Deposited Silicon Dioxide Research Articles

Effect of deposition temperature and surface reactions in atomic layer deposition of silicon oxide using Bis(diethylamino)silane and ozone

We investigated the effect of deposition temperature on the properties of the silicon oxide films produced by alternating exposures to bis(diethylamino)silane (BDEAS) and ozone (O3). The surface reactions during the deposition were studied using in situ characterization techniques and density functional theory (DFT) calculations. The atomic layer deposition (ALD) temperature window was between 250 and 350 °C with a nearly constant growth rate of ∼ 0.10 nm/cycle and the step coverage higher than 94%. The saturation doses of BDEAS and O3/O2 were 5 × 106 L and 5 × 107 L. Among the films deposited in genuine ALD mode, the film deposited at 350 °C exhibited the lowest leakage current of 2.4 × 10-8 A/cm2 at −2 MV/cm and the lowest oxide trapped charge density of 6.5 × 1011/cm2. The in situ quartz crystal microbalance analysis showed that approximately 0.5 diethylamine ligand per BDEAS molecule was expected to remain on the surface after the BDEAS feeding. The in situ Fourier-transform infrared difference spectrum confirmed the presence of the ligand on the surface. DFT simulations showed that all NEt2 ligands are released on vicinal and geminal hydroxyl groups to form –SiH2*. However, only one NEt2 ligand can be removed on isolated hydroxyls because no other hydroxyls are nearby, resulting in –SiH2(NEt2)*.

Surface Modification of Nanoporous Anodic Alumina during Self-Catalytic Atomic Layer Deposition of Silicon Dioxide from (3-Aminopropyl)Triethoxysilane.

Changes associated to atomic layer deposition (ALD) of SiO2 from 3-aminopropyl triethoxysilane (APTES) and O3, on a nanoporous alumina structure, obtained by two-step electrochemical anodization in oxalic acid electrolyte (Ox sample) are analysed. A reduction of 16% in pore size for the Ox sample, used as support, was determined by SEM analysis after its coverage by a SiO2 layer (Ox+SiO2 sample), independently of APTES or O3 modification (Ox+SiO2/APTES and Ox+SiO2/APTES/O3 samples). Chemical surface modification was determined by X-ray photoelectron spectroscopy (XPS) technique during the different stages of the ALD process, and differences induced at the surface level on the Ox nanoporous alumina substrate seem to affect interfacial effects of both samples when they are in contact with an electrolyte solution according to electrochemical impedance spectroscopy (EIS) measurements, or their refraction index as determined by spectroscopic ellipsometry (SE) technique. However, no substantial differences in properties related to the nanoporous structure of anodic alumina (photoluminescent (PL) character or geometrical parameters) were observed between Ox+SiO2/APTES and Ox+SiO2/APTES/O3 samples.

Fully vertical gallium nitride trench MOSFETs fabricated with metal-free gate first process

We report on the fabrication and characterization of fully vertical gallium nitride trench metal oxide semiconductor field effect transistors on native substrates with a metal-free gate first process and a chlorine-free trench etching method. Trenches were fabricated using sulfur hexafluoride and argon plasma etching in combination with alkaline wet etching posttreatment to create crystal oriented trenches along the a- and m-planes. Low pressure chemical vapor deposited silicon dioxide was used as gate dielectric with a poly-silicon gate contact. The metal-free gate structure was separated by a silicon dioxide passivation from any subsequent metal containing contact formation processing steps. The breakdown robustness of the gate structure was examined in the forward direction and no temperature dependence was observed up to 450 K. Fabricated trench MOSFETs showed only small hysteresis effects during transfer characterization but a positive threshold shift was observed. An inversion channel carrier field effect mobility of ≈10 cm2/V s was extracted. The area specific on resistance was calculated to be 5.8 mΩ cm2. Results for devices with differently oriented trenches were comparable and no significant performance difference was observed.

Unprotected sidewalls of implantable silicon-based neural probes and conformal coating as a solution

Silicon-based implantable neural devices have great translational potential as a means to deliver various treatments for neurological disorders. However, they are currently held back by uncertain longevity following chronic exposure to body fluids. Conventional deposition techniques cover only the horizontal surfaces which contain active electronics, electrode sites, and conducting traces. As a result, a vast majority of today’s silicon devices leave their vertical sidewalls exposed without protection. In this work, we investigated two batch-process silicon dioxide deposition methods separately and in combination: atomic layer deposition and inductively-coupled plasma chemical vapor deposition. We then utilized a rapid soak test involving potassium hydroxide to evaluate the coverage quality of each protection strategy. Focused ion beam cross sectioning, scanning electron microscopy, and 3D extrapolation enabled us to characterize and quantify the effectiveness of the deposition methods. Results showed that bare silicon sidewalls suffered the most dissolution whereas ALD silicon dioxide provided the best protection, demonstrating its effectiveness as a promising batch process technique to mitigate silicon sidewall corrosion in chronic applications.

The Use of Additive Laser Technology for the Synthesis of Silicate Coatings in the Correction of the Shape of Precision Optical Surfaces

The work is devoted to the development of the technology for the formation of the required microrelief of the optical surfaces of glass-ceramic substrates. The solution of the problem using a controlled local deposition of silicon dioxide on the polished surface by laser pyrolysis of tetraethoxysilane vapor in the presence of ozone is shown. The characteristics of the experimental samples, their comparison with the data of mathematical modeling of the results of technological processes are presented. The possibility of using the developed technology for the production of substrates of optical parts with a defined wedge-shaped value is shown.

Improved Long-Term Stability of Low-Temperature Polysilicon Thin-Film Transistors by Using a Tandem Gate Insulator with an Atomic Layer of Deposited Silicon Dioxide

In this study, we report a substantial improvement in the long-term stability of low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) with a tandem gate insulator composed of silicon dioxide (SiO2) deposited by using atomic layer deposition (ALD) and plasma-enhanced chemical vapor deposition (PECVD). Negative-bias temperature instability (NBTI) tests showed that threshold-voltage (ΔVth) shifts were significantly smaller than when only a plasma-enhanced chemical vapor deposition (PECVD) structure was used. We believe that the unique stoichiometric characteristics and the reduction in the interfacial trap density (Dit) produced by the SiO2 gate insulator that had been fabricated using ALD enhanced the long-term stability of the LTPS TFTs. These results suggest a tandem structure gate insulator with high-quality ALD-based SiO2 thin film can provide an important improvement in the characteristics of the p-channel LTPS TFTs required for advanced active matrix organic light-emitting diodes (AMOLEDs) applications.

Development of High-Quality Gate Oxide on 4H-SiC Using Atomic Layer Deposition

A systematic post-deposition annealing study on Silicon Carbide (SiC) metal-oxide-semiconductor capacitors (MOSCAPs) using atomic layer deposition (ALD)-deposited silicon dioxide (SiO2) layers was carried out. Anneals were done in oxidising (N2O), inert (Ar) and reducing (H2:N2) ambients at elevated temperatures from 900°C to 1300°C for 1 hour. Electrical characterisation results show that the forming gas treatment at 1100°C reduces the flatband voltage to 0.23 V from 10 V for as-deposited SiO2 layers. The density of interface traps (DIT) was also reduced by one order of magnitude to 2×1011 cm-2 eV-1 at EC-ET = 0.2 eV. As an indicator of the improvement, characterisation by x-ray photoelectron spectroscopy (XPS) showed that silicon enrichment present in as-deposited layers was largely reduced by the forming gas anneal, improving the stoichiometry. Time-dependent dielectric breakdown (TDDB) results showed that the majority of forming gas annealed samples broke down at breakdown fields of 12.5 MV × cm-1, which is about 2.5 MV × cm-1 higher than for thermally oxidised samples.

Ultra-Short Pulse HiPIMS: A Strategy to Suppress Arcing during Reactive Deposition of SiO2 Thin Films with Enhanced Mechanical and Optical Properties

In this contribution, based on the detailed understanding of the processes’ characteristics during reactive high-power impulse magnetron sputtering (HiPIMS), we demonstrated the deposition of silicon oxide (SiO2) thin films with improved optical and mechanical performances. A strategy for stabilizing the arc-free HiPIMS of Si target in the presence of oxygen was investigated. Arcing was suppressed by suitable pulse configurations, ensuring good process stability without using any feedback control system. It was found that arcing can be significantly alleviated when ultra-short HiPIMS pulses are applied on the target. The optical and mechanical properties of SiO2 coatings deposited at various pulsing configurations were analyzed. The coatings prepared by ultra-short pulse HiPIMS exhibited better optical and mechanical performance compared to the coatings prepared by long pulse HiPIMS. The optimized SiO2 coatings on quartz substrates exhibited an average transmittance of 98.5% in the 190–1100-nm wavelength range, hardness of 9.27 GPa, hardness/Young’s modulus ratio of 0.138, and critical adhesion load of 14.8 N. The optical and mechanical properties are correlated with the film morphology, which is inherently related to energetic conditions and process stability during film growth.

Bistable Threshold Humidity Sensor Switch with Rectangular Bimorph Bending Plate.

Energy-autonomous bistable threshold sensor switches have the potential to reduce costs because they do not need any electrical energy supply for monitoring physical quantities, such as relative humidity. In previous work, a bistable beam-like sensor switch with switching hysteresis was manufactured from sheet metal and a partially coated water vapor-sensitive hydrogel (poly(vinyl alcohol)/poly(acryl acid)). Based on the beam theory, a corresponding mechanical model was developed. However, bending plates should be used instead of bending beams to separate the humidity to be measured from the electrical contacts. For this reason, this work deals with the development and realization of a mechanical model based on the plate theory to describe the deflection of a silicon bimorph bending plate partially coated with hydrogel that swells with increasing humidity. For implementing a switching hysteresis a plasma-enhanced chemical vapor deposition silicon dioxide (SiO2) layer is used, which was deposited and structured on top of the silicon plate. The hydrogel layer itself is patterned on the surface of the bending plate using a stamp technique. To validate the mechanical model, the switching hysteresis of the miniaturized sensor switch was measured optically by a camera measurement device.

Evaluation of Argon as a Carrier Gas of Liquid Material Vaporization During the Plasma-Enhanced Chemical Vapor Deposition (PECVD) Silicon Oxide Process

This paper investigated the potential use of argon (Ar) as an alternative carrier gas to helium (He) during the tetraethyl orthosilicate–silicon dioxide (TEOS–SiO2) process using a plasma-enhanced chemical vapor deposition (PECVD) system. Due to the shortage or depletion of conventional He gas, it is important to find alternative gases. This study investigated the effects of the Ar carrier gas on the vaporization efficiency and properties of SiO2 film in the PECVD TEOS–SiO2 process for different process conditions, such as flow rate and plasma power. Ar showed a much higher vaporization efficiency and faster deposition rate than He due to its higher molecular weight and plasma density, indicating that SiO2 film can be deposited considerably faster with less Ar gas. While changes in the film density and residual film stress were also noted depending on the types of carrier gas and amounts or types of plasma power, these changes were insignificant and within the controllable process range during the PECVD process. Therefore, the use of Ar gas can reduce costs and contribute to improvements in productivity without affecting the quality of SiO2 film.

Effect of PP Nanocomposite Multi-layered Film on Physicochemical Properties of Ready-To-Cook (RTC) Idli Batter and Prepared Idli Cake

Aim: The current study focuses on the effect of PP nanocomposite multi-layered film on physicochemical properties of stored idli batter and prepared idli cakes.
 Place and Duration of Study: Department of Food Packaging and System Development at Indian Institute of Food Processing Technology, Thanjavur, Tamil Nadu, India, between Aug 2018 and Dec 2019.
 Methodology: The developed PP nanocomposite multi-layered film composed with depositing silicon dioxide (SiO2) on polypropylene (PP) film (0.010 mm) and attached with ethylene-vinyl alcohol (EVOH 32%) film (0.066 mm). The Physico-chemical properties of developed multi-layered and commercial PP film stored idli batter with different blend ratios of rice to black gram (3:1 and 4:1) were evaluated in terms of pH, percent titrable acidity (% TA), colour value (∆E), viscosity (cP) and volume measurement (ml). Idli cake prepared with batter stored in multi-layered film and evaluated in terms of colour, texture and percent pore characteristics. The percent pore presents in per square inches of prepared idli cake with different blend ratios and fermentation time were analysed using the grayscale image in MATLAB.
 Results and Discussion: The pH value of stored batter ranges from 6.7 to 4.5 or lower, to reach pH below 4.5 or lower commercially stored batter took 24 h and batter stored in the multi-layered film took 36 h at ambient temperature. The multi-layered stored batter showed better results of physicochemical properties in terms of fermentation time. Idli cake prepared with 3:1 blend ratio showed good results in terms of textural properties with compared to 4:1 blend ratio. Idli cake prepared with 3:1 blend ratio showed more pore percentage (21.88-36.80%) as compared to 4:1 blend ratio (18-32.98%) in per square inch. Due to higher barrier properties of the multi-layered film, the bacterial count increases at a slow rate and help to extend the shelf life of packaged batter more than 30 h at ambient temperature.

Development of High Oxygen Barrier Multi-layered Packaging Film for Shelf Life Extension of Ready-to-Cook (RTC) Idli Batter

Aim: The current study focuses on development of high oxygen barrier multi-layered packaging film for shelf life extension of Ready-to-Cook (RTC) idli batter.
 Place and Duration of Study: Department of Food Packaging and System Development at Indian Institute of Food Processing Technology, Thanjavur, Tamil Nadu, India, between Aug 2018 and Dec 2019.
 Methodology: The developed multi-layered film composed with polypropylene (PP) nanocomposite by depositing silicon dioxide (SiO2) on PP (0.010 mm) film and attached with different thickness of barrier layers were PP (0.010–0.053 mm) and ethylene-vinyl alcohol (EVOH 32%) film (0.066 mm) using layer-by-layer (LbL) process. The physical and chemical characteristics of commercial (A) and all developed multi-layered (B, C, D, E and F) films were tested for barrier and mechanical properties.
 Results and Discussion: The SEM analysis confirmed that the developed PP nanocomposite multi-layered films have a presence of SiO2 with quasi-spherical structure with diameter ranging from 200 to 500 nm. FTIR analysis also identified the presence of Si-O-Si group on all the developed PP nanocomposite films at wavenumber ranges from 1100-900 cm-1 and 467 cm-1. The film composed with PP++SiO2+EVOH (sample F) showed lower in oxygen transmission rate (OTR) of 452.46±33.94 cc/m2/24h and water vapour transmission rate (WVTR) of 1.07±0.16 g/m2 day. The batter stored in sample F film help to extend the shelf life upto 33 h at ambient temperature and commercially stored batter spoiled quickly (24 h) at ambient temperature.

Extreme Antiscaling Performance of Slippery Omniphobic Covalently Attached Liquids.

Scale formation presents an enormous cost to the global economy. Classical nucleation theory dictates that to reduce the heterogeneous nucleation of scale, the surface should have low surface energy and be as smooth as possible. Past approaches have focused on lowering surface energy via the use of hydrophobic coatings and have created atomically smooth interfaces to eliminate nucleation sites, or both, via the infusion of low-surface-energy lubricants into rough superhydrophobic substrates. Although lubricant-based surfaces are promising candidates for antiscaling, lubricant drainage inhibits their utilization. Here, we develop methodologies to deposit slippery omniphobic covalently attached liquids (SOCAL) on arbitrary substrates. Similar to lubricant-based surfaces, SOCAL has ultralow roughness and surface energy, enabling low nucleation rates and eliminating the need to replenish the lubricant. To enable SOCAL coating on metals, we investigated the surface chemistry required to ensure high-quality functionalization as measured by ultralow contact angle hysteresis (<3°). Using a multilayer deposition approach, we first electrophoretically deposit (EPD) silicon dioxide (SiO2) as an intermediate layer between the metallic substrate and SOCAL. The necessity of EPD SiO2 is to smooth (<10 nm roughness) as well as to enable the proper surface chemistry for SOCAL bonding. To characterize antiscaling performance, we utilized calcium sulfate (CaSO4) scale tests, showing a 20× reduction in scale deposition rate than untreated metallic substrates. Descaling tests revealed that SOCAL dramatically decreases scale adhesion, resulting in rapid removal of scale buildup. Our work not only demonstrates a robust methodology for depositing antiscaling SOCAL coatings on metals but also develops design guidelines for the creation of antifouling coatings for alternate applications such as biofouling and high-temperature coking.

Inductively Coupled Plasma Chemical Vapor Deposition for Silicon‐Based Technology Compatible with Low‐Temperature (≤220 °C) Flexible Substrates

Herein, an inductively coupled plasma chemical vapor deposition (CVD) (ICP‐CVD) technique is adopted for deposition of silicon dioxide and silicon thin films to fabricate metal–oxide–semiconductor (MOS) capacitors and thin film transistors (TFTs). Prior to the fabrication and characterization of the TFTs, C–V measurements and breakdown tests are conducted on MOS capacitors based on silicon dioxide deposited under temperatures as low as 20 °C. The breakdown field of 9 MV cm−1 is validated afterward, which implies the good electrical insulating property for acting as a gate insulator and the feasibility of the TFTs. After going through forming gas and thermal annealing with the highest temperature of 220 °C, the TFTs yield good gate insulating properties, a threshold voltage of 3.7 V, an on/off ratio of 6.4 × 102, field effect mobility of 1.2 cm2 (V s)−1, and a subthreshold slope of 3.9 V dec−1. They show promising electrical properties under such a low‐temperature fabrication process using ICP‐CVD technique compatible for silicon electronics using low‐cost flexible substrates.

Применение селективного контакта MoO-=SUB=-x-=/SUB=-/p-Si для оценки деградации приповерхностной области кремния

The possibility of evaluation the degree of damage to the near-surface layer of p-type silicon using a selective contact based on MoOx/p-Si is shown. A strong sensitivity of the current-voltage characteristics to the states on the silicon surface formed during the deposition of silicon oxide by magnetron sputtering is demonstrated.

Novel approach to passivation of InAs/GaSb type II superlattice photodetectors

The innovative two-step passivation by octadecanethiol (ODT) self-assembled monolayers (SAMs) and the following silicon dioxide (SiO2) deposition was used for the type-II InAs/GaSb superlattice photodetector. To understand the mechanism of passivation, the (100) GaSb surface covered with the ODT and, for comparison, with the biphenyl thiol (BPT), was characterized by the atomic force microscopy, Raman spectroscopy and contact angle analysis. The results of the study indicated the presence of the homogeneous both the ODT and the BPT monolayers; however, the ODT SAMs were more stable. Therefore, the ODT-based wet treatment was used in the two-step passivation resulting in a reduction of the dark current by one order of magnitude for passivated detector compared with an unpassivated device.

Effect of post-deposition annealing on atomic layer deposited SiO2 film for silicon surface passivation

We have investigated the passivation performance of atomic layer deposited silicon dioxide (ALD-SiO2) films on crystalline silicon surface with various post-annealing temperatures. A maximum effective lifetime of 2157 μs can be achieved at the optimized annealing temperature of 650 °C on 3 Ω cm n-type silicon wafers. The improved passivation quality can be attributed to the low interface defect density and extremely high positive fixed charge density. Especially, the high positive fixed charge density of over 4 × 1012 cm-2 can be observed after annealing at high temperature. Therefore, it is inferred that the passivation mechanism for ALD-SiO2 films is based on not only chemical passivation but also field-effect passivation, which is more similar with the ALD-Al2O3 films rather than the thermally grown SiO2 films. X-ray photoelectron spectroscopy, secondary ion mass spectroscopy and thermal effusion measurement revealed the variation of elements content and distribution of silicon, oxygen, hydrogen and carbon during the post-deposition thermal treatment process, indicating that the rearrangement and release of these elements create more oxygen vacancies and result in the improvement of interface quality and positive fixed charge density of ALD-SiO2 films.

Graphene-Induced in Situ Growth of Monolayer and Bilayer 2D SiC Crystals Toward High-Temperature Electronics.

A reproducible graphene-induced in situ process is demonstrated for the first time for growing large-scale monolayer and bilayer cubic silicon carbide (SiC) crystals on a liquid Cu surface by chemical vapor deposition (CVD) method. Precise control over the morphology of SiC crystals is further realized by modulating growth conditions, thus leading to the formation of several shaped SiC crystals ranging from triangular, rectangular, pentagonal, and even to hexagonal kind. Simulations based on density functional theory are carried out to elucidate the growth mechanism of SiC flakes with various morphologies, which are in striking consistency with experimental observations. In the liquid Cu-assisted CVD system, growth temperature (∼1100 °C) enables sublimation and deposition of silicon oxide (SiO2) derived from quartz tube, while liquid Cu facilitates preformation of graphene originated from methane. The SiO2 and graphene, grown and reacted in situ in the CVD process, are served as the silicon and carbon source for the cubic SiC crystals, respectively. Moreover, the gradual transformation process from SiO2 particles to SiC flakes is directly observed, with several middle stages clearly displayed. The direct in situ growth of SiC crystals offers a novel method for scaled production of SiC crystals and is beneficial to understand its growth mechanism, and thus push forward the way to develop high-temperature and high-frequency electronic devices.

Structure of Highly Porous Silicon Dioxide Thin Film: Results of Atomistic Simulation

The high-energy glancing angle deposition of silicon dioxide films with alternation of deposition angle is studied using classical atomistic simulation. Both slow and fast alternations are investigated. The growth of vertical tree-like columns and chevron-like regular structures is demonstrated under fast and slow alternations, respectively. Due to high porosity, the density of the deposited silicon dioxide films is reduced to 1.3 ÷ 1.4 g/cm3. This results in reduction of the refractive index to 1.3, which agrees with known experimental data. For slow continuous substrate rotation, formation of a helical structure is demonstrated.

Design, fabrication and characterization of high temperature thin film heat flux sensors

Thin film thermopile (TFTP) heat flux sensors have been developed in this paper. The property of TFTPs was modeled and analyzed by FEA COMSOL in order to optimize performance. Two types of TFTPs were fabricated by surface micromachining technology. For the TFTPs operating at temperature no more than 400 °C, spin coated polyimide was used as the thermal insulator. While for high temperature operation, the ion beam deposited silicon dioxide was chosen as the thermal insulator. Furthermore, thermally grown oxide (TGO) of aluminum layer inserted between metal and silicon dioxide improved TFTPs reliability at high temperature. The TFTPs was calibrated by a halogen tungsten lamp calibration system. The results showed that the output voltage of TFTPs responded linearly with the heat flux, which indicated that the TFTPs with optimized design were capable of providing surface heat flux measurement, and the TFTPs with silicon oxide as thermal insulator had the potential to work at 1000 °C.