SiNx Deposition Research Articles

Enhancement of the barrier performance in organic/inorganic multilayer thin-film structures by annealing of the parylene layer

A multilayered barrier structure was fabricated by chemical vapor deposition of parylene and subsequent plasma-enhanced chemical vapor deposition of SiOx or SiNx. The barrier performance against water vapor ingress was significantly improved by annealing the parylene layer before the deposition of either SiOx or SiNx. The mechanism of this enhancement was investigated using atomic force microscopy, Raman spectroscopy, and X-ray diffraction. The surface roughness of the parylene before the deposition of either SiOx or SiNx was found to correlate closely with the barrier performance of the multilayered structures. In addition, removing absorbed water vapor in the film by annealing results in a lower water vapor transmission rate in the transient region and a longer lag time. Annealing the parylene leads to a large decrease in the effective water vapor transmission rate, which reaches 7.2±3.0×10−6g/m2/day.

Silicon nitride thin films deposited using electron-beam evaporation in an RF plasma MBE system

Silicon nitride (SiNx) thin films were deposited on (100) Si wafers in a molecular-beam epitaxy growth chamber equipped with a customized multipocket electron-beam evaporator, a Si effusion cell, and an RF plasma source for reactive nitrogen. The films were characterized using atomic-force microscopy, spectroscopic ellipsometry, and specular x-ray reflectivity. For films deposited using an electron-beam Si source with N/Si > 1.33, the deposition temperature determined the density and refractive index. Stoichiometric Si3N4 films were produced when the deposition temperature was greater than 725 °C, in agreement with our previous results that used an effusion cell for Si. By using the electron-beam Si source, an order of magnitude increase in SiNx deposition rate was achieved over the conventional effusion cell method.

Growth of semipolar {11$ \bar 2 $2} GaN using SiNx intermediate layer by hydride vapor phase epitaxy

AbstractSemipolar {11‐22} plane GaN layer was grown using a SiNx intermediate layer by hydride vapor phase epitaxy (HVPE). By optimizing the deposition time of the SiNx intermediate layer, the dislocation density decreased compared to that of a conventional {11‐22} GaN layer. The reduction in the dislocation density was due to three dimensional regrowth of the {11‐22} GaN layer at the interface. However, basal plane stacking faults (BSFs) were increased by use of the SiNx intermediate layer, and with increasing the SiNx deposition time. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

PECVD-AlOx/SiNx Passivation Stacks on Silicon: Effective Charge Dynamics and Interface Defect State Spectroscopy

The charge dynamics and the interface defect state density of AlOx/SiNx passivation stacks deposited by plasma-enhanced chemical vapor deposition (PECVD) on crystalline silicon (c-Si) wafers are investigated. High frequency (1MHz) capacitance voltage (C-V) measurements were performed on stacks in the as deposited state and after an annealing step. C-V sweeps reveal an initially high negative charge density for the as deposited sample, activated by the thermal budget during SiNx deposition. However, this charge state is unstable and reduced owning to electron detrapping and emission into the c-Si upon applying moderate voltages. In the annealed sample, the AlOx/SiNx stack has a stable negative fixed charge. Both for as deposited and for annealed samples, applying a positive or negative constant gate voltage stress (Vstress) enhances or reduces the negative effective charge density (Qox,eff), respectively. Injection of charges from the c-Si into traps in the AlOx/SiNx stack is identified as the mechanism responsible for this behavior. We conclude that in addition to fixed negative charges trapping of negative charges near the interface is a crucial mechanism contributing to the total effective negative charge of the stack. Their contribution depends on the temperature and duration of the thermal treatment. Additionally, a large Vstress leads to generation of additional Si dangling bond defects over the entire c-Si bang gap at the c-Si/AlOx interface.

Synthesis and properties of SiNx coatings as stable fluorescent markers on vertically aligned carbon nanofibers

The growth of vertically aligned carbon nanofibers (VACNFs) in a catalytic dc ammonia/acetylene plasma process on silicon substrates is often accompanied by sidewall deposition of material that contains predominantly Si and N. In fluorescent microscopy experiments, whereby VACNFs are interfaced to cell and tissue cultures for a variety of applications, it was observed that this material is broadly fluorescent. In this paper, we provide insight into nature of these silicon/nitrogen in-situ coatings. We propose a potential mechanism for deposition of SiNx coating on the sidewalls of VACNFs during PECVD synthesis and explore the origin of the coating's fluorescence. It is most likely that the substrate reacts with process gases similar to reactive sputtering and chemical vapor deposition (CVD), forming silane and other silicon bearing compounds prior to isotropic deposition as a SiNx coating onto the VACNFs. The formation of Sinanoclusters (NCs) is also implicated due to a combination of strong fluorescence and elemental analysis of the samples. These broadly luminescent fibers can prove useful as registry markers in fluorescent cellular studies and for tagging and tracing applications.

Synthesis and properties of SiNx coatings as stable fluorescent markers on vertically aligned carbon nanofibers

The growth of vertically aligned carbon nanofibers (VACNFs) in a catalytic dc ammonia/acetylene plasma process on silicon substrates is often accompanied by sidewall deposition of material that contains predominantly Si and N. In fluorescent microscopy experiments, whereby VACNFs are interfaced to cell and tissue cultures for a variety of applications, it was observed that this material is broadly fluorescent. In this paper, we provide insight into nature of these silicon/nitrogen in-situ coatings. We propose a potential mechanism for deposition of SiNx coating on the sidewalls of VACNFs during PECVD synthesis and explore the origin of the coating's fluorescence. It is most likely that the substrate reacts with process gases similar to reactive sputtering and chemical vapor deposition (CVD), forming silane and other silicon bearing compounds prior to isotropic deposition as a SiNx coating onto the VACNFs. The formation of Sinanoclusters (NCs) is also implicated due to a combination of strong fluorescence and elemental analysis of the samples. These broadly luminescent fibers can prove useful as registry markers in fluorescent cellular studies and for tagging and tracing applications.

Self-organization during growth of ZrN/SiNx multilayers by epitaxial lateral overgrowth

ZrN/SiNx nanoscale multilayers were deposited on ZrN seed layers grown on top of MgO(001) substrates by dc magnetron sputtering with a constant ZrN thickness of 40 Å and with an intended SiNx thickness of 2, 4, 6, 8, and 15 Å at a substrate temperature of 800 °C and 6 Å at 500 °C. The films were investigated by X-ray diffraction, high-resolution scanning transmission electron microscopy, and energy dispersive X-ray spectroscopy. The investigations show that the SiNx is amorphous and that the ZrN layers are crystalline. Growth of epitaxial cubic SiNx—known to take place on TiN(001)—on ZrN(001) is excluded to the monolayer resolution of this study. During the course of SiNx deposition, the material segregates to form surface precipitates in discontinuous layers for SiNx thicknesses ≤6 Å that coalesce into continuous layers for 8 and 15 Å thickness at 800 °C, and for 6 Å at 500 °C. The SiNx precipitates are aligned vertically. The ZrN layers in turn grow by epitaxial lateral overgrowth on the discontinuous SiNx in samples deposited at 800 °C with up to 6 Å thick SiNx layers. Effectively a self-organized nanostructure can be grown consisting of strings of 1–3 nm large SiNx precipitates along apparent column boundaries in the epitaxial ZrN.

Atomic Layer Epitaxy AlN for Enhanced AlGaN/GaN HEMT Passivation

Enhancements in AlGaN/GaN high-electron-mobility transistor (HEMT) performance have been realized through ultrathin (4 nm) AlN passivation layers, formed by atomic layer epitaxy (ALE). A combination of ex situ and in situ surface cleans prepare the surface for deposition of ALE AlN. HEMTs passivated by high crystallinity AlN, grown at 500 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}{\rm C}$</tex></formula> , show improvements in 2-D electron gas sheet carrier density, gate leakage current, off-state drain leakage current, subthreshold slope, and breakdown voltage. In addition, degradation of dynamic on resistance during pulsed off-state voltage switching stress is suppressed by <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\sim}{50\%}$</tex></formula> compared with HEMTs passivated by conventional plasma enhanced chemical vapor deposition <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm SiN}_{x}$</tex></formula> .

Islands stretch test for measuring the interfacial fracture energy between a hard film and a soft substrate

We present a technique for measuring the interfacial fracture energy, Γi, between a hard thin film and a soft substrate. A periodic array of hard thin islands is fabricated on a soft substrate, which is then subjected to uniaxial tension under an optical microscope. When the applied strain reaches a critical value, delamination between the islands and the substrate starts from the edge of the islands. As the strain is increased, the interfacial cracks grow in a stable fashion. At a given applied strain, the width of the delaminated region is a unique function of the interfacial fracture energy. We have calculated the energy release rate driving the delamination as a function of delamination width, island size, island thickness, and applied strain. For a given materials system, this relationship allows determination of the interfacial fracture energy from a measurement of the delamination width. The technique is demonstrated by measuring the interfacial fracture energy of plasma-enhanced chemical vapor deposition SiNx islands on a polyimide substrate. We anticipate that this technique will find application in the flexible electronics industry where hard islands on soft substrates are a common architecture to protect active devices from fracture.

Structural and electrical anisotropies of Si-doped a-plane (11–20) GaN films with different SiNx interlayers

The effects of different SiNx interlayers on the structural and electrical properties of nonpolar Si-doped a-plane (11–20) GaN films grown on r-plane (1–102) sapphire were investigated. The surface roughness depends strongly on the SiNx coverage, deposition temperature and number of SiNx layers. The in-plane anisotropy of on-axis x-ray rocking curves (XRCs) (full width at half-maximum) was significantly decreased by the introduction of multiple SiNx-treated GaN interlayers, indicating coherently scattering domains of uniform size. Off-axis XRC measurements were also employed to investigate the effects on the mosaic twist corresponding to edge dislocation and the I1-type basal-plane stacking fault (BSF) density. Hall effect measurement showed that the electrical conductivity was the highest when multiple SiNx/GaN interlayers were employed. The measured sheet resistances (Rsh) along the c-axis were higher than those along the m-axis. These anisotropic conductivities could be explained by BSFs acting as carrier scattering centers. The ratios of Rsh along the two in-plane orientations also correlated well with the BSF densities.

Double-layered passivation film structure of Al2O3/SiNx for high mobility oxide thin film transistors

The optimization of the passivation process for oxide thin film transistors with high carrier mobility was investigated. Hydrogen incorporation into oxide channels during the deposition of SiNx could degrade device stability and uniformity, especially for high-mobility devices. A novel double-layered passivation film structure composed of Al2O3/SiNx was proposed, in which thin and dense Al2O3 film prepared by atomic layer deposition was introduced underneath the SiNx layer. In-Ga-Zn-O TFT passivated with the proposed double-layered films showed no significant negative shift in turn-on voltage, even after passivation. The field-effect mobility and subthreshold swing were typically measured as 27.7 cm2 V−1 s−1 and 0.11 V/dec, respectively. Hydrogen doping was effectively protected by the introduction of Al2O3 as thin as 15 nm.

Optimal hydrogenated amorphous silicon/silicon nitride bilayer passivation of n-type crystalline silicon using response surface methodology

This study reports the highest quality surface passivation achieved with hydrogenated amorphous silicon and amorphous silicon nitride (SiNx) bilayer stack deposited using plasma enhanced chemical vapour deposition on 1–2 Ωcm n-type crystalline silicon. The SiNx deposition conditions were investigated using response surface methodology (RSM). Optimized deposition parameters obtained from the RSM study yielded a low surface recombination velocity (SRV) of 3.5 cm/s. Interface defect and charge densities, inferred using the interface dangling bond recombination model, revealed a strong influence of charge on the SRV reduction. The model predicts a lower SRV of 1.5 cm/s for the bilayer passivation scheme.

Experimental study on the elimination of over-plating problems in industrial manufacturing of large-area acidic-textured laser-doped multi-crystalline solar cells

Light-induced plating (LIP) techniques, which are self-aligned and are used in the fabrication of well-shaped metal grids, have been widely studied and used in solar cells, particularly in laser-doped selective emitter (LDSE) ones. However, the application of LIP techniques in standard acidic-textured multi-crystalline silicon wafers with SiNx-coated surfaces can be challenging because of the presence of some unwanted metals on the SiNx surface during the plating process. This phenomenon is called over-plating, a problem in industrial LDSE multi-crystalline Si solar cell manufacturing that this paper aims to eliminate without the addition of any new process steps. The feasibility of changing the texturing process as well as the pretreatment before plating and the deposition of SiNx to reduce over-plating was investigated. The effects of over-plating on solar cell performance were also investigated to determine the mechanism of performance degradation. The cells reached a maximum efficiency of 17.2% and an average efficiency of 17.1% on large-area, commercial-grade, p-type multi-crystalline Si substrates when the over-plating problem was eliminated.

High-quality surface passivation of silicon using native oxide and silicon nitride layers

We report on the attainment of high quality surface passivation of crystalline silicon using facile native oxide and plasma enhanced chemical vapour deposition SiNx. Using systematic measurements of excess carrier density dependent minority carrier lifetime, it is observed that the inferred interface defect density decreases with increasing native oxide thickness while the interface charge density remains unchanged with thickness, which ranges from 0.2 Å to 10 Å. A surface recombination velocity of 8 cm/s is attained corresponding to a native oxide layer thickness of ∼10 Å. Similar chemically grown oxide layer followed by SiNx deposition is shown to yield comparable passivation, indicating practical viability of the passivation scheme.

Two-dimensional micro-Raman mapping of stress and strain distributions in strained silicon waveguides

Micro-Raman scattering experiments were performed on strained silicon waveguides designed for nonlinear optical experiments. Thin stressing silicon nitride (Si3N4 or SiNx) cladding layers, deposited on a light-guiding silicon core layer, strain silicon to enable χ(2), the second-order nonlinear susceptibility. Different deposition treatments allow varying the applied stress. The resulting strained waveguides are investigated by micro-Raman confocal spectroscopy performed on the waveguide facet. By modelling the measured Raman shifts, the local stress and strain are extracted. Thus, two-dimensional maps of the stress distribution as a function of the SiNx deposition parameters are drawn. A comparison of different samples allows underlying the non-uniformity of resulting strain.

Plasma diagnostics of an Ar/NH3 direct-current reactive magnetron sputtering discharge for SiNx deposition

We have performed the deposition of silicon nitride thin films with the DC reactive magnetron sputtering technique from a silicon target in an Ar/NH3 gas mixture. Usually, the control of the process is carried out with discharge voltage measurements, which give information on the nature of the sputtering mode: metallic or reactive. To have a more complete view of the sputtering process, we have performed X-ray photoelectron spectroscopy (XPS) to investigate the chemistry of the silicon target racetrack and optical emission spectroscopy (OES) to investigate the Ar/NH3 gas phase near the target surface. When the NH3 molar fraction is increased, XPS measurements reveal the progressive formation of a silicon nitride layer on the target surface, thereby demonstrating a continuous transition to the reactive mode. OES measurements have highlighted the presence of several species which, according to the literature, are believed to be directly sputtered from the surface of the target: Si, SiH and SiN. Their intensities could be related to the chemical state of the target surface and provide a better insight into the sputtering process on the target surface.

Kelvin probe force microscopy-based characterization techniques applied for electrostatic MEMS/NEMS devices and bare dielectric films to investigate the dielectric and substrate charging phenomena

In this study, two different characterization techniques based on Kelvin probe force microscopy (KPFM) have been used to investigate the dielectric and substrate charging in electrostatic micro- and nano-electromechanical systems (MEMS and NEMS). The first technique (KPFM-MEMS) has been employed to study the discharging process on a microscopic scale in a charged MEMS dielectric film. This has been performed by monitoring the surface potential decay with time of charged PECVD silicon nitride films implemented in electrostatic capacitive MEMS switches. The second methodology, KPFM-thin films (KPFM-TF), has been applied to investigate the charging/discharging processes in bare SiNx films as well as the substrate charging phenomenon. It makes use of the atomic force microscope tip to simulate charge injection through a single asperity, and then measure the induced surface potential. The influence of the SiNx film thickness and deposition conditions has been studied. Moreover, the impact of bias amplitude and bias polarity applied during charge injection has been explored. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy material characterization techniques have been used to determine the chemical bonds and compositions, respectively, of the SiNx films being investigated. The nanoscale KPFM results obtained in this study reveal an accurate understanding of both the dielectric charging and the substrate charging that take place in electrostatic MEMS/NEMS devices.

In‐situ deposited SiNx nanomask for crystal quality improvement in AlGaN

AbstractWe report the growth of high crystal quality Al0.3Ga0.7N directly on sapphire substrates with metalorganic vapour phase epitaxy. We studied the improvements in crystal quality by introducing an in‐situ deposited SiNx interlayer. It acts as a nanomask which results in termination of the dislocations near the interface between the nanomask and epilayer. The epilayers with no SiNx interlayer have very low density of screw type dislocations evident from transmission electron microscopy (TEM) investigations confirmed by a very narrow X‐ray diffraction symmetric reflection (60”). This is a result of our oxygen doped AlN nucleation layer used to grow such epilayers. On the other hand, such epilayers have very broad XRD asymmetric reflections (typically a few thousand arcsec) indicating a high density of edge type dislocations. We could decrease the latter which are the main existing dislocations in our AlGaN epilayers. In TEM micrographs, we observed the formation of dislocation “bundles” when introducing SiNx interlayers. This phenomenon promotes the dislocation free areas on the surface of the wafer. We carried out accurate optimizations of the SiNx deposition. Consequently, we could grow high quality Al0.3Ga0.7N epilayers with much narrower XRD asymmetric peaks–782” with total sample thickness of 1.4 µm (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Effects of silicon nitride passivation on isolation-blocking voltage in algan/gan high electron mobility transistors

The effects of plasma enhanced vapor deposited silicon nitride (SiNx) passivation layer thickness and the spacing between the contact windows openings in the SiNx layer on the isolation-blocking voltage of nitrogen ion implanted AlGaN/GaN high electron mobility transistors were studied. The isolation-blocking voltage was proportional to the thickness of the SiNx passivation layer. Early breakdown was observed for the samples without thick enough SiNx due to surface breakdown. The device was permanently damaged after the occurrence of this early breakdown. The dependence of the isolation-blocking voltage on the SiNx thickness was also modeled and the general trends of the simulated results were in good agreement with the experiment data. The effect of rf power used for depositing the SiNx layer on the isolation-blocking voltage was also studied. Ion bombardments during the SiNx deposition could cause the reduction of breakdown voltage. By employing optimized SiNx passivation conditions, a saturation drain current and a drain breakdown voltage of 300 mA/mm and 1000 V, respectively, for HEMTs with gate dimension of 1×200 μm2 and gate to drain distance of 37.5 μm were achieved.

High efficiency screen printed bifacial solar cells on monocrystalline CZ silicon

AbstractWe present industrialized bifacial solar cells on large area (149 cm2) 2 cm CZ monocrystalline silicon wafers processed with industrially relevant techniques such as liquid source BBr3 and POCl3 open‐tube furnace diffusions, plasma enhanced chemical vapor deposition (PECVD) SiNx deposition, and screen printed contacts. The fundamental analysis of the paste using at boron‐diffused surface and the bifacial solar cell firing cycle has been investigated. The resulting solar cells have front and rear efficiencies of 16.6 and 12.8%, respectively. The ratio of the rear JSC to front JSC is 76.8%. It increases the bifacial power by 15.4% over a conventional solar cell at 20% of 1‐sun rear illumination, which equals to the power of a conventional solar cell with 19.2% efficiency. We also present a bifacial glass–glass photovoltaic (PV) module with 30 bifacial cells with the electrical characteristics. Copyright © 2010 John Wiley &amp; Sons, Ltd.