layers Deposited on Native Silicon Oxide

This work presents a novel insight to the aspects of silicon surface passivation and the influence of thin intermediate layers generated by chemically grown silicon oxides. Strong light induced effects on passivation properties are investigated. After exposure to light (0.25 suns) for about 60 s, samples based on a PECVD layer system consisting of SiNx and SiO2 deposited on crystalline silicon with native silicon oxides show an improvement of more than 100% in minority carrier lifetime. These improvements are stable over months and lead to effective surface recombination velocities as low as 10cm/s on chemically polished p-type FZ wafers. With the use of different light sources, corona charging and annealing experiments the effect is investigated in detail. Finally, the effect is proposed to be a photo induced curing process of defects in the Si/SiO2 interface with the incorporation of hydrogen.

Growth and electrical properties of silicon oxide grown by atomic layer deposition using Bis(ethyl-methyl-amino)silane and ozone

Silicon oxide thin film grown at low temperatures (<300–500 °C) is essential for a range of applications in semiconductor devices. In this study, silicon oxide films were deposited at a substrate temperature of ∼300 °C by an atomic layer deposition (ALD) process using Bis(ethyl-methyl-amino)silane (BEMAS). BEMAS precursors adsorbed on the growing surface reacted with ozone but not with H2O. This suggests that the Si–H bonds in the BEMAS precursors adsorbed on the surface are robust and could be cleaved only by ozone. The reaction using BEMAS and ozone exhibited ALD saturation behavior. The dielectric constant of the ALD-SiO2 was measured to be ∼9, which is 2.3 times higher than that (∼3.9) of normal amorphous SiO2. This was attributed to the existence of the ∼10% OH species in the film.

20% Efficient Passivated Large-Area Metal Wrap Through Solar Cells on Boron-Doped Cz Silicon

We present metal wrap through passivated emitter and rear solar cells (MWT-PERC) on monocrystalline p-type silicon featuring laser-doped selective emitter structures in combination with either screen-printed (SP) or more advanced dispensed front side contacts. Thermally grown silicon oxide layers serve as emitter and rear surface passivation. Laser-fired contacts connect the SP aluminum rear contact to the silicon base. The rear side features solder contacts for both polarities. Conversion efficiency values of 20.6% for float-zone and 20.1% for Czochralski-grown silicon (not stabilized) are achieved on large-area cells with 149 wafer size. These are within the highest values reported for large-area p-type silicon solar cells to date. Analytical modeling enables a consistent description of the devices and allows for determining the dominating loss mechanisms.

Wafer Surface Charging Model for Single-Wafer Wet-Spin Processes

Wet chemical processes in integrated circuit (IC) manufacturing are used in many applications, e.g., post-etch residue removal and pre-deposition surface treatment. While advanced single-wafer wet spin tools are part of the critical tool-set for advanced IC fabrication, non-optimized tool hardware and/or process may induce different types of wafer surface charging issues. In this paper, a physical model to fundamentally explain surface charging induced by a single-wafer wet spin tool is described. The model is based on the advection of surface charges from wafer-center to wafer-edge resulting from the shear flow of the liquid. The charge distribution in the diffuse layer adjacent the wafer surface is calculated by solving the coupled Poisson's and current continuity equations. As often practiced in the industry in characterizing this type of wafer surface charging, a thermally grown silicon dioxide surface is used as the model surface and de-ionized water as the liquid medium. Good agreement is obtained between experimental and calculated surface charging potentials for radial positions extending from wafer-center to approximately 130 mm on standard 300 mm diameter wafers. The observed charging potential trends with respect to radial position, wet process time, and wafer spin speed are well explained by the current model.

Effect of PZT annealing on structural changes in PZT/SiO 2 surface and its masking behaviour to KOH/TMAH

This Letter reports the effect of piezoelectric (PZT) annealing on structural changes in silicon dioxide layer and for the first time its masking behaviour during PZT thin film processing. The PZT thin film is radio frequency sputtered on thermally grown silicon dioxide layer. The PZT on SiO2 film is annealed using conventional furnace annealing at 650°C, 120 min. The effect of annealing cycle on Pb and Zr diffusion in SiO2 is studied using energy dispersive X-ray analysis. The effect of potassium hydroxide (KOH) and tetra methyl ammonium hydroxide (TMAH) treatment on masking behaviour of PZT/SiO2 layer is investigated and the obtained results are presented. The structural changes in film are studied using scanning electron microscopy characterisation and the results are discussed. The process repeatability is tested with KOH and TMAH solutions.

The low-complexity RF MEMS switch at EADS: an overview

This paper gives an overview of the low-complexity radio frequency microelectromechanical systems (RF MEMS) switch concept and technology of EADS Innovation Works in Germany. Starting in 2003, a capacitive switch concept, which is unique in several aspects, was developed to address specific needs in the aeronautic and space. Thermally grown silicon oxide as dielectric layer, the silicon substrate as actuation electrode, and a conductive zone realized by ion implantation make the EADS RF MEMS switch a very simple, low-cost, and reliable approach. In this document, data on experimental investigations are presented, which demonstrate outstanding performance figures in terms of insertion loss, isolation, frequency range, bandwidth, RF-power handling, and robustness with respect to thermal load. Based on this concept, numerous different circuits in particular single-pole single-throws (SPSTs), single-pole multi-throws (SPMTs), tunable filters, phase shifters, and electronically steerable antennas between 6 and 100 GHz have been designed, fabricated, and characterized.

Organo-silane coated substrates for DNA purification

The use of blood as DNA source to be employed in genetic analysis requires a purification process in order to remove proteins, lipids and any other contaminants, such as hemoglobin, which inhibit PCR. On the other hand, the increasing demand of miniaturized and automated biological tests able to reduce time and cost of analysis, requires the development and the characterization of materials aimed to perform the DNA purification processes in micro-devices. In this work we studied the interaction of DNA molecules with modified silicon based substrates, positively charged after deposition of a (3-aminopropyl)triethoxysilane (APTES) or 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (AEEA) interfacial layer. The evaluation of the DNA adsorption and elution capacity of different substrates (thermally grown silicon oxide, silicon oxide obtained by plasma enhanced chemical vapour deposition, and Pyrex ®) was studied taking into account the nature of the substrate and the effect of DNA length (in the 208–50,000 base pairs range). Main findings are that DNA elution capacity depends both on the utilized substrate and on the choice of the silanizing agent. Higher DNA recovery was obtained from AEEA-modified substrates, but the eluted DNA had different electrophoretic properties from native DNA. DNA with the same electrophoretic behaviour as genomic DNA was instead recovered from APTES-treated surfaces. Furthermore, the length of DNA present in the starting material strongly modulates the elution efficiency, longer DNA being released in a lesser amount, suggesting that opportunely modified surfaces could be used as systems for differential DNA separation.

High resolution photoemission study of the thermal stability of the HfO2/SiOx/Si(111) system

Synchrotron radiation based photoemission has been used to investigate the thermal stability of HfO2 dielectric films deposited in-situ on ultra-thin thermally grown silicon oxide. Chemical interactions resulting in the limited formation of hafnium silicide is first detected at 700°C. Progressively longer anneals at this temperature and subsequently at 800°C results in the gradual reduction in thickness of the interfacial silicon oxide layer without a corresponding increase in the silicide signal. Annealing at 900°C results in a complete removal of the interfacial oxide and a substantial increase in the silicide signal. These results suggest that the presence of a thin buffer oxide layer does not completely prevent silicide formation at 700°C but plays an important role in increasing the decomposition temperature of the hafnium oxide layer to 900°C.

Evolution of Ar Implanted Amorphous Silicon Dioxide under High Voltage Electron Beam

Amorphous silicon dioxide layers were implanted with 100 keV Ar ions to a relatively high fluence in a tentative to generate cavities in the oxide. Different oxide layers were used, obtained either by thermally growth or by chemical vapor deposition (CVD) on Si substrate. In all SiO2 layers, cavities are not formed in the as-implanted state. However, in the transmission electron microscope, under electron beam, the combined effect of irradiation induced defects and implanted rare gas leads to the formation of cavity bands giving the unique opportunity to observed in-situ cavity growth. The cavity morphology and their distribution are found to be dependent on the silicon dioxide growth process. For thermally grown SiO2 layer, a homogeneous cavity band is formed, centered at the mean ion path, with an average cavity size of 20 nm. For CVD SiO2 layer, slightly smaller cavities are formed in two distinct bands. The formation of cavities is discussed in light of gas and defects interaction and field-induced migration whereas the cavity distribution is discussed in terms of self-organization.