Amorphous Silicon Nitride Films Research Articles

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

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

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.

Transient thermal conductivity in PECVD SiN[formula omitted] at high temperature: The thermal signature of an on-going irreversible modification

PECVD amorphous silicon nitride (a-SiNx) films are largely used into the dielectric stacks of integrated circuits, as passivation or capping layers, and are today an important alternative to silicon for integrated nonlinear optical applications, such as waveguides. In such applications, a-SiNx presents also the advantage of having a very low thermal conductivity, about 0.7 W/m K at room temperature, which is of relevance, as such films contribute to the thermal balance of the devices, and thus play a role in solving the thermal management problem in microelectronics. The deposition parameters, and more specifically the deposition temperature, have been found to be critical in determining its physical properties, like density, elastic properties and intrinsic stress, as they influence the microstructure of the amorphous film. In this work, we report the first investigation of the effect of the temperature deposition on the thermal conductivity in amorphous SiNx films of thicknesses between 200 and 500 nm, as measured by thermoreflectance technique up to 773 K. Surprisingly, for all deposition temperatures between 300 and 573 K, thermal conductivity exhibits a steep decrease above 473 K, decreasing by more than 30% down to a minimum around 673 K, before increasing back to values comparable with the room temperature one. This transient behavior, observed only for a first heating of the sample, is associated to an irreversible modification of the thin film, and may be related to a partial desorption of the hydrogen trapped in a-SiNx during the deposition.

Study of Optical Properties of Single and Double Layered Amorphous Silicon Nitride Films for Photovoltaics Applications

Study of Optical Properties of Single and Double Layered Amorphous Silicon Nitride Films for Photovoltaics Applications

Amorphous silicon nitride deposited by an NH3-free plasma enhanced chemical vapor deposition method for the coatings of the next generation laser interferometer gravitational waves detector

Cryogenic mechanical loss of the mirror coatings will result in thermal noise and limit the sensitivity of the next generation laser interferometer gravitational wave detectors operated at cryogenics. Amorphous silicon nitride (aSiN) films deposited by NH3 plasma enhanced chemical vapor deposition (NH3-PECVD), a coating method with potential in large area uniform coatings for the next generation detectors, were found previously to have a low cryogenic mechanical loss and without loss peaks that are common in current coatings for room temperature detectors. A positive correlation between N–H bond density and cryogenic mechanical loss in the aSiN films has been observed previously, and the existence of an N–H bond-related asymmetrical two-level system was postulated to account for the cryogenic mechanical loss. In this report, we studied an NH3-free PECVD process to reduce the N–H bond concentration and hence reducing the cryogenic mechanical loss. The N–H bond density of all films deposited by the NH3-free PECVD method was reduced to below the detection limit (<1020 cm−3). The composition of the optimized film is SiN0.33H0.58 which shows the lowest extinction coefficient (1.21 × 10−5 @ 1550 nm), a high refractive index (2.68 @ 1550 nm), and excessively low stress (20.8 MPa), respectively. From 10 K to 120 K, cryogenic mechanical loss of the as-deposited SiN0.33H0.58 varies from 5 × 10−5 to 8 × 10−5 which is two to three times lower than that of the best NH3-PECVD silicon nitride previously obtained. No distinctive cryogenic loss peak was found as well.

Nitrogen rich PECVD silicon nitride for passivation of Si and AlGaN/GaN HEMT devices

In this work, we have investigated the material properties of PECVD (Plasma Enhanced Chemical Vapor Deposition) amorphous Silicon nitride (SiN) films and the influence of deposition conditions on gate-leakage increase of AlGaN/GaN HEMT’s (High Electron Mobility Transistor) after passivation. We have studied the effect of gas flow ratio (SiH4/NH3) on the structural and compositional properties of SiNx deposited on crystalline Silicon (Si). Based on the inference, electrical properties of the SiNx films were examined by depositing on AlGaN/GaN HEMT as a passivation layer. The optimized SiNx which is N-rich with a refractive index of 1.83, tensile stress of 681 MPa and NH3/SiH4 ratio of 18 shows only a 1.2x variation in gate leakage, 1.4x increase in gm, minimum left shift of 0.03 V in Vth and 1.26x increase Ion/Ioff ratio after passivation. We believe that the 3x reduction in Si-H bonds resulting in reduced interface traps at SiN/AlGaN interface is the reason for the minimal increase in gate leakage after passivation.

Mechanical and Optical Properties of Amorphous SiN-Based Films Prepared By ECR PECVD and CCP PECVD

Hydrogenated amorphous silicon nitride (a-SiN:H) and silicon carbonitride (a-SiCN:H) films grown by plasma enhanced chemical vapor deposition (PECVD) are widely investigated for their interesting optical and electrical properties [1]. In this work, we discuss the effect of the deposition power on SiN-based films during plasma deposition. The influence on the optical and mechanical properties of the films was investigated. In order to study this issue on a broader basis, two types of plasmas were applied to deposit 0.5 to 1.5 μm a-SiN:H and a-SiCN:H films. First, a-SiN:H and a-SiCN:H films were deposited by electron cyclotron resonance (ECR) PECVD using the same deposition parameters for all films. During the deposition process, the carbon content in the a-SiCN:H thin films was introduced into the chamber through a pure CH4 gas source to avoid any perturbation on the deposition pressure. Second, a-SiN:H films were deposited by a capacitively coupled plasma reactor CCP PECVD using a SiH4/NH3/N2/Ar precursor mixture. In both deposition processes, the ion bombardment energy was tuned only by the deposition power. The mechanical properties of the films were determined ex-situ by profilometry to evaluate the residual stress using the wafer curvature method and by nanoindentation to determine Young’s modulus and hardness of the films. The thickness and the refractive index were measured by variable angle spectroscopic ellipsometry (VASE). It was observed that the evolution of the residual stress according to the deposition power in the ECR PECVD was different from the CCP PECVD. Besides, we notice a slight increase in the refractive index when the residual stress becomes more compressive as illustrated in figure 1 for a-SiN:H and a-SiCN:H films. Through this discussion, we try to have a better understanding of the different interactions taking place when the deposition power increases in terms of ion bombardment energy. Then, we will study the effect of ion bombardment on the film structure based on the composition and structure of the films and the hydrogen bond concentration measured by Fourier transmission infrared spectroscopy (FTIR). In addition, we have also investigated the influence of carbon incorporation on a-SiN:H thin film properties. We notice a decrease in the refractive index and an increase in the compressive residual stress caused by the carbon incorporation.[1] A. Abdelal, Z. Khatami, and P. Mascher, “Optical and Electrical Properties of ECR-PECVD Grown SiCN Thin Films,” ECS Meet. Abstr., vol. MA2018-01, no. 17, p. 1189, Apr. 2018, doi: 10.1149/ma2018-01/17/1189. Figure 1

Effect of Thermal Annealing on the Photoluminescence of Dense Si Nanodots Embedded in Amorphous Silicon Nitride Films.

Luminescent amorphous silicon nitride-containing dense Si nanodots were prepared by using very-high-frequency plasma-enhanced chemical vapor deposition at 250 °C. The influence of thermal annealing on photoluminescence (PL) was studied. Compared with the pristine film, thermal annealing at 1000 °C gave rise to a significant enhancement by more than twofold in terms of PL intensity. The PL featured a nanosecond recombination dynamic. The PL peak position was independent of the excitation wavelength and measured temperatures. By combining the Raman spectra and infrared absorption spectra analyses, the enhanced PL was suggested to be from the increased density of radiative centers related to the Si dangling bonds (K0) and N4+ or N20 as a result of bonding configuration reconstruction.

Structural and gas barrier properties of hydrogenated silicon nitride thin films prepared by roll-to-roll microwave plasma-enhanced chemical vapor deposition

Hydrogenated amorphous silicon nitride films (a-SiNx:H) have attracted attention as barrier layers to prevent the diffusion of water vapor and other gases into electronic devices. Herein, the chemical composition and physical properties of a-SiNx:H films prepared using a roll-to-roll microwave plasma-enhanced chemical vapor deposition (MW-PECVD) process at low temperatures and variable NH3/SiH4 flow-rate ratios (R) were analyzed. This study was performed to identify the factors affecting the gas permeability of these films as represented by their water vapor transmission rate (WVTR) values. The films fabricated under SiH4-rich conditions (R < 2.75) were oxidized during storage in air to produce silicon oxynitride (SiOxNy), whose properties differed from those of silicon nitride (SiNx). It was found that gas barrier properties were affected by both the film and the Si–H bond densities. Under optimal conditions, the WVTR of a 100-nm-thick SiNx single layer was as low as 7 × 10−3 g m−2 d−1, and the Si–H bond density was 6.71 × 1021 cm−3. The compressive and tensile stresses of the SiNx:H films depended on the values of R, with excellent mechanical stability and moisture barrier properties having been obtained for R = 2.75–3.00.

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.

Radio Frequency Plasma-Enhanced Reactive Magnetron Sputtering Deposition of α-SiN x on Photonic Crystal-Laser Diodes for Facet Passivation.

Amorphous silicon nitride (α-SiNx) films were coated on a photonic crystal-laser diode by the radio frequency magnetron sputtering method. Sputtering deposition conditions were changed to obtain α-SiNx films with different properties. The optical parameters and morphologies of the products were systemically characterized by spectroscopic ellipsometry fitting, energy-dispersive X-ray spectroscopy, atomic force microscopy, and performance of LDs coated with α-SiNx films were tested at 25 °C. Physical mechanisms of sputtering were explained in detail. α-SiNx with a band gap of 4.4 eV and a refractive index of 2.03 at 980 nm were grown. The extinction coefficient equal to 0 at 980 nm, and the surface morphology tended to be homogeneous and dense. The main influencing factors related to the catastrophic optical mirror damage (COMD) phenomenon were investigated. Then plasma pretreatment was implemented to eliminate defects and improve the cavity surface quality and further optimized by measuring the intensity of photoluminescence. Afterward, a rapid annealing method was also carried out to improve coating performance. Finally, α-SiNx acted as a passivation layer in the antireflection film coated on the LD facet, and the COMD threshold increased from 5 to 15.2 W, which led to a higher reliability than nonoptimized LDs and elimination of the COMD phenomenon.

The use of MACE technique on amorphous silicon-rich silicon nitride thin films for the formation of spherical silica nanoparticles

We present a method that employs the metal-assisted chemical etching technique and a subsequent NH3 plasma treatment for obtaining silica nanoparticles (SNPs) uniformly distributed on an amorphous silicon-rich silicon nitride (SRN) film. These particles ranging from 50 to 300 nm are formed directly from the SRN films, and their density is related to the flow rate of the precursor gas (SiCl4). We determined that the SNPs are a SiOx compound (x > 1) with amorphous structure. Furthermore, the chemical composition of the bulk of the remaining SRN film after the etching in a HF/H2O2-based solution and plasma treatment maintain the properties of a pristine one if the initial thickness of the film is large enough (≥ 1 µm). This method enables the formation of silica nanoparticles directly on a silicon-rich silicon nitride film that could have potential optoelectronic applications, implicit in the optical measurements.

Measurement of local temperature around the impact points of fast ions under grazing incidence

Gold and platinum nanoparticles of few-nm size were deposited on amorphous silicon nitride (a-SiN) films. These samples were irradiated with 380 MeV Au ions at grazing incident angles (θi = 2°–5°) to a fluence of ∼1 × 1010 ions/cm2. The irradiated samples were observed using transmission electron microscopy (TEM). Ion tracks were clearly observed as long bright lines. Nanoparticles were found to be desorbed from long and narrow regions along the ion tracks. The surface temperature at the thermal spike produced by the ion impact was evaluated from the observed nanoparticle desorption. The observed temperature distribution is qualitatively explained by a one-dimensional two temperature model (1D-TTM) although there are some discrepancies which may be attributed to the surface effects which are not taken into account in 1D-TTM.

Scattering intensity distribution dependence on collection angles in annular dark-field STEM-in-SEM images

A scanning electron microscope (SEM) equipped with a zero-dimensional solid-state transmission electron detector and a modular aperture system was used to examine the relationship between annular dark-field image intensity distributions and several imaging parameters. The effects of primary electron energy, transmission detector acceptance angle and span, and beam convergence angle on scattering intensity distributions exhibited by a 10 nm thick amorphous silicon nitride film were examined. Results showed that angular distributions varied significantly with only minor changes in transmission detector acceptance angle span. Distributions collected with narrow apertures and normalized to acceptance angle span exhibited broad, distinct peaks that shifted to greater angles with decreasing primary electron energy, while even modestly wide apertures resulted in large distribution variations. A comparison between scattering distributions (i.e., diffraction patterns) quantified using the modular aperture system and a two-dimensional pixelated detector demonstrated that equivalent information could be obtained with either detector for this sample.

Imaging the Thickness of Passivation Layers for Crystalline Silicon with Micron‐Scale Spatial Resolution Using Spectral Photoluminescence

Thin films deposited on crystalline silicon surfaces are critical components of many silicon‐based devices, including high‐efficiency photovoltaic cells. Knowledge of their optical and electronic properties is important in designing and fabricating efficient solar cells, especially as the device complexity increases and includes micron‐scale features. Here, a camera‐based photoluminescence (PL) technique is developed to image the thickness of specific passivating films on silicon wafers. The technique is entirely contactless and nondestructive, requires minimal sample preparation, and provides a large dynamic range in terms of field of view, with micron‐scale spatial resolution possible. It retains the advantages of PL imaging, a mainstream technique for photovoltaic material and device characterization, and it has some extra capabilities similar to those of ellipsometry. This newly developed technique is demonstrated on hydrogenated amorphous silicon and silicon nitride films, two important passivation technologies for high‐efficiency silicon solar cells.

Stabilization of Si rich nitride phase by swift heavy ion irradiation in non-stoichiometric a-SiNx:H thin films

Abstract We report the effect of swift heavy ion irradiation on non-stoichiometric hydrogenated amorphous silicon nitride films (a-SiNx:H), grown on Si substrate by Photo- Chemical vapor deposition. A significant increase in refractive index of films due to Si rich phase stabilization upon irradiation is observed, which is supported by UV–Vis spectroscopy. Further, X-ray photoelectron spectroscopy (XPS) shows the improved Si rich SiNx phase at surface of films. Fourier transform Infrared spectroscopy suggests increased bond density of Si–N in thin films. This is due to out-diffusion of hydrogen upon ion irradiation as bond density for Si–H decreases upon irradiation. It leads to phase separation and stabilization of Si rich nitride phase as unbounded excess Si and N further form Si–Si or Si–N bond configuration, resulting in prominent Si rich silicon nitride phase.

Local heating induced by single MeV C60 ion impacts

Gold and platinum nanoparticles of few-nm size were deposited on amorphous silicon oxide and amorphous silicon nitride films. These films were irradiated with 0.72 and 1.1MeV C603+ ions. Local heating of these films induced by the single ion impact was evaluated by observing desorption of the nanoparticles from the target surfaces upon ion impact. It was found that the local heating at the exit surface is very sensitive to the film thickness. For thinner films, the observed local heating at the exit surface is enhanced compared to the entrance surface while the result is opposite for thicker films. The observed result can be well explained by the unified thermal spike model taking account of the broadening of the spatial distribution of constituent carbon ions during the passage across the film.

Al2O3/SiON stack layers for effective surface passivation and anti-reflection of high efficiency n-type c-Si solar cells

Excellent surface passivation and anti-reflection properties of double-stack layers is a prerequisite for high efficiency of n-type c-Si solar cells. The high positive fixed charge (Qf) density of N-rich hydrogenated amorphous silicon nitride (a-SiNx:H) films plays a poor role in boron emitter passivation. The more the refractive index (n) of a-SiNx:H is decreased, the more the positive Qf of a-SiNx:H is increased. Hydrogenated amorphous silicon oxynitride (SiON) films possess the properties of amorphous silicon oxide (a-SiOx) and a-SiNx:H with variable n and less positive Qf compared with a-SiNx:H. In this study, we investigated the passivation and anti-reflection properties of Al2O3/SiON stacks. Initially, a SiON layer was deposited by plasma enhanced chemical vapor deposition with variable n and its chemical composition was analyzed by Fourier transform infrared spectroscopy. Then, the SiON layer was deposited as a capping layer on a 10 nm thick Al2O3 layer, and the electrical and optical properties were analyzed. The SiON capping layer with n = 1.47 and a thickness of 70 nm resulted in an interface trap density of 4.74 = 1010 cm−2 eV−1 and Qf of −2.59 = 1012 cm−2 with a substantial improvement in lifetime of 1.52 ms after industrial firing. The incorporation of an Al2O3/SiON stack on the front side of the n-type solar cells results in an energy conversion efficiency of 18.34% compared to the one with Al2O3/a-SiNx:H showing 17.55% efficiency. The short circuit current density and open circuit voltage increase by up to 0.83 mA cm−2 and 12 mV, respectively, compared to the Al2O3/a-SiNx:H stack on the front side of the n-type solar cells due to the good anti-reflection and front side surface passivation.

Temperature of thermal spikes induced by swift heavy ions

Few-nm sized gold, platinum and palladium nanoparticles were deposited on amorphous silicon nitride films. These films were irradiated with 420MeV Au and 100MeV Xe ions. Temperature distributions of thermal spikes produced by these ions were evaluated by observing desorption of the nanoparticles from the target surfaces upon ion impact. It was found that the temperature of the thermal spike produced by 420MeV Au is higher than 100MeV Xe. The observed temperature of the thermal spike at the entrance surface is slightly lower than that at the exit surface both for 420MeV Au and 100MeV Xe ions. These results can be well explained by the inelastic thermal spike model.

Dielectric barrier characteristics of Si-rich silicon nitride films deposited by plasma enhanced atomic layer deposition

This work proposes a new method toward improving dielectric barrier characteristics through low dielectric permittivity (k) amorphous silicon nitride films (SiNx) deposited by plasma enhanced atomic layer deposition (PEALD). The dielectric constants of the atomic layer deposition (ALD) SiNx films were in the range of 4.25–4.71 and were relatively lower than that of SiNx deposited by plasma enhanced chemical vapor deposition (PECVD). The dielectric constants of the PEALD SiNx films were nearly identical to the values for PECVD silicon carbon nitride films (SiCN). Although the ALD SiNx films were low-k, they exhibited similar levels of film stress as PECVD SiNx, and the density of ALD SiNx film was higher than that of PECVD SiCN films. The ability to suppress copper (Cu) diffusion through 10-nm thick SiNx dielectric barriers in silicon dioxide/barrier/Cu/tantalum nitride structures on Si substrates was evaluated via Auger electron spectroscopy analysis. Although PEALD SiNx films possessed low dielectric constants (&amp;lt;5), their barrier property to Cu diffusion was nearly equivalent to that of PECVD SiNx. The PECVD SiCN films also exhibited low dielectric constants but showed weak barrier property. Therefore, the low-k ALD SiNx reported herein could be used as a thin film thickness dielectric barrier layer in future advanced technologies.