Chemical Vapor Deposited Silicon Dioxide Research Articles

Recess-Free E-Mode AlGaN/GaN MIS-HFET with Crystalline PEALD AlN Passivation Process

We utilized a plasma-enhanced atomic layer deposition (PEALD) process to deposit an AlN passivation layer on AlGaN/GaN surface to enhance the polarization effects, which enabled the fabrication of an enhancement-mode (E-mode) AlGaN/GaN metal-insulator-semiconductor heterojunction field-effect transistor (MIS-HFET) without the need for a gate recess process. The AlN film deposited by PEALD exhibited a crystalline structure, not an amorphous one. The enhanced polarization effect of introducing the PEALD AlN film on a thin AlGaN barrier was confirmed through electrical analysis. To fabricate the E-mode AlGaN/GaN MIS-HFET, the PEALD AlN film was deposited on a 4.5 nm AlGaN barrier layer and then a damage-free wet etching process was used to open the gate region. The MIS-gate structure was formed by depositing a 15 nm plasma-enhanced chemical vapor deposition (PECVD) silicon dioxide (SiO2) film. The fabricated thin-AlGaN/GaN MIS-HFET demonstrated successful E-mode operation, with a threshold voltage of 0.45 V, an on/off ratio of approximately 109, a specific on-resistance of 7.1 mΩ·cm2, and an off-state breakdown voltage exceeding 1100 V.

Determination of the nonlinear thermo-optic coefficient of silicon nitride and oxide using an effective index method.

There is little literature characterizing the temperature-dependent thermo-optic coefficient (TOC) for low pressure chemical vapor deposition (LPCVD) silicon nitride or plasma enhanced chemical vapor deposition (PECVD) silicon dioxide at temperatures above 300 K. In this study, we characterize these material TOC's from approximately 300-460 K, yielding values of (2.51 ± 0.08) · 10-5K-1 for silicon nitride and (5.67 ± 0.53) · 10-6K-1 for silicon oxide at room temperature (300 K). We use a simplified experimental setup and apply an analytical technique to account for thermal expansion during the extraction process. We also show that the waveguide geometry and method used to determine the resonant wavelength have a substantial impact on the precision of our results, a fact which can be used to improve the precision of numerous ring resonator index sensing experiments.

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.

Selective mono-alkylbenzene disproportionation over silylated MFI zeolite

Silica chemical vapor deposition (Si-CVD) technique was applied in the silylation of ZSM-5 zeolite to enhance para isomer product selectivity in the disproportionation of toluene (TDP) and ethylbenzene (EBDP). A threshold value in Si-CVD deposition for enhancement in para isomer selectivity in TDP and EBDP was determined. Beyond the threshold value, the para selectivity increased with increasing silica deposition amount. Upon Si-CVD modification, while the micropore size of the MFI zeolite stayed the same with the parent MFI zeolite, the enhancement in para selectivity could be due to the passivation of external active sites. The p-diethylbenzene isomer selectivity of>99 % was demonstrated at EB conversion up to 35 %. Nevertheless, p-xylene isomer product selectivity of around 83 % was obtained only at a reasonable conversion level of 20 %. The difference in selectivation efficiency between TDP and EBTDP reactions could be attributed to the difference in the relative ratio of reaction kinetics rate to the diffusion rate in associated with different reaction temperature range.

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.

Copper indium gallium selenide (CIGS) solar cell devices on steel substrates coated with thick SiO2-based insulating material

Flexible copper indium gallium selenide (CIGS)-based solar cells were developed on stainless steel (STS) substrates covered with an insulating layer. The properties of the CIGS films fabricated on STS foils coated with SiO2-based soluble material (“sol-SiO2”) were compared with those on plasma enhanced chemical vapor-deposited silicon oxide (“PE-SiO2”)/MoNa/STS and SLG substrates. The decrease in compensating donor due to sufficient Na doping from the insulating layer was attributed to higher open-circuit voltage and fill factor. Furthermore, the double graded Ga composition in the CIGS films grown on the STS substrates was preserved, and the open-circuit voltage was enhanced with a minor decrease in the short-circuit current. As a result, solar cells with 14% efficiency were produced on sol-SiO2/STS samples with a Fe atom diffusion barrier and external Na incorporation. This was far higher than the 9.5% and 12.8% obtained from the solar cells on PE-SiO2/MoNa/STS and SLG, respectively.

Thermal annealing effects on the stress stability in silicon dioxide films grown by plasma-enhanced chemical vapor deposition

The stress stability in plasma-enhanced chemical vapor deposition (PECVD) silicon dioxide (SiO2) films is a key factor of device performance. In this study, the PECVD SiO2 films are annealed at 400–1000 °C in a nitrogen (N2) or oxygen (O2) ambience for 2 h. The influences of annealing parameters on the stress state and stress stability in PECVD SiO2 films are investigated. The bonding nature and surface morphology of the films are also studied to analyze the physical mechanism involved. It is demonstrated that the stress stability is first deteriorated and then improved with increasing annealing temperature. In addition, O2 ambience is more appropriate to improve stress stability than N2, and the stress in PECVD SiO2 film can be stabilized when it is annealed at 1000 °C in O2 ambience. These results should be able to provide important insights into the design of device fabrication processes.

Improving stress stability in low-pressure chemical vapor deposited silicon dioxide films by ion implantation

The stress state of low-pressure chemical vapor deposition (LPCVD) silicon dioxide (SiO2) films fluctuates upon aging due to the ambient moisture. The related variation of the SiO2 films is a key factor of device reliability. In this study, ion implantation is introduced to improve film stress stability. The stress state modified by ion implantation is discussed in detail and an analytical model is presented. The evolution of the stress in as-deposited and P+-, As+-, and B+-implanted LPCVD SiO2 films upon aging is investigated, and the bonding nature of the films is also studied to provide insight into the physical mechanisms involved. It is demonstrated that low implantation energy slightly modifies the stress in films. In addition, P+ ion is the most appropriate impurity ion to improve film stress stability, and the stress in P+-implanted LPCVD SiO2 film can be stabilized with a low tensile stress of 67MPa when the film is implanted at 15keV with a dose of 1×1015cm−2.

Mass densification and defect restoration in chemical vapor deposition silicon dioxide film using Ar plasma excited by microwave

Silicon dioxide (SiO2) films formed by chemical vapor deposition (CVD) have been treated with Ar plasma excited by microwave. The changes of the mass densities, carrier trap densities, and thicknesses of the CVD-SiO2 films with the Ar plasma treatments were investigated. The mass density depth profiles were estimated with X-Ray Reflectivity (XRR) analysis using synchrotron radiation. The densities of carrier trap centers due to defects of Si-O bond network were estimated with X-ray Photoelectron Spectroscopy (XPS) time-dependent measurement. The changes of the thicknesses due to the oxidation of Si substrates were estimated with the XRR and XPS. The mass densities of the CVD-SiO2 films are increased by the Ar plasma treatments. The carrier trap densities of the films are decreased by the treatments. The thicknesses of the films are not changed by the treatments. It has been clarified that the mass densification and defect restoration in the CVD-SiO2 films are caused by the Ar plasma treatments without the oxidation of the Si substrates.

A Sub-Critical Barrier Thickness Normally-Off AlGaN/GaN MOS-HEMT

A new high-performance normally-off gallium nitride (GaN)-based metal-oxide-semiconductor high electron mobility transistor that employs an ultrathin subcritical 3 nm thick aluminium gallium nitride (Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.25</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.75</sub> N) barrier layer and relies on an induced two-dimensional electron gas for operation is presented. Single finger devices were fabricated using 10 and 20 nm plasma-enhanced chemical vapor-deposited silicon dioxide (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) as the gate dielectric. They demonstrated threshold voltages (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> ) of 3 and 2 V, and very high maximum drain currents (IDSmax) of over 450 and 650 mA/mm, at a gate voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GS</sub> ) of 6 V, respectively. The proposed device is seen as a building block for future power electronic devices, specifically as the driven device in the cascode configuration that employs GaN-based enhancement-mode and depletion-mode devices.

Hot-wire polysilicon waveguides with low deposition temperature

We fabricated and measured the optical loss of polysilicon waveguides deposited using hot-wire chemical vapor deposition at a temperature of 240°C. A polysilicon film 220 nm thick was deposited on top of a 2000 nm thick plasma-enhanced chemical vapor deposition silicon dioxide layer. The crystalline volume fraction of the polysilicon film was measured by Raman spectroscopy to be 91%. The optical propagation losses of 400, 500, and 600 nm waveguides were measured to be 16.9, 15.9, and 13.5 dB/cm, respectively, for transverse electric mode at the wavelength of 1550 nm. Scattering loss is expected to be the major contributor to the propagation loss.

One-Step-Process Composite Colloidal Monolayers and Further Processing Aiming at Porous Membranes

Composite materials consisting of a monolayer of polystyrene spheres (diameters of 430 and 520 nm) and porous silica, filling in the interstices, have been fabricated and characterized. The proposed growth method introduces some novelties as far as the fabrication of this kind of monolayers is concerned, as it probes the compatibility of coassembly (in which a silica precursor, tetraethyl orthosilicate (TEOS), is added to the base colloid) with confined growth in a wedge-shaped cell, while profiting from the advantages of both techniques. Using this method, it is possible to fabricate the composite monolayer in a single growth step. A systematic study of the influence of TEOS concentration in the initial colloid was performed in order to improve the quality of the two-dimensional crystals produced. Thus, it was demonstrated that the two methods are compatible. Furthermore, the composites were then subjected to thermal treatment so that the polymer is removed to reveal the inverse structure. After the calcination the membranes still present very good quality and so the proposed approach is effective for the fabrication of porous membranes. A comparison of reflectance spectra, between composite monolayers fabricated using this method and composites achieved by infiltrating polystyrene bare opals with silica chemical vapor deposition, is also established. The procedure presented is expected to establish the route for an easier and quicker fabrication of inverse monolayers of high refractive index materials with applications in light control.

Hollow Waveguides With Low Intrinsic Photoluminescence Fabricated With PECVD Silicon Nitride and Silicon Dioxide Films

A new type of integrated hollow core anti-resonant reflecting optical waveguide (ARROW) with low intrinsic photoluminescence (PL) fabricated with plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (SiN) and silicon dioxide (SiO2) films is demonstrated. The waveguide is fabricated by surrounding the hollow core with alternating layers of SiN and SiO2. The thicknesses and indices of the layers are designed to meet an anti-resonance condition. Compared to earlier ARROW structures made by depositing high-temperature (HT) SiN (250 °C), the PL background decreases by a factor of ~ 10 when low-temperature (LT) SiN (100 °C ) films are used. Therefore, LT SiN ARROWs are attractive platforms for sensitive fluorescence and Raman spectroscopy measurements of biomolecules.

Cryogenic inductively coupled plasma etching for fabrication of tapered through-silicon vias

Vertical interconnects pose an interesting method for heterogeneous integration of electronic technologies allowing three-dimensional (3D) stacking of microelectromechanical systems devices and integrated circuit components. The vertical interconnects, referred to as through-silicon vias, begin with the formation of blind vias in silicon that are eventually exposed by mechanically lapping and polishing the wafer back side. Inductively coupled plasma (ICP) etching using SF6∕O2 gas chemistry at cryogenic temperatures has been investigated as a way to form vias with a tapered sidewall. The point in creating a controlled taper is so that subsequent thin films can be deposited along the sloped sidewall that line the via with insulation, barrier, and seed films. This tapering is necessary if the via lining processes do not provide adequate conformal coverage, a common problem for conventional low temperature deposition processes. In our process for lining the via sidewall, plasma enhanced chemical vapor deposited silicon dioxide is used to insulate vias from the surrounding silicon. Both Ti and Cu are sputter deposited and provide protection from copper migration and a seed film for Cu electrodeposition, respectively. After etching and lining, the vias are filled by reverse pulse plating of Cu. Vias are 20–25μm in diameter and etched using different masking materials. The effect of changing gas flow rates, chamber pressure, ICP power, and substrate temperature on etch rate, via profile, and sidewall morphology will be presented. These parameters are critical in the optimization of an etch process for vias of specific dimensions to be used in 3D integration.

Equilibrium molecular dynamics and mean first passage time analysis of the separation of exhaust gases at high temperatures by silica nanoporous membranes

An investigation of mechanisms associated with the high selectivity of a gas mixture at high temperatures by silica nanoporous membranes has been conducted in the framework of equilibrium classical molecular dynamic simulations and formalism of fractional diffusion equation on a sample of a gas mixture of exhaust gases. The important feature is the quite realistic modeling of the silica nanoporous membranes based on the use of an analytic bond order potential and the conception of dangling bonds. The last two were successfully employed to model the realistic silica chemical vapor deposition process (Burlakov et al 2001 Phys. Rev. Lett. 86 3052). The dependence of the selective properties on temperature, density (voidage volume) and morphology has been investigated. The selectivity at a low temperature (673 K) is found to be more efficient than at a high temperature (873 K). When only Lennard-Jones interaction between a gas and a solid is included the selectivity is found to be changed at the low temperature (673 K) from 1.2 : 1 for a density of 50% to 1.03 : 1 for a density of 80%. Including an additional electrostatic interaction increases the selectivity from 1.79 : 1 for a density of 50% to 2.26 : 1 for a density of 80%. At the high temperature (873 K) when only Lennard-Jones potential is included the selectivity is found to be changed from 1.21 : 1 for a density of 50% to 1.13 : 1 for a density of 80%. With an additional electrostatic force the selectivity is found to be the same for all densities at around 1.43 : 1. The conclusion is that the most efficient conditions for the selective membrane are a temperature of 673 K and a high density. Under these conditions the mean first passage times for species O2 and N2 are almost the same and much less than for species CO2. The methodology developed is general. This paper is based on the author's PhD thesis.

Techniques of cryogenic reactive ion etching in silicon for fabrication of sensors

Cryogenic etching of silicon, using an inductively coupled plasma reactive ion etcher (ICP-RIE), has extraordinary properties which can lead to unique structures difficult to achieve using other etching methods. In this work, the authors demonstrate the application of ICP-RIE techniques which capitalize on the cryogenic properties to create different sensors geometries: optical, electrical, magnetic, and mechanical. The three techniques demonstrated are (1) single step deep etches with controllable sidewall profiles. Demonstrating this, silicon pillars with over 70μm depth and less than 250nm sidewall roughness were etched using only 1.6μm of photoresist for use as solar cells. (2) Using the cryogenic etch for thick metallization and liftoff with a thin photoresist mask. Demonstrating this second technique, a magnetic shim was created by deposition of 6.5μm of iron into 20μm deep etched trenches, using the remaining 1.5μm photoresist etch mask as the liftoff mask. Using the same technique, 15μm of copper was lifted off leaving a 20μm deep plasma enhanced chemical vapor deposition silicon oxide coated, silicon channel with copper. (3) Use of a two step cryogenic etch for deep etching with reduced sidewall undercutting. This was demonstrated by fabrication of deep and anisotropic microelectromechanical systems structures; a mechanical resonator was etched 183μm deep into silicon with less than 3μm of undercutting. This work also describes the etch parameters and etch controls for each of these sensors.

Ultrathin tunnel insulator films on silicon for electrochemiluminescence studies

Thin insulating films on conductive substrates have been used for tunnel emission of hot electrons into aqueous solution. The hydrated electrons thus formed induce electrochemiluminescence (ECL) in various luminophores, e.g. rare-earth metal chelates, which can be detected in sub-nanomolar concentrations. The luminophores can be used as labels for antibodies, enabling simple and highly sensitive immunoassays. This paper compares thermal silicon dioxide, low pressure chemical vapor deposited silicon nitride, plasma enhanced chemical vapor deposited silicon dioxide and nitride, atomic layer deposited alumina, and liquid phase deposited silicon dioxide for electrodes in ECL applications.

Direct patterning of plasma enhanced chemical vapor deposition silicon dioxide by electron beam lithography

Hydrogen silsesquioxane (HSQ) is a popular high resolution negative tone resist for electron beam lithography. This work investigates whether a HSQ-like film can be mimicked via plasma enhanced chemical vapor deposition (PECVD) rather than spin coating. It is shown that PECVD oxide acts as mainly a negative tone resist.

Fabrication and characterization of m‐plane (1‐100) GaN based metal‐oxide‐semiconductor capacitors

AbstractM‐plane non‐polar, Gallium Nitride(GaN) based metal‐oxide‐semiconductor (MOS) capacitors were fabricated by depositing 150 nm thick low‐pressure chemical vapor deposition silicon dioxide at 900 °C. No positive shift in the flat band voltage of m‐plane GaN MOS capacitors was observed versus temperature, confirming the absence of pyroelectric effects. In contrast, c‐plane (0001) polar, GaN MOS capacitors, show a positive flat band voltage shift versus temperature and the pyroelectric coefficient of –3×109 q/cm2‐K was measured. A small negative shift in flat band voltage was observed in m‐plane GaN consistent with changes in the bulk potential and corresponding decrease in the occupancy of interface traps. Time dependent dielectric(TDDB) measurements were performed at 200 °C and a mean time to failure (MTTF) of 40 hours was measured at an electric field of 5 MV/cm. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Surfaces with high solar reflectance and high thermal emittance on structured silicon for spacecraft thermal control

Presented here is an examination of unstructured and structured (by anisotropic etching), monocrystalline silicon wafers coated with sputter deposited aluminum and chemical vapor deposited silicon dioxide for high solar reflectance and high thermal emittance, respectively. The topography of the samples was characterized with optical and scanning electron microscopy. Optical properties were examined with reflectance and transmittance spectroscopy, partly by usage of an integrating sphere. The measurement results were used to estimate the equilibrium temperature of the surfaces in space. The suitability of the surfaces with high solar reflectance and high thermal emittance to aid in the thermal control of miniaturized, highly integrated components for space applications is discussed. A silicon dioxide layer on a metal layer results in a slightly lower reflectance when compared to surfaces with only a metal layer, but might be beneficial for miniaturized space components and modules that have to dissipate internally generated heat into open space. Additionally, it is an advantage to microstructure the emitting surface for enhanced radiation of excess heat.