Vapor Deposition Silicon Research Articles

Stress-Dependent Optical Extinction in Low-Pressure Chemical Vapor Deposition Silicon Nitride Measured by Nanomechanical Photothermal Sensing.

Understanding optical absorption in silicon nitride is crucial for cutting-edge technologies like photonic integrated circuits, nanomechanical photothermal infrared sensing and spectroscopy, and cavity optomechanics. Yet, the origin of its strong dependence on the film deposition and fabrication process is not fully understood. This Letter leverages nanomechanical photothermal sensing to investigate optical extinction κext at a 632.8 nm wavelength in low-pressure chemical vapor deposition (LPCVD) SiN strings across a wide range of deposition-related tensile stresses (200-850 MPa). Measurements reveal a reduction in κext from 103 to 101 ppm with increasing stress, correlated to variations in Si/N content ratio. Within the band-fluctuations framework, this trend indicates an increase of the energy bandgap with the stress, ultimately reducing absorption. Overall, this study showcases the power and simplicity of nanomechanical photothermal sensing for low absorption measurements, offering a sensitive, scattering-free platform for material analysis in nanophotonics and nanomechanics.

The Effect of Silicon Nanoparticle Size on Cycle and Calendar Life

Lithium-ion batteries are now ubiquitous in modern electronics, electric vehicles, and many other applications. As the battery industry continues to push for better, longer lasting batteries, many have turned to using a different anode material that would provide higher-energy density and require less frequent charges. While graphite is the tried-and-true anode material for lithium-ion batteries, a silicon anode battery could provide up to ten times higher theoretical energy density than graphite. However, there are a lot of challenges standing in the way between silicon anode batteries and commercialization—the large volume expansion of silicon (around 200-300% expansion, compared to graphite at 10%) and the unstable solid-electrolyte-interface (SEI) of silicon results in anodes that mechanically degrade and calendar age faster than their graphite counterparts.Previous research has demonstrated that plasma-enhanced chemical vapor deposition (PECVD) silicon nanoparticles with a hydrophilic coating such as polyethylene oxide (PEO) results in silicon anodes with good cycle life [1, 2, 3, 4]. In this system, smaller particle sizes typically yielded better cyclability than larger particle sizes, which is contrary to conventional wisdom that more surface area is detrimental as it allows for more SEI formation and side reactions. However, since silicon anodes experience large volume changes during cycling, the surface area might not be the dominant contribution to capacity fade. Larger silicon particles result in larger total expansions of the electrode, which causes more mechanical damage like cracks to form, exposing fresh surface area to electrolyte and SEI formation.This research investigates the performances of PEO-coated PECVD Si electrodes with nanoparticles ranging from 3 to 27 nm in diameter. We measure the cycle life at a rate of 0.333C, as well as the calendar lifetimes of each electrode. We characterize each electrode with SEM imaging, tortuosity measurements, and electrochemical impedance spectroscopy to understand the differences in microstructure that contribute to capacity fade and impedance rise.

Near‐Infrared Light Trapping and Avalanche Multiplication in Silicon Epitaxial Microcrystals

AbstractThe chemical vapor deposition of silicon on a patterned silicon substrate leads to the formation of 3D microcrystals, which, due to their inclined top facets and high aspect ratio, produce a light‐trapping effect enhancing the optical absorption in the near‐infrared (NIR). In this work, it is demonstrated that Si microcrystals can form the building blocks of a new class of NIR sensitive photodetectors operating in a linear or avalanche regime. Microcrystal‐based devices are designed by coupling a 2D kinetic‐growth model with a Poisson drift‐diffusion solver and fabricated by combining electron beam lithography and low‐energy plasma‐enhanced chemical vapor deposition (LEPECVD). The optoelectronic properties of microcrystal‐based p–i–n photodiodes are investigated both theoretically and experimentally by means of finite‐difference time‐domain (FDTD) simulations and responsivity measurements. At 1000 nm wavelength, the responsivity of microcrystal‐based devices is six times higher than that of an equivalent mesa diode. Moreover, the photocurrent gains of Si microcrystals operating as an avalanche photodiode (APD), at the same wavelength, reaches 2 × 104 demonstrating the potentialities of substrate patterning, combined with epitaxial growth, for amplified photodetection applications.

Power-efficient programmable integrated multiport photonic interferometer in CMOS-compatible silicon nitride

Silicon nitride (SiN x ) is an appealing waveguide material choice for large-scale, high-performance photonic integrated circuits (PICs) due to its low optical loss. However, SiN x PICs require high electric power to realize optical reconfiguration via the weak thermo-optic effect, which limits their scalability in terms of device density and chip power dissipation. We report a 6-mode programmable interferometer PIC operating at the wavelength of 1550 nm on a CMOS-compatible low-temperature inductance coupled plasma chemical vapor deposition (ICP-CVD) silicon nitride platform. By employing suspended thermo-optic phase shifters, the PIC achieves 2× improvement in compactness and 10× enhancement in power efficiency compared to conventional devices. Reconfigurable 6-dimensional linear transformations are demonstrated including cyclic transformations and arbitrary unitary matrices. This work demonstrates the feasibility of fabricating power-efficient large-scale reconfigurable PICs on the low-temperature ICP-CVD silicon nitride platform.

Damage characteristics and material removal mechanisms of CVD-SiC in nanotests: A comparative with sintered SiC

High sensitivity to crack and damage of chemical vapor-deposited silicon carbide (CVD- SiC) restricts the high-efficiency and low-damage manufacturing of CVD-SiC components. This paper aims to reveal the damage and material removal mechanisms of CVD-SiC after being scratched by diamond abrasives. The mechanical properties, scratching force, depth of ductile-brittle transition, residual depth and material removal damages of the CVD-SiC were discussed by the indentation, nano-scratching experiments, and compared with sintered silicon carbide (SSiC) ceramics. The results demonstrated that the mechanical properties of CVD-SiC are better than SSiC. In terms of hardness and fracture toughness, CVD-SiC demonstrates a 10– 20% and 20– 30% higher level of performance than SSiC, respectively. SSiC exhibits a brittleness level approximately 30% higher than that of CVD-SiC. SSiC ceramics are prone to crack deflection, intergranular fracture and transgranular fracture during indentation, indicating a higher propensity for brittle fracture in SSiC. The crack propagation in CVD-SiC is relatively regular. Both materials undergo the ductile, ductile-brittle transition and brittle stage, and the fluctuation variability of CVD-SiC material is notably lower than that of SSiC during the brittle stage. Compared with SSiC, the residual depth, groove width and transverse force of CVD-SiC are smaller under the same normal load. The critical depth of ductile-brittle transition of CVD-SiC is about 2 times that of SSiC in experimental and theoretical, indicating that CVD-SiC easily achieves ductile grinding. The mechanical properties, crack system and crystal structure of the CVD-SiC and SSiC materials cause the divergences in brittle removal. The radial-median crack system dominates the material removal of CVD-SiC. The disparity of deformations on the inside and outside of the crystal in the brittle stage leads to significant fluctuation variability of force and depth of SSiC during the scratching.

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.

COMPARATIVE STUDY OF THE RECOMBINANT ACTIVITY EFFECT AT THE GRAIN BOUNDARIES IN SILICON SOLAR CELLS

This work studies the effect of carrier trapping and the recombination activity at the grain boundaries in the p-layer of polysilicon solar cells with respect to the deposition temperature. The dependence of the grain size on the deposition temperature was studied in different samples of boron-doped low-pressure chemical vapor deposition (LPCVD) silicon deposits, conducted in a horizontal low-pressure atmospheric pressure reactor where the temperature varied over a range from 520 °C to about 605 °C. The obtained results show clear evidence of dependence on effective changes in the trapping effect as a function of the trapping density states, the doping level and the thickness dimension of the deposited layer.

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.

The Effects of Electrostatic Interactions on Abnormal Growth of Particles Deposited by Charged Nanoparticles During Chemical Vapor Deposition of Silicon

The Effects of Electrostatic Interactions on Abnormal Growth of Particles Deposited by Charged Nanoparticles During Chemical Vapor Deposition of Silicon

Selectively patterned Mg-doped GaN by SiNx-driven hydrogen injection

We demonstrate a method to achieve selectively patterned Mg-doped GaN layers using hydrogen drive-in through plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (SiNx) films. Activated Mg-doped GaN layers were selectively deactivated by patterned PECVD SiNx films with low-temperature annealing and showed high-resistive behavior. Spatially resolved photoluminescence measurements were used to optically verify the deactivation of Mg acceptors and showed distinct features corresponding to activated and deactivated Mg in GaN. The method suggested here provides a simple and effective method to achieve patterned Mg-doped GaN regions without thermal and plasma damage, which could cause degradation of device performance. The proposed method could provide a way to achieve future high-performance GaN lateral and vertical devices that rely on laterally patterned doping.

Effect of rapid thermal annealing on the mechanical stress and physico-chemical properties in plasma enhanced atomic layer deposited silicon nitride thin films

The present study reports the impact of process conditions and post annealing treatment on the stress and physico-chemical properties in different types of plasma enhanced atomic layer deposited (PEALD) SiNx films. More specifically, the SiNx films deposited at 500 °C were annealed subsequently at 1000 °C in N2 ambient for different times ranging between 30 and 6750 s and were subjected to thickness, mass, refractive index, chemical bonds and structure, H content, N/Si stoichiometry, morphology, roughness, and uniformity monitoring. Depending on the deposition process conditions, we confirm the possibility to form, at 500 °C with PEALD, some very compressive SiN films with reduced hydrogen content by controlling the plasma conditions along the deposition process. More interestingly, these compressive films with low hydrogen concentration exhibit high thermo-mechanical stability compared to hydrogenated PEALD and plasma enhanced chemical vapor deposition silicon nitride from this study or reported in the literature, films which typically tend to become tensile with a similar annealing sequence. These results confirm the importance of the plasma power to engineer the as-deposited silicon nitride stress but also highlight the role of hydrogen in the thermal instability of these layers, a low H concentration being needed for a better mechanical stability.

Demonstration of DC Kerr effect induced high nonlinear susceptibility in silicon rich amorphous silicon carbide

In this study, we demonstrate the DC Kerr effect in plasma-enhanced chemical vapor deposition silicon rich amorphous silicon carbide (a-SiC). Using the resonance shift of the transmission spectra of a ring resonator, we experimentally extract the third order nonlinear susceptibility χ3 to be 6.90×10−19 m2/V2, which is estimated to be more than six times higher than previous reported values in stoichiometric a-SiC. The corresponding induced second order nonlinear susceptibility χ2 of 44.9 pm/V is also three times higher than the reported value in silicon and silicon rich nitride utilizing the DC Kerr effect. The high nonlinearity makes silicon rich a-SiC a good materials candidate for nonlinear photonic applications.

Gas-phase kinetics in atmospheric-pressure plasma-enhanced chemical vapor deposition of silicon films

Atmospheric-pressure (AP) plasma-enhanced chemical vapor deposition of silicon (Si) films was numerically simulated. The AP plasma used for Si depositions was excited by a 150-MHz very high-frequency (VHF) electric power, which was capable of generating continuous glow discharges covering the entire electrode surface. The experimental film thickness profiles could be well fitted by the simulations by adjusting the electron density in the plasma. The results showed that, although neutral–neutral reactions proceed very rapidly due to the frequent collisions between the gas species, the dissociation of the source SiH4 molecules by electron impact is the key factor that governs the chemistry occurring in the AP-VHF plasma and promotes the film growth on the substrate. The input power dependences of electrical property of the Si films could be explained by the contribution of SiH3 radical to the deposition. It was also shown that, even though the plasma was continuous glow, the electron density changed in the direction of gas flow, suggesting that the very rapid nucleation of clusters and their growth into nanoparticles were occurring in the AP-VHF plasma.

HF Under-Etching Prevention for Advanced THz Micromachined Waveguide Devices

This letter presents an under-etching prevention method for an aqueous hydrofluoric acid (HF) releasing process by adding a single-side low-pressure chemical vapor deposition (LPCVD) silicon protection layer. The proposed method enables advanced silicon-on-insulator (SOI) based millimeter-wave/terahertz (mmW/THz) MEMS waveguide devices, which require for RF performance a complete metallization film over the SOI buried-oxide (BOX) layer, and simultaneously need a locally under-etched BOX layer for implementing MEMS actuators reconfiguring the devices. A comparison between the WR-3.4 waveguide (220-330 GHz) using the proposed under-etching prevention method and the one without using it proves the effectiveness and feasibility during HF releasing processes. A MEMS tunable phase shifter driven by comb-drive actuators has been successfully implemented by applying this method in a micromachined waveguide. [2021-0036]

Dispersion Optimization of Silicon Nitride Waveguides for Efficient Four-Wave Mixing

Silicon nitride waveguides have emerged as an excellent platform for photonic applications, including nonlinear optical signal processing, owing to their relatively high Kerr nonlinearity, negligible two photon absorption, and wide transparent bandwidth. In this paper, we propose an effective approach using 3D finite element method to optimize the dispersion characteristics of silicon nitride waveguides for four-wave mixing (FWM) applications. Numerical studies show that a flat and low dispersion profile can be achieved in a silicon nitride waveguide with the optimized dimensions. Near-zero dispersion of 1.16 ps/km/nm and 0.97 ps/km/nm at a wavelength of 1550 nm are obtained for plasma-enhanced chemical vapor deposition (PECVD) and low-pressure chemical vapor deposition (LPCVD) silicon nitride waveguides, respectively. The fabricated micro-ring resonator with the optimized dimensions exhibits near-zero dispersion of −0.04 to −0.1 ps/m/nm over a wavelength range of 130 nm which agrees with the numerical simulation results. FWM results show that near-zero phase mismatch and high conversion efficiencies larger than −12 dB using a low pump power of 0.5 W in a 13-cm long silicon nitride waveguide are achieved.

Development of MEMS-based piezoresistive 3D stress/strain sensor using strain technology and smart temperature compensation

This paper presents the microfabrication and testing of a membrane-free eight-element single-polarity (n-type) sensing rosette integrated with strained silicon technology over (111) silicon plane to measure the full 3D stress/strain tensor with full temperature compensation. Such n-type piezoresistive (PR) sensor has low sensitivity to the out-of-plane components compared to the in-plane components. To improve the sensitivity of such sensors to the out-of-plane components, a strained silicon technique was integrated into the sensing rosette during the microfabrication process using a highly compressive film produced by plasma enhanced chemical vapor deposition silicon nitride. For experimental verification, a prototype device featuring the proposed sensing rosette was microfabricated using semiconductors fabrication processes. The experimental analysis applied both, in-plane and out-of-plane stresses at different temperatures over a range from −20 °С to 60 °С. In this work, a smart sensing calibration algorithm, utilizing machine learning, is employed to reduce the temperature impact on both sensitivity and resistance of PR coefficients during stress measurement. The developed sensor is capable of accurately extracting the applied stress/strain components with temperature compensation.

Origin of area selective plasma enhanced chemical vapor deposition of microcrystalline silicon

Plasma-enhanced chemical vapor deposition of silicon from a SiF4/H2/Ar gas mixture is observed on a SiOxNy surface, while under the same plasma conditions, silicon films do not grow on AlOx or on Al surfaces. Transmission electron microscopy confirms that the silicon deposited on SiOxNy has a microcrystalline structure. After the plasma process, fluorine is detected in abundance on the AlOx surface by x-ray photoelectron spectroscopy and energy dispersive x-ray chemical analyses. This suggests that Al–F bonds are formed on this surface, blocking any deposition of silicon on it. In situ ellipsometry studies show that deposition can be initiated on AlOx surfaces by increasing the temperature of the electrodes or increasing the RF plasma power, leading to a loss of selectivity.

Microstructural evolution of carbon fibers by silicon vapor deposition and its effect on mullite-corundum castables

Carbon fibers (CFs) can be introduced to castables, due to the relative higher thermal conductivity and stronger damping properties. In this research, microstructural evolution of carbon fibers (CFs) in the presence of mixture of silicon and silica powders under the protection of carbon black was studied in the temperature range of 1000–1300 °C by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that some small amorphous SiOx globules were formed on the surface of CFs at the temperature below 1200 °C. With the increase of the treated temperature, the size of globules became bigger and reached maximum at 1200 °C. The growth of SiOx globules can be controlled by vapor-solid mechanism. In addition, the effects of these CFs on properties and microstructure of mullite-corundum castables were studied. The results showed that the CFs with SiOx globules (CFs/SiOX) could significantly improve the mechanical properties of the castables because the interfacial bonding strength between CFs/SiOx and matrix is much stronger than the untreated CFs.

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.

Rational-design micro-nanostructure of porous carbon film/silicon nanowire/graphite microsphere composites for high-performance lithium-ion batteries

Silicon-based anodes are promising anode materials for lithium-ion batteries. However, during the charge–discharge processes, the huge volume change of silicon leads to the repeated formation of solid-electrolyte interphase layer, structure fracture and loss of electric contact, which seriously limits their practical applications. In this paper, a rational design combining graphite microsphere, silicon nanowire and porous carbon film is established, forming a micro-nanostructure that can effectively solve the above issues. Employing chemical vapor deposition method, silicon nanowire and polypyrrole are successively in situ synthesized on the graphite surface. After carbonizing the deposited composites, a porous carbon film and a silicon carbide layer locating between silicon and carbon film are obtained. It establishes a novel microstructure that possesses a strong bonding strength among interfaces of carbon film/silicon and silicon/graphite. Therefore, the porous carbon film/silicon nanowire/graphite microsphere composites anode exhibits a high capacity of 530 mA h g−1 at a current density of 0.2 C after 100 cycles. Significantly, the prepared composites anode could satisfy the practical application because their initial coulomb efficiency can reach to 80%.