Si3N4 Layer Research Articles

Complex Analysis of the Stress-Strain State of the Surface Layer of Ground Si3N4–TiC Ceramics

Complex Analysis of the Stress-Strain State of the Surface Layer of Ground Si3N4–TiC Ceramics

Thermal Analysis of the Stress-Strain State of the Surface Layer of Ground Si3N4–TiC-Ceramics

Thermal Analysis of the Stress-Strain State of the Surface Layer of Ground Si3N4–TiC-Ceramics

Patterning of transition metal dichalcogenides catalyzed by surface plasmons with atomic precision

Summary Plasmon-induced charge transfer has drawn considerable interests and spurred rapid developments of photovoltaics and photocatalysis. Various plasmonic metal/transition metal dichalcogenide (TMD) heterostructures have been developed to promote charge separation. For plasmon-induced catalysis, the transformation of TMDs is rare, and the erosion of TMDs has not yet been reported. Here, we report the etching of two-dimensional TMDs by planar surface plasmon polaritons (SPPs). We found that SPPs can etch various TMDs into desired layers and lateral size through controlling the light power and incident direction. In aqueous media, the strong plasmonic coupling at Au/MoS2 interface generates holes in the valence band of MoS2 that can weaken its interlayer interaction. As a synergistic effect, the plasmonic hot electrons produce oxidizing H2O2 to dissolve MoS2 from the top layers. Our results provide a new perspective for understanding the plasmonic coupling at metal-TMD interfaces and a reliable route toward fabricating well-defined TMDs.

Photochromic Response of Encapsulated Oxygen‐Containing Yttrium Hydride Thin Films

Photochromic oxygen‐containing yttrium‐hydride thin films are synthesized by argon magnetron sputtering on microscope slides. Some of them are encapsulated with a thin, transparent, and nonphotochromic diffusion‐barrier layer of either Al2O3 or Si3N4. Ion‐beam‐based methods prove that these protective diffusion barriers are stable and free from pinholes, with thicknesses of only a few tens of nanometers. Optical spectrophotometry reveals that the photochromic response and relaxation time for both protected and unprotected samples are almost identical. Ageing effects in the unprotected films lead to degradation of the photochromic performance (self‐delamination), whereas the photochromic response for the encapsulated films is stable. The results show that the environment does not play a decisive role for the photochromic process and the encapsulation of oxygen‐containing rare‐earth hydride films with transparent and nonorganic thin diffusion‐barrier layers provides long‐time stability of the films, mandatory for applications as photochromic coatings on, e.g., smart windows.

Alternating Multilayered Si3N4/SiC Aerogels for Broadband and High-Temperature Electromagnetic Wave Absorption up to 1000 °C

Lightweight electromagnetic (EM) wave absorbers made of ceramics have sparked tremendous interest for applications in EM wave interference protection at high temperatures. However, EM wave absorption by pure ceramics still faces huge challenges due to the lack of efficient EM wave attenuation modes. Inspired by the energy dissipation mechanism during fracture of lobster shells with a soft and stiff multilayered structure, we fabricate a high-performance EM wave absorption ceramic aerogel composed of an alternating multilayered wave transparent Si3N4 (N) layer and wave absorption SiC (C) layer by a simple restack method. The obtained N/C aerogel shows ultralow density (∼8 mg/cm3), broad effective absorption bandwidth (8.4 GHz), strong reflection loss (-45 dB) at room temperature, and excellent EM wave absorption performance at high temperatures up to 1000 °C. The attenuation of EM wave mainly results from a "reflection-absorption-zigzag reflection" process caused by the alternating multilayered structure. The superior absorption performance, especially at high temperatures, makes the N/C aerogel promising for next-generation wave absorption devices served in high-temperature environments.

Green Manufacturing of Silyl-Phosphate for Use in 3D NAND Flash Memory Fabrication

Three-dimensional NAND flash memory featuring dozens of vertically stacked memory cells is the state-of-the-art technology for most storage platforms. To fabricate three-dimensional (3D) NAND memory, lateral etching of the Si₃N₄ layer over SiO₂ is an essential step that is conducted through a wet etching process using a phosphoric acid-based etchant. Silyl-phosphate or highly selective nitride serves as an etching solution additive to control the SiO₂ layer dissolution rate. However, silyl-phosphate is prepared with an expensive monomeric silica precursor and at high reaction temperatures and generates environmentally harmful byproduct gases, such as HCl, HF, and CH₃OH. This study demonstrates that silyl-phosphate can be prepared using low-cost polymeric silica under a mild reaction temperature by changing the characteristic acidity of phosphoric acid. The possibility of tuning the phosphoric acid acidity was first studied by molecular dynamics simulations, and phosphoric acids with stronger acidity were prepared by the evaporation of water from H₃PO₄ (85%). The concentrated phosphoric acid enabled a fast reaction of polymeric silica and phosphate at a low reaction temperature (80 °C). The obtained silyl-phosphate lowered the SiO₂ layer dissolution rate, thereby yielding a Si₃N₄/SiO₂ layer etching ratio of up to 940. The proposed method offers an environmentally friendly production process for special chemicals used in 3D NAND flash memory fabrication.

Effects of Different Amounts of Nb Doping on Electrical, Optical and Structural Properties in Sputtered TiO2−x Films

Highly conductive TiO2 films with different Nb doping levels (up to 5 at%) were prepared by reactive DC magnetron sputtering under precise control of the oxygen partial pressure. They were deposited on unheated substrates, covered with a protective Si3N4 layer, and subsequently annealed at 300 °C. The doping efficiency of Nb is greater than 90%. Conductivity is a maximum for a partly oxidized target in the transition range. The best films exhibit a resistivity of 630 µΩ cm and a mobility of 7.6 cm2/Vs combined with a high transparency above 70%. Comparing the behavior of undoped and Nb-containing films, intrinsic limits of the conductivity in the TiO2−x:Nb system could be observed, and a consistent model explaining these findings is presented. The conductivity is limited—by decreasing electron density due to Nb oxidation—by increasing incorporation formation of Nb2O5 clusters as scattering centers with increasing oxygen partial pressure and Nb concentration, by a transition from the crystalline to the amorphous state of the films below a critical oxygen partial pressure.

Force Analysis of the Stress-Strain State of the Surface Layer of Ground Si3N4–TiC Ceramics

Force Analysis of the Stress-Strain State of the Surface Layer of Ground Si3N4–TiC Ceramics

Unraveling the selective etching mechanism of silicon nitride over silicon dioxide by phosphoric acid: First-principles study

Highly selective etching of a target silicon compound is essential in semiconductor fabrication. Searching for alternatives to conventional etchant that contain hazardous chemicals is challenging, largely due to the unclear understanding of the chemical reaction. In this study, we elucidate etching machinery of phosphoric acid and its outstanding selectivity toward silicon nitride (Si3N4) over silicon dioxide (SiO2) surfaces in atomistic level. Ab-initio thermodynamic and kinetic formalisms integrated with density functional theory computation propose that pyrophosphoric acid (H4P2O7), a condensed form of orthophosphoric acid.(H3PO4) at high concentration and temperature, is even more reactive toward Si3N4 than H3PO4 which has been regarded as a dominant species for decades. We demonstrate that the superior etching selectivity derives from reaction mechanism of thermodynamic control, where H4P2O7 is much more exergonic than H3PO4. Notably, we find that water molecules close to the H4P2O7 assist sequential etching process in two ways: catalysis via structural proton transfer, and hydrolysis of diphosphate group in the Si3N4 surface. Our study guides a quick and accurate screening as well as designing efficient and safe etchants, which facilitates the fabrication of nanoscale semiconductor devices that accompanies selective etching of alternately stacked hundreds of atomic layers of Si3N4 and SiO2.

Investigation of interface states between GaAs and Si3N4 after He+ implantation

The cross-sectional morphology of GaAs/Si3N4/SiO2 composite wafer after He+ implantation has been systematically observed. Experiment sample is prepared by focused ion beam system to meet the observation requirements of transmission electron microscope. The results show that implantation of 300 keV, 5 × 1016/cm2 He+ gives rise to formation of bubbles and dislocations in GaAs material, but no cracks are observed. In addition, after annealing, interface separation and micro-gap appear at the interface between GaAs layer and Si3N4 layer. Finally, the mechanisms of bond fracture and blisters formation at the interface are explained by density function theory calculation.

Germanium lead alloy on insulator grown by rapid melting growth

High-quality single crystalline germanium lead (GePb) alloys were successfully grown on Si3N4 layer using Si seed by rapid melting growth. The strip composition distribution was studied by Raman spectroscopy and energy dispersive X-ray spectroscopy; the highest Pb content in the GePb strip was 2%. Cross-sectional transmission electron microscopy and selected-area electron diffraction analyses indicated that the GePb strip had a high crystal quality with no dislocations or stacking faults. The GePb strip photodetectors were fabricated and showed good optical properties, with underestimated responsivities of 107, 71, and 20 mA/W at 1310, 1550, and 1630 nm, respectively. Therefore, the rapid melting growth is an effective method for obtaining high Pb content GePb alloys. In addition, GePb devices show high potential for photodetection.

Development of Polycrystalline Diamond Compatible with the Latest N-Polar GaN mm-Wave Technology

Integration of diamond on GaN can ease the challenges associated with thermal management of GaN-based power amplifiers which need to base on highly scaled transistors to push toward higher frequencies at high powers for 5G networks. The integration of diamond was achieved by growing polycrystalline (PC) diamond on nitrogen-polar GaN. A standard 5 nm Si3N4 layer which forms the gate dielectric was used as an interlayer between diamond and the GaN channel for etching protection. Since diamond growth conditions involve high temperature and H2 plasma, it can easily decompose the underlying dielectric as well as the GaN channel and degrade the channel conductivity and hence the device performance. Due to the incompatibility of conventional growth recipes with thin dielectrics (<5 nm), a novel two-stage-three-step growth recipe was designed for PC diamond integration on top of nitrogen-polar GaN high-electron-mobility transistors in a H2/CH4-plasma environment. Using only H2 and CH4 in the chamber guarantees a higher-phase-purity diamond than chambers with added argon or nitrogen for lower substrate etching. This recipe maintains the performance of the two-dimensional-electron gas and provides a less columnar diamond structure with a larger grain size. Our observations were supported by scanning transmission electron microscopy and Hall mobility measurements using the van der Pauw technique before and after diamond growth. A mobility of ∼1250 cm2/V s, a sheet carrier concentration of ∼1.30 × 1013 cm–2, and a sheet resistivity of ∼380 Ω/□ were maintained after the growth of diamond. The anisotropy ratio has been decreased from 3.75 to 1.12 with this growth recipe. Using long channel devices, we measured the difference in the channel temperature, which decreased by more than 100 °C in the range of 10–24 W/mm power after the integration of the diamond on top of the device.

Extraction of Nitride Trap Profile in 3-D NAND Flash Memory Using Intercell Program Pattern

The extraction of nitride trap density (Nt) filled with electrons emitted by thermal emission (TE) in the charge-trapping layer of 3-D NAND flash memory is demonstrated. The intercell program (IP) pattern was adopted to intentionally inject electrons into the intercell region to minimize the influence of lateral migration (LM) on the trap profiles. This was confirmed by the retention characteristics observed at 120 °C, where the charge loss is mainly caused by the TE of the trapped electrons in the nitride layer. The extracted peak value of Nt at EC-ET value of 1.20 eV using the IP pattern was as low as 1.01×1019 cm-3eV-1, in the scan range of 0.96 eV to 1.27 eV. This value was 17% lower than that from the conventional adjacent cell program (P-P-P) pattern. Therefore, the IP pattern can be used in extracting trap profiles in the SiN layer in scaled 3-D NAND memories.

Исследование ионной имплантации азота через слой нитрида кремния для межприборной изоляции силовых GaN/Si-транзисторов

This letter reports a nitrogen ion implantation through silicon nitride passivation layer deposited on AlGaN/GaN on Si heterojunction structure. Employment of Si3N4 layer simplify HEMT fabrication process and helps to obtain high resistivity isolation due to the shift of implanted ions distribution towards the surface of semiconductor. This isolation process in combination with C-doped heterostructure buffer layer results in increased up to 650 V breakdown voltage.

Reflectivity reduction of nanopatterned c-Si solar cells with antireflective coatings exposed to a wide range of incidence angles

The scope of the present study is to assess through numerical calculations the effect of nanopatterning the photovoltaics (PV) and that of imposing additional superstrate layers to the efficiency of the PV’s, under normal and wide incidence angles. The numerical calculations were performed with the Rigorous Coupled-Wave Analysis (RCWA) method where we examined several types of Si wafers including additional Si3N4 and SiO2 superstrate layers, and periodic patterns of grooves affecting either the superstrates or both the superstrates and Si substrate. A very broad parameter space was investigated (thickness of the superstrates, and the depth, diameter and periodicity constant of hole and pillar-like patterns) from which we derived the optimal set of parameters for each wafer type. The performance of the optimized wafers was then evaluated over a broad range of incident angles. Both the deposition of the superstrates as well as the imposition of periodic patterns improve drastically the absorption efficiency of the wafers and they allow for maintaining the maximum efficiency across the high incidence angle regime.

Growth of Si3N4 Thin Films on Si(111) Surface by RF-N2 Plasma Nitriding

Ultra-thin Si3N4 films were grown on Si(111) surface by radio frequency (RF)-N2 plasma exposure at 900 °C with 1–1.2 sccm of a flux of atomic nitrogen. We discuss the effect of various conditions such as N2 flow rate, nitriding time and RF power on the optical, chemical, and structural properties of a nitrided Si3N4 layer. The optical properties, surface morphology and chemical composition are investigated by using ellipsometry, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Cross-sectional TEM images show that an RF power of 350 W induced some damage to the Si(111) surface. The thickness of nitrided Si3N4 was measured to be about 5–7 nm. XPS results shown that the binding energy of Si 2p3/2 located at 101.9 ± 0.1 eV is attributed to the Si–N bonds in the Si3N4 compound. Smooth Si3N4 ultra-thin films were obtained at a nitridation time close to 1 h with an RF power of 300 W, with a measured refractive index (n) nearly to 1.88 at 632 nm. The increase in refractive index with decreased RF-plasma power and nitrogen flow rate is probably attributed to the change in the stoichiometry of the film and less surface damage.

Improved Pulse-Controlled Conductance Adjustment in Trilayer Resistors by Suppressing Current Overshoot.

In this work, we demonstrate the enhanced synaptic behaviors in trilayer dielectrics (HfO2/Si3N4/SiO2) on highly doped n-type silicon substrate. First, the three dielectric layers were subjected to material and chemical analyses and thoroughly investigated via transmission electron microscopy and X-ray photoelectron spectroscopy. The resistive switching and synaptic behaviors were improved by inserting a Si3N4 layer between the HfO2 and SiO2 layers. The electric field within SiO2 was mitigated, thus reducing the current overshoot in the trilayer device. The reset current was considerably reduced in the trilayer device compared to the bilayer device without a Si3N4 layer. Moreover, the nonlinear characteristics in the low-resistance state are helpful for implementing high-density memory. The higher array size in the trilayer device was verified by cross-point array simulation. Finally, the multiple conductance adjustment was demonstrated in the trilayer device by controlling the gradual set and reset switching behavior.

Optical switching in multilayer structures based on Ge2Sb2Te5

In this work, we have studied the phase switching in structures based on the Ge2Sb2Te5 (GST) composition and their optical parameters of reflectivity and transmissivity at 1550 nm wavelength after exposure to the pulse of nanosecond laser at 403 nm wavelength. We investigated 24 nm GST single-layer structure and found about 50% optical losses due to the double reflection and transmission at 1550 nm radiation. To achieve the least optical losses, we added additional SiO2, Si and Si3N4 layers to the structure. This allowed reducing optical losses up to 5 and 4% for absorption and undesirable reflection, respectively, for the amorphous GST layer, and 16 and 5% for absorption and undesirable transmittance, respectively, for the crystalline GST layer.

(Invited) Temperature Stable III-V/Si/Si3N4 Heterogeneous Integrated Laser

Silicon nitride (Si3N4) is a widely used complementary metal–oxide–semiconductor (CMOS) compatible material in modern IC industry and recent years have witnessed tremendous development of Si3N4 in photonics. The benefits of Si3N4 in photonics include low loss, low thermo optic coefficient and negligible nonlinear absorption at telecom wavelengths. Devices based on Si3N4 waveguides innovates in the field of nonlinear photonics, sensing, microwave photonics and so on. However, they are all dependent on the excellent passive properties of Si3N4. There are no successful demonstrations of fully integrated laser with Si3N4 yet.For an external cavity laser design, it is beneficial to have a low loss waveguide. A low loss waveguide platform can enable a long optical cavity which can greatly reduce the laser phase noise. Butt-coupled hybrid integrated lasers are extensively studied using Si3N4 cavity, but they are based on separate chips and are not scalable for large volume integration.Heterogeneous integration of III-V material and Si has achieved great success in the past years, offering the silicon photonics industry with low-cost, high-performance silicon photonic integrated circuits fully integrated with lasers. For the heterogeneous integration of III-V material with Si3N4, the biggest challenge is the large index mismatch. Typical III-V epi used for heterogeneous lasers is about 2 μm thick and extreme tapering cannot facilitate a high coupling efficiency between the III-V layer and Si3N4 layer.In this work, we used an intermediate Si layer to bridge the index mismatch between the III-V and Si3N4 layer. By using multilayer heterogeneous integration shown in Fig.1 (a), we enable a III-V/Si/Si3N4 structure to efficiently couple the mode between III-V/Si and Si/Si3N4. Based on this structure, we designed the III-V/Si/Si3N4 laser using an external Si3N4 spiral grating as the feedback cavity. This spiral grating provides the narrow-band optical feedback and determines the laser wavelength. The laser configuration is shown in Fig. 1(b).The laser performance is summarized in Fig. 1 (c)-(e). The lasing wavelength is at 1546 nm and the laser has over 58 dB side mode suppression ratio (SMSR). This shows the excellent mode selectivity from the 20 mm long Si3N4 spiral grating. We measured the frequency noise of the laser. With optimized loop mirror reflectivity, the laser fundamental linewidth is about 4 KHz. This linewidth can be further improved by lowering the Si3N4 waveguide loss. We anticipate the laser fundamental linewidth can be reduced to below 100 Hz using this design.Another advantage of integrating Si3N4 into the laser cavity is to have much higher temperature stability. By comparison, III-V/Si/Si3N4 laser wavelength shifts by only 0.47 nm for 45 oC change, while for a III-V/Si DBR laser this wavelength shift is 3.3 nm. This is over 7x difference and is a result of the low thermo-optic coefficient of Si3N4. When combined with Si3N4 based arrayed waveguide gratings, our laser can be potentially used in dense wavelength-division-multiplexing (DWDM) systems.The successful demonstration of this multilayer heterogeneous integration will enable a whole new class of devices that require low loss waveguides and are presently not integrated. This is a key step in fully exploiting the capabilities of wafer-bonding technologies. We anticipate this platform can take narrow-linewidth semiconductor laser performance to a new level. Figure 1

Impact of Passivation System on Device Performance and Proton Radiation Hardness in GaN-Based MIS-HEMTs

GaN-based metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) are intensively investigated for high power, high frequency [1] and aerospace application [2] due to its wide bandgap, high breakdown field, and high carrier density and mobility at AlGaN/GaN interface [3]. For the demonstration of high power radio-frequency and aerospace applicable devices, the passivation layer introduced on the AlGaN barrier plays significant roles for the enhancement of the frequency characteristics [4] and proton radiation hardness [2]. From this point of view, diverse passivation materials and systems have been researched in GaN-based MIS-HEMTs [2, 5, 6]. However, the detailed impact of passivation layer on the device properties and the immunity to the proton irradiation is not clear in many cases, so far.In this work, we have prepared the SiN/Al2O3 bi-layer passivation system to study the impact of mechanical stress introduced by the passivation layer deposition on the device performance (Sample A: SiN = 20 nm, Sample B: SiN/Al2O3 = 5/15 nm, Sample C: SiN/Al2O3 = 5/35 nm). The correlation between the induced mechanical stress on the GaN channel and carrier transport properties in terms of carrier concentration and mobility at hetero-interface in GaN-based MIS-HEMTs was examined. The Al2O3 layer deposited by the atomic layer deposition (ALD) provided the tensile stress which compensated the compressive stress generated by the SiN layer deposited by the plasma enhanced chemical vapor deposition (PEDVD). When the compressive stress reduces through the deposition of Al2O3 on the SiN layer, the carrier concentration and mobility at hetero-interface were increased. With decreasing compressive stress, the piezoelectric field enlarges that enhances polarization charges [7] and carrier concentration. The carrier mobility was also improved with diminishing compressive stress since the mean free path related to the lattice scattering is decreased, enhancing transconductance as well. As a result, GaN-based MIS-HEMTs with slight tensile stress in Sample C exhibits the best device performance.The proton radiation hardness according to the passivation system was studied for various passivation systems. When we compared the device characteristics before and after the proton irradiation with the fluences of 1013 and 1014 cm-2 at an energy of 5 MeV, the device properties such as threshold voltage, drain current, and transconductance were changed. After the proton radiation, the threshold voltage was negatively shifted that is identical characteristics to the metal-oxide-semiconductor device [8], rather than GaN-based HEMTs [9] as relatively large amount of holes was trapped inside of the passivation system due to the lower hole mobility than electron. The alternation of the device characteristics depended on the passivation system. The ALD-deposited Al2O3 showed superior quality compared to the PECVD-deposited SiN that was revealed by the pulse-mode stress measurements. Therefore, the hole trap sites generated by the proton irradiation and located interior of the passivation system are less when the Al2O3 layer was employed as a passivation layer, showing smaller threshold voltage shift. Moreover, the carrier mobility deterioration caused by the Coulomb scattering between the trapped holes inside the passivation system and carriers at hetero-interface was improved with the Al2O3 passivation layer. The drain current and transconductance degradation were improved by applying Al2O3 passivation layer.Our systematic measurement results highlight that the optimized SiN/Al2O3 bi-layer passivation system is promising technique for the enhancement of the device performance and improvement of proton radiation hardness in GaN-based MIS-HEMTs.AcknowledgementThis work was supported by the National Research Council of Science & Technology (NST) grant by the Korean government (MSIP) (No. CRC-19-02-ETRI).