Low Temperature Silicon Nitride Research Articles

Power-efficient programmable integrated multiport photonic interferometer in CMOS-compatible silicon nitride

Silicon nitride (SiN x ) is an appealing waveguide material choice for large-scale, high-performance photonic integrated circuits (PICs) due to its low optical loss. However, SiN x PICs require high electric power to realize optical reconfiguration via the weak thermo-optic effect, which limits their scalability in terms of device density and chip power dissipation. We report a 6-mode programmable interferometer PIC operating at the wavelength of 1550 nm on a CMOS-compatible low-temperature inductance coupled plasma chemical vapor deposition (ICP-CVD) silicon nitride platform. By employing suspended thermo-optic phase shifters, the PIC achieves 2× improvement in compactness and 10× enhancement in power efficiency compared to conventional devices. Reconfigurable 6-dimensional linear transformations are demonstrated including cyclic transformations and arbitrary unitary matrices. This work demonstrates the feasibility of fabricating power-efficient large-scale reconfigurable PICs on the low-temperature ICP-CVD silicon nitride platform.

Low temperature silicon nitride grown by very high frequency (VHF, 162MHz) plasma enhanced atomic layer deposition with floating multi-tile electrode

Important issues for silicon nitride (SiNx) plasma enhanced atomic layer deposition (PEALD) are lowering the process temperature and minimization of plasma damage. In this study, the characteristics of PEALD SiNx films deposited at a low processing temperature of 100 °C with di-isopropylamino silane (DIPAS) and N2 plasma excited by using a very high frequency (VHF, 162 MHz) floating multi-tile electrode capacitively coupled plasma (CCP) source and a conventional VHF CCP source are reported in addition to the characteristics of both plasma sources. The PEALD SiNx film deposited with the floating multi-tile electrode exhibited higher growth rate (∼ 0.6 Å/cycle), higher N/Si ratio film (N/Si ∼ 0.98, even though it is lower than the stoichiometric ∼1.33 of N/Si for Si3N4) with no trace of carbon, lower surface roughness, and higher conformality in a trench compared to those deposited by the conventional CCP. In addition, improved electrical properties of the SiNx films such as lower leakage current, lower interface trap density, and higher breakdown voltage of PEALD SiNx film were obtained with the floating multi-tile electrode. These enhanced properties of SiNx films deposited by the floating multi-tile electrode are believed to be related to the higher plasma density, higher radical density, and lower ion energy bombarding the substrate observed for the multi-tile electrode through the enhanced power efficiency of the differentially-coupled multi-tile plasma source.

Effect of 2 MHz frequency power applied to the substrate for low-temperature silicon nitride thin film deposition

Silicon nitride (SiNx) thin films were deposited at a low temperature of 80 °C using a dual-frequency plasma-enhanced chemical vapor deposition (PECVD) equipment. The density of the thin film was increased by 17% by increasing the low-frequency (LF) power of 2 MHz applied to the lower electrode to 100 W separately from the plasma generated by the 180 W power of 13.56 MHz applied to the upper electrode. The advantage of this dual-frequency PECVD process is that even if it is deposited at a low temperature, it shows similar effects to high-temperature deposition or post-deposition annealing process. Due to the LF power applied to the substrate, the hydrogen concentration in the deposited SiNx thin film decreases, which in turn leads to an increase in the film density. The increase in SiNx thin film density eventually results in a 21% increase in dielectric constant. It was shown that the use of SiNx thin films with improved properties as a dielectric layer of a thin film transistor can increase mobility and on-off ratio and reduce leakage current and subthreshold swing of the transistor.

Low-Temperature and Low-Pressure Silicon Nitride Deposition by ECR-PECVD for Optical Waveguides

We report on low-temperature and low-pressure deposition conditions of 140 °C and 1.5 mTorr, respectively, to achieve high-optical quality silicon nitride thin films. We deposit the silicon nitride films using an electron cyclotron resonance plasma-enhanced chemical vapour deposition (ECR-PECVD) chamber with Ar-diluted SiH4, and N2 gas. Variable-angle spectroscopic ellipsometry was used to determine the thickness and refractive index of the silicon nitride films, which ranged from 300 to 650 nm and 1.8 to 2.1 at 638 nm, respectively. We used Rutherford backscattering spectrometry to determine the chemical composition of the films, including oxygen contamination, and elastic recoil detection to characterize the removal of hydrogen after annealing. The as-deposited films are found to have variable relative silicon and nitrogen compositions with significant oxygen content and hydrogen incorporation of 10–20 and 17–21%, respectively. Atomic force microscopy measurements show a decrease in root mean square roughness after annealing for a variety of films. Prism coupling measurements show losses as low as 1.3, 0.3 and 1.5 ± 0.1 dB/cm at 638, 980 and 1550 nm, respectively, without the need for post-process annealing. Based on this study, we find that the as-deposited ECR-PECVD SiOxNy:Hz films have a suitable thickness, refractive index and optical loss for their use in visible and near-infrared integrated photonic devices.

SiNx Deposition at Low Temperature Using UV-Irradiated NH3

We developed a low-temperature silicon nitride (SiNx) film deposition technique using ultraviolet (UV)-irradiated ammonia (NH3) as the reactant gas. In this work, to determine the effect of UV-irradiated NH3, we deposited SiNx films using the developed chemical vapor deposition technique and then evaluated their characteristics. The energy of UV light was only used to excite NH3. Disilane (Si2H6) without UV irradiation was used as the precursor gas. The results demonstrated that using UV-irradiated NH3 as the reactant gas enabled deposition of SiNx films at 30 and 450°C. The N/Si ratio of the SiNx film deposited at 450°C was close to 1.33.

Active area cell efficiency (19%) monocrystalline silicon solar cell fabrication using low-cost processing with small footprint laboratory tools

A high efficiency (> $$18\%$$ ) industrial large area crystalline silicon wafer solar cell fabrication process generally requires industrial equipment with large footprint, high capital and running costs. Stricter processing window, continuous monitoring and automated functioning are the reasons for it. However, for any conventional laboratory (lab) it is always difficult to manage these requirements with limited available lab space or insufficient fund and other related resources. In this work, we report a novel way to fabricate high efficiency full area aluminium back surface field monocrystalline silicon wafer solar cells in our lab using low-cost processing with small-footprint fabrication tools for 6 inch pseudo-square industrial wafers. The novelty of our work includes optimization of every fabrication process step, e.g., texturization, emitter diffusion, emitter passivation and anti-reflection coating deposition, edge-isolation, screen printing and co-firing individually. These modifications include tuning of processing tools and processes, utility changes and inclusion of additional process steps. Beaker-based chemical processes, manual diffusion furnace, introduction of low temperature oxidation, low temperature silicon nitride deposition processes, plasma-edge isolation tool, single manual screen printer, single oven drying of metal pastes and co-firing using rapid thermal processing tools were used at our lab. For our cells, actual and active area efficiencies of 18.5 and 19% (measured under AM1.5G 1 Sun condition), respectively, were achieved.

Low-Temperature Deposition of Silicon Nitride Films Using Ultraviolet-Irradiated Ammonia

A low-temperature silicon nitride (SiNx:H) film-deposition technique that utilizes ultraviolet (UV)-irradiated ammonia (NH3) as the reactant gas and nonirradiated disilane (Si2H6) as the precursor gas was investigated. The UV light was only used to generate active species from NH3, not to irradiate the substrate. To determine the effect of the active species on the deposition process, SiNx:H films were deposited via chemical vapor deposition and their refractive index and composition ratio were evaluated. The results demonstrate that the highly reactive species generated from UV-light-irradiated NH3 enabled the deposition of nitrogen-containing films between 30°C and 450°C. N/Si ratio and refractive index of approximately 1.33 and 1.9–2.0, were obtained for a SiNx:H film deposited at 350°C and 450°C, respectively.

Hybrid light-emitting polymer/SiN_x platform for photonic integration

Organic semiconductors have potentials for a broad range of applications; however, it is difficult to be integrated with traditional inorganic material to meet the need of further application. Based on low-temperature silicon nitride (SiNx) deposition technique, here we demonstrate a hybrid structure fabricated by directly depositing high-quality SiNx on organic polymer film Poly[2-(2',5'-bis(2"-ethylhexyloxy)- phenyl) -1,4-phenylene vinylene] (BEHP-PPV). Stacked BEHP-PPV/SiNx hybrid structures with different periods are obtained and their optical properties are systematically characterized. Moreover, a group of BEHP/PPV embedded SiNx micro-disk is fabricated and amplification of spontaneous emission (ASE) is observed under optical pumping, further confirming that the gain properties of BEHP/PPV are well preserved. Our technique offers a platform to fabricate organic/inorganic hybrid optical devices compatible with integrated components.

Novel Anhydrous Hydrazine Delivery for Low Temperature Silicon Nitride Passivation of Sige(110)

New high mobility channel materials such as SiGe, Ge, and InGaAs create difficult thermal constraints on Metal-Nitride deposition, where limits range from 300-400C. It is necessary to: limit atomic diffusion; prevent undesirable phase transitions, strain relaxation and defect formation. Feasibility for low temperature hydrazine (H2NNH2) ALD was reported by George.3 In addition, a new technology that is capable of generating and delivering stable and highly concentrated anhydrous hydrazine gas has been developed by RASIRC. A thin layer of silicon nitride or silicon oxynitride can act as a diffusion barrier or channel passivation layer prior to dielectric deposition in FinFets or MOSFETs. When employed as a channel passivation layer, further oxidation with anhydrous peroxide leaves Si-N-OH termination, thereby providing good nucleation for High K deposition (Figure 1). This study focuses on developing <400C silicon nitride ALD process. STM/STS and XPS are employed to characterize SiNx film growth on Si0.5Ge0.5(110) (Figure 2). HfO2 is then grown on a Si-N-OH functionalized surface. Electrical characterization of MOSCAP structures has been obtained will be compared to other passivation methods such as ammonia plasma. Figure 1

Neural Network Modeling of Deposition Rate Characteristics of Low Temperature Silicon Nitride Deposited by Inner Two Parallel Coil Inductively Coupled Plasma Chemical Vapor Deposition

In this study, a neural network model for silicon nitride (SiN) deposition process is proposed. SiN thin films were deposited by a direct inner two parallel inductively coupled plasma chemical vapor deposition (ICPCVD) system that can control the activated radical and charged species in plasma. This system can produce SiN thin films at low temperature for flexible displays. The input parameters considered for deposition conditions were the N2 gas flow rate, NH3 gas flow rate, and substrate temperature. These were varied within the ranges of 0-20 sccm, 0-20 sccm, and 100-300 degrees C, respectively. For those of input parameters and the output of deposition rate, we developed a back propagation neural network model with a pre-processor. It is shown that the model accuracy and learning speed of the proposed model are better than those of a conventional neural network model. In the experiments conducted, it was found that the deposition rate increased as the flow rates of ammonia (NH3) and nitrogen (N2) increased up to a certain amount. On the contrary, when the flow rates of NH3 and N2 went over a certain amount, the deposition rate decreased. It was also found that an increase in temperature resulted in an increase in the deposition rate.

All hot wire chemical vapor deposition low substrate temperature transparent thin film moisture barrier

We deposited a silicon nitride/polymer hybrid multilayer moisture barrier for flexible electronics in a hot wire chemical vapor deposition process, entirely below 100°C. We were able to reach a water vapor transmission rate (WVTR) as low as 5×10−6g/m2/day at a temperature of 60°C and a relative humidity of 90% for a simple three-layer structure consisting of two low-temperature silicon nitride (SiNx) layers and a polymer layer in between. This WVTR is low enough for organic and polymer devices. In a second experiment it is investigated how the yield of our samples increases with the number of SiNx layers, while keeping the total SiNx thickness constant. Cross sectional scanning electron microscopy images of degraded samples reveal a high structural robustness of our multilayers.

Characteristics of Low-Temperature(≤200 °) PECVD Silicon Nitride for Gate Dielectric of TFTs by Using N2 Highly Diluted SiH4

not Available.

Hollow Waveguides With Low Intrinsic Photoluminescence Fabricated With PECVD Silicon Nitride and Silicon Dioxide Films

A new type of integrated hollow core anti-resonant reflecting optical waveguide (ARROW) with low intrinsic photoluminescence (PL) fabricated with plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (SiN) and silicon dioxide (SiO2) films is demonstrated. The waveguide is fabricated by surrounding the hollow core with alternating layers of SiN and SiO2. The thicknesses and indices of the layers are designed to meet an anti-resonance condition. Compared to earlier ARROW structures made by depositing high-temperature (HT) SiN (250 °C), the PL background decreases by a factor of ~ 10 when low-temperature (LT) SiN (100 °C ) films are used. Therefore, LT SiN ARROWs are attractive platforms for sensitive fluorescence and Raman spectroscopy measurements of biomolecules.

Deposition and characterization of low temperature silicon nitride films deposited by inductively coupled plasma CVD

Silicon nitride films have been deposited at a low temperature (70 °C) by inductively coupled plasma chemical vapor deposition (ICP-CVD) technique and their physical and chemical properties were studied. For a deposited SiN sample, β-phase was observed and refractive index of 2.1 at 13.18 nm/min deposition rate was obtained. The attained stress of 0.08 GPa is lower as compared to the reported value of 1.1 GPa for SiN thin films. To study the deposited film, characterization was performed using X-ray photoelectron spectra (XPS), X-ray diffraction (XRD), micro Raman spectroscopy, Fourier transfer infrared spectroscopy (FTIR), cross-section scanning electron microscopy (SEM) and atomic force microscopy (AFM).

Effect of DC Bias Voltage on the Characteristics of Low Temperature Silicon–Nitride Films Deposited by Internal Linear Antenna Inductively Coupled Plasma Source

The characteristics of silicon–nitride deposited at the temperature lower than 100 °C using an internal linear-type inductively coupled plasma were investigated as functions of the NH3/SiH4 ratio and ion bombardment energy applied to the substrate (dc bias voltage) for use as the gate dielectric material of flexible display devices. Decreasing the NH3/SiH4 ratio to 2 and increasing the dc bias voltage to -150 V decreased the Si–O bonding and increased the Si–N bonding, resulting in a more nitrogen-rich SiNx thin film. In addition, the capacitance-voltage measurement of the metal-insulator-semiconductor devices fabricated with the SiNx thin film deposited at various dc bias voltages showed a hysteresis curve in the cyclic voltage measurement and the increase of the dc bias voltage with decreasing hysteresis voltage. The interface trap density measured at a dc bias voltage of -150 V and NH3/SiH4 ratio of 2 showed the lowest interface trap charge density of about 2×1011 cm-2. Under these conditions, the dielectric constant was as high as 7.2.

Effect of NH3-Free Silicon Nitride for Protection Layer of Magnetic Tunnel Junction on Magnetic Properties of Magnetoresistive Random Access Memory

The effects of plasma and precursors during low-temperature silicon nitride (LT-SiN) film deposition on the magnetic properties of a CoFeB alloy layer, which is one magnetic material in a magnetic tunnel junction (MTJ) in magnetoresistive random access memory (MRAM), were investigated. The NH3 plasma exposure was found to nitride the CoFeB alloy layer, resulting in degradation of the magnetic properties of the CoFeB alloy layer. To suppress this degradation, NH3-free LT-SiN films deposited using silane and nitrogen source gases with helium or argon dilution in a conventional plasma enhanced chemical vapor deposition (PECVD) apparatus were evaluated. The LT-SiN film deposited under conditions of a highly dilute helium flow in the SiH4–N2–He gas mixture exhibited high density, sufficient moisture-blocking ability, and low leakage current. On the other hand, the film deposited at the SiH4–N2–Ar gas mixture exhibited poor film qualities. It is revealed that helium gas has enhanced the generation of N2 radicals and the decomposition of silane gas during the deposition of the SiH4–N2–He gas mixture. Finally, we demonstrated that the electrical properties of 8-kbit MRAM arrays have been improved by using the optimized NH3-free LT-SiN film for the MTJ-protection layer.

Characterization of low-temperature silicon nitride films produced by inductively coupled plasma chemical vapor deposition

Silicon nitride films were synthesized at 170°C by using inductively coupled plasma chemical vapor deposition under three microwave power conditions of 500, 800, and 1000W. The chemical, physical and electrical properties of the deposited silicon nitride films were characterized by Fourier transform infrared, wet etching, atomic force microscopy, ellipsometry, J-V, and C-V measurements of metal-insulator-semiconductor. The microwave power for film deposition is found to play an important role at the films’ properties. A high microwave power reduces the retention of hydrogen in a form of Si–H and N–H atomic bonds. The microwave power significantly affects the density of pin holes; the 800W film has the lowest density of pin holes. In general, the low-temperature silicon nitride films possess better surface roughness than the conventional silicon nitride films produced at higher temperatures. The low-temperature silicon nitride films exhibit an abrupt breakdown, a characteristic of avalanche breakdown. The ...

Effect of deposition conditions on charging processes in SiN x: Application to RF-MEMS capacitive switches

The paper presents a systematic investigation of dielectric charging in low temperature silicon nitride for RF-MEMS capacitive switches. The dielectric charging is investigated with the aid of Metal-Insulator-Metal (MIM) capacitors with different thickness dielectric film and symmetric and asymmetric metal contacts. The experimental results demonstrate that the charging process is almost symmetric in low temperature deposited silicon nitride. Experiments performed in both MIM and MEMS reveal that the charging process is strongly affected by temperature. Specifically at high temperatures the charging rate increases exponentially with temperature.

Influences of low temperature silicon nitride films on the electrical performances of hydrogenated amorphous silicon thin film transistors

Influences of silicon nitride (SiNx) films on the electrical performances of hydrogenated amorphous silicon thin film transistors (a-Si : H TFTs) are studied. Relatively low temperature (200 °C) SiNx films are prepared by plasma enhanced chemical vapour deposition at different radio-frequency powers. Results indicate that the SiNx films at a radio-frequency power of 340 W (Power density = 1.96 × 10−1 W cm−2) are near-stoichiometric and have better interface quality. Therefore, a-Si : H TFTs with this SiNx gate dielectric layer have a high field effect mobility and sustain the bias stress. The field effect mobility is 0.59 cm2 V−1 s−1 and the threshold voltage shift after a constant voltage stress (CVS) for 2.8 h is 3.18 V. The electrical degradation mechanism of a-Si : H TFTs is studied from the capacitance–voltage measurement. The degradation of the a-Si : H TFT after CVS is due to the defect generation in the SiNx gate dielectric and a-Si : H active layers. However, when the surface roughness of the SiNx film is poor, the degradation from the a-Si : H/SiNx interface is predominated. Therefore, if the SiNx film is used as a gate dielectric layer to fabricate a-Si : H TFTs, the surface roughness and chemical composition of the SiNx film should be considered simultaneously.

Highly Reliable Cu Interconnect Using Low-Hydrogen Silicon Nitride Film Deposited at Low Temperature as Cu-Diffusion Barrier

We demonstrated highly reliable Cu interconnects using a high-quality silicon nitride film grown at temperatures below 300 °C. The low-temperature silicon nitride (LT-SiN) film, which was used as a Cu-diffusion barrier layer and a final passivation layer, was deposited at 275 °C by plasma-enhanced chemical vapor deposition at a low SiH4 flow ratio. The low SiH4 flow ratio was due to the use of a highly dilute nitrogen flow, leading to the generation of many nitrogen radicals or ions in the plasma. These radicals or ions might reduce the hydrogen concentration and defect density of the film. As a result, a stoichiometric silicon nitride (Si3N4) film with a low hydrogen concentration was successfully obtained. By applying this LT-SiN film in 130-nm-node Cu interconnects for magnetoresistive random access memory, highly reliable via-hole electromigration (Via-EM) and line-to-line time-dependent dielectric breakdown (TDDB) characteristics were obtained.