Chemical Vapor Deposition SiO2 Research Articles

Highly selective isotropic gas-phase etching of SiO2 using HF and methanol at temperatures –30 °C and lower

The gas-phase etching of SiO2 was examined using HF and methanol vapor at temperatures below 0 °C and at low pressure. The etching rate of SiO2 increased with decreasing temperature and showed a maximum around –30 °C. The obtained etching rate was a maximum of 40 nm min−1 at plasma-enhanced chemical vapor deposition SiO2. The etching rate of SiN examined for comparison was more than ten times smaller than that of SiO2 under the same condition. As a result, the etching selectivity of SiO2 to SiN was found to be over 20 at –40 °C. When utilizing a low temperature of less than –30 °C, gas-phase etching of SiO2 showing a high etching rate and selectivity was achieved.

Investigations of Sidewall Passivation Using the Sol-Gel Method on the Optoelectronic Performance for Blue InGaN Micro-LEDs

The optoelectronic effects of sidewall passivation on micro-light-emitting diodes (Micro-LEDs) were investigated using sol-gel chemical synthesis. Blue InGaN/GaN multi-quantum well (MQW) Micro-LEDs, ranging in size from 20 × 20 μm to 100 × 100 μm and with high EQE, were fabricated and distinguished by the passivation method used, including no passivation, sol-gel SiO2, and plasma-enhanced chemical vapor deposition (PECVD) SiO2. Impressively, the sol-gel method is advantageous in improving the optoelectronic performance of Micro-LEDs. The fabricated 20 × 20 μm Micro-LEDs showed an EQE of 27.7% with sol-gel passivation, which was a 14% improvement compared to devices without sidewall passivation. Sol-gel sidewall passivation allows Micro-LEDs to effectively achieve sharper edge emission, superior surface luminous uniformity, and intensity, providing the possibility for the fabrication of low-cost and high-efficiency Micro-LEDs.

Size dependent swift heavy ion induced Au nanoparticle elongation in SiO2 matrix

The elongation of spherical Au nanoparticles embedded in SiO2 under swift heavy ion (SHI) irradiation is an extensively studied phenomenon. The use of a TEM grid as a substrate facilitates the identification of the same nanoparticle before and after the irradiation. Since the underdensification of SiO2 inside the ion track plays a key role, the elongation is sensitive to the matrix material properties. Therefore, we studied the elongation process of SHI irradiated Au spherical nanoparticles of various diameters (5–80 nm) embedded either in atomic layer deposition (ALD) or plasma-enhanced chemical vapor deposition (PECVD) SiO2. The results show that a different elongation ratio is achieved depending on the particle initial size, ion fluence, and a different SiO2 deposition method. The embedded nanoparticles in ALD SiO2 elongate roughly 100% more than the nanoparticles embedded in PECVD SiO2 at the biggest applied fluence (5×1014ions/cm2). On the other hand, at fluences lower than 1014ions/cm2, nanoparticles elongate slightly more when they are embedded in PECVD SiO2.

Investigating Substrate Loss in MEMS Acoustic Resonators and On-Chip Inductors.

This work studies the influence of substrate loss on the performance of acoustic resonators and on-chip inductors and investigates the effective substrate resistivity of seven commonly used substrates in silicon-based devices. The substrates include X-cut lithium niobate (LiNbO3) film with two different thicknesses (400 nm and 1.6 [Formula: see text]) on high-resistivity Si (HR-Si) and amorphous Si wafers, SiO2 film with two different thicknesses on HR-Si, and bare HR-Si. The effective resistivities of these substrates are extracted using coplanar waveguides (CPWs) over a frequency range from 1 to 40 GHz. Using the effective resistivity approach, the efficiency of two substrate loss reduction techniques-Si wafer removal and amorphous Si-in reducing substrate loss is quantified. Comparison of the extracted substrate resistivities of the suspended and un-suspended dielectric-on-Si structures and comparison of LiNbO3 on HR-Si and amorphous Si are carried out. Substrate loss reduction techniques are more advantageous for a thinner dielectric film and at a lower frequency range due to the higher filling factor of the electric field in the Si wafer. Finally, by comparison of the effective substrate resistivity of SiO2 film on an HR-Si with bare HR-Si, thick plasma-enhanced chemical vapor deposition (PECVD) SiO2 film is found to be a good insulation layer to reduce substrate loss.

Impact of carrier wafer on etch rate, selectivity, morphology, and passivation during GaN plasma etching

The choice of carrier wafer was found to significantly influence etch rates, selectivity, and morphology in GaN micropillar etching in a Cl2-Ar high-density inductively coupled plasma. 7 × 7 mm2 GaN on sapphire chips with a plasma-enhanced chemical vapor deposition SiO2 hard mask was etched on top of 4-in. fused silica, silicon carbide, silicon, sapphire, aluminum nitride, and high purity aluminum carriers. Silicon and silicon carbide carriers reduced GaN:SiO2 selectivity because incidental SiClx and CClx etch products from the carriers attack the SiO2 mask. Aluminum nitride and high-purity aluminum carriers yielded the highest GaN:SiO2 selectivities due to the deposition of Al-based etched by-products, while the highest GaN etch rate was achieved using the sapphire carrier since it was the most inert carrier and did not sink any Cl2. Results indicate that SiO2 and Al may be used as passivation materials during GaN etching, as vertical profiles were achieved when SiO2 or Al is redeposited from the fused silica and aluminum carriers, respectively. Floor pitting, trenching, sidewall roughness, and faceting were all influenced by carrier wafer type and will be discussed.

Scaling effects and brittle fracture mechanisms in laser punching of PECVD SiO2 films

We experimentally investigate the removal of several microns thick plasma-enhanced chemical vapour deposition SiO2 films by a localized dynamic fracture due to confined laser–matter interaction with the silicon substrate (punching) using 10 ps laser pulses at 355 nm. A near order of magnitude increase in the punching threshold fluence (from ∼0.1 to ∼1 J cm−2) is observed as the ratio between the spot size and the film thickness is scaled down, in order to produce high aspect ratio openings in the film. An opening radius of about twice the film thickness appears to be an approximate practical limit. A high aspect ratio opening is created by a cone fracture of the film and the ejection of a conoid film segment (flyer). We discuss mechanisms of brittle fracture that may lead to the observed patterns.

Role of oxygen in surface kinetics of SiO2 growth on single crystal SiC at elevated temperatures

Understanding surface kinetics of SiO2 growth on single crystal SiC at elevated temperatures is crucial to fabricate high-performance SiC-based devices. However, the role of oxygen in the evolution mechanism of SiC surface at atomic scale has not been comprehensively elaborated. Here, we reveal the manipulation effect of oxygen on the competitive growth of thermal oxidation SiO2 (TO-SiO2) and thermal chemical vapor deposition SiO2 (TCVD-SiO2) on the 4H-SiC substrate at 1500 °C. TO-SiO2 is formed by the thermal oxidation of SiC, in which the substrate undergoes layer-by-layer oxidation, resulting in an atomically flat SiC/TO-SiO2 interface. TCVD-SiO2 growth includes the sublimation of Si atoms, the reaction between sublimated Si atoms and reactive oxygen, and the adsorption of gaseous SixOy species. A relatively high sublimation rate of Si atoms at SiC atomic steps causes the transverse evolution of the nucleation sites, leading to the formation of nonuniform micron-sized pits at the SiC/TCVD-SiO2 interface. The low oxygen concentration favors TCVD-SiO2 growth, whose crystal quality is much better than that of TO-SiO2 due to the high surface mobility in the thermal CVD process. We further achieve the epitaxial growth of graphene on 4H-SiC in an almost oxygen-free reaction atmosphere. Additionally, ReaxFF reactive molecular dynamic simulation results illustrate that the decrease in oxygen concentration can promote the growth kinetics of SiO2 on single crystal SiC from being dominated by thermal oxidation to being dominated by thermal CVD.

Improving the Leakage Characteristics and Efficiency of GaN-based Micro-Light-Emitting Diode with Optimized Passivation

We investigated the effect of atomic layer deposition (ALD) Al2O3 (50 nm)/plasma-enhanced chemical vapour deposition (PECVD) SiO2 (250 nm) and PECVD SiO2 (300 nm) passivation layers on the leakage current and efficiency of InGaN-based micro-LEDs with different sizes. Regardless of passivation layers, the leakage current increased with decreasing LED size and increasing reverse bias. Emission microscopy examination showed that with increasing reverse bias, the number of defect-related emission spots and their intensities increased. For the micro-LEDs <50 μm, the emission spots were mainly located at the sidewall regions. Above −10 V, the single PECVD SiO2 passivation layer gave higher leakage current than the double ALD-Al2O3/PECVD-SiO2 layer. The micro-LEDs with the single passivation layer gave the ideality factors of about 2.0, while that with the double layer exhibited values smaller than 2.0. The micro-LEDs with the double passivation layer exhibited external quantum efficiency peaks at lower current density compared to those with the single layer. It was shown that smaller micro-LEDs were more sensitively dependent on the types of the passivation layers. These results exhibit that the ALD-Al2O3/PECVD-SiO2 passivation layer is more effective in suppressing the sidewall damage-induced current than the PECVD-SiO2 layer.

Application of SiOx-coated poly (ε-caprolactone) film for preservation of cherry tomato

The poly( ε-caprolactone)/silicon oxide (PCL/SiO x)-coated film was prepared by plasma-enhanced chemical vapor deposition of SiO x. The result showed that the PCL/SiO x film presented increased elongation at break and appropriate gas permeability and CO2/O2 permselectivity. The PCL/SiO x film was further used for window packing container of equilibrium-modified atmosphere packaging of fresh cherry tomato. The gas composition within containers depended on the permeability of PCL/SiO x film and respiration of cherry tomato, which finally reached steady states that 4–6% CO2 and 11–13% O2 at room temperature and 2–3% CO2 and 17–19% O2 at 5°C, respectively. High sensory score, firmness, soluble solid concentration, ascorbic acid content, lower weight loss, and retarded respiration climacteric could be found for the cherry tomato packaged by PCL/SiO x film, indicating that delayed ripening, higher nutrient content, and extended shelf life were achieved.

(Invited) Photoemission-Based Characterization of Gate Dielectrics and Stack Interfaces

We have demonstrated quantitative evaluation of dielectric function and optical constants for gate dielectrics such as remote plasma-assisted chemical-vapor-deposition (CVD) SiO2 and plasma-assisted atomic-layer-deposition (ALD) alumina-silicate in the energy range of 5 ~ 30 eV from the combination of the analysis of energy loss signals (ELS) of core-line photoelectrons and the results of Kramers-Kronig transformation of measured ELS. We have also show quantification of the energy distributions of occupied gap states in gate dielectrics and dielectric stack interfaces such as CVD SiO2, ALD HfO2 and ALD hafnia-silicates on GaN by means of total photoelectron yield spectroscopy (PYS) in the photo-excitation energy range from 3 ~ 10eV.

Plasma enhanced chemical vapor deposition of SiO2 and SiNx on AlGaN: Band offsets and interface studies as a function of Al composition

In this work, the authors characterized the interface of plasma enhanced chemical vapor deposition (PECVD) dielectrics, SiO2 and SiNx with AlGaN as a function of Al composition. SiO2 is found to exhibit type I straddled band alignment with positive conduction and valence band offsets for all Al compositions. However, the interface Fermi level is found to be pinned within the bandgap, indicating a significant density of interface states. Hence, SiO2 is found to be suitable for insulating layers or electrical isolation on AlGaN with breakdown fields between 4.5 and 6.5 MV cm−1, but an additional passivating interlayer between SiO2 and AlGaN is necessary for passivation on Al-rich AlGaN. In contrast, Si-rich PECVD SiNx is found to exhibit type II staggered band alignment with positive conduction band offsets and negative valence band offsets for Al compositions &amp;lt;40% and type I straddled band alignment with negative conduction and valence band offsets for Al compositions &amp;gt;40% and is, hence, found to be unsuitable for insulating layers or electrical isolation on Al-rich AlGaN in general. In contrast to passivating stoichiometric LPCVD Si3N4, no evidence for interface state reduction by depositing SiNx on AlGaN is observed.

Fabrication and Sensitivity Analysis of Guided Beam Piezoelectric Energy Harvester

This paper reports the fabrication of MEMS-based guided two-beam piezoelectric energy harvester for low-frequency operation. A highly c-axis-oriented zinc oxide thin film of 2.5- $\mu \text{m}$ thickness covered with 0.5- $\mu \text{m}$ plasma-enhanced chemical vapor deposition SiO2 is sandwiched between the aluminum electrodes to form split electrodes on the two beams. A pyramidal-shaped seismic mass that gives a higher electric potential is realized by bulk micromachining using CMOS compatible 25 wt% tetramethyl ammonium hydroxide wet etching. The thickness of the beams is optimized using deep reactive-ion etching to achieve a low-frequency operation. COMSOL Multiphysics has been used to study the stress distribution to optimize the dimension and placement of the split electrodes. The optimized split electrodes give a reduced resonance frequency by 4.2% when compared with previously used electrode pattern ensuring maximum electric potential generation for guided two-beam structure. The resonance frequency of the device measured experimentally using laser Doppler vibrometer comes to be 466 Hz. The packaged device exhibits a maximum sensitivity of 1.5089 mV/m/s2 in the frequency range from 160 to 1000 Hz.

Development of a kinetic model for the moderate temperature chemical vapor deposition of SiO2 films from tetraethyl orthosilicate and oxygen

An apparent kinetic model for the chemical vapor deposition of SiO2 from tetraethyl orthosilicate (TEOS) and O2 was developed in a poorly investigated range of operating conditions, that is, at atmospheric pressure and between 350 and 500°C, based on literature survey and experimental results obtained in a hot wall tubular reactor. The kinetic model was implemented into the computational fluid dynamics code FLUENT and validated both in shape and value by comparison with experimental deposition rate profiles. It reveals that for the conditions tested, a possible mechanism of SiO 2 deposition involves two intermediate species formed from TEOS homogeneous decomposition, the first one being active from 300°C and the second one contributing to deposition for temperatures higher than 370°C. The calculated local profiles of gas flow, gas temperature, species mass fraction, and silica deposition rate indicate that the first intermediate species leads to marked film thickness gradients, the second one being more stable as producing uniform thicknesses. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3958–3966, 2018

Time-dependent dielectric breakdown of recessed AlGaN/GaN-on-Si MOS-HFETs with PECVD SiO2 gate oxide

This paper reports the first-time evaluation of the time-dependent dielectric breakdown of recessed AlGaN/GaN-on-Si metal-oxide-semiconductor heterostructure field-effect transistors (MOS-HFETs) with plasma enhanced chemical vapor deposition (PECVD) SiO2 gate oxide. The interface fixed charge density and oxide bulk charge density extracted from the flat-band voltage characteristics were 2.7 × 1011 ± 6.54 × 1010 cm−2 and -9.71 × 1017 ± 5.18 × 1016 cm−3, respectively. The time dependent dielectric breakdown (TDDB) characteristics exhibited longer lifetime estimation as the SiO2 thickness increased. The excellent reliability of the PECVD SiO2 film was validated for use as the gate oxide of recessed AlGaN/GaN MOS-HFET.

Hybrid-Phase Microstructural ITO-Stabilized ZnO TFTs With Self-Aligned Coplanar Architecture

In this letter, hybrid-phase microstructural ITO-stabilized ZnO thin films, which were capped by silane-sourced or tetraethyl-orthosilicate-sourced plasma-enhanced chemical vapor deposition (PECVD) SiO2 layers, were found to present remarkably different resistivity variation after O2 annealing treatment. Besides hydrogen-related factors, the silicon-doping phenomenon along with the silane-sourced PECVD process was also responsible for the durable low-resistivity state of the hybrid-phase microstructural ITO-stabilized ZnO thin films. Via a combination of differentiatedPECVD andO2 annealingprocesses, the self-aligned coplanar TFTs were fabricated, and they exhibited good electrical characteristics with an average field-effect mobility of 19.56 cm2/Vs, and a subthreshold swing of 105 mV/decade, as well as robust stability against gate-bias stress.

Run-to-Run Yield Evaluation of Improved Nb 9-layer Advanced Process using Single Flux Quantum Shift Register Chip with 68,990 Josephson Junctions

We have improved an Nb 9-layer advanced process (ADP2) using a plasma-enhanced chemical vapor deposition (PECVD) SiO2 insulator. We could solve the problems due to the surface profile of the PECVD SiO2 by adding an ion-milling process. The reliability of the ADP2 was evaluated by the operating yield of the SFQ shift registers (SRs). The SRs with six different bit sizes from 16 to 2560 were designed to evaluate the circuit size dependency of their yields. The total number of SRs is 16, and the total number of junctions per chip is 68,990. By introducing the PECVD SiO2 insulator, we could obtain a high operating yield of more than 80% even for large-scale 2560-bit shift registers with more than 10,000 junctions. Moreover, we could obtain nine perfect chips (in which all the SRs in the chip functioned) out of 26 measured chips fabricated using the PECVD SiO2. From these results, we believe that the fabrication yield of the ADP2 is at a level of 100,000 Josephson junction circuits.

Deposition of DNA Nanostructures on Highly Oriented Pyrolytic Graphite.

We report the deposition of DNA origami nanostructures on highly oriented pyrolytic graphite (HOPG). The DNA origami goes through a structural rearrangement and the DNA base is exposed to interact with the graphite surface. Exposure to ambient air, which is known to result in a hydrophilic-to-hydrophobic wetting transition of HOPG, does not significantly impact the deposition yield or the shape deformation of DNA nanostructures. The deposited DNA nanostructures maintain their morphology for at least a week and promote site-selective chemical vapor deposition of SiO2. This process is potentially useful for a range of applications that include but are not limited to nanostructure fabrication, sensing, and electronic and surface engineering.

Single Chip Gas Sensor Array for Air Quality Monitoring

This paper describes the fabrication of a four element gas sensor array for monitoring air pollutants, namely CO, CO2, NO2, and SO2. The four micro-heaters share a single suspended SiO2 diaphragm, utilizing thermal proximity to achieve low power consumption (~10 mW for 300 °C). Plasma enhanced chemical vapour deposition SiO2 diaphragm is demonstrated to give higher yield compared with thermally grown SiO2. Sensor array elements are fabricated by customizing each element to sense a specific gas, using different sensing materials. Optimized thin films of ZnO, BaTiO3-CuO doped with 1% Ag, WO3, and V2O5 are used for selective sensing of CO, CO2, NO2, and SO2. Four sensors can be independently controlled to operate at different temperatures to get high selectivity for test gases. The sensor array is packaged on Kovar header, and then characterized for gas sensing. It is demonstrated that the sensors exhibit good sensitivity and selectivity. We report a maximum repeatable response to CO (~78.3% for 4.75 ppm), CO2 (~65% for 900 ppm), NO2 (~1948.8% for 0.9 ppm), and SO2 (~77% for 3 ppm) at operating temperatures of 330 °C, 298 °C, 150 °C, and 405 °C, respectively. [2016-0047]

Mitigating Water Absorption in Waveguides Made From Unannealed PECVD SiO2.

Water absorption was studied in two types of waveguides made from unannealed plasma enhanced chemical vapor deposition (PECVD) SiO2. Standard rib anti-resonant reflecting optical waveguides (ARROWs) were fabricated with thin films of different intrinsic stress and indices of refraction. Buried ARROWs (bARROWs) with low and high refractive index differences between the core and cladding regions were also fabricated from the same types of PECVD films. All waveguides were subjected to a heated, high humidity environment and their optical throughput was tested over time. Due to water absorption in the SiO2 films, the optical throughput of all of the ARROWs decreased with time spent in the wet environment. The ARROWs with the lowest stress SiO2 had the slowest rate of throughput change. High index difference bARROWs showed no decrease in optical throughput after 40 days in the wet environment and are presented as a solution for environmentally stable waveguides made from unannealed PECVD SiO2.

High Temperature Coupling of IR Inactive CC Mode in Complementary Metal Oxide Semiconductor Metamaterial Structure

High temperature (up to 400 °C) coupling of infrared (IR) inactive &gt;CC&lt; mode is reported in complementary metal oxide semiconductor (CMOS)‐compatible refractory metamaterial filter and absorber structure by leveraging the carbon defects in tetraethyl orthosilicate obtained plasma enhanced chemical vapor deposition SiO2 thin film. Here, the role of strain gradient induced dipole moment in high stress configuration on the activation of otherwise inactive &gt;CC&lt; vibration at IR is confirmed. The unusual suppression of the transition is also observed in the absorber structure when the cavity mode strongly overlaps with it. Finally, 14 times better modulation of resonance spectrum is reported by such coupling in absorber configuration that supports thin film interference. The numerical and analytical study of the effect is found to be qualitatively in agreement with the experimental results. The study can set new paths toward more efficient design of spectrally selective thermophotovoltaic energy emitter at mid‐IR and novel mechanism for high temperature sensing on the ubiquitous CMOS platform.