Silicon-rich Nitride Films Research Articles

Optimization of LPCVD Deposition Conditions of Silicon-Rich Silicon Nitride to Obtain Suitable Optical Properties for Photoluminescent Coating

Silicon nitride is a commonly used material for ceramic applications and in the fabrication processes of integrated circuits (ICs). It has also increased in interest from the scientific community for use as a functional coating due to its physical, mechanical, electrical, and optoelectronic properties. In particular, silicon-rich silicon nitride (SRSN) has been considered in the photovoltaic industry as a down-conversion film for solar cells. In this work, SRSN films have been obtained by the Low-Pressure Chemical Vapor Deposition (LPCVD) technique at low to moderate deposition temperatures with a variation in the precursor gas pressure ratio. The SRSN films showed a wide photoluminescence (PL) in the visible region (without a high-deposition temperature or annealing process) and suitable optical properties (refractive index and absorption in the UV) to be used as photoluminescent coating on silicon solar cells. The absence of high-deposition temperatures could preserve the original structure of silicon solar cells, once the SRSN layer was applied. In addition, control of the reactive gas pressure ratio and deposition temperature showed an influence on the refractive index, the surface roughness, and the PL emission.

Dynamics of Nonlinear Optical Losses in Silicon‐Rich Nitride Nano‐Waveguides

AbstractFree carrier absorption (FCA) is established to be the cause of nonlinear losses in plasma‐enhanced chemical vapor deposition (PECVD) silicon‐rich nitride (SRN) waveguides. To validate this hypothesis, a photo‐induced current is measured in SRN thin films with refractive indices varying between 2.5 and 3.15 when a C‐band laser light is illuminating the SRN films at various powers, indicating the generation of free carriers. Furthermore, nonlinear loss dynamics is, for the first time, measured and characterized in detail in SRN waveguides by utilizing high peak power C‐band complex shape optical pulses for estimation of free carrier generation (FCG) and free carrier recombination (FCR) lifetimes and their dynamics. Both FCG and FCR are found to decrease with an increase in the refractive index of SRN, and, specifically, the FCR lifetimes are found (92 ± 7) ns, (39 ± 3) ns, and (31 ± 2) ns for the SRN indices of 2.7, 3, and 3.15, respectively. Lastly, nonlinear losses in high refractive index SRN waveguides are demonstrated to be minimized and altogether avoided when the pulse duration reduced below the free carrier generation lifetime, thus providing a way of taking a full advantage of the large inherent SRN nonlinear properties.

Influence of high-temperature thermal annealing on paramagnetic point defects in silicon-rich silicon nitride films formed in a single-wafer-type low-pressure chemical vapor deposition reactor

The influence of high-temperature thermal annealing on silicon dangling bonds called K centers in Si-rich silicon nitride films grown in a single-wafer-type low-pressure chemical vapor deposition reactor with the SiH2Cl2-NH3 system at 750 °C has been investigated by combining thermal desorption spectroscopy (TDS), Fourier transform infrared spectroscopy-attenuated total reflection, spectroscopic ellipsometry, and electron spin resonance. In the TDS analysis, H2 desorption from the nitride films was detected above about 600 °C. It is found that thermal annealing at 750 and 900 °C caused a slight decrease in the K center density and a change in the g value of K centers, which are considered to be caused by changes in the atomic structure of the nitride films. On the other hand, thermal annealing at 1050 °C resulted in a substantial decrease in the K center density and the generation of paramagnetic defects with unprecedented characteristics. The findings in this study are expected to provide important guidelines for the design of manufacturing processes of nonvolatile memories.

Optical bistability in PECVD silicon-rich nitride.

We present a study of optical bi-stability in a 3.02 refractive index at 1550nm plasma enhanced chemical vapor deposition (PECVD) silicon-rich nitride (SRN) film, as it pertains to bi-stable switching, memory applications, and thermal sensing applications. In this work we utilize an SRN ring resonator device, which we first characterize at low-power and then compare thermo-optic coefficients, (2.12 ± 0.125) × 10-4/°C, obtained from thermal-heating induced resonance shifts to optically induced resonance shifts as well as estimated propagation loss and absorption. We then measure the time response of this nonlinearity demonstrating the relaxation time to be 18.7 us, indicating the mechanism to be thermal in nature. Finally, we demonstrate bi-stable optical switching.

Optical characterization of deuterated silicon-rich nitride waveguides

Chemical vapor deposition-based growth techniques allow flexible design of complementary metal-oxide semiconductor (CMOS) compatible materials. Here, we report the deuterated silicon-rich nitride films grown using plasma-enhanced chemical vapor deposition. The linear and nonlinear properties of the films are characterized, and we experimentally confirm that the silicon-rich nitride films grown with SiD4 eliminates Si–H and N–H related absorption. The performance of identical waveguides for films grown with SiH4 and SiD4 are compared demonstrating a 2 dB/cm improvement in line with that observed in literature. Waveguides fabricated on the SRN:D film are further shown to possess a nonlinear parameter of 95 W−1 m−1, with the film exhibiting a linear and nonlinear refractive index of 2.46 and 9.8 times 10–18 m2W−1 respectively.

Thermo-optical properties of high-refractive-index plasma-deposited hydrogenated amorphous silicon-rich nitride films on glass

Optical and thermo-optical studies of hydrogenated amorphous silicon-rich nitride films were carried out. The films were produced by plasma-assisted chemical vapor deposition on glass. It is shown that the films deposited under appropriately selected processing conditions contain little nitrogen, as confirmed by Fourier-transform infrared spectroscopy therefore they are referred to as silicon-rich nitrides, a-SRN:H. Spectroscopic ellipsometry, reflectance, and transmittance spectroscopy were used to determine the optical indexes of the films and their thicknesses. It results from the ellipsometric measurements performed within a 190-1700nm spectral wavelength range that a-SRN:H films exhibit a high refractive index of about 3.7. It is also shown that post-deposition annealing up to 300°C does not affect the optical parameters of the films. Additionally, they are transparent in the near-infrared region, which makes them a good candidate for applications in various optoelectronic systems.

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.

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.

Opto-structural properties of Si-rich SiNx with different stoichiometry

This study deals with the fabrication and characterization of silicon nanoparticles in a SiNx dielectric matrix to have thin films of different gap energies, films essentially based on silicon. Hydrogenated silicon-rich nitride films SiNx:H with different stoichiometry X = N/Si were grown on Si substrate using industrial low-frequency plasma-enhanced chemical vapor deposition (LF-PECVD). Optical, electrical, and structural properties of the obtained films have been studied after rapid thermal annealing at 950 °C. The GIXRD and Raman analysis demonstrate that the films contain simultaneously the hexagonal β-Si3N4 phase and crystalline silicon nanoparticles and the average size of silicon nanocrystallites is within the range of 2.5–11 nm according to the stoichiometry. A strong visible photoluminescence (PL) can be observed in silicon nitride and the evolution of PL with the NH3/SiH4 ratio is correlated with the evolution of the structure. The layers having a luminescence in the visible region present a photocurrent (PC) in the high-energy region. PC spectroscopy has clearly demonstrated the existence of increased absorption on the high-energy side associated with Si-Ncs and confirms the potential of Si-Ncs for photovoltaic applications.

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.

On the observation of dispersion in tunable second-order nonlinearities of silicon-rich nitride thin films

Abstract

Nonlinear optics on silicon-rich nitride—a high nonlinear figure of merit CMOS platform [Invited

CMOS platforms with a high nonlinear figure of merit are highly sought after for high photonic quantum efficiencies, enabling functionalities not possible from purely linear effects and ease of integration with CMOS electronics. Silicon-based platforms have been prolific amongst the suite of advanced nonlinear optical signal processes demonstrated to date. These include crystalline silicon, amorphous silicon, Hydex glass, and stoichiometric silicon nitride. Residing between stoichiometric silicon nitride and amorphous silicon in composition, silicon-rich nitride films of various formulations have emerged recently as promising nonlinear platforms for high nonlinear figure of merit nonlinear optics. Silicon-rich nitride films are compositionally engineered to create bandgaps that are sufficiently large to eliminate two-photon absorption at telecommunications wavelengths while enabling much larger nonlinear waveguide parameters (5x–500x) than those in stoichiometric silicon nitride. This paper reviews recent developments in the field of nonlinear optics using silicon-rich nitride platforms, as well as the outlook and future opportunities in this burgeoning field.

Evolution of Optical and Structural Properties of Silicon Nanocrystals Embedded in Silicon Nitride Films with Annealing Temperature

In this work, Hydrogenated silicon rich nitride (SRN) films were deposited by varying NH3/SiH4 ratio and thermally annealed within the temperature range of 700-1000 °C in N2 ambient to precipitate silicon nanocrystals in the film. The optical and structural properties of SiNx:H films were studied. Chemical composition and structural investigations were performed by Secondary ion mass spectrometry (SIMS), Infrared and Raman spectrometry experiments.Fourier Transform Infrared Spectroscopy (FTIR) indicates a new band which appeared as a “shoulder” in the 850-900 cm−1 range and is attributed to a reordering in the films towards an increased SiN4 bonding configuration resulting from the precipitation of silicon nanocrystals.The Raman analysis clearly evidences a high density of Si nanoclusters as shown by the broadened and asymmetric Raman peak approaching 520 cm-1.Strong visible photoluminescence (PL) can be observed in silicon nitride and the evolution of the photoluminescence with annealing temperature is correlated to the evolution of the structure. Radiative defects in the films and the quantum confinement effect in silicon nanoparticles were proposed to explain the origin of light emission from the samples.

Silicon rich nitride ring resonators for rare \u2013 earth doped telecommunications-band amplifiers pumped at the O-band

Ring resonators on silicon rich nitride for potential use as rare-earth doped amplifiers pumped at 1310 nm with amplification at telecommunications-band are designed and characterized. The ring resonators are fabricated on 300 nm and 400 nm silicon rich nitride films and characterized at both 1310 nm and 1550 nm. We demonstrate ring resonators exhibiting similar quality factors exceeding 10,000 simultaneously at 1310 nm and 1550 nm. A Dysprosium-Erbium material system exhibiting photoluminescence at 1510 nm when pumped at 1310 nm is experimentally demonstrated. When used together with Dy-Er co-doped particles, these resonators with similar quality factors at 1310 nm and 1550 nm may be used for O-band pumped amplifiers for the telecommunications-band.

Low-Absorbing and Thermally Stable Industrial Silicon Nitride Films With Very Low Surface Recombination

Amorphous silicon nitride has become the state-of-the-art antireflection coating for silicon solar cells. Optimization of silicon nitride films requires consideration of both the film's optical and electrical properties. It is commonly assumed that silicon-rich silicon nitride films (films with high refractive index) provide better surface passivation, compared to that obtained by films with lower indices. However, silicon-rich films are usually very absorptive in the short (and even medium) wavelength range. Development of low absorption silicon nitride films, that provide good surface passivation, is therefore highly valuable. In this study we compare nine different industrial silicon nitride films, all with similarly low refractive index of 2.09 ± 0.01 measured at 633 nm. We demonstrate that these films exhibit very different electrical, chemical, and optical properties despite their similar refractive index values and correlate these differences with the specific deposition conditions. As a result of this investigation, we have developed industrial thermally stable low-absorbing silicon nitride films that provide excellent surface passivation, with surface saturation current density of 7 fA/cm2 on both n- and p-type wafers. We demonstrate that the developed low absorption films provide surface passivation with equal quality to that obtained by industrial silicon-rich silicon nitride films.

Emission Dependent on composition of Si-rich-SiNX Films obtained by PECVD

Silicon-rich silicon nitride films with different stoichiometry were grown on silicon substrate using the plasma-enhanced chemical vapor deposition. The excess silicon content in the films was monitored via a variation of the NH3/SiH4 gas flow ratio from 0.45 up to 1.0. Morphology and luminescence properties of the films were studied by means of atomic force microscopy (AFM) and photoluminescence (PL) methods. High-temperature annealing was employed to produce the silicon nanocrystals in the films and to enhance the photoluminescence in the range of 1.6-3.0 eV. The PL spectrum was found to be complex due to the contribution of several radiative channels in emission process. It was determined that their competition leads to the non-monotonous variation of total PL peak position with the increase of the Si excess content. It was observed that the shape of PL spectra depends on an excitation wavelength. The ways to control the PL emission is proposed based on the discussion of the PL mechanism.

Optical properties of Si nanocrystals formed with laser pulse annealing

Nano- and femtosecond laser pulse annealings were applied for crystallization of thin amorphous Si films and amorphous Si nanoclusters in silicon-rich nitride and oxide films. Laser assisted formation of amorphous Si nanoclusters in the non-stoichiometric dielectric films was observed. Non-thermal effects in crystallization of amorphous Si by femtosecond annealing were supposed. This approach is applicable for the creation of dielectric films with Si nanoclusters on non-refractory substrates.

Study of narrow and intense UV electroluminescence from ITO/SRO/Si-p and ITO/SRN/SRO/Si-p based light emitting capacitors

In this work, multiple narrow and highly intense ultraviolet (UV) electroluminescent (EL) bands were observed in light emitting capacitors (LECs) using silicon rich oxide (SRO) films as active layer. Besides, the effect of a thin silicon rich nitride (SRN) film on top of the SRO (as SRN/SRO bilayer) layer was also studied. LECs were fabricated using simple metal–insulator–semiconductor (MIS) structures with indium tin oxide (ITO) and aluminum as gate and substrate electrodes, respectively. SRO and SRN films contain 41.85±1.1 and 46.96±1.1at% of silicon, respectively. Both structures exhibited a resistance switching (RS) behavior from a high conduction state (HCS) to a low conduction state (LCS), enhancing an intense UV EL. This RS behavior produces structural changes in the active layer and probably in the ITO contact. Seven narrow bands with half-peak width of 7±0.6nm at ~250, 270, 285, 305, 325, 415 and 450nm were clearly observed once the LCS was reached. These bands could be related to a combination of emissions through defects inside SRO (252, 288.2 and 415nm), and characteristic radiation of neutral tin (252.39 and 286.33nm), neutral indium (271.02, 303.93 and 325.85nm), single (444.82nm) and doubly ionized indium (403.07nm). Furthermore, red EL was observed at the HCS and it was similar to the PL spectra indicating the same radiative process involved. The charge transport is improved when the SRN/SRO bilayer is used as active layer in the LEC. An EL band at ~590nm is observed when the SRN/SRO bilayer is formed at both conduction states. This band has been observed before and attributed to transitions from the minimum conduction band to K° centers in SRN films. The conduction mechanism responsible of the EL at both conduction states was also studied.

Light emitting mechanisms dependent on stoichiometry of Si-rich-SiNx films grown by PECVD

Light emission and morphology of silicon-rich silicon nitride films grown by plasma-enhanced chemical vapor deposition were investigated versus film’s stoichiometry. The excess silicon content in the films was controlled varying the NH3/SiH4 gas flow ratio from 0.45 up to 1.0. High-temperature annealing was employed to form the silicon quantum dots (QDs) and to enhance the photoluminescence (PL) in visible spectral range. The PL spectrum was found to be complex. The competition of five PL bands leads to the non-monotonous variation of total PL peak position in the range of 1.55–2.95 eV when the Si excess content increases. The shape of PL spectra depends also on an excitation light wavelength. It is shown that for the films fabricated with R ≤ 0.56 and R ≥ 0.67 the dominant contribution into PL spectra is given by native SiNx defects, whereas in the films obtained with R = 0.59–0.67 the Si-QDs form the main radiative channel. The highest PL intensity is detected in Si-rich SiNx films grown at R = 0.59–0.67 as well. PL mechanisms are discussed in terms of the contribution of different radiative channels in the light emission process that can show the ways for the optimization of SiNx light-emitting properties.

PECVD silicon-rich nitride and low stress nitride films mechanical characterization using membrane point load deflection

An analysis of the mechanical properties of plasma enhanced chemical vapor (PECVD) silicon nitrides is presented, using micro fabricated silicon nitride membranes under point load deflection. The membranes are made of PECVD silicon-rich nitride and low stress nitride films. The mechanical performance of the bended membranes is examined both with analytical models and finite element simulation in order to extract the elastic modulus and residual stress values. The elastic modulus of low stress silicon nitride is calculated using stress free analytical models, while for silicon-rich silicon nitride and annealed low stress silicon nitride it is estimated with a pre-stressed model of point-load deflection. The effect of annealing both in nitrogen and hydrogen atmosphere is evaluated in terms of residual stress, refractive index and thickness variation. It is demonstrated that a hydrogen rich annealing atmosphere induces very little change in low stress silicon nitride. Nitrogen annealing effects are measured and shown to be much higher in silicon-rich nitride than in low stress silicon nitride. An estimate of PECVD silicon-rich nitride elastic modulus is obtained in the range between 240–320 GPa for deposited samples and 390 GPa for samples annealed in nitrogen atmosphere. PECVD low stress silicon nitride elastic modulus is estimated to be 88 GPa as deposited and 320 GPa after nitrogen annealing.