Silicon-rich Nitride Films Research Articles

Plasma etching of virtually stress-free stacked silicon nitride films

Stacked silicon nitride films for use in manufacturing of surface micromachined membranes were deposited using custom made plasma-enhanced chemical vapor deposition instrument with silane (SiH 4) and ammonia (NH 3) gas mixture as deposition precursor. Deposition conditions were adjusted by varying substrate temperature and SiH 4 to NH 3 flow ratio and temperature to obtain the required stress related and electrical properties of the membranes. Transmission Fourier transformed infrared spectroscopy and scanning electron microscopy were used to investigate the chemical composition and morphology of the stacked film components. An increase in the SiH 4 to NH 3 flow ratio and a decrease in temperature resulted in a silicon-rich silicon nitride film, as well as an increased silicon oxide concentration. To avoid underetch and sidewall defects, the plasma power density during the plasma etching was changed from 0.5 W/cm 2 during the etching of both top and bottom layers in a stacked film, to 1.0 W/cm 2 during the etching of the middle both silicon and silicon oxide rich film. This resulted in an improved overall stacked film sidewall quality and reduced the unwanted underetch.

The Effects of Deposition and Processing Parameters on the Electronic Structure and Photoluminescence from Nitride-Passivated Silicon Nanoclusters

Silicon nanoclusters (Si-ncs) embedded in silicon nitride films have been studied to determine the effect that deposition and processing parameters have on their growth, luminescent properties, and electronic structure. Luminescence was observed from Si-ncs formed in silicon-rich silicon nitride films with a broad range of compositions and grown using three different chemical vapour deposition (CVD) based systems: plasma-enhanced CVD (PECVD), inductively coupled plasma CVD (ICP CVD), and electron cyclotron resonance PECVD (ECR PECVD). Photoluminescence experiments revealed broad, tunable emissions with peaks ranging from the near-infrared across the full visible spectrum. The emission energy was highly dependent on the film composition and changed only slightly with annealing, which primarily affected the emission intensity. X-ray absorption spectra at the Si K- and L3,2-edges exhibited composition dependent phase separation and structural re-ordering of the Si-ncs and silicon nitride host matrix under different post-deposition annealing conditions.

Luminescence mechanisms of silicon-rich nitride films fabricated by atmospheric pressure chemical vapor deposition in N2 and H2 atmospheres

This work examines possible luminescence mechanisms of silicon-rich nitride (SRN) films that were fabricated by atmospheric pressure chemical vapor deposition (APCVD). Under an ambient gas of either H2 or N2, two SRN films were deposited using the same precursors of Si and N. While photoluminescence (PL) measurements of both as-deposited specimens revealed an intense luminescence band (1.8–3.8 eV), which was observable by the naked eye, a detailed examination of the high energy band of the PL spectra over 2.8 eV yielded different results for those samples that were fabricated in different ambiences. To determine the reason for these differences, Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy were conducted, suggesting unique chemical bonds and elemental ratio of nitrogen to silicon in SRN films. Further analysis involving plan-view high-resolution transmission electron microscopic observations of SRN films demonstrated the embedding of Si quantum dots (Si QDs), but with some differences depending on the deposition environment. Analyses of the results obtained suggest that the emission from SRN films that were deposited by APCVD is not only dominated by the quantum confinement effect of Si QDs, but also subordinately affected by the surface states around these Si QDs.

Fourier transform infrared spectroscopy of annealed silicon-rich silicon nitride thin films

A correlation between bonding changes in silicon-rich silicon nitride films, subjected to high temperature annealing under N2 ambient, and the formation of silicon nanocrystals is presented. The postannealing appearance of a shoulder between 1000 and 1100 cm−1 in the Fourier transform infrared (FTIR) spectra of silicon-rich silicon nitride films is attributed to a reordering in the films toward an increased SiN4 bonding configuration resulting from the precipitation of silicon nanocrystals. The FTIR monitoring of bonding changes in these films allows for the indirect verification of silicon nanocrystal formation.

Preparation of dense, smooth and homogeneous amorphous silicon nitride films by nitrogen-ion-beam assisted evaporation

Amorphous silicon-rich silicon nitride films were deposited by ion-beam-assisted evaporation onto silicon substrates maintained at 100 °C without substrate bias or with a substrate bias of −250 V. The structure, the composition of the films and the effect of the substrate bias were studied by x-ray photoelectron spectroscopy, infrared absorption measurements, chemical etch rate experiments, atomic force and scanning electron microscopies. While the films prepared without bias are nanoporous and columnar, it is shown that accelerating the nitrogen ions by biasing the substrate enables us to produce homogeneous, dense and smooth amorphous Si-rich silicon nitride (a-SiNx) films free of oxygen and hydrogen.

Enhanced electroluminescence of silicon-rich silicon nitride light-emitting devices by NH 3 plasma and annealing treatment

Silicon-rich silicon nitride (SRSN) films were deposited on p-type silicon substrates using a conventional plasma-enhanced chemical vapor deposition (PECVD) system. Before deposition, silicon substrate was pre-treated by NH 3 plasma in the PECVD system. And devices with metal–insulator–semiconductor (MIS) structure were fabricated using indium tin oxides (ITO) as anode and aluminum (Al) film as cathode. It was found that after 1100 °C annealing the electroluminescence (EL) intensity of NH 3 plasma pre-treated MIS devices was increased greatly comparing with that of without NH 3 plasma pre-treated devices. It is due to the passivation or reducing of interfacial states and nonradiative defects in SRSN films by the NH 3 plasma pre-treatment and high-temperature annealing that enhanced the EL intensity of the SRSN MIS devices.

Formation of nanocrystals embedded in a silicon nitride film at a low temperature (⩽200 °C)

Silicon-rich silicon nitride films with embedded silicon nanocrystals (Si NCs) were fabricated successfully on plastic substrates at a low temperature by catalytic chemical vapor deposition. A mixture of SiH 4 , NH 3 and H 2 was used as a source gas. Formation of the silicon nanocrystals was analyzed by photoluminescence spectra and was confirmed by transmission electron microscopy. The formation of Si NCs required an H 2 /SiH 4 mixture ratio that was higher than four.

Fabrication of Whitely Luminescent Silicon-Rich Nitride Films by Atmospheric Pressure Chemical Vapor Deposition

Silicon-rich nitride (SRN) films that can exhibit an intense white-light emission were fabricated by atmospheric pressure chemical vapor deposition. SRN films were deposited on Si substrates using gaseous SiH2Cl2 (DCS) and NH3 as the source materials for Si and N, respectively. The deposition temperature was kept at 850 °C, and H2 was used as the carrier gas with its flow rate modulated to maintain chamber pressure at 1 atm during the deposition. The optical properties of films obtained at various deposition times from 15 to 60 min were examined by photoluminescence (PL) measurement. An intense luminescence band (1.5–3.5 eV) was observed by the naked eye for all as-deposited samples. Besides, time-resolved PL exhibited a short radiative lifetime of about 1 ns for SRN films. Moreover, high resolution plan-view transmission electron microscopy demonstrated the existence of Si dots in SRN films with the dot sizes ranging from 2 to 6 nm and a dot density of about 4×1012/cm2. On the basis of the results obtained, we considered that the related luminescence mechanism for SRN films is connected to crystalline Si dots produced therein.

Enhanced light emission in photonic crystal nanocavities with Erbium-doped silicon nanocrystals

Photonic crystal nanocavities are fabricated in silicon membranes covered by thermally annealed silicon-rich nitride films with Erbium-doped silicon nanocrystals. Silicon nitride films were deposited by sputtering on top of silicon on insulator wafers. The nanocavities were carefully designed in order to enhance emission from the nanocrystal sensitized Erbium at the 1540nm wavelength. Experimentally measured quality factors of ∼6000 were found to be consistent theoretical predictions. The Purcell factor of 1.4 was estimated from the observed 20-fold enhancement of Erbium luminescence.

PHOTOLUMINESCENCE OF Si-RICH SiNx FILMS DEPOSITED BY LPCVD UNDER DIFFERENT CONDITIONS

The silicon-rich silicon-nitride thin films deposited by low pressure chemical vapor deposition at 800° C ~950° C , using dichlorosilane and ammonia as precursors, have the mosaic structure of crystallized silicon nanoclusters embedded in amorphous silicon nitride matrix, showing visible photoluminescence (PL) emission at room temperature with one to five separate peaks. The microstructures of the films change with the deposition temperatures and flux ratios of dichlorosilane to ammonia, which causes changes in the PL spectra of the films. In this paper, we report the experimental results and try to explain it with our gap states model.

Luminescence and structural properties of silicon-rich nitride by X-ray absorption spectroscopy

The luminescence and structural properties of silicon-rich nitride thin films were comprehensively examined by X-ray absorption spectroscopy. The near-edge X-ray absorption fine structures demonstrated the formation of silicon clusters in the silicon-rich nitride films. In addition, atomic resolved images of transmission electron microscope evidenced constitution of ultra-small (2–5 nm) silicon clusters. The X-ray absorption near-edge fine structures surveyed in photoluminescence yield and total electron yield configurations revealed that the luminescence are mainly coming from the Si–N bonding sites for lower degree of silicon-rich films. For higher silicon-rich samples, the Si–Si bonding sites increasingly contribute to the band edge absorption in the photoluminescence yield near-edge fine structures. These results strongly suggested that the transitions from the gap states localized in the surface of embedded silicon clusters and quantum confinement states within silicon clusters might contribute to the luminescence. The contribution weightiness of quantum confinement states increase while increasing the silicon-richness. It provides a reasonable explanation for the prolonged debates on the luminescence origins.

Nonvolatile polycrystalline silicon thin film transistor memory using silicon-rich silicon nitride as charge storage layer

In this work, the authors report a memory device based on a Si thin film transistor (TFT) structure by incorporating silicon-rich silicon nitride (SRSN) film in the gate dielectric stacks as the charge storage layer. The SRSN film has a lower barrier for hole injection than the barrier for electron injection. Therefore, the memory window is dominated by hole injection. The memory window for TFT nonvolatile memory at steady state as large as 6.8V is observed, and the memory window is around 3V under pulse operation. In addition, this TFT memory has no significant degradation after 500 times of switching operation.

Electron Trap Characteristics of Silicon Rich Silicon Nitride Thin Films

Charge localization causes initial retention loss and memory window narrowing after write/erase cycling in a nonvolatile memory device using a metal–oxide–nitride–oxide–semiconductor (MONOS) structure. To overcome these problems, we propose the use of silicon-rich silicon nitride (SRN) thin film as a charge-trapping layer. It was found that most of the electrons injected from the substrate were trapped at the interface between the SRN film and the top oxide and the number of electrons captured by bulk traps of the nitride is negligible. When negative bias is applied to the gate electrode, the electrons trapped at the top interface move back to the bottom interface with SRN. The high effective mobility of the electrons is presumably due to donor-like traps at 0.8 eV below the conduction band bottom of SRN.

Silicon-based photonic crystal nanocavity light emitters

The authors have demonstrated an up to sevenfold enhancement of photoluminescence from silicon-rich silicon nitride film due to a single photonic crystal cavity. The enhancement is partially attributed to the Purcell effect [Purcell, Phys. Rev. 69, 681 (1946)], which is predicted to be up to 35-fold by finite difference time-domain calculations for emitters spectrally and spatially aligned with the electric field. Experimentally measured cavity quality factors vary in the range of 200–300, showing excellent agreement with calculations. The emission peak can be tuned to any wavelength in the 600–800nm range.

Light-Emitting Silicon Nanocrystals and Photonic Structures in Silicon Nitride

In this paper, we review our main results on the optical and electrical properties of light-emitting silicon nanocrystals (Si-ncs) obtained from the thermally induced nucleation in amorphous silicon-rich nitride (SRN) films deposited either by plasma-enhanced chemical vapor deposition (PE-CVD) or magnetron sputtering. In particular, we discuss the Si-ncs microscopic light emission mechanism combining the optical data with the first-principle calculations of the absorption/emission Stokes shifts and recombination lifetimes. In addition, we report on the electrical injection characteristics of simple p-i-n device structures showing efficient bipolar transport and room temperature electroluminescence, and demonstrate efficient energy sensitization of erbium (Er) ions from the Si-ncs embedded in the SRN matrices. We further show that the light-emitting nanocrystals in SRN can be embedded in aperiodic photonic environments, where the localized optical modes can be used to significantly enhance the Si-ncs emission intensity at different emission wavelengths. These results suggest that the Si-ncs embedded in the SRN matrices have a large potential for the fabrication of optically active photonic devices based on the Si technology

Light emission efficiency and dynamics in silicon-rich silicon nitride films

Light-emitting Si-rich silicon nitride (SRN) films were fabricated by plasma enhanced chemical vapor deposition followed by thermal annealing and the SRN external quantum efficiency was measured. The SRN light emission temperature dependence and recombination dynamics were also studied. Small emission thermal quenching from 4to330K with wavelength dependent, nanosecond recombination lifetime was observed. Light emission from SRN systems can provide alternative routes towards the fabrication of efficient Si-based optical devices.

Light-emitting silicon-rich nitride systems and photonic structures

In this paper we report recent results on the optoelectronic properties of silicon-rich nitride (SRN), a novel material for microphotonics applications compatible with silicon technology. We have investigated optical emission, energy transfer phenomena to erbium ions and PbS colloidal quantum dots in SRN films and grown active photonic SRN structures. The optical properties of the films were studied by micro-Raman and photoluminescence spectroscopy and, as confirmed by transmission electron microscopy analysis, indicate the presence of small (1–2 nm) Si clusters characterized by efficient (7% quantum efficiency at room temperature), broad-band and near-infrared emission with very large absorption/emission Stokes shift. Time and temperature resolved photoluminescence measurements demonstrate nanosecond-fast, wavelength-dependent recombination dynamics with negligible light emission thermal quenching from 4 to 330 K. First-principles simulations of 1 nm size crystalline and amorphous silicon dots show that nitrogen atoms bonded to the surface of nanometre silicon clusters play a crucial role in the emission mechanism of SRN films. In addition, we show that SRN is a suitable material for the fabrication of light-emitting complex photonic crystals and novel waveguide structures based on resonant transmission of localized light states in aperiodic dielectrics. The versatility of light-emitting SRN systems can provide alternative routes towards the fabrication of optically active CMOS devices.

Effect of low temperature oxidation on dielectric properties of mercury sensitized photo-deposited silicon nitride films

Low temperature thermal oxidation of mercury-sensitized photo-CVD deposited silicon-rich silicon nitride films has been carried out to obtain high quality silicon oxynitride films with less incorporated hydrogen. The absence of Si H and N H stretching mode indicates that the incorporated hydrogen in these bonding forms is a few atomic percent, below the detection level of Fourier transform infrared spectroscopy (FTIR). X-ray photoelectron (XPS) studies suggest that oxygen is mainly incorporated in the film in the form of N (SiO) x . No significant change in the relative contributions from the Si 3N 4 network to the overall N 1s peak takes place as a result of oxidation, but there is a decrease in the unreacted silicon from 15.3% to 5.5%. The interface electronic state densities, flat band voltage, fixed insulating charges and leakage current are reduced after oxidation, indicating an improvement of the electrical properties of the oxidized film.

Effects of Silicon Nitride Passivation Layer on Mean Dark Current and Quantum Efficiency of CMOS Active Pixel Sensors

AbstractIn the present study, we have analyzed the influence of the silicon nitride (SiN) passivation layer properties on the mean dark current and the quantum efficiency of CMOS APS (Active Pixel Sensor) through electrical characterization of lot wafers processed with three different SiN passivation films. The SiN layers were characterized by Spectroscopic Ellipsometry (SE) and Fourier Transform Infra Red (FTIR) spectroscopy to get the optical indices and the hydrogen content of the films, respectively. Hydrogen desorption was also studied by Thermal Desorption Spectrometry (TDS) experiments.The different chemical bond concentrations enable to explain the device performance. It is shown that high [Si-H] and low [Si-N] bonds concentrations lead to high hydrogen desorption from the SiN films. Thus, the lowest dark current values have also been obtained with such silicon nitride passivation layers. Consequently, results are in agreement with the hydrogen passivation of defects being responsible of thermally generated carriers. Concerning the quantum efficiency (QE), it is highly influenced by the optical indices of the SiN passivation layer.Actually, the thickness and complex refractive index of the SiN layer affect the light reflection, while the light absorption, in the visible range, is controlled by the [Si-Si] bonds concentration. There are also competing requirements to minimize dark current and to maximize quantum efficiency. In fact, high [Si-H] and low [Si-N] bonds concentrations (for good passivation) are generally observed in silicon-rich SiN films, which also contain high amount of [Si-Si] bonds (inducing high absorption, thus low QE). Increasing simultaneously the [Si-H] and [N-H] bonds concentrations in the passivation layer can be a way to have high hydrogen desorption during passivation anneal just preserving a transparent layer.

Batch Fabrication of Sharpened Silicon Nitride Tips

A novel sharpening technique for silicon nitride protrusions is reported. A silicon-rich nitride film, which contains more silicon than a stoichiometric silicon nitride film, shows low film stress and has been applied to micro mechanical devices. We found that the edge of the silicon nitride pattern on the silicon wafer became thinner and tapered by thermal oxidation, followed by the removal of the oxidized layer. By applying this technique for sharpening the apex of a beak-like cantilever of silicon nitride, the tip of the acute-angle triangular plate portion of the cantilever terminated into one and was sharpened with a radius of curvature of 17 nm. The small cantilevers integrated with the sharp protrusions for high speed atomic force microscopy in water were batch fabricated. The technique is useful for the fabrication of small cantilevers when low cost is required.