Silicon Nitride Films Research Articles

Buckling of thin films: Lateral growth and kinetic evolution of telephone cords

We conduct a thorough investigation of the lateral growth and kinetic evolution of telephone cord buckles within thin films, employing both experimental and numerical techniques. Our exploration begins with in-situ experiments conducted on annealed silicon nitride films, aimed at capturing empirical data on the formation and evolution of these distinctive patterns. These experiments yield valuable insights into the morphological changes of telephone cords, such as wave flipping and merging, which lead to the enlargement of buckles at double wavelengths and widths. Subsequently, we employ a combined approach of geometrically nonlinear plate modeling and surface-based cohesive interface framework within a finite element numerical model to analyze the interplay between buckling-induced delamination and growth triggered by mode mixity-dependent interfacial toughness. Through this integrated approach, we effectively capture the mutual evolution of buckling and delamination occurrences, thus highlighting their inherently dynamic nature. Our numerical simulations show that the width and wavelength of telephone cords are doubled, consistent with experimental findings.

CMOS-Compatible High-Performance Silicon Nanowire Array Natural Light Electronic Detection System.

In this article, we propose a novel natural light detector based on high-performance silicon nanowire (SiNW) arrays. We achieved a highly controllable and low-cost fabrication of SiNW natural light detectors by using only a conventional micromachined CMOS process. The high activity of SiNWs leads to the poor long-term stability of the SiNW device, and for this reason, we have designed a fully wrapped structure for SiNWs. SiNWs are wrapped in transparent silicon nitride and silicon oxide films, which greatly improves the long-term stability of the detector; at the same time, this structure protects the SiNWs from breakage. In addition, the SiNW arrays are regularly distributed on the top of the detector, which can quickly respond to natural light. The response time of the detector is about 0.015 s. Under the illumination of 1 W·m-2 light intensity, multiple SiNWs were detected together. The signal strength of the detector reached 1.82 μA, the signal-to-noise ratio was 47.6 dB, and the power consumption was only 0.91 μW. The high-intensity and highly reliable initial signal reduces the cost and complexity of the backend signal processing circuit. A low-cost and high-performance STM32 microcontroller can realize the signal processing task. Therefore, we built a high-performance SiNW natural optoelectronic detection system based on an STM32 microcontroller, which achieved the real-time detection of natural light intensity, with an accuracy of ±0.1 W·m-2. These excellent test performances indicate that the SiNW array natural light detector in this article meey the requirements of practicality and has broad potential for application.

Tunable Ag Nanocavity Enhanced Green Electroluminescence from SiNx:O Light-Emitting Diode.

As the driving source, highly efficient silicon-based light emission is urgently needed for the realization of optoelectronic integrated chips. Here, we report that enhanced green electroluminescence (EL) can be obtained from oxygen-doped silicon nitride (SiNx:O) films based on an ordered and tunable Ag nanocavity array with a high density by nanosphere lithography and laser irradiation. Compared with that of a pure SiNxO device, the green electroluminescence (EL) from the SiNx:O/Ag nanocavity array device can be increased by 7.1-fold. Moreover, the external quantum efficiency of the green electroluminescence (EL) is enhanced 3-fold for SiNx:O/Ag nanocavity arrays with diameters of 300 nm. The analysis of absorption spectra and the FDTD calculation reveal that the localized surface plasmon (LSP) resonance of size-controllable Ag nanocavity arrays and SiNx:O films play a key role in the strong green EL. Our discovery demonstrates that SiNx:O films coupled with tunable Ag nanocavity arrays are promising for silicon-based light-emitting diode devices of the AI period in the future.

Influence of bias voltage on the Ar/CH2F2/O2 plasma etching of Si3N4 films

The etching mechanism of silicon nitride (Si3N4) films depending on peak-to-peak bias voltage ( Vpp ) in an Ar/CH2F2/O2 gas-mixture plasmas for high-aspect-ratio etching process was investigated. It was observed that the Si3N4 film etch rate initially decreased with an increase in the Vpp up to 3630 V, but then increased beyond this threshold. This unusual etching behavior can be attributed to the formation of a modified layer on the surface of the Si3N4 film. The characteristics of the modified layer, such as thickness and atomic composition, were found to be strongly influenced by the ion energy and gas chemistry of the process conditions.

Influence of high-temperature thermal annealing on paramagnetic point defects in silicon-rich silicon nitride films formed in a single-wafer-type low-pressure chemical vapor deposition reactor

The influence of high-temperature thermal annealing on silicon dangling bonds called K centers in Si-rich silicon nitride films grown in a single-wafer-type low-pressure chemical vapor deposition reactor with the SiH2Cl2-NH3 system at 750 °C has been investigated by combining thermal desorption spectroscopy (TDS), Fourier transform infrared spectroscopy-attenuated total reflection, spectroscopic ellipsometry, and electron spin resonance. In the TDS analysis, H2 desorption from the nitride films was detected above about 600 °C. It is found that thermal annealing at 750 and 900 °C caused a slight decrease in the K center density and a change in the g value of K centers, which are considered to be caused by changes in the atomic structure of the nitride films. On the other hand, thermal annealing at 1050 °C resulted in a substantial decrease in the K center density and the generation of paramagnetic defects with unprecedented characteristics. The findings in this study are expected to provide important guidelines for the design of manufacturing processes of nonvolatile memories.

Impact of H-Related Chemical Bonds on Physical Properties of SiNx:H Films Deposited via Plasma-Enhanced Chemical Vapor Deposition

SiNx:H film deposition via plasma-enhanced chemical vapor deposition has been widely used in semiconductor devices. However, the relationship between the chemical bonds and the physical and chemical properties has rarely been studied for films deposited using tools in terms of the actual volume production. In this study, we investigated the effects of the deposition conditions on the H-related chemical bonding, physical and chemical properties, yield, and quality of SiNx:H films used as passivation layers at the 28 nm technology node. The radiofrequency (RF) power, electrode plate spacing, temperature, chamber pressure, and SiH4:NH3 gas flow ratio were selected as the deposition parameters. The results show a clear relationship between the H-related chemical bonds and the examined film properties. The difference in the refractive index (RI) and breakdown field (EB) of the SiNx:H films is mainly attributed to the change in the Si–H:N–H ratio. As the Si–H:N–H ratio increased, the RI and EB showed linear growth and exponential downward trends, respectively. In addition, compared with the Si–H:N–H ratio, the total Si–H and N–H contents had a greater impact on the wet etching rates of the SiNx:H films, but the stress was not entirely dependent on the total Si–H and N–H contents. Notably, excessive electrode plate spacing can lead to a significant undesired increase in the non-uniformity and surface roughness of SiNx:H films. This study provides industry-level processing guidance for the development of advanced silicon nitride film deposition technology.

Photothermophoretic Splitting of Gold Nanoparticles for Plasmonic Nanopores and Nanonets Sensing.

Optical processing of single plasmonic nanoparticles reinvents the way of high-density information storage, high-performance sensing, and high-definition displays. However, such laser-fabricated nanoplasmonics with well-defined hot spots remain elusive due to the diffraction limit of light. Here we show Au nanoparticle (NP) decorated nanopores can be facilely generated with photothermal splitting of single Au NPs embedded in a silica matrix. The extremely high local temperature induced by plasmonic heating renders gradients of the temperature and surface tension around the Au NP, which drives the nanoscale thermophoretic and Marangoni flow of molten Au/silica. As a result, a nanopore decorated with fragmented Au NPs is formed in the silica film, which presents much stronger surface-enhanced Raman scattering as compared to a single Au NP due to the emergence of hot spots. This strategy can be used to generate plasmonic nanopores of various sizes in the silicon nitride (SiNx) films, which further transforms into nanonets at ambient conditions via light-induced reconstruction of silicon nitride membrane. These nanonets can serve as a robust platform for single particle trapping and analysis.

Effects of Hydrogen Bonding in Silicon Nitride/Polyimide Passivation Bilayer in SiC Power Devices

Composition and morphology of two types of bilayers of plasma‐enhanced chemical vapor deposition hydrogened silicon nitride (SiNx:H) and polyimide (PI), as effcient barrier against moisture in SiC‐based power devices, are investigated. Two types of silicon nitrides are obtained by changing the flow ratios of the SiH4 and NH3 precursors. Rutherford Backscatterered analyses show that the Si/N ratio varies from 0.6 to 0.8. Elastic recoil detection analyses show that the sample with higher nitrogen content has a higher total bound hydrogen content of 7.8 × 1017 cm−2 with respect to the 7.1 × 1017 cm−2. Fourier‐transform infrared spectroscopy characterizations show Si–H group concentrations of 0.96 × 1017 and 6.86 × 1017 cm−2 and NH groups of 4.82 × 1017 and 2.28 × 1017 cm−2, respectively. Silicon nitride films with higher concentration of N–H groups show higher reactivity and permeability to water, making them less effective as a barrier layer. Atomic force microscopy analyses of a PI layer deposited on the nitride layer, SiNx:H/PI show for both type of samples a similar roughness, indicating planarization that can increase the adhesion of SiNx:H/PI and resistance to moisture. The delamination mechanism of the bilayer under pressure pot test conditions is proposed.

Measurement of atomic dispersion on buried Ag nanoparticles decomposed by Ne[formula omitted] ion irradiation

The effects of room temperature 200keV Ne+ ion irradiation on Ag nanoparticles (NPs) embedded in a silicon nitride film have been studied via Medium Energy Ion Scattering (MEIS), Scanning Transmission Electron Microscopy (STEM), and the results are discussed in comparison with Monte Carlo TRI3DYN simulations. The experiment was designed to test the mechanisms controlling the room temperature irradiation-induced microstructure evolution of individual NPs and the overall system. We present an innovative MEIS approach capable of quantitatively determining Ag’s content and spatial distribution in solution. The STEM observations demonstrate the nucleation of smaller Ag NPs distributed within the solute field. The TRI3DYN simulations suggest that a fraction of the solute content is reincorporated within the NPs. These results are discussed considering that room-temperature thermal diffusion processes are significantly retarded in silicon nitride substrates, which leads to an interpretation primarily based on the irradiation-induced atomic displacements that render a microstructure evolution driven by the minimization of chemical potential as an elemental thermodynamic force. Our findings are of applied interest concerning the application of ion beams to manipulate NP ensembles.

Angle-resolved X-ray photoelectron spectroscopy intensity modeling of SiNx ultrathin layer grown on Si (100) and Si (111) substrates by N2 plasma treatment

In this work, we investigate the silicon nitridation process using a N2 plasma Glow Discharge Source (GDS) in an ultra-high vacuum chamber. In situ Angle Resolved X-ray Photoelectron Spectroscopy (ARXPS) measurements were performed to determine various chemical environments of the surface species. The main goals of this study are determination of the film chemical composition, to estimate its thickness and identify various phenomena taking place during the nitridation process under different experimental conditions. To achieve these objectives, we developed an ARXPS intensity model for an ultrathin SiNx overlayer. Based on the ARXPS results, which indicate that the silicon nitride film is not homogenous, we adopted a bi-layer model composed of two SixNyOz layers with varying thickness and chemical composition. The model is built from analysis of photoelectron intensities, considering a comparison between experimental and theoretical data. This bi-layer model revealed that the silicon nitride layer consists of a surface layer composed of approximately equal amounts of silicon and nitrogen (50% each), and an interfacial layer containing varying amounts of oxygen depending on experimental parameters. The presence of oxygen is due to residual air contamination in the vacuum chamber and/or to Si native oxide. The estimated thickness of silicon nitride film is less than 9 nm, depending on the nitridation time and temperature.The model developed in this work enabled us to study the effects of initial surface state (as received or chemically cleaned), Si substrate crystallographic orientation (such as (100) and (111)), and the nitridation temperature (room temperature and 500°C). The diffusing species (N+, N2+, O+), which play a crucial role during nitridation, were found to be influenced by temperature, treatment time, and substrate orientation. The diffusion phenomenon competed with other processes such as NO desorption, leading to a significant impact on formation of the SiNx film. Furthermore, we compared the thickness obtained from the ARXPS model using cross-sectional High-Resolution Transmission Electron Microscopy (HR-TEM) images. Additional Low-Energy Electron Diffraction (LEED) measurements indicated that the SiNx film was amorphous.

Damascene Process Development for Low-Loss Photonics Devices with Applications in Frequency Comb

Silicon nitride (SiN) is emerging as a material of choice for photonic integrated circuits (PICs) due to its ultralow optical losses, absence of two-photon absorption in telecommunication bands, strong Kerr nonlinearity and high-power handling capability. These properties make SiN particularly well-suited for applications such as delay lines, chip-scale frequency combs and narrow-linewidth lasers, especially when implemented with thick SiN waveguides, which is achieved through low-pressure chemical vapor deposition (LPCVD). However, a significant challenge arises when the LPCVD SiN film thickness exceeds 300 nm on an 8-inch wafer, as this can result in cracking due to high stress. In this work, we successfully develop a damascene process to fabricate 800 nm-thick SiN photonics devices on an 8-inch wafer in a pilot line, overcoming cracking challenges. The resulting 2 × 2 multimode interference (MMI) coupler exhibits low excess loss (−0.1 dB) and imbalance (0.06 dB) at the wavelength of 1310 nm. Furthermore, the dispersion-engineered SiN micro-ring resonator exhibits a quality (Q) factor exceeding 1 × 106, enabling the generation of optical frequency combs. Our demonstration of photonics devices utilizing the photonics damascene process sets the stage for high-volume manufacturing and widespread deployment.

Measuring the refractive index and thickness of a thin film: an optical polarization experiment

We propose a teaching experiment for simultaneous measurement of the refractive index and thickness of a thin film. The experimental apparatus includes: a diode laser, a polarizer, a spectrometer, a photodiode and a portable digital multimeter. With the apparatus, we measure the refractive index and thickness of two thin films (a silicon dioxide film on silicon, a silicon nitride film on silicon). The maximum discrepancy between the results of our apparatus and an ellipsometer is 1.4%. The experiment described here can be used in optical polarization teaching for undergraduate sophomores and has several valuable pedagogical outcomes: (1) understanding the multi-beam interference in a film; (2) applying chi-square minimization; (3) carrying out the nonlinear curve fitting with multiple parameters.

Hydrogen Role on the Properties of Silicon Nitride for Flexible Thin Film Encapsulation

High transmittance, high density, and good mechanical properties of silicon nitride (SiNx) make it a potential candidate for barrier layers of flexible organic light emission diodes (FOLEDs). However, the overall characteristics and water oxygen barrier properties of the films are easily affected by the dangling bonds in the films. After adding hydrogen flow rate to the deposition conditions of SiNx films, the hydrogen content interacts with the dangling bonds in amorphous SiNx, which could reduce the number of dangling bonds and improve the density of the hydrogenated amorphous silicon nitride (SiNxHy) films. The high‐density film layer could effectively prevent the invasion of water vapor due to its smaller pinhole density. Therefore, the water oxygen barrier performance of SiNxHy is significantly improved, the maximum decrease in water vapor transmittance rate (WVTR) value is approximately 22.4%. In addition, the increase of hydrogen content also changed the overall properties of the films, including transmittance, elastic modulus, hardness, residual stress, and fracture strain. Therefore, compared with SiNx films, SiNxHy films have more excellent mechanical and optical properties. The SiNxHy films featuring a simplified preparation process with high efficiency, low cost, and superior barrier performance is of great potential for the commercial applications.

Impact of hydrogen plasma treatment on fluorine-contained silicon nitride films

It has been suggested that the trap energy level in silicon nitride (SiN) films becomes shallow due to hydrogen and fluorine incorporation, which causes a charge migration in the MONOS memory cells and deteriorates the data retention characteristics. To solve these issues, we have proposed the hydrogen plasma treatment and demonstrated the reduction of the shallow trap density consequent to the removal of hydrogen from SiN films. In this study, the hydrogen plasma treatment is applied to the fluorine-contained SiN films. The results show that deepening of the trap energy level contributing to hole current, decreasing of the shallow trap density contributing to charging and the fluorine concentration near at the SiN surface. These results are regarded to be due to the removal of fluorine in the SiN film through the reaction with hydrogen radicals (H*) during the hydrogen plasma treatment.

Etching mechanism of amorphous hydrogenated silicon nitride by hydrogen fluoride

We report the etching mechanism of amorphous hydrogenated silicon nitride by hydrogen fluoride (HF) gas using density functional theory (DFT) calculations. Since silicon nitride films are deposited as amorphous with a significant amount of hydrogen, we constructed an amorphous substrate model with a hydrogen concentration of 25 at.% using molecular dynamics simulation and DFT calculations. We then created slab models with different degrees of fluorination and simulated all possible fluorination pathways. The pathways involving cleavage of Si–N or Si–Si bonds showed low activation energies of 0.90 eV or lower, while the pathways involving cleavage of a Si–H bond showed high activation energies of 1.54 eV or higher. NH3, SiF4, SiH2F2, and SiHF3 were released with low activation energies, indicating that etching would be favorable. Next, we modeled the formation and desorption of the (NH4)2SiF6 salt on the fluorinated surface. The salt formation was exothermic with low activation energies, consistent with self-limited etching at low temperatures. At temperatures of 152 °C or higher, (NH4)2SiF6 would desorb, leaving no solid residue, consistent with the high etch rate at elevated temperatures. Our DFT calculations using the amorphous hydrogenated slab model successfully explained the silicon nitride etching process, which could not be explained by a crystalline Si3N4 slab model.

Ion Concentration Polarization Tunes Interpore Interactions and Transport Properties of Nanopore Arrays

AbstractBiological processes require concerted function of many channels embedded in the cell membrane. While single solid‐state nanopores are already designed to mimic properties of individual biological channels, it is not yet known how to connect the pores to achieve biomimetic ionic circuits with interacting components. To identify fundamental processes that control interactions between nanopores embedded in the same membrane, a model system of minimal arrays consisting of two and three nanopores in silicon nitride films is designed. The constituent nanopores have an opening diameter <10 nm, and the interpore spacing is tuned between 15 and 200 nm. The experimental and modeling results reveal that nanopores in an array interact with each other via overlapping depletion zones created by the process of concentration polarization. The interactions can be further controlled by salt concentration and voltage. These results showcase a possibility of tuning interactions between nanopores and transport properties of arrays by chemical modification of the pore walls. Arrays consisting of nanoporous ionic diodes feature depletion zones with higher concentrations, and lower current suppression than homogeneously charged pores. These experiments and modeling provide the first steps to leave the constraints of single nanopores and to design biomimetic ionic circuits.

Theoretical study of the gas-phase reaction of hexachlorodisilane by thermodynamic analysis and kinetics calculation

We conducted thermodynamic analysis and kinetics calculations for hexachlorodisilane (Si2Cl6), which is used as source gas for the CVD of silicon nitride films. Thermodynamic analysis clarified Si2Cl6 decomposes almost completely to SiCl4 and SiCl2 in the range of 600 °C–1100 °C under equilibrium condition. Therefore, it is estimated that the main gas-phase reaction of Si2Cl6 is represented by the reaction Si2Cl6 → SiCl4 + SiCl2. Thermodynamic analysis also shows that the Si2Cl6 system has a larger equilibrium partial pressure of SiCl2 than SiHxCl4-x (x = 1 ~ 3) systems. Kinetics calculations revealed Si2Cl6 decomposes by 90% in 0.11 s at 600 °C, and 0.55 × 10−3 s at 800 °C, respectively. The time-dependent pyrolysis ratio of Si2Cl6 becomes larger as the total pressure decreases at 600 °C. On the other hand, the ratio is almost the same regardless of total pressure at 800 °C. These results will help optimize CVD process conditions using Si2Cl6.

Noise spectrum analysis of superconducting kinetic inductance detectors

As a newly developed pair-breaking superconducting detector, microwave kinetic inductance detectors are simple to integrate in the frequency domain and have already been used in astronomical detection and array imaging at the (sub)millimeter and optical wavelengths. For these applications, the dark noise level of kinetic inductance detector is one of the key performance indicators. Herein a noise power spectrum analysis method is introduced in detail, which can accurately and effectively analyze the noise spectrum of kinetic inductance detector in a wide frequency range. This method can well balance the noise spectrum resolution and variance performance, by taking the noise data at the resonance frequency with two sampling rates and setting the appropriate frequency resolutions for different frequency bands. This method is used to characterize and compare the noise of aluminum (Al) kinetic inductance detectors made from two different micromachining processes. We deposite a 25-nm-thick aluminum film on high-resistivity silicon substrate for one device, while place one silicon nitride (SiN<sub><i>x</i></sub>) film on the top and one on the bottom of the aluminum film for another device. It is found that the frequency noise of the device with two silicon nitride films is about 25% to 50% of the bare aluminum device. Using this double silicon nitride film fabrication technique, we further fabricate a few groups of lumped-element aluminum kinetic inductance detectors with various inductor and interdigitated capacitor designs. We investigate the noise properties of these devices at different microwave driven power and bath temperatures, and the experimental results show typical two-level system noise behaviors. Our work provides a standard method to characterize the noise power spectrum of kinetic inductor detector, and also paves the way to developing low-noise aluminum kinetic inductance detectors for terahertz imaging, photon-counting and energy-resolving applications.

Low-density plasmas generated by electron beams passing through silicon nitride window

In general, more attention is paid to how to improve the characteristic parameters of plasma in plasma applications. However, in some cases, it is necessary to produce plasma with low-electron density, such as in the laboratory simulation of ionospheric plasma in space science. In this study, a low-density plasma is generated by electron beams passing through a silicon nitride transmission window under low pressure condition. The transmission properties of electron beam passing through silicon nitride films are investigated by Monte Carlo simulation, and the plasma feature is studied by a planar Langmuir probe and a digital camera. It is found that the plasma exhibits a conical structure with its apex located at the transmission window. At a constant pressure, the cone angle of conical plasma decreases with the electron energy increasing. This is qualitatively consistent with the Monte Carlo simulation result. The frequency of electron-neutral collisions increases as the working pressure rising, which leads the plasma cone angle to increase. When the beam current is reduced from 10 μA to 0.5 μA at 40 keV, the electron density decreases, in a range between 10<sup>5</sup> and 10<sup>6</sup> cm<sup>–3</sup>, while the electron temperature does not change significantly but approaches 1 eV. It can be inferred that the electron density decreases with the distance <i>z</i> from the transmission window in the incident direction of the electron beam. A low-density plasma of less than 10<sup>5</sup> cm<sup>–3</sup> can be obtained further away from the transmission window.

Enhancing and confining light in hybrid plasmonic nanowire-integrated V-groove silicon waveguides

In recent years, the field of dielectric-plasmonic photonics has made remarkable strides, leading to the successful development of various technologies. The realization of sophisticated optical circuits on a single platform has become increasingly viable. Here we propose and investigate a hybrid dielectric waveguide integrated with plasmonics. This hybrid optical waveguide comprises a copper nanowire situated in close proximity to a silicon V-groove channel, separated by a nanoscale gap. This configuration is particularly advantageous, as achieving precise alignment of the nanowire within the V-groove addresses a fundamental challenge in engineering a fully functional integrated component. Additionally, a silicon nitride film coats the V-groove. Utilizing finite element analysis, we conduct numerical simulations to analyze field properties and modal propagation at a specific wavelength of 1550 nm. Our simulations reveal that meticulous optimization of the nanowire and V-groove channel’s geometrical parameters enables effective tailoring of the hybrid mode. This optimization results in strong mode coupling between the dielectric waveguide mode and the surface plasmon, leading to substantial field enhancement, confinement, and extended propagation length. These waveguides also hold promise for sensing applications, facilitating the detection of sample variations and locations due to pronounced mode characteristics. The proposed hybrid approach demonstrates potential for integration into high-level photonic circuits and on-chip optical computing systems.