Si3N4 Films Research Articles

Stress-released Si3N4 fabrication process for dispersion-engineered integrated silicon photonics.

We develop a stress-released stoichiometric silicon nitride (Si3N4) fabrication process for dispersion-engineered integrated silicon photonics. To relax the high tensile stress of a thick Si3N4 film grown by low-pressure chemical vapor deposition (LPCVD) process, we grow the film in two steps and introduce a conventional dense stress-release pattern onto a ∼400nm-thick Si3N4 film in between the two steps. Our pattern helps minimize crack formation by releasing the stress of the film along high-symmetry periodic modulation directions and helps stop cracks from propagating. We demonstrate a nearly crack-free ∼830nm-thick Si3N4 film on a 4" silicon wafer. Our Si3N4 photonic platform enables dispersion-engineered, waveguide-coupled microring and microdisk resonators, with cavity sizes of up to a millimeter. Specifically, our 115µm-radius microring exhibits an intrinsic quality (Q)-factor of ∼2.0×106 for the TM00 mode and our 575µm-radius microdisk demonstrates an intrinsic Q of ∼4.0×106 for TM modes in 1550nm wavelengths.

Fabrication of silicon electrodes used for micro electrochemical machining

In micro electrochemical machining (ECM), stray corrosion always causes undesired material dissolution and deteriorates the machining localization. Adopting sidewall insulating films on the electrode is proven to be an effective approach for reducing stray corrosion. Sidewall films with characteristics of good insulation, thin thickness, and excellent durability are required. In previous work, we proposed a heavily-doped silicon electrode, on which silicon-based films were prepared and acted as the insulating films. To fabricate silicon electrodes, this research investigates wet etching behavior of heavily doped Si (100) and then presents a fabrication process. Firstly, shapes of micro electrodes are designed on photomasks of lithography. Aiming at patterned profiles, effects of etchants on etch rate, dimension accuracy and surface integrity are investigated. Experimental results indicate that tetramethylammonium hydroxide (TMAH) leads to smoother electrode surfaces and fewer defects compared with potassium hydroxide. Then, insulation and durability performances of silicon-based films are investigated. 500 nm SiO2 and 300 nm Si3N4 composite film achieves more durable insulation and excellent compactness. Consequently, silicon electrodes with the dimension of 86 × 54 μm are fabricated on the Si (100) wafer with 25 wt% TMAH etchant, on which SiO2 and Si3N4 film is deposited by low-pressure chemical vapor deposition. In ECM experiments, stray corrosion of the non-machined surface is significantly reduced, and the sidewall taper of the machined structure is reduced to 5.5°. The validity and durability of silicon electrodes for micro ECM processes are verified.

Morphology and Magneto‐Transport in Exfoliated Graphene on Ultrathin Crystalline β‐Si3N4(0001)/Si(111)

AbstractThis work reports the first experimental study of graphene transferred on β‐Si3N4(0001)/Si(111). A comprehensive quantitative understanding of the physics of ultrathin Si3N4 as a gate dielectric for graphene‐based devices is provided. The Si3N4 film is grown on Si(111) under ultra‐high vacuum (UHV) conditions and investigated by scanning tunneling microscopy (STM). Subsequently, a graphene flake is deposited on top of it by a polymer‐based transfer technique, and a Hall bar device is fabricated from the graphene flake. STM is employed again to study the graphene flake under UHV conditions after device fabrication and shows that the surface quality is preserved. Electrical transport measurements, carried out at low temperature in magnetic field, reveal back gate modulation of carrier density in the graphene channel and show the occurrence of weak localization. Under these experimental conditions, no leakage current between back gate and graphene channel is detected.

Electron beam injection from a hollow cathode plasma into a downstream reactive environment: Characterization of secondary plasma production and Si3N4 and Si etching

A material etching system was developed by combining beam electron injection from a direct current hollow cathode (HC) electron source with the downstream reactive environment of a remote CF4/O2 low temperature plasma. The energy of the injected beam electrons is controlled using an acceleration electrode biased positively relative to the HC argon discharge. For an acceleration voltage greater than the ionization potential of Ar, the extracted primary electrons can produce a secondary plasma in the process chamber. The authors characterized the properties of the secondary plasma by performing Langmuir probe measurements of the electron energy probability function (EEPF) 2.5 cm below the extraction ring. The data indicate the existence of two major groups of electrons, including electrons with a primary beam electron energy that varies as the acceleration voltage is varied along with low energy electrons produced by ionization of the Ar gas atoms in the process chamber by the injected beam electrons. When combining the HC Ar beam electron with a remote CF4/O2 electron cyclotron wave resonance plasma, the EEPF of both the low energy plasma electron and beam electron components decreases. Additionally, the authors studied surface etching of Si3N4 and polycrystalline Si (poly-Si) thin films as a function of process parameters, including the acceleration voltage (0–70 V), discharge current of the HC discharge (1–2 A), pressure (2–100 mTorr), source to substrate distance (2.5–5 cm), and feed gas composition (with or without CF4/O2). The direction of the incident beam electrons was perpendicular to the surface. Si3N4 and polycrystalline silicon etching are seen and indicate an electron-neutral synergy effect. Little to no remote plasma spontaneous etching was observed for the conditions used in this study, and the etching is confined to the substrate area irradiated by the injected beam electrons. The electron etched Si3N4 surface etching rate profile distribution is confined within a ∼30 mm diameter circle, which is slightly broader than the area for which poly-Si etching is seen, and coincides closely with the spatial profile of beam electrons as determined by the Langmuir probe measurements. The magnitude of the poly-Si etching rate is by a factor of two times smaller than the Si3N4 etching rate. The authors discuss possible explanations of the data and the role of surface charging.

Visualizing the Redox Reaction Dynamics of Perovskite Nanocrystals in Real and Reciprocal Space.

Redox reaction, involving the gain and loss of electrons between reactants, is one type of common chemical reaction governing fundamental energy issues in nature. However, reports of vividly visualizing such key processes with simultaneous structural determination of new phases that are involved are rare. Here, by achieving simultaneous recording in both real and reciprocal space, we demonstrate in situ imaging of the redox reaction dynamics in perovskite nanocrystals. The thorough atomic-scale movies enable an in-depth understanding of the reaction-induced nucleation and growth mechanism of clusters with the aid of carbon, and a simple way of using SiN films at room temperature to fully prevent the irradiation-induced degradation in perovskites is proposed, in contrast to the costly low-temperature strategy. Real-time atomic-scale imaging in both real and reciprocal space paves the way for revealing various chemical and physical events at targeted nanoscale positions with complementary structural information.

Thermal atomic layer etching of silicon nitride using an oxidation and “conversion etch” mechanism

Thermal atomic layer etching (ALE) of silicon nitride was achieved using sequential exposures of oxygen (O2) or ozone (O3), hydrofluoric acid (HF), and trimethylaluminum [TMA, Al(CH3)3]. Thermal Si3N4 ALE will be useful to etch Si3N4 in semiconductor, optoelectronic, and MEMS devices. Thermal Si3N4 ALE was performed with Si3N4 thin films deposited on silicon wafers using low pressure chemical vapor deposition. In situ spectroscopic ellipsometry (SE) was employed to monitor the changes in the Si3N4 film thickness as well as the SiO2 layer thickness. The SE results at 290 °C yielded an Si3N4 etch rate of 0.25 Å/cycle with an O2-HF-TMA reactant sequence using partial pressures of 250, 0.65, and 1.2 Torr for O2, HF, and TMA, respectively. The O2, HF, and TMA reactants were held statically at the indicated partial pressures for 10, 5, and 5 s, respectively. Larger etch rates were observed using O3 instead of O2 as the oxidant. A higher Si3N4 etch rate of 0.47 Å/cycle was measured at 290 °C using an O3-HF-TMA reactant sequence at the same partial pressures and static exposure times as the O2-HF-TMA sequence. The Si3N4 etch rate was observed to decrease at lower temperatures. An Si3N4 etch rate of 0.07 Å/cycle was measured at the lowest temperature of 210 °C using an O3-HF-TMA reactant sequence. The Si3N4 surface roughness was reduced after Si3N4 ALE. The SiO2 layer on Si3N4 could be removed using sequential HF and TMA exposures. These sequential HF and TMA exposures could also very slowly etch the Si3N4 substrate. The Si3N4 etch rate was dependent on the reaction sequence. When an O3-TMA-HF sequence was employed with reactant partial pressures of 250, 0.65, and 1.2 Torr for O3, HF, and TMA, respectively, the Si3N4 etch rate was 0.20 Å/cycle at 290 °C. Thermal Si3N4 ALE adds to the growing list of materials that can be etched with atomic layer control using thermal chemistry.

Will Polyethylene furanoate (PEF) challenge Polyethylene terephthalate (PET)?

The preparation and characterization of SiN thin films using an aerosol-type liquid precursor delivery system (LDS) for application as a water-vapor permeation barrier layer in organic electronic devices is described. The proposed LDS consisted of three major parts: 1) an aerosol generator that transformed the liquid precursor to an aerosol molecule using a piezoelectric ultrasonic vibrator, 2) a vaporizer that transformed the injected aerosol molecules to a vapor state, and 3) a vapor storage canister. The instant evaporation fraction and maximum evaporation mass rate were measured to be 98.3% and 2.55 g/min, respectively. The temperature in the vaporizer was stable, showing a 1 °C variation from the set temperature. As the LDS temperature increased, the evaporation mass rate also increased from 0.035 to 2.55 g/min. A 30 nm thick SiN layer was prepared to evaluate the performance of the LDS, which was attached to a cyclic chemical vapor deposition system. The prepared SiN layer had a smooth surface with no defects or pinholes; the root mean square surface roughness of the prepared SiN film was measured to be 0.185 nm, which is adequate to be used as encapsulation layers in organic electronic devices. The water vapor transmission rate through the 30 nm thick SiN layer was calculated to be 1.31 × 10−6 g/m2/day by Ca-degradation test. The results indicated that the produced films meets the requirement for application as an encapsulation layer to protect the organic layer in organic electronic devices from water vapor penetration, especially in organic light-emitting diodes.

A New High Selectivity Acidic Slurry for Chemical Mechanical Planarization of Carbon-Doped Ge2Sb2Te5 Film

During the industrial application of the new phase change memory material carbon-doped Ge2Sb2Te5 (GSTC), it is necessary to perform planarization for the confined memory cell structure through the chemical mechanical polishing (CMP) process. The goal of CMP is to acquire a high material removal rate and selectivity while ensuring that the polished surface is free of scratches and corrosion pits. A new acidic slurry added with potassium persulfate (OXONE) as an oxidizer was developed. The acidic slurry added with 5000 ppm OXONE has a amorphous GSTC film material removal rate of 5200 Å min−1, a high selectivity between GSTC and Si3N4 films of 950:1, and no corrosion-induced pit. In order to clarify the mechanism of GSTC CMP with OXONE, the Energy Dispersive Spectrometer, potentiodynamic polarization curve and X-ray photoelectron spectroscope were adopted to analyze the surface of GSTC. It is found that the chemical reaction mechanism is significantly different from that of hydrogen peroxide (H2O2). Finally, the mechanism of GSTC during the CMP with OXONE in the acidic slurry is depicted.

Two-step cycling process alternating implantation and remote plasma etching for topographically selective etching: Application to Si3N4 spacer etching

This article proposes an original method to achieve topographically selective etching. It relies on cycling a two-step process comprising a plasma implantation step and a removal etching step using remote plasma source process. Both steps can be achieved in the same reactor prototype chamber, which has the capability to produce both capacitively coupled plasma and remote plasma (RP) discharges. It is shown that in RP processes, an incubation time exists before the etching starts. The introduction of a plasma implantation step prior to the RP step allows us to selectively functionalize the horizontal surfaces of the material with respect to the vertical surfaces, thanks to the ion directionality. The modifications induced by the implantation allow us to modify the incubation time between an implanted and a nonimplanted material offering a process window with infinite etch selectivity between horizontal and vertical surfaces. This approach has been demonstrated on Si3N4 blanket films with the perspective to be applied to the Si3N4 spacer etching process in which etch selectivity is a key issue. For this particular application, a cycling process comprising an H2 plasma implantation and a He/NH3/NF3 remote plasma process has been developed. The H2 implantation modifies the Si3N4 surface state by incorporating oxygen contaminants coming from the reactor wall and creating dangling bonds. This surface functionalization considerably reduces the incubation time. New insights into the etching mechanisms of Si3N4 films exposed to NH3/NF3 remote plasma are proposed and explain why the presence of Si–O bonds is mandatory for the initiation of the etching.

Controlled gradual and local thinning of free-standing nanometer thick Si3N4 films using reactive ion etch

Nanometer-scale devices are fabricated using numerous fabrication techniques since the last couple of decades. However, the advancement in nanotechnology gives new horizons to the researcher to develop nanometer-scale devices in a controlled manner while also providing high accuracy and precision with cost and time-effectiveness. This article focuses on the production of free-standing nano-scale thick Si3N4 films using Reactive Ion Etch technique. Although there are many reports in the literature on the required conditions to etch Si3N4, unfortunately, there are not many technical reports that illustrate the step-by-step fabrication and characterization together with the detailed optimization steps. Here in this study, the thinning of a membrane is achieved using CF4/Ar in controlled RF power conditions and a well-defined protocol is given with several preliminary optimization steps. By doing so, free-standing locally thinned Si3N4 membranes of about 20 nm thickness are successfully realized in a precise manner. Further assessments are given an offer to the readers of interest the ways to characterize the samples with the required cautions. The detailed procedure given here would potentially provide practical aspects for the researchers working in the field of nanofabrication.

Flatband voltage stability and time to failure of MOCVD-grown SiO2 and Si3N4 dielectrics on N-polar GaN

The flat-band voltage (VFB) stability and time-dependent-dielectric-breakdown of SiO2 and Si3N4 films grown in situ on (000–1) N-polar GaN by metal organic chemical vapor deposition are investigated. The VFB of the SiO2-film was unstable only above a critical electric-field stress of 4.3 MV cm−1, while the VFB of Si3N4 was unstable at both low and high electric fields. The Si3N4 film exhibited time to failure of 20 years occurring at an electric field of 4.9 MV cm−1 which was 3 MV cm−1 higher than that of SiO2. This study contributes to the understanding of dielectrics performance, devoted to next-generation N-polar GaN-based transistors.

Memory effect in silicon nitride deposition using ICPCVD technique

In this study, a plasma-based low-temperature, low-pressure SiN film deposition is investigated for device applications. Ammonia, nitrogen and silane are being used for optimization of the quality of SiN film for device passivation by ICPCVD. Characterization of SiN film is done using elastic recoil detection analysis, AFM, FTIR and ellipsometry. The effect of previous process parameters on subsequent process is called memory effect, which has been investigated by all the characterization techniques. During deposition, this effect has been observed for the same parameters that are used to maintain the stoichiometry of the film. It has been observed that some of the residues of gases used for SiN deposition remain present even after the deposition in the chamber and are carried over for the next deposition process and alter the film property, though parameters such as flow rate, temperature, pressure and time remain fixed. This memory effect alters the film surface roughness and stoichiometry thus affecting device characteristics after passivation.

Selective Si3N4 Etching in Si3N4/SiO2 Pair-Layer Stack Using Non-H3PO4-Based Superheated Water

It is necessary to selectively etch Si3N4 in Si3N4/SiO2 multi-stack structure for the fabrication of 3D NAND [1]. The etching reaction of Si3N4 in phosphoric acid is known as 3Si3N4 + 4H3PO4 + 27H2O → 4(NH4)3PO4 + 9H2SiO3 [2]. However, as the number of Si3N4 etching batch process increases, the Si3N4 etching performance of H3PO4 decreases. Therefore, a fresh H3PO4 solution should be used for each process. As a result, the consumption of H3PO4 and process cost increase. In addition, the etching by-products could be reattached to SiO2 layers, which causes problems in the subsequent processes. In this study, the etching of Si3N4 and SiO2 in superheated water was investigated. In addition, by adding proper additives to superheated water, the Si3N4 etching rate and Si3N4/SiO2 etch selectivity were controlled. Blanket Si3N4 and SiO2 films on Si wafer were used. A patterned Si3N4/SiO2 pair-layered structure was also used. HCl, NH4OH, H2SiO3 and HF were used as additives. The thicknesses of the Si3N4 and SiO2 films were measured using spectroscopic ellipsometry and FE-SEM. The etching rates of Si3N4 and SiO2 were shown in Figure 1. The etch rate of Si3N4 and SiO2 in superheated water (pH 7) was 23 and 1.5 Å/min, respectively. When HCl was added, the etching rate of Si3N4 was decreased. On the other hand, when NH4OH was added, the etching rate of Si3N4 was increased. Therefore, it is believed that OH- generated from the self-ionization of water in the superheater water plays an important role in the etching of Si3N4. In addition, proper additives were added to superheated water to improve the etching performance. The result of patterned Si3N4/SiO2 structure using superheated water with additive was shown in Fig. 2(a). For comparison, the result of the 85 wt% H3PO4 process was shown in Fig. 2(b). In the superheated water with additive and the H3PO4 process, the lateral etched depths of the Si3N4 were similar. However, in the superheated water process, the thickness of the remaining SiO2 layers was maintained without thinning. Therefore, optimized superheated water without H3PO4 show a very promising selective etch performance at the 3D Si3N4/SiO2 pair-layer structure.

(Invited) Challenges of Graphene Process Integration in CMOS Technology

Compatibility of graphene device fabrication process with Si integrated circuit (IC) manufacturing platforms can enhance the implementation of graphene in electronic and optoelectronic applications and their commercialization. Recent demonstrations of hybrid graphene-Si devices on a wafer scale [1, 2] clearly indicate increasing maturity of the graphene technology. However, there are remaining questions about the manufacturability, as well as the integration and compatibility with Si technology which are seen as prerequisites to the commercialization of graphene (opto-) electronic devices [3, 4]. Despite the remarkable progress in recent years, protocols used for the fabrication of graphene devices often lack the required stability and compatibility which in turn hinders access to the large-scale semiconductor device manufacturing infrastructure. From this point of view, it is of utmost importance to investigate preparation of graphene devices in conditions resembling as close as possible to the Si-based IC production environment. Although this approach may pose inherent risks to the fabrication toolsets, it provides a rare opportunity to explore the engineering aspects of graphene device preparation in a relevant production environment. In this paper we focus on engineering aspects of graphene device fabrication under constraints of manufacturability. We demonstrate some of the key stepping stones which can form a pathway to the fabrication of graphene-based components using tools and processes applied in the IC manufacturing in a 200 mm wafer Si technology environment. As a case study, we present insights into processes of cleaning, patterning, encapsulation, and contacting graphene in a 200 mm wafer pilot line routinely used for the fabrication of ICs in 0.13/0.25um SiGe BiCMOS (bipolar-complementary metal-oxide-semiconductor) technologies. Following the presentation of key process steps and selected electrical characterization results, we point out to the challenges and roadblocks which need to be overcome to enable integration of this material with Si devices. Although Cu substrates offer graphene an outstanding quality, layer transfer from Cu is associated with a significant risk of metallic contaminations which pose limitations on handling of graphene in CMOS processing lines. For this reason, our experiments rely on graphene grown on Ge surfaces which has been proven to be front-end-of-line compatible in terms of purity. Chip-size patches of graphene are transferred from the epi-Ge/Si growth wafer by electrochemical delamination to various sorts of patterned 200 mm wafers on which the further process development takes place. This method of graphene transfer is not yet fully compatible with the Si technology; however, it offers convenient prototyping opportunities as an intermediate solution until full 200mm wafer transfer processes as for example the wafer bonding is developed. Encapsulation of deposited graphene is essential to protect its properties from the environment and the destructive influences of subsequent processing. The key element of the encapsulation in our fabrication scheme is a thin (20 nm-50 nm) SiN layer deposited by low power plasma-enhanced chemical vapor deposition (PECVD). It has been demonstrated that layers of SiN can be grown by PECVD directly on the graphene with excellent uniformity and electrical performance while preserving its crystalline quality and transport properties. The added value of PECVD technique is that it is widely used in the Si IC manufacturing. We adapted this approach to form closed and smooth (rq = 0.47 nm) encapsulating layers of SiN (refractive index n = 2.02 at l = 633 nm) directly on transferred graphene. The second element of the encapsulation is realized by the deposition of a SiO2 layer on the SiN film by using CVD. References Y.-M. Lin, A. Valdes-Garcia, S.-J. Han, D.B. Farmer, I. Meric, Y. Sun, Y. Wu, C. Dimitrakopoulos, A. Grill, P. Avouris, K.A. Jenkins, Science, 332, 1294 (2011)S. Goossens, G. Navickaite, C. Monasterio, S. Gupta, J.J. Piqueras, R. Perez, G. Burwell, I. Nikitskiy, T. Lasanta, T. Galan, E. Puma, A. Centeno, A. Pesquera, A. Zurutuza, G. Konstantatos, F. Koppens, NaturePhotonics, 11, 366 (2017) S. Park, Nature Reviews Materials, 1, 16085 (2016)G. Ruhl, S. Wittmann, M. Koenig, D. Neumaier, Beilstein J. Nanotechnol., 8, 1056 (2017)

Simple Non-Destructive Method of Ultrathin Film Material Properties and Generated Internal Stress Determination Using Microcantilevers Immersed in Air

Recent progress in nanotechnology has enabled to design the advanced functional micro-/nanostructures utilizing the unique properties of ultrathin films. To ensure these structures can reach the expected functionality, it is necessary to know the density, generated internal stress and the material properties of prepared films. Since these films have thicknesses of several tens of nm, their material properties, including density, significantly deviate from the known bulk values. As such, determination of ultrathin film material properties requires usage of highly sophisticated devices that are often expensive, difficult to operate, and time consuming. Here, we demonstrate the extraordinary capability of a microcantilever commonly used in a conventional atomic force microscope to simultaneously measure multiple material properties and internal stress of ultrathin films. This procedure is based on detecting changes in the static deflection, flexural and torsional resonant frequencies, and the corresponding quality factors of the microcantilever vibrating in air before and after film deposition. In contrast to a microcantilever in vacuum, where the quality factor depends on the combination of multiple different mechanical energy losses, in air the quality factor is dominated just by known air damping, which can be precisely controlled by changing the air pressure. Easily accessible expressions required to calculate the ultrathin film density, the Poisson’s ratio, and the Young’s and shear moduli from measured changes in the microcantilever resonant frequencies, and quality factors are derived. We also show that the impact of uncertainties on determined material properties is only minor. The validity and potential of the present procedure in material testing is demonstrated by (i) extracting the Young’s modulus of atomic-layer-deposited TiO2 films coated on a SU-8 microcantilever from observed changes in frequency response and without requirement of knowing the film density, and (ii) comparing the shear modulus and density of Si3N4 films coated on the silicon microcantilever obtained numerically and by present method.

69‐1: Etch Properties of Silicon Nitride Films Using a New In‐Line Equipment with Atmospheric Glow Plasma for the OLED Flexible Display

DBD non‐thermal atmospheric pressure plasma (NAPP) is suitable for the OLED display manufacturing process using flexible substrate because it is low‐temperature atmospheric pressure process, low cost process and does not need a vacuum system. High dynamic etch rate of 220À·cm/s in Si3N4 thin films was obtained in flow rate ratio (O2/CF4) of 0.13, rf 480W, the speed of 10mm/s in a 200mm new inline NAPP system. About 5% increase of dynamic etch rate by N2 gas injection was conformed. Etch profile of Si3N4 film with patterned PR shows perfectly isotropic without undercut because the species such as CF3, COF2, F and O have low energy and chemical reaction.

A method for high selective etch of Si3N4 and SiC with ion modification and chemical removal

We demonstrated a high selective and anisotropic plasma etch of silicon nitride (Si3N4) and silicon carbide (SiC). The demonstrated process consists of a sequence of ion modification and chemical dry removal steps. The Si3N4 etch with hydrogen (H) ion modification showed a high selectivity to silicon dioxide (SiO2) and SiC films without hydro fluorocarbon film deposition which has been used in a conventional Si3N4 etch process. A self-limiting reaction was observed by changing the ion modification and removal step times. The SIMS analyzes indicated that the etch amount of Si3N4 depends on not only penetration depth of H ion but also H concentration in the ion modification step. In addition, we have developed selective etch of SiC with nitrogen (N) ion modification. These results suggest that the ion modification assisted etch enables us to obtain the high selective Si3N4 or SiC film by H or N ion modification, respectively.

Microscopic mechanisms of Si(111) surface nitridation and energetics of Si3N4/Si(111) interface

Nitridation of silicon surface is an important step in GaN or AlN nanostructures growth process which determines quality of fabricated devices. In this work modeling of gas-surface reaction of the Si(111) surface nitridation was performed using density functional theory calculations. We show that interface structure corresponding to first stoichiometric Si3N4 monolayer may be generated in a great number of different ways by means of vacancy-assisted mechanism. The nearly continuum distribution of total energies may be associated with such structures formed after exothermic reaction with considerable energy gain. Nevertheless founded global minimum corresponds to abrupt interface and crystalline-like Si3N4 monolayer structure. Suggested mechanism of silicon nitride film growth is based on the calculated energy barriers for diffusion of volatile species such as N, N2, SiN and SiN2 which are building blocks for the growth of Si3N4 film. At first stage atomic nitrogen diffusion from vacuum to substrate occurs. Then silicon vacancies in substrate and volatile SiN radicals are formed. The back diffusion of SiN from substrate to Si3N4-vacuum side is the main mechanism responsible for silicon nitride film growth.

Reassessment of different antireflection coatings for crystalline silicon solar cell in view of their passive radiative cooling properties

In outdoor condition, the performance of the commercial solar photovoltaic (PV) modules depends on various parameters like (1) amount of direct solar radiation, (2) ambient temperature, (3) the location of installation, (4) wind speed, (6) aerosol, and most of these parameters are uncontrollable. The first two of these parameters increase the solar cell operating temperature which in turn decreases the performance of the solar cell. This simulation-based study presents the development of a passive radiative cooling system for a simple flat crystalline silicon (c-Si) solar cell using a thin film of SiO2, Al2O3, Si3N4, HfO2 or TiO2. Some of these materials are being used as an antireflection coating (ARC) in the commercial solar panel for having a suitable refractive index (n) and very low extinction coefficient (k) values in 300–1200 nm wavelength range. In the 8–13 µm wavelength range, the variation of emissivity of the materials w.r.t. thickness and angle have been calculated. The thickness of ARC, the absorptivity of Silicon, the emissivity of ARC in the atmospheric window was also estimated. Suitable ARC cum emissive layer helps the solar cell in absorptivity improvement as well as keeping its temperature near the ambient temperature. The present study finds that Si3N4 is having a higher emissive power than the other materials and increases (10–161.63 W m−2) with the increase in thickness from 20 to 1000 nm in 8–13 µm wavelength range. Material like SiO2 and Al2O3 have emissivity lower than Si3N4 of comparable thickness.

Click chemistry on silicon nitride for biosensor fabrication

Biosensors are of essential importance in medical and biological diagnostics. Often, they are produced using silane chemistry on glass or silicon oxide surfaces. However, controlling that silane chemistry is challenging. Here, we present an alternative strategy to form functional organic layers and biosensors on silicon nitride (Si3N4). H-terminated Si3N4 films are used to generate reactive azide groups by various azidation methods. Biomolecular probes can then be immobilized using click chemistry reactions with the azide groups and due to its high sensitivity in XPS a fluorine-substituted test alkyne was utilized to optimize click chemistry conditions. After that a biotinylated alkyne was clicked to Si3N4 surfaces followed by immobilization of streptavidin as analyte in a model assay. The functionalized surfaces were thoroughly characterized by surface chemical analysis using X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy.