Si-rich SiNx Research Articles

Improved LPCVD-SiNx/AlGaN/GaN MIS-HEMTs by using in-situ MOCVD-SiNx as an interface sacrificial layer

In this paper, the effects of a thin in-situ SiNx layer, grown by metal–organic chemical vapor deposition (MOCVD), on the performances of GaN-based metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) with low-pressure chemical vapor deposition (LPCVD) SiNx gate dielectric were systematically investigated. We found that the MIS-HEMT with the in-situ SiNx as an interface sacrificial layer exhibits better DC electrical properties than that with the in-situ SiNx reserved as part of the gate dielectric. The results of second ion mass spectroscopy and electron spin resonance spectrum show that this in-situ SiNx is a Si-rich SiNx dielectric which can induce additional ≡Si0 and ≡Si- trap states by Si dangling bonds and affects significantly electron trapping and detrapping processes. Based on temperature-dependent gate current and frequency-dependent capacitance-voltage analyses, a trap model at the SiNx/AlGaN interface and in the in-situ SiNx bulk was proposed and well explains the performance discrepancies between the above mentioned two MIS-HMETs. In addition, positive bias temperature instability was carried out to further confirm the rationality of the proposed trap model. This work verifies that in-situ SiNx can be employed as a sacrificial layer for the fabrication of high performance LPCVD-SiNx/AlGaN/GaN MIS-HEMTs.

Understanding Electrical Conduction and Nanopore Formation During Controlled Breakdown.

Controlled breakdown has recently emerged as a highly appealing technique to fabricate solid-state nanopores for a wide range of biosensing applications. This technique relies on applying an electric field of approximately 0.4-1 V nm-1 across the membrane to induce a current, and eventually, breakdown of the dielectric. Although previous studies have performed controlled breakdown under a range of different conditions, the mechanism of conduction and breakdown has not been fully explored. Here, electrical conduction and nanopore formation in SiNx membranes during controlled breakdown is studied. It is demonstrated that for Si-rich SiNx , oxidation reactions that occur at the membrane-electrolyte interface limit conduction across the dielectric. However, for stoichiometric Si3 N4 the effect of oxidation reactions becomes relatively small and conduction is predominately limited by charge transport across the dielectric. Several important implications resulting from understanding this process are provided which will aid in further developing controlled breakdown in the coming years, particularly for extending this technique to integrate nanopores with on-chip nanostructures.

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.

Etching Mechanisms of SiO2 and SiNx:H Thin Films in HF/Ethanol Vapor Phase: Toward High Selectivity Batch Release Processes

The etch dynamics of low-density undoped silica glass oxide (USG) and Si-rich SiNx:H thin films in a 25-wafer batch vapor HF tool operating at low etching pressure were studied. Up to etching temperatures approaching the water boiling point, as defined by the etching pressure, the kinetics of the etch as a function of the etching temperature is found to be driven by adsorption phenomena for both oxide and nitride layers. The etch rate increases with etching time before reaching a stable regime, according to adsorption laws in the case of the USG layers and to more complex phenomena that might include a partial oxidation of the layer and/or the creation of solids by-product residues sticking to the surface, in the case of nitride layers. Selectivities in the etch rates of oxide versus nitride layers higher than 60 were achieved, together with a high within-wafer and wafer-to-wafer uniformity. The etching mechanisms are proposed to be a similar to liquid phase etching: low-density USG layers are preferentially etched through nucleophilic substitutions, while monofluorides are tentatively identified as the most reactive agent in the case of Si-rich SiNx:H layers where Si-N or, depending on the composition of the etching media, Si-Si bonds have to be broken.

Hollow Cathode Plasma (HCP) Enhanced Atomic Layer Deposition of Silicon Nitride (SiNx) Thin Films Using Pentachlorodisilane (PCDS)

In this work, effects of NH3/N2 and N2-H2/Ar plasma gases for the growth of PEALD SiNx films using pentachlorodisilane (PCDS, HSi2Cl5) were studied using a hollow cathode PEALD system. At identical process conditions, the combination of PCDS and N2−H2/Ar plasma showed a relatively lower (approximately < 10 %) growth rate as compared to NH3/N2 plasma under a range of process temperatures (240−300 °C) whereas the wet etch resistance to HF acid was improved (> 1.6 nm/min, 500:1 HF). Using XPS and FTIR analysis, it was identified that N2−H2/Ar gas mixture results in a Si-rich SiNx film with less N−Hx bonds when compared to NH3/N2 mixture, thereby resulting in a decreased wet etch rate.

Enhanced gate stack stability in GaN transistors with gate dielectric of bilayer SiNx by low pressure chemical vapor deposition

We report enhanced gate stack stability in GaN metal insulator semiconductor high electron mobility transistors (MISHEMTs) by using a bilayer SiNx as the gate dielectric. To obtain the bilayer gate dielectric scheme, a thin Si-rich SiNx interlayer was deposited before a high-resistivity SiNx layer by low pressure chemical vapor deposition. The Si-rich SiNx can effectively suppress the trapping phenomenon at the interface of the dielectric/AlGaN barrier. The upper high-resistivity SiNx layer can greatly block the gate leakage current to enable a large gate swing. Compared with the MISHEMTs using a single Si-rich or high-resistivity SiNx layer, the MISHEMTs with a bilayer gate dielectric take the advantages of both, realizing a gate stack with a stable threshold voltage and low leakage current. These results thus present great potential for developing high-performance GaN MISHEMTs using the bilayer SiNx gate dielectric scheme for highly efficient power applications.

Plasma enhanced chemical vapor deposition of SiO2 and SiNx on AlGaN: Band offsets and interface studies as a function of Al composition

In this work, the authors characterized the interface of plasma enhanced chemical vapor deposition (PECVD) dielectrics, SiO2 and SiNx with AlGaN as a function of Al composition. SiO2 is found to exhibit type I straddled band alignment with positive conduction and valence band offsets for all Al compositions. However, the interface Fermi level is found to be pinned within the bandgap, indicating a significant density of interface states. Hence, SiO2 is found to be suitable for insulating layers or electrical isolation on AlGaN with breakdown fields between 4.5 and 6.5 MV cm−1, but an additional passivating interlayer between SiO2 and AlGaN is necessary for passivation on Al-rich AlGaN. In contrast, Si-rich PECVD SiNx is found to exhibit type II staggered band alignment with positive conduction band offsets and negative valence band offsets for Al compositions &amp;lt;40% and type I straddled band alignment with negative conduction and valence band offsets for Al compositions &amp;gt;40% and is, hence, found to be unsuitable for insulating layers or electrical isolation on Al-rich AlGaN in general. In contrast to passivating stoichiometric LPCVD Si3N4, no evidence for interface state reduction by depositing SiNx on AlGaN is observed.

Low atomic number silicon nitride films for transmission electron microscopy

Low stress silicon (Si)-rich silicon nitride (SiNx) films are usually used as membranes of microcapsules for transmission electron microscopy (TEM). Their relatively high atomic number has a negative impact on resolution, which is a key factor that affects imaging performance. To improve resolution, reducing Si content in films is an effective approach. However, the non-Si-rich SiNx films have large tensile stress and are ease to crack. In this study, ion implantation is utilized to adjust the stress of nearly stoichiometric (NS) SiNx films. The effects of ion implantation and thermal annealing on film properties are carefully analyzed. It is found that the NS SiNx films implanted with nitrogen (N) and annealed at low anneal temperature have both low atomic number and low stress, and their properties are very close to low stress Si-rich SiNx films. Moreover, a simple microcapsule is fabricated using the low atomic number SiNx films, and performs a TEM observation of water-soluble polypeptides growth. Polypeptides much smaller than 100 nm in size are observed.

Structural transformation of Si-rich SiNx film on Si via swift heavy ions irradiation

The effects of 200 MeV-Xe+ irradiation with fluencies of (109–1014) cm−2 on the phase-structural transformation of Si-rich SiNx film deposited on Si substrate by low-pressure chemical vapor deposition have been reported. It has been shown from Raman scattering data that the swift heavy ions irradiation results in the dissolution of amorphous Si nanoclusters in nitride matrix. It has been shown, too, that the swift heavy ion irradiation leads to quenching a visual photoluminescence from nitride films.

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.

A comparison study of boron emitter passivation by silicon oxide and a PECVD silicon nitride stack

Surface recombination of minority charge carriers is a significant loss mechanism in crystalline-Si (c-Si) solar cells. For n+ (phosphorous) doped regions a sufficient surface passivation is achieved by using a silicon nitride (SiNX) film deposited by Plasma Enhanced Chemical Vapour Deposition (PECVD). However, on p+ boron doped regions, SiNX does not passivate the surface. Instead, a stack of layers comprising of a thin silicon dioxide (SiO2), or aluminium oxide (Al2O3), and a SiNX film is commonly used to passivate boron doped regions.In this study we investigated the passivation quality of boron doped emitters by varying the composition of SiO2/SiNX stack layers. For this purpose, n-PERT (passivated emitter, rear totally-diffused) solar cells with boron doped front side emitter and phosphorous doped back-surface-field (BSF), as well as symmetrical boron doped structures, were fabricated on 6-inch n-type wafers.The results show that the optimum passivation is achieved by a stack layer of a thermal SiO2, with a thickness of at least 10 nm, and a SiNX layer with a low refractive index. The chemical composition of SiNX capping layer plays an important role for surface passivation. A more Si-rich SiNX layer show significant degradation in surface passivation of the stack, due to the increase in the density of interface states (Dit) and fixed positive charges (Qtot) at the interface.

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.

Degenerate Four-Wave Mixing in Si Quantum Dot Doped Si-Rich SiNx Channel Waveguide

The degenerate four-wave-mixing (DFWM) effect in Si quantum dot doped SiNx (SiNx:Si-QD) channel waveguide has been preliminarily demonstrated. By enhancing the optical nonlinearity of SiNx at 1550 nm with doped Si-QDs, the DFWM can be enhanced with its conversion efficiency of −46 dB in the SiNx:Si-QD channel waveguide with length of 8 mm. The nonlinear refractive index of the SiNx:Si-QD is estimated to be $\rm{3 \times 10}^{-14}\rm{ cm}^{2}\rm{/ W}$ . The chromatic dispersion analysis indicates that the SiNx:Si-QD channel waveguide exhibits 3-dB conversion bandwidth of larger than 16 nm. Such a SiNx:Si-QD waveguide is free of multi-photon absorption at 1550 nm even when injecting an intense laser pulse as large as 1.3 GW/cm2. These results show great potential of Si-QD doped SiNx waveguide for nonlinear optical processing.

Opto-Structural Properties of Silicon Nitride Thin Films Deposited by ECR-PECVD

Amorphous hydrogenated silicon nitride thin films a-SiNx:H (abbreviated later by SiNx) were deposited by Electron Cyclotron Resonance plasma enhanced chemical vapor deposition method (ECR-PECVD). By changing ratio of gas flow (R = NH3/SiH4) in the reactor chamber different stoichiometric layers x = [N]/[Si] ([N] and [Si] atomic concentrations) are successfully deposited. Part of the obtained films has subsequently undergone rapid thermal annealing RTA (800°C/1 s) using halogen lamps. Optical and structural characterizations are then achieved by spectroscopic ellipsometry (SE), ion beam analysis and infrared absorption techniques. The SE measurements show that the tuning character of their refractive index n(λ) with stoichiometry x and their non-absorption properties in the range of 250 - 850 nm expect for Si-rich SiNx films in the ultraviolet UV range. The stoichiometry x and its depth profile are determined by Rutherford backscattering spectrometry (RBS) while the hydrogen profile (atomic concentration) is determined by Elastic Recoil Detection Analysis (ERDA). Vibrational characteristics of the Si-N, Si-H and N-H chemical bonds in the silicon nitride matrix are investigated by infrared absorption. An atomic hydrogen fraction ranging from 12% to 22% uniformly distributed as evaluated by ERDA is depending inversely on the stoichiometry x ranging from 0.34 to 1.46 as evaluated by RBS for the studied SiNx films. The hydrogen loss after RTA process and its out-diffusion depend strongly on the chemical structure of the films and less on the initial hydrogen concentration. A large hydrogen loss was noted for non-thermally stable Si-rich SiNx films. Rich nitrogen films are less sensitive to rapid thermal process.

Enhancing Optical Nonlinearity in a Nonstoichiometric SiN Waveguide for Cross-Wavelength All-Optical Data Processing

Nonstoichiometric SiNx with enhancing optical nonlinearity is enabled to facilitate the waveguide microring resonator for cross-wavelength all-optical data processing applications. The Si/N composition ratio of the nonstoichiometric SiNx can be detuned from stoichiometric to Si-rich by adjusting the SiH4/NH3 fluence ratios. Under pumping with incoming pulsed data, the comb-like transmittance of the nonstoichiometric SiNx microring resonator can spectrally red-shift by 100 pm as its effective refractive index changed by more than 1 order of magnitude due to the enhanced nonlinear Kerr effect. The enlarged refractive index of Δn = 1.6 × 10–4 with increasing nonlinear refractive index to n2 = 1.6 × 10–13 cm2/W at 1550 nm is observed at a Si concentration of 66.2% in the Si-rich SiNx film. In application, a cross-wavelength all-optical data conversion/inversion processor based on the nonstoichiometric SiNx microring resonator is presented. The dense nanoscale Si content formed by a higher Si/N composition rat...

Visible Photoluminescence of Non-Stoichiometric Silicon Nitride Films: The Effect of Annealing Temperature and Atmosphere

The radiative properties of non-stoichiometric silicon nitride SiNx fi lms produced by plasma-enhanced chemical vapor deposition were studied. Intense room-temperature photoluminescence (PL) in the visible region was recorded after annealing for both Si-rich (x = 1.13) and N-rich (x = 1.5) silicon nitride fi lms. The position of the PL band maximum depended signifi cantly on the fi lm composition. The PL band maxima for Si-rich and N-rich SiNx fi lms were detected in the red (660 nm) and blue (450 nm) spectral regions, respectively. The effect of the annealing atmosphere on PL of the SiNx fi lms was studied. It was shown that the PL intensity depended not only on the annealing temperature but also on the annealing atmosphere. The observed features of the non-stoichiometric SiNx PL spectra were explained in terms of defect states in the SiNx band gap.

Si-rich SiNx based Kerr switch enables optical data conversion up to 12 Gbit/s.

Silicon photonic interconnection on chip is the emerging issue for next-generation integrated circuits. With the Si-rich SiNx micro-ring based optical Kerr switch, we demonstrate for the first time the wavelength and format conversion of optical on-off-keying data with a bit-rate of 12 Gbit/s. The field-resonant nonlinear Kerr effect enhances the transient refractive index change when coupling the optical data-stream into the micro-ring through the bus waveguide. This effectively red-shifts the notched dip wavelength to cause the format preserved or inversed conversion of data carried by the on-resonant or off-resonant probe, respectively. The Si quantum dots doped Si-rich SiNx strengthens its nonlinear Kerr coefficient by two-orders of magnitude higher than that of bulk Si or Si3N4. The wavelength-converted and cross-amplitude-modulated probe data-stream at up to 12-Gbit/s through the Si-rich SiNx micro-ring with penalty of −7 dB on transmission has shown very promising applicability to all-optical communication networks.

Sonosynthesis of microstructures array for semiconductor photovoltaics

The properties of the silicon samples subjected to cavitation impacts have been studied. It was shown that high-intensity (15W/cm2) and high-frequency (1–6MHz) sonication of silicon samples in the liquid nitrogen induces changes of the physical, chemical, and structural properties of semiconductor surface. Optical, atomic force and scanning electron microscopy techniques as well as energy dispersive X-ray spectroscopy, X-ray diffraction and photoresponse spectroscopy were used. The experimental study demonstrates the microstructure formation as well as a change of the chemical composition at the silicon surface. It was found that a significant rise in value and expansion of the spectral range of photosensitivity take place after cavitation treatment. The photoresponse of about 2.0eV can be connected with the formation of Si-rich SiNx compound inside the ultrasonically structured region of Si. The obtained value of the refractive index confirms this assumption.

Raman study of light-emitting SiNx films grown on Si by low-pressure chemical vapor deposition

Si-rich silicon nitride (SRSN) films were deposited on Si wafers by low pressure chemical vapor deposition (LPCVD) technique and, subsequently, annealed at (800–1200) °C to form Si precipitates. The composition of SiNx films was measured by Rutherford backscattering spectrometry (RBS). Two sets of samples differed by the amount of excessive Si (Siexc) in silicon nitride were studied. Evolution of Si nanoclusters from amorphous to crystalline ones during high temperature treatment was examined by Raman scattering (RS) spectroscopy. The amorphous Si clusters were already revealed in as-deposited SiNx while the annealing results in their crystallization. The crystalline nanoprecipitates are only registered in nitride films after annealing at 1200°C. A dependence of Raman scattering intensity from the Si wafer on the temperature of annealing of SiNx/Si structures was revealed. This information was used to explain the phase transformations in SRSNs during high temperature treatments. The peculiarities of photoluminescence (PL) spectra for two sets of Si-rich SiNx films are explained taking into account the contribution from the quantum confinement effect of Si nanocrystals and from the native defects in silicon nitride matrix, such as N- and K-centers.

Effect of hydrogen on passivation quality of SiNx/Si-rich SiNx stacked layers deposited by catalytic chemical vapor deposition on c-Si wafers

We investigate the role of hydrogen content and fixed charges of catalytic chemical vapor deposited (Cat-CVD) SiNx/Si-rich SiNx stacked layers on the quality of crystalline silicon (c-Si) surface passivation. Calculated density of fixed charges is on the order of 1012cm−2, which is high enough for effective field effect passivation. Hydrogen content in the films is also found to contribute significantly to improvement in passivation quality of the stacked layers. Furthermore, Si-rich SiNx films deposited with H2 dilution show better passivation quality of SiNx/Si-rich SiNx stacked layers than those prepared without H2 dilution. Effective minority carrier lifetime (τeff) in c-Si passivated by SiNx/Si-rich SiNx stacked layers is as high as 5.1ms when H2 is added during Si-rich SiNx deposition, which is much higher than the case of using Si-rich SiNx films prepared without H2 dilution showing τeff of 3.3ms.