Deposited Silicon Nitride 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.

Suppression of crack formation in wafer-scale amorphous SiNx films by residual hydrogen-ligands manipulation

Plasma-Enhanced Chemical Vapor Deposition (PECVD) of amorphous silicon nitride (SiNx) thin films is a critical procedure in microelectronics serving as a surface passivation layer and dielectric barrier. However, intrinsic film stress continuously builds up along with PECVD growth, leading to film cracking. How to achieve crack-free PECVD amorphous SiNx film within a large thickness range remains a critical unresolved challenge in semiconductor industry. In this study, we revealed that high residual NH ligands from the NH3 precursor could induce excessive tensile strain at the SiNx/Si wafer interface and consequently aggravate SiNx film crack formation. With a heating pretreatment on the wafer, residual H ligands were effectively reduced to achieve homogenous chemical composition in SiNx film. As a result, the crack number declined ∼42% and the remaining crack length was substantially shorter in contrast to the original SiNx film. This work demonstrates the crucial role of residual ligands on internal strain regulation and points out a pathway to achieve crack-free PECVD SiNx films in industrial manufacturing.

Plasma enhanced atomic layer deposition of silicon nitride using magnetized very high frequency plasma

To obtain high-quality SiN x films applicable to an extensive range of processes, such as gate spacers in fin field-effect transistors (FinFETs), the self-aligned quadruple patterning process, etc, a study of plasma with higher plasma density and lower plasma damage is crucial in addition to study on novel precursors for SiN x plasma-enhanced atomic layer deposition (PEALD) processes. In this study, a novel magnetized PEALD process was developed for depositing high-quality SiN x films using di(isopropylamino)silane (DIPAS) and magnetized N2 plasma at a low substrate temperature of 200 °C. The properties of the deposited SiN x films were analyzed and compared with those obtained by the PEALD process using a non-magnetized N2 plasma source under the same conditions. The PEALD SiN x film, produced using an external magnetic field (ranging from 0 to 100 G) during the plasma exposure step, exhibited a higher growth rate (∼1 Å/cycle) due to the increased plasma density. Additionally, it showed lower surface roughness, higher film density, and enhanced wet etch resistance compared to films deposited using the PEALD process with non-magnetized plasmas. This improvement can be attributed to the higher ion flux and lower ion energy of the magnetized plasma. The electrical characteristics, such as interface trap density and breakdown voltage, were also enhanced when the magnetized plasma was used for the PEALD process. Furthermore, when SiN x films were deposited on high-aspect-ratio (30:1) trench patterns using the magnetized PEALD process, an improved step coverage of over 98% was achieved, in contrast to the conformality of SiN x deposited using non-magnetized plasma. This enhancement is possibly a result of deeper radical penetration enabled by the magnetized plasma.

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.

Chemisorption of silicon tetrachloride on silicon nitride: a density functional theory study.

We studied the chemisorption of silicon tetrachloride (SiCl4) on the NH2/NH-terminated silicon nitride slab model using density functional theory (DFT) for atomic layer deposition (ALD) of silicon nitride. Initially, two reaction pathways were compared, forming HCl or NH3+Cl- as a byproduct. The NH3+Cl- complex formation was more exothermic than the HCl formation, with an activation energy of 0.26 eV. The -NH2* reaction sites are restored by desorption of HCl from the NH3+Cl- complexes at elevated temperatures of 205 °C or higher. Next, three sequential ligand exchange reactions forming Si-N bonds were modeled and simulated. The reaction energies became progressively less exothermic as the reaction progressed, from -1.31 eV to -0.30 eV to 0.98 eV, due to the stretching of Si-N bonds and the distortion of the N-Si-N bond angles. Also, the activation energies for the second and third reactions were 2.17 eV and 1.55 eV, respectively, significantly higher than the 0.26 eV of the first reaction, mainly due to the additional dissociation of the N-H bond. The third Si-N bond formation is unfavorable due to the endothermic reaction and higher activation energy. Therefore, the chemisorbed species would be -SiCl2* when the surface is exposed to SiCl4.

Permeation of oxygen and water into a plasma-enhanced chemical vapor deposited silicon nitride film as function of deposition pressure

In this work, we demonstrate that the permeability of a SiNx thin film (prepared by plasma-enhanced chemical vapor deposition) to water and oxygen is closely related to the deposition pressure. By dynamic secondary ion mass spectrometry, we confirmed that water penetration occurs into the SiNx film only in the oxidized layer. Furthermore, positron annihilation lifetime spectroscopy indicated that a SiNx film with a lower deposition pressure provides a smaller pore (free volume hole) radius, which is more effective in terms of blocking ambient molecular diffusion or penetration. The SiNx films were also applied as an encapsulation layer for organic light-emitting diodes; SiNx films with a lower deposition pressure exhibited higher encapsulation properties.

Employment of Silicon Nitride Films Prepared by DC Reactive Sputtering Technique for Ion Release Applications

In this work, silicon nitride (Si3N4) thin films were deposited on metallic substrates (aluminium and titanium sheets) by the DC reactive sputtering technique using two different silicon targets (n-type and p-type Si wafers) as well as two Ar:N2 gas mixing ratios (50:50 and 70:30). The electrical conductivity of the metallic (aluminium and titanium) substrates was measured before and after the deposition of silicon nitride thin films on both surfaces of the substrates. The results obtained from this work showed that the deposited films, in general, reduced the electrical conductivity of the substrates, and the thin films prepared from n-type silicon targets using a 50:50 mixing ratio and deposited on both surfaces of a titanium substrate reduced the electrical conductivity of this substrate by 30%. This reduction in the release of ions from the coated metal substrate is attributed to the dielectric properties of the deposited silicon nitride thin films. This result is very important and applicable. This work represents the first attempt in Iraq to study such effects and may represent a good starting point for advanced studies in biomedical engineering.

Optimization of the Si3N4 coating formation through plasma spraying on Inconel 738

ABSTRACT In the present study, the deposition of silicon nitride (Si3N4) coating on Inconel 738 through plasma spray has been investigated. For producing the Si3N4 coating, different times (6, 8 and 10 s), different distances of the plasma spray torch from the substrate (30, 35 and 40 mm) and different currents for plasma spraying (3000, 3250 and 3500 A) were employed. For the characterisation of the coatings, SEM (thickness), XRD, micro-hardness and adhesion of the samples were measured. The coatings’ surface morphology was investigated through SEM. Based on the experimental results, by using a spraying time of 10 s, a distance of the torch of 40 mm and a current of 3500 A, high microhardness and adhesion of the coatings are obtained. On the other hand, the thickness of the coating increased by reducing the distance and increasing spray time and current.

Highly conductive Ag-SiNx composite thin film anode engineering for transparent battery

Silicon nitride-based electrodes (SiNx), have been proposed as promising candidates for high-capacity transparent anode electrodes in earlier studies. Unfortunately, they have low electrical conductivity, resulting in some disadvantages such as power density for application in thin film batteries. To improve electrical conductivity, bulk batteries use conductive carbon additives, which also impair transmittance. Thus, we conducted this research to enhance the electrochemical properties by improving the conductivity without compromising the transmittance by uniformly dispersed Ag nanoparticles in SiNx thin film. We obtained an Ag-SiNx composite thin-film anode via continuous composition spread sputtering and investigated the effect of the Ag concentration. The capacity of the thin-film battery raised to 242.8 μAh/cm2·μm with Ag0.236SiO0.7N anode compared to the SiO0.7N anode which had a capacity of 37.2 μAh/cm2·μm. In addition, while SiO0.7N was operated only up to 2 C, Ag0.236SiO0.7N has driven up to 5 C and 10 C, which are high C rates, was also possible. AgxSiO0.7N thin film with less than 0.236 mol content demonstrates an optical transmittance of over 60% in the visible area. These results indicate that improving the electrical conductivity by the addition of an Ag during the silicon nitride deposition can increase its electrochemical performance while maintaining its applicability to transparent batteries.

Plasma Enhanced Atomic Layer Deposition of Silicon Nitride for Two Different Aminosilane Precursors Using Very High Frequency (162 MHz) Plasma Source.

Plasma enhanced atomic layer deposition (PEALD) of silicon nitride (SiNx) using very high frequency (VHF, 162 MHz) plasma source was investigated at the process temperatures of 100, 200, and 300 °C. Two aminosilane precursors having different numbers of amino ligands, bis(tert-butylamino)silane (BTBAS) and di(sec-butylamino)silane (DSBAS), were used as Si precursors. A comparative study was also conducted to verify the effect of the number of amino ligands on the properties of SiNx film. At all process temperatures, DSBAS, having one amino ligand, performed better than BTBAS in various aspects. SiNx films deposited using DSBAS had lower surface roughness, higher film density, lower wet etch rate, improved electrical characteristics, and higher growth rate than those deposited using BTBAS. With the combination of a VHF plasma source and DSBAS with one amino ligand, the SiNx films grown at 300 °C exhibited low wet etch rates (≤2 nm/min) in a dilute HF solution (100:1 of deionized water:HF) as well as low C content below the XPS detection limit. Also, excellent step coverage close to 100% on high aspect ratio (30:1) trench structures was obtained by using VHF plasma, which could provide sufficient flux of plasma species inside the trenches in conjunction with DSBAS having fewer amino ligands than BTBAS.

Microkinetic based growth and property modeling of plasma enhanced atomic layer deposition silicon nitride thin film

We demonstrate a microkinetic modeling framework which is a first principle-based surface reaction thermodynamics modeling methodology to describe the plasma-enhanced atomic layer deposition process of silicon nitride thin film formation. The results illustrating the relationship between silicon nitride growth per cycle (GPC) and quasi self-limiting behavior on both dichlorosilane precursor dose amount and plasma nitridation time are consistent with the experiment. Ultimately, GPC is limited to the equivalent of a half monolayer of a Si3N4 crystalline structure. Importantly, we have observed a strong correlation between subsurface NH terminated Si group concentration and HF wet etch rate by an experiment, which varies with substrate temperature.

Micromachined Infrared Thermopile Detector Based on a Suspended Film Structure

The micro-electromechanical system (MEMS) infrared thermopile is the core working device of modern information detection systems such as spectrometers, gas sensors, and remote temperature sensors. We presented two different structures of MEMS infrared thermopiles based on suspended film structures. They both deposited silicon nitride over the entire surface as a passivated absorber layer in place of a separate absorber zone, and the thermocouple strip was oriented in the same direction as the temperature gradient. The same MEMS preparation process was used and finally two different structures of the thermopile were characterized separately for testing to verify the impact of our design on the detector. The test results show that the circular and double-ended symmetrical thermopile detectors have responsivities of 27.932 V/W and 23.205 V/W, specific detectivities of 12.1×107 cm·Hz1/2·W−1 and 10.1×107 cm·Hz1/2·W−1, and response time of 26.2 ms and 27.06 ms, respectively. In addition, rectangular double-ended symmetric thermopile has a larger field of view than a circular thermopile detector, but is not as mechanically stable as a circular thermopile.

A Comparative Study on Self‐Aligned Top‐Gate Thin‐Film Transistors with Silicon Nitride as the Interlayer

Thin-film transistors (TFTs) with self-aligned top-gate structure are fabricated, in which the source/drain region is pretreated to be highly conductive during the deposition of silicon nitride as the interlayer. Without deteriorating the properties of the device's channel layer, the basic performance of TFTs can be simply controlled by altering the SiH4 flow rate during the deposition of silicon nitride film. Furthermore, the diffusion of hydrogen dissociated from SiH4 precursor, which can passivate the electron traps at the interface between the channel and dielectric layer or in the bulk of the dielectric layer, can significantly improve the positive bias temperature stress stability. The charge trapping mechanism is verified using the stretched-exponential model, and the rising values of the fitting parameters (ΔVth0 and τ) show that the TFTs stability improves as the flow rate of SiH4 rises. This approach can reduce the cost and simplify the manufacturing of thin-film transistors.

Atmospheric-Pressure Plasma-Enhanced Spatial Atomic Layer Deposition of Silicon Nitride at Low Temperature

Atmospheric-Pressure Plasma-Enhanced Spatial Atomic Layer Deposition of Silicon Nitride at Low Temperature

A Universal Approach to High‐Index‐Contrast Flexible Integrated Photonics

AbstractFlexible integrated photonics is an essential technology for emerging applications, including flexible optical interconnects, optogenetic stimulation, and implantable conformal sensing. Here, a novel and universal route for fabricating flexible photonic components with high‐refractive‐index contrast is reported. Central to such a unique method is the utilization of germanium oxide (GeO) as the sacrificial layer for releasing nanostructures from rigid substrates to flexible substrates. Various high‐quality inorganic optical materials can be grown directly on GeO by different thin‐film deposition methods due to its resistance to both high temperature and high‐power oxygen plasmas. In addition to the absence of restrictions on the material choices and integration processes for flexible photonic structures, the approach uses water as the etchant to remove the sacrificial layer, which has minimal impact on the optical performance of the photonic structures. Using this approach, a strain‐insensitive/sensitive microring resonator based on plasma‐enhanced chemical vapor deposited silicon nitride and reactive sputtered titanium oxide, respectively, is demonstrated, establishing the strategy as a facile and universal route for the fabrication of high‐index‐contrast flexible integrated photonic devices with various functionalities.

Widely tunable refractive index silicon nitride films deposited by ion-assisted pulsed DC reactive magnetron sputtering

Silicon nitride films were deposited by ion-assisted pulsed DC reactive magnetron sputtering, where the regulation of power on the refractive index was emphasized. The power of the ion source and target was found to affect the refractive index. Refractive indices ranged from 2.13 to 2.63 (@632 nm) at ion source powers of 150, 300, 450, and 600 W, and from 2.45 to 3.02 (@632 nm) at target powers of 800, 1000, and 1200 W. The refractive index range was further extended to 1.89–3.02 (@632 nm) by co-adjustment, and extinction coefficients remained low in the visible to near-infrared band. The composition of deposited amorphous silicon nitride films varies with power, covering nitride-rich to silicon-rich. With no obvious defects on the surface and cross-section, the roughness slightly decreased with power, and the minimum roughness recorded was only 0.12 nm. In this work, a method for depositing silicon nitride films with a widely tunable refractive index range was proposed, which is promising for the application of optical thin films and waveguides.

Long-Term Stability of Novel Crucible Systems for the Growth of Oxygen-Free Czochralski Silicon Crystals

The replacement of the silica glass crucible by oxygen-free crucible materials in silicon Czochralski (Cz) growth technology could be a key factor to obtaining Cz silicon, with extremely low oxygen contamination < 1 × 1017 at/cm3 required for power electronic applications. So far, isostatic pressed graphite or nitrogen-bonded silicon nitride (NSN) crucible material, in combination with a chemical vapor deposited silicon nitride (CVD-Si3N4) surface coating, could be identified as promising materials by first short-term experiments. However, for the evaluation of their potential for industrial scale Cz growth application, the knowledge about the long-term behavior of these crucible setups is mandatory. For that purpose, the different materials were brought in contact with silicon melt up to 60 h to investigate the infiltration and dissolution behavior. The chosen graphite, as well as the pore-sealed NSN material, revealed a subordinated infiltration-depth of ≤1 mm and dissolution of ≤275 µm by the silicon melt, so they basically fulfilled the general safety requirements for Cz application. Further, the highly pure and dense CVD Si3N4 crucible coating showed no measurable infiltration as well as minor dissolution of ≤50 µm and may further acts as a nucleation site for nitrogen-based precipitates. Consequently, these novel crucible systems have a high potential to withstand the stresses during industrial Cz growth considering that more research on the process side relating to the particle transport in the silicon melt is needed.

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.

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.