Silicon Nitride Films Research Articles

Effect of a silicon nitride film on the potential-induced degradation of n-type front-emitter crystalline silicon photovoltaic modules

We investigate the effect of silicon nitride (SiNx) films in n-type front-emitter (n-FE) crystalline Si (c-Si) solar cells on the potential-induced degradation (PID) of n-FE photovoltaic (PV) modules. A negative-bias PID test for a few min does not degrade the performance of PV modules with n-FE cells without SiNx/Si dioxide (SiO2) stacks, unlike in the case of PV modules with cells with SiNx/SiO2. This is because of the absence of polarization-type PID. After a longer PID test, the PV modules with n-FE cells without SiNx/SiO2 show a slower decrease in fill factor (FF), originating from Na introduction into the depletion layer of a p–n junction, than the modules with cells with SiNx/SiO2. The mitigation of PID by eliminating SiNx is partly consistent with the results of PV modules with p-type conventional cells without SiNx in which no PID occurs. SiNx thus has a function of enhancing Na introduction into c-Si.

Passivation of textured crystalline silicon with small pyramids by silicon nitride films formed by catalytic chemical vapor deposition and phosphorus catalytic impurity doping

Abstracts Silicon nitride (SiNx) films formed by catalytic chemical vapor deposition (Cat-CVD) and phosphorus (P) catalytic impurity doping (Cat-doping) are applied on textured crystalline silicon (c-Si) wafers with a pyramid size of 1–2 µm to reduce the surface recombination of minority carriers. SiNx single layer passivation realizes a surface recombination velocity (SRV) of less than 10 cm/s. The addition of a P Cat-doped layer results in a reduction in a SRV to ~7 cm/s owing to field-effect passivation. These values are comparable to those obtained in our previous study for textured c-Si surface with larger-sized pyramids, indicating the high passivation ability of Cat-CVD SiNx films and P Cat-doping independent of the size of pyramids. In addition to the double-side textured wafers, we also prepare a single-side textured wafer using Cat-CVD SiNx as an etching barrier. We find that Cat-CVD SiNx films can be utilized as an etching barrier against alkali solution, and a high effective minority carrier lifetime (τeff) of 2.3 ms has been obtained by the passivation with Cat-CVD SiNx films. These achievements will contribute to an improvement in the performance of back-contact c-Si solar cells.

Evaluation of Silicon Nitride Film Formed by Atomic Layer Deposition on the Silicon Substrate with Trench Structure Using Angle-Resolved Hard X-ray Photoelectron Spectroscopy

We evaluated the silicon nitride (SiN) films fabricated by plasma enhanced atomic layer deposition (PEALD) on the trench Si substrate. The transmission electron microscopy (TEM) observation showed that the SiN film was conformally deposited along the trench. However, from the angle-resolved hard X-ray photoelectron spectroscopy (HAXPES) measurements, the chemical bonding states in the SiN film on the trench sidewall from top to the bottom were different. On the sidewall of the trench, we found that N deficiency was generated in the SiN film, resulting in the non-stoichiometric SiN film formation. The precursor energy might not be sufficient and deactivated in the deep trench. The stoichiometric SiN film was deposited on the sidewall of the deep trench by increasing the deposition temperature.

Effects of Radio-Frequency Power and Deposition Pressure on Structures and Properties of Silicon-Rich Silicon Nitride Thin Films

Silicon-rich silicon nitride thin films have been grown by plasma enhanced chemical vapor deposition (PECVD) at 13.56MHZ on glass and N-type monocrystalline silicon substrate using high purity NH3,N2 and SiH4 as reactant gas sources by changing of radio-frequency (RF) power and deposition pressure. The samples were characterized by the ultraviolet-visible (UV-UIS) light transmittance spectra, Fourier transform infrared absorption spectroscopy (FTIR) and an X-ray (XRD) diffraction, respectively. The results showed that both the RF power and deposition pressure increase promote the deposition rates. However, the increase of rf power leads to the decrease of optical band gap, the increase of refractive index, and the increase of deposition pressure leads to the widening of optical band gap. The increase of rf power leads to the increase of the silicon atoms in the thin films and the transition of the films to the silicon-rich state. As the deposition pressure increase, the probability of N atoms entering the films increase and the thin films change to a nitrogen-rich state. At a certain pressure, when the rf power is changed, the average grain size in the films decrease by XRD analysis. Based on the above analysis, both the deposition pressure and rf power have an important effect on the microstructure, and optical properties of the thin films. By properly adjusting these two parameters, the silicon-rich silicon nitride films with good density can be obtained.

Memristor structure with the effect of switching resistance based on silicon nitride thin layers

The electrophysical properties and the resistive switching effect of the ITO/SiN x /Si memristor structure were studied. A silicon nitride film with a thickness of ~200 nm with an inhomogeneous element depth distribution was deposited by low-pressure chemical vapor deposition. Based on the Rutherford backscattering data, it was shown that the concentration of excess silicon atoms in the SiN x film increases from 9 to 44 % when approaching the Si substrate. The analysis of the current-voltage characteristics of ITO/SiN x /Si structures revealed that the conduction mechanism in the high-resistance state is determined by the nitride film properties and is described by the Poole-Frenkel model taking into account the hopping model of electron transport between traps. Switching to the low-resistance state is probably caused by the migration of indium or tin ions from the ITO contact to the SiN x layer. The conduction of the ITO/SiN x /Si structure in the low-resistance state is determined by both the mechanisms of charge-carrier injection from the contact and charge-carrier transport through the dielectric layer. Reverse polarity results in destructing the conductive channel and switching the structure to the high-resistance state. The photo-switching effect was found for the ITO/SiN x /Si structure, which opens up new possibilities of using memristors in silicon optoelectronic systems.

Titanium Silicon Nitride Films With Low Silicon Content Deposited via Reactive High-Power Pulsed Sputtering Penning Discharge

Reactive high-power pulsed sputtering Penning discharge at a total pressure of 0.7 Pa and an N2 fraction of 20% in gas phase was used to synthesize titanium silicon nitride (TiSiN) films. The content ratio ( $R_{\mathrm {TS}}$ ) of Si in a target containing a Ti component and an Si component was varied from 0% to 15%. The properties of the as-deposited films were compared with those of the films deposited on high-temperature substrates. The chemical compositions and bonding states of the films were investigated via X-ray photoelectron spectroscopy (XPS). Film structure was evaluated via X-ray diffraction (XRD) and transmission electron microscopy-energy dispersive X-ray spectroscopy. Through XPS, the relative content ratio of Si to Ti was found to increase from 0% to ~25% with increasing $R_{\mathrm {TS}}$ , and the nitrogen content ranged between 47.5% and 50% for all films. The grain size of the films deposited at an $R_{\mathrm {TS}}$ lower than 10% was estimated using the XRD peak of the (111) orientation and found to be ~10 nm. The hardness and elastic modulus of the films deposited on high-temperature substrate at an $R_{\mathrm {TS}}$ value of 8% had the highest values of 43 and 360 GPa, respectively.

Thermo-optic properties of silicon-rich silicon nitride for on-chip applications.

We demonstrate the thermo-optic properties of silicon-rich silicon nitride (SRN) films deposited using plasma-enhanced chemical vapor deposition (PECVD). Shifts in the spectral response of Mach-Zehnder interferometers (MZIs) as a function of temperature were used to characterize the thermo-optic coefficients of silicon nitride films with varying silicon contents. A clear relation is demonstrated between the silicon content and the exhibited thermo-optic coefficient in silicon nitride films, with the highest achievable coefficient being as high as (1.65±0.08) ×10-4 K-1. Furthermore, we realize an SRN multi-mode interferometer (MMI) based thermo-optic switch with over 20 dB extinction ratio and total power consumption for two-port switching of 50 mW.

Surface kinetics and feature scale particle model of SixNy atomic layer deposition using Si2Cl6 precursor

One of the important steps in the fabrication of semiconductor memory devices is the deposition of ultrathin silicon nitride films with uniform film thickness and electrical properties. Such high-quality films have made atomic level control during deposition a necessity and can be achieved via atomic layer deposition (ALD) with excellent step coverage. While ALD has been studied experimentally by many authors, there exist significant gaps between their observations and the practical application of the ALD process in large-scale manufacturing. In this work, a computational model of thin film deposition for a silicon based ALD application was developed. The model includes a surface chemistry mechanism for the deposition of hexachlorodisilane (Si2Cl6) on a growing SixNy film. This mechanism quantifies the sticking probability of the Si2Cl6 precursor on the growth surface as well as an effective active reaction site density on these surfaces. This surface reaction chemistry was used in the context of a feature scale particle transport model to simulate ALD in 100 nm–1 μm critical dimension, ∼10–100 high aspect ratio holes. The model demonstrates the effects of hole size and aspect ratio dependence on the overall kinetics of the deposition process. An increase in the completion time for ALD processes with increasing hole aspect ratio and the increasing statistical nature of the deposition process with smaller critical dimension of the hole were predicted.

Silicon Nitride Deep-Ultraviolet Photoconductive Detector

In this letter, amorphous silicon nitride (Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) film grown by inductively coupled plasma chemical vapor deposition (ICPCVD) method is used as the photosensitive layer of deep ultraviolet (DUV) detection, whose thickness and roughness are 200 nm and 0.92 nm, respectively. The transverse symmetrical photoconductive detector with interdigital electrodes spacing of 4 μm is fabricated by photolithography, exhibiting ultrahigh photo-to-dark current ratio (PDCR) more than 105, fast fall speed of 127 ms and also a satisfying responsivity of 1.09 mA/W. This work lays a foundation for further researches on Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> in photonics and electronics.

Precise resonance energies measured for energy calibration of particle accelerator using thin silicon–nitride foils

In this work resonance parameters of the 28Si(p,p′γ)28Si (Eγ = 1779 keV) and 14N(p,p′γ)14N (Eγ = 2313 keV) reactions were measured between 3 and 4 MeV proton energies for absolute proton beam energy calibration of particle accelerators. For the measurements commercially available self-supporting thin silicon–nitride films and a HPGe gamma-detector were used which are readily available in most accelerator laboratories. Based on our measurement and on the assessment of literature data, the following resonance energies and widths are recommended: 3100.6 ± 0.9 keV (Γ = 11.9 ± 0.4 keV) and 3338.1 ± 1.0 keV (Γ = 11.0 ± 0.5 keV) in 28Si(p,p′γ)28Si and 3903.1 ± 1.7 keV (Γ = 98 ± 1 keV) and 3991.6 ± 1.1 keV (Γ = 10.8 ± 0.5 keV) in 14N(p,p′γ)14N. In addition to the resonance measurements, absolute thick target yields and gamma-ray angular distributions were measured for the 28Si(p,p′γ)28Si (Eγ = 1779 keV) reaction in the vicinity of Ep = 3.10 and 3.34 MeV for ion beam analysis purposes using a thick silicon wafer target.

Etching Characteristics of SixNy Film on Textured Single Crystalline Silicon Surface Using Ar/CF4 and He/CF4 Surface-Discharge Plasma

In this study, we investigated the characteristics of electrode grooves formed by etching silicon nitride (SixNy) films using surface-discharge plasma under Ar/CF4 and He/CF4 gases on the basis of differences in the widths of the electrode grooves etched on the SixNy film. The widths of the grooves etched using Ar as the carrier gas were narrower than those etched using He, and the etching speed achieved using Ar was higher than that achieved using He. Furthermore, the electrode groove created by surface-discharge plasma gradually widened as etching time and applied voltage increased.

Novel fabrication of fixed suspended silicon nitride structure for MEMS devices with dry etching

A method of fabricating suspended LPCVD and PECVD silicon nitride structure is demonstrated for a wide range of MEMS (Micro-Electro-Mechanical Systems) applications. Low stress LPCVD and PECVD silicon nitride film of 1 μm thickness were selected for the structure separately. Optical Lithographic parameters, viz, photoresist (PR) thickness, PR variety and baking parameters were optimized to obtain the PR suitable for selective etching of silicon and silicon nitride. Parameters of the dry etching process were also optimized to achieve anisotropic etching of silicon nitride and isotropic etching of Si to release the silicon nitride beam. The silicon nitride structures, thus released, were characterized using Scanning Electron Microscope (SEM) and Laser Doppler Vibrometer (LDV). Finite Element Method (FEM) analysis was carried out using COMSOL, to compare with the experimental modes of vibration investigated using the Laser Doppler Vibrometer (LDV). Thus we demonstrate that the first mode at 30 kHz was indeed the optimum match.

Characterization of Europium Doped Silicon Oxide, Silicon Oxynitride, and Silicon Nitride Films Prepared By Integrated Ecr-PECVD and Magnetron Sputtering

The compatibility of Si-based light sources with mainstream metal-oxide semiconductor technology has become very interesting over the past decades due to their potential in integrated optoelectronics circuits of monolithic Si [1]. A very promising approach to improve the light emission from silicon-based materials is doping silicon with rare earth elements, and numerous research is involved in this field [1]. However, there are only a few works on europium (Eu) doped silicon-based matrix. In this work, Eu doped silicon oxide, silicon oxynitride, and silicon nitride thin films were deposited on P (100) Si substrates using integrated electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) and magnetron sputtering. Silane (SiH4), oxygen (O2), and Nitrogen(N2) gases were used as precursors and solid Eu as the sputtering target. The integrated ECR-PECVD and sputtering system allows tunable and highly consistent Eu doping concentration, better control of the layer stoichiometry along with less hydrogen incorporation in the deposited film compared to conventional CVD systems [2]. Several thin films were investigated using room temperature photoluminescence (PL) and X-ray diffraction (XRD). A detailed investigation of the effect of annealing on the PL was performed. The annealing temperature was varied from 500 OC to 1200 OC in nitrogen and a mixture of nitrogen and hydrogen atmospheres. It was observed that the intensity of the PL spectra increased with increasing annealing temperature. Besides, the hydrogen passivation effect has been studied in this work, which shows that hydrogen passivation increases the intensity of the peak. Based on the XRD measurements, we have found that the amorphous silicon oxide structure changes to a crystalline structure by adding nitrogen in the film. Interestingly silicon oxynitride and silicon nitride films do not show any luminescence at room temperature. The influence of the precursors' gases in the atomic percentage of the thin films was analyzed by Rutherford Backscattering spectrometry (RBS). In addition to it, the thickness and the index of refraction were characterized by variable angle spectroscopic ellipsometry (VASE).Reference: 1. Lin, Z., Huang, R., Wang, H., Wang, Y., Zhang, Y., Guo, Y., ... & Li, H. (2017). Dense nanosized europium silicate clusters induced light emission enhancement in Eu-doped silicon oxycarbide films. Journal of Alloys and Compounds, 694, 946-951.2. Miller, J. W., Khatami, Z., Wojcik, J., Bradley, J. D. B., & Mascher, P. (2018). Integrated ECR-PECVD and magnetron sputtering system for rare-earth-doped Si-based materials. Surface and Coatings Technology, 336, 99-105.

Hydrogenation behaviors in passivated emitter and rear silicon solar cells with variously hydrogenated SiNx films

From the point of view in sustainable energy, photovoltaic (PV) technology has been recognized as one of the most suitable solutions to replace fossil fuel technologies for electrical generation. However, in PV modules, 95% of solar cells made from P-type boron doped CZ-grown silicon substrates have a reliability issue, called light induced degradation (LID), which strongly affects their practically long-term use. Carrier induced hydrogenation (CIH) is one of the solutions through injection of excess carrier into Si solar cells with moderate thermal treatment. The mechanism of CIH process is the passivation of B-O related defects by hydrogen atoms with negative charge state. In the report, we can find the efficiency enhancement of commercial passivated emitter and rear cells (PERC) by hydrogenated silicon nitride (SiNx:H) films which were prepared by plasma-enhanced chemical vapor deposition and released hydrogen for Si passivation. In order to understand the behaviors of hydrogenation in Si solar cells, we manipulate the amount of hydrogen effused from the rear SiNx:H layers into the silicon substrate. A quadratic trend of average conversion efficiency gain for solar cells was observed after CIH treatment process. The mechanism of hydrogenation for PERC, including carrier induced hydrogenation and excess-hydrogen induced degradation, was investigated.

Latent ion tracks in amorphous and radiation amorphized silicon nitride

The microstructure of 265, 402 and 710 MeV Bi ion induced latent tracks in amorphous thin films of silicon nitride is studied using HRSTEM combined with EELS techniques. The results are compared with latent ion tracks in 220 MeV Xe and 710 MeV Bi irradiated polycrystalline silicon nitride, which was amorphized as a result of irradiation with swift heavy ions only. The results suggest that the track sizes are weakly dependent on defect structure of Si3N4. 710 MeV Bi ions induce tracks with radii that are similar in both amorphous and radiation-amorphized Si3N4, 1.5 ± 0.3 nm and 1.4 ± 0.1 nm, respectively. The situation for Xe is not as clear cut most likely due to the much higher irradiation fluence as compared to Bi.

Effects of etching processes on surface dark current of long-wave infrared InAs/GaSb superlattice detectors

Surface leakage in long-wave infrared InAs/GaSb superlattice detectors is closely related to the state of Sb on the sidewall surface. The presence of free Sb on the sidewall surface after wet etching and GaSb after dry etching at 90 °C can considerably deteriorate the electrical performance of the detector. By using a Cl2/N2 inductively coupled plasma dry etching process at 170 °C, the formation of free Sb or GaSb on the sidewall surface of the sample was prevented, resulting in a low dark current density. The 640 × 512 focal plane array which mesa sidewalls were passivated with silicon nitride film had a cut-off wavelength of 12 μm. The dark current density measured on a single pixel was 1.3 × 10−5 A/cm2 at the bias of −0.05 V and the corresponding resistance-area product at zero resistance (R0A) was 830 Ω∙cm2. The mean peak detectivity (D*) was measured to be 6.6 × 1010 cm Hz1/2/W and the noise equivalent differential temperature as low as 17.2 mK at 60 K.

Adhesion analysis of silicon nitride film deposited on stainless steel surface by adding transition layer

Adhesion is a major factor in film failure. Based on the basic theory of interfacial toughness, the relationship between film thickness and internal stress and adhesion is qualitatively analyzed. The adhesive properties of silicon nitride deposited on stainless steel substrate by plasma enhanced chemical vapor deposition methods is discussed. The case where nickel, nickel–chromium and alumina films are respectively used as transition layers is compared. After vacuum annealing thermal treatment of these films, the results show that the alumina film has better matching performance with 304 stainless steel, and the interface toughness is improved by 51.2% compared with the silicon nitride film. After the samples are stretched, the silicon nitride film show a large number of cracks when the transition layer is nickel or nickel–chromium, possibly due to the large thermal stress in the film. At the same time, the process parameters of magnetron sputtered alumina are optimized, and the optimal deposition rate of alumina film is determined to be 40.25 nm min−1. Then, the effect of film thickness on adhesion is investigated by theoretical analysis and tape breakage test. As the film thickness ratio of alumina and silicon nitride increases, the adhesion is optimal.

Study on effect of process and structure parameters on SiNxHy growth by in-line PECVD

This paper builds a physical model by using the finite element method on COMSOL simulation platform to simulate the in-line PECVD process. The in-line PECVD simulation model couples the flow field, thermal field, chemical reaction field and plasma field and is verified through experiments. In addition, a new simulation strategy is proposed to solve the problem of dynamic coating silicon nitride film. Through this simulation method, process parameters and structural parameters of the in-line PECVD equipment are optimized. Effects of microwave tube position, microwave shield size, total gas flow, pressure and temperature on main coating reaction region is studied. The results have shown that the position of microwave tube, the total gas flow and temperature have greater influence on the region of reaction zone, the concentration distribution of reactants and the thickness of SiNxHy film. Through optimizing process parameters and structural parameters, the coating rate of SiNxHy film can be increased from 0.0607 nm/s to 0.15 nm/s and the deposition thickness can be increased from 6.78 nm to 15.59 nm. The molar concentration of SiNxHy particles in the reaction region has grown by more than 23.5%. And the relative intensity of reaction field inside PECVD chamber has increased by 1.3–2.3, which is calculated by molar concentration ratio of SiNxHy particles. This paper provides a reference for the optimization of in-line PECVD equipment.

Mechanism of Metallization-Induced Losses in the Rear-Side of Fully Screen-Printed p-type PERC Solar Cells

This article investigates metallization-induced recombination losses associated with the presence of silicon (Si) in the 1) rear passivation layers and 2) aluminum (Al) paste in fully screen-printed p -type passivated emitter and rear cell (PERC) solar cells. For 1), the rear sides of PERCs passivated with aluminum oxide films stacked with silicon nitride (SiN y ) films with various refractive indexes (n), as defined by the composition of the SiN y films, were fabricated. Si-rich SiN y films strongly degraded the implied open-circuit voltages of symmetrically passivated samples, that include cells. Elemental mapping analysis confirmed further metallization-induced losses at the cell level because of the formation of an Al-Si alloy within the passivation stacks, with the density of the alloy dependent on the refractive index. For 2), the rear sides of PERCs were metallized with Si-free Al paste or Al pastes that contain Si. High-Si paste had both good and bad effects: it produced thicker aluminum back surface fields but left partially-formed Al-Si alloy within the passivation films.

Charge Inversion and Calcium Gating in Mixtures of Ions in Nanopores.

Calcium ions play important roles in many physiological processes, yet their concentration is much lower than the concentrations of potassium and sodium ions. The selectivity of calcium channels is often probed in mixtures of calcium and a monovalent salt, e.g., KCl or NaCl, prepared such that the concentration of cations is kept constant with the mole fraction of calcium varying from 0 and 1. In biological channels, even sub-mM concentration of calcium can modulate the channels' transport characteristics; this effect is often explained via the existence of high affinity Ca2+ binding sites on the channel walls. Inspired by properties of biological calcium-selective channels, we prepared a set of nanopores with tunable opening diameters that exhibited a similar response to the presence of calcium ions as biochannels. Nanopores in 15 nm thick silicon nitride films were drilled using focused ion beam and e-beam in a transmission electron microscope and subsequently rendered negatively charged through silanization. We found that nanopores with diameters smaller than 20 nm were blocked by calcium ions such that the ion currents in mixtures of KCl and CaCl2 and in CaCl2 were even ten times smaller than the ion currents in KCl solution. The ion current blockage was explained by the effect of local charge inversion where accumulated calcium ions switch the effective surface charge from negative to positive. The modulation of surface charge with calcium leads to concentration and voltage dependent local charge density and ion current. The combined experimental and modeling results provide a link between calcium ion-induced changes in surface charge properties and resulting ionic transport.