Si3N4 Substrates Research Articles

Substrate Interference and Strain in the Second-Harmonic Generation from MoSe2 Monolayers.

Nonlinear optical materials of atomic thickness, such as non-centrosymmetric 2H transition metal dichalcogenide monolayers, have a second-order nonlinear susceptibility (χ(2)) whose intensity can be tuned by strain. However, whether χ(2) is enhanced or reduced by tensile strain is a subject of conflicting reports. Here, we grow high-quality MoSe2 monolayers under controlled biaxial strain created by two different substrates and study their linear and nonlinear optical responses with a combination of experimental and theoretical approaches. Up to a 15-fold overall enhancement in second-harmonic generation (SHG) intensity is observed from MoSe2 monolayers grown on SiO2 when compared to its value on a Si3N4 substrate. By considering an interference contribution from different dielectrics and their thicknesses, a factor of 2 enhancement of χ(2) was attributed to the biaxial strain: substrate interference and strain are independent handles to engineer the SHG strength of non-centrosymmetric 2D materials.

Sputtering of (111) highly-oriented nanotwinned Ag on polycrystalline Si3N4 substrates for high-power electronic packaging

Nanotwinned silver (NT-Ag) exhibits excellent mechanical and electrical properties, attributed to its high-density and (111) highly-oriented twinning structure in nanoscale. Therefore, it has recently drawn much attention in the field of electronic packaging, where it can be utilized as interconnection or metallization materials. However, it has been a critical challenge to fabricate the high-density and highly-oriented NT-Ag onto polycrystalline ceramic substrates, whose crystal structure does not support the epitaxial growth of NT-Ag films. In the current work, a high-density and highly-oriented NT-Ag film has been fabricated onto a polycrystalline ceramic substrate, i.e., NT-Ag on silicon nitride (NT-Ag@Si3N4), using the magnetron sputtering method. As results, a close-packed arrangement of high-density NT-Ag has been observed within columnar grains aligned along its growth direction, whereas the nanoindentation hardness of the NT-Ag film reached 1.82 GPa, with an electrical resistivity of 2.06 μΩ‧cm. Moreover, this study has discussed and explained the growth kinetics and mechanism of NT-Ag films, by controlling magnetron sputtering process parameters, such as sputtering power and argon flow rate. Additionally, the differences in the growth mechanism of NT-Ag on (100) Si and polycrystalline Si3N4 have also been investigated. With its superior material properties, NT-Ag@Si3N4 holds great promise in the applications of advanced packaging technology for high-power electronics.

Stress–strain behavior of Cu on the AMB‐Si3N4 substrate undergoing thermal cycles via in situ strain measurement

AbstractThe active metal brazing of a Si3N4 substrate with Cu has been evaluated for excellent reliability, demonstrating durability up to 1000 cycles in a cycling test ranging from −40°C to 250°C. While the finite element method (FEM) is commonly used for predicting thermal stress–strain in cyclic tests, experimental data on the measurement of thermal stress–strain on metallized substrates have remained limited. In this study, a digital image correlation (DIC) method was employed for the in situ measurement of thermal strain on a fully Cu‐coated Si3N4 substrate (AMB‐SN substrate) in various consecutive thermal cycles, ranging from 1–2 to 199–200. The thermal strains exhibited hysteresis curves that expanded slightly with cycles. By incorporating the coefficients of thermal expansion (CTE) of plain Cu and Si3N4, both the thermal stress and strain of Si3N4 and Cu on the AMB‐SN substrate were computed. The stress–strain curves of Cu revealed that the yield stress of Cu increased with the number of cycles, attributed to the cyclic hardening of the Cu layer. The Cu stress–strain curve calculated in this work showed a good agreement with the previous results obtained from compression/tension test of Cu at room temperature, which indicates the stress–strain curve of Cu on the composite was not sensitive to the temperature during the thermal cycle.

Dynamic bending analysis of metallized silicon nitride substrate during thermal cycling via digital image correlation

AbstractDigital image correlation (DIC) method was employed to analyze the dynamic bending of a metallized Si3N4 substrate in thermal cycles ranging from −40°C to 250°C. The substrate was monitored by DIC over several consecutive cycles, spanning from 0 to 2501. Three DIC measurement intervals, specifically during 999–1001, 1999–2001, and 2499–2501 cycles, were selected to analyze the bending behavior in response to temperature fluctuations. By the scanning acoustic microscope (SAM), the substrate revealed negligible delamination after 1001 cycles, light delamination after 2001 cycles, and serious delamination post‐2501 cycles. The dynamic bending remained unchanged during 999–1001 cycles. A curve with a negative bending was observed during 1999–2001 cycles, with a peak curvature of .024 mm−1 at −40°C; the negative bending intensified with a curvature reaching .050 mm−1 at −40°C during 2499–2501 cycles. The bending curve then decreased during the heating phase and returned to a non‐bent state at elevated temperatures. The bending curve reversed to positive at 250°C during thermal cycles from 2499 to 2501. The bending behavior throughout thermal cycles was discussed in relation to the asymmetric delamination observed on both sides of the substrate, as well as the distribution of delamination.

Selective nitride passivation using vapor-dosed aldehyde inhibitors for area-selective atomic layer deposition

We present a methodology for achieving selective deposition of Ru films through surface modification via vapor-phase functionalization of aldehyde inhibitor molecules. We conduct a comparative evaluation of the blocking capability using vapor-dosing of two different types of aldehyde molecules: undecylaldehyde and benzaldehyde as aliphatic and aromatic ring inhibitors, respectively, on W, TiN, SiN, and SiO2 substrates. By adjusting the vapor-process conditions of both aldehydes, we confirm chemo-selective adsorption on nitride surfaces, resulting in significant growth retardation during subsequent Ru atomic layer deposition. Under optimized conditions for achieving nitride versus oxide selectivity, we successfully demonstrated area-selective atomic layer deposition (AS-ALD) of Ru films on patterned-TiN/SiO2 substrates.

Area-selective atomic layer deposition of Ru thin films by chemo-selective inhibition of alkyl aldehyde molecules on nitride surfaces

Area-selective atomic layer deposition (AS-ALD) on pre-defined areas is of crucial importance nowadays in significantly reducing complexities associated with current top-down fabrication processes. In this work, we report the effects of surface modification using various alkyl aldehyde inhibitors with different chain lengths—hexanal, decanal, and undecanal—on nitride surfaces such as TiN and SiN to achieve AS-ALD. On the basis of density functional theory calculations and experimental analysis, including water contact angle and X-ray photoelectron spectroscopy, it is evident that aldehydes would chemo-selectively react with the –NH2 functional groups present on the nitride surfaces. Then, we further investigate their blocking ability against subsequent Ru ALD, a promising next-generation electrode material. It is worth noting that the Ru deposition thickness decreased by 4–10 nm with the presence of undecanal adsorbed on SiN and TiN substrates. Finally, we successfully demonstrate AS-ALD of Ru thin films over 8 nm on a patterned TiN/SiO2 substrate. These results hold potential for applications in bottom-up nanofabrication techniques for next-generation nanoelectronic applications.

Structural and Optical Properties of Aluminium Nitride Thin Films Fabricated Using Pulsed Laser Deposition and DC Magnetron Sputtering on Various Substrates

Abstract Aluminium nitride thin films were fabricated using pulsed laser deposition and DC magnetron sputtering. Different technological parameters and the effects of different substrates on the optical and structural parameters of AlN samples were studied. An X-ray diffraction study was performed for the layer deposited on the Si3N4 substrate. A high-energy electron diffraction study was also carried out for the layer deposited on a KCl substrate. Transmission spectra of layers on quartz, sapphire, and glass substrates were obtained. An evaluation of the optical band gap of the obtained layers was carried out (Eg form 3.81 to 5.81 eV) and the refractive index was calculated (2.58). The relative density of the film (N1TN-AlN sample) is 1.26 and was calculated using the Lorentz-Lorentz relationship. Layers of aluminium nitride show an amorphous character with a polycrystalline region. It was shown that the properties of AlN films strongly depend on the method, growth conditions, and substrate used.

Quasi-direct Cu–Si3N4 bonding using multi-layered active metal deposition for power-module substrate

The advancement of power modules demands more reliable insulating circuit substrates. Traditional substrates, comprising Cu and Si3N4, are produced using active metal brazing (AMB). However, AMB substrates have reliability concerns owing to electrochemical migration and void formation from brazing filler metals. This study introduces a quasi-direct Cu–Si3N4 bonding technique using a Ti/Al bilayer active metal deposition at the bonding interface. A sputtered Ti/Al bilayer was formed on the Si3N4 surface, then heated and pressurized the sputtered Si3N4 substrate with Cu sheets in vacuum to bond each other without voids or delamination. The Ti/Al layers reacted with Si3N4 and Cu, forming a 300 nm intermediate layer. TEM observations show this layer contains segregated Ti–N and Cu–Al phases, with a good lattice match to Si3N4 and Cu–Al. Temperature-cycling tests on the Cu/Si3N4/Cu substrate revealed delamination caused by increased tensile stress at the periphery of the bonding area due to asymmetrical Cu patterns. This novel quasi-direct Cu–Si3N4 bonding technique addresses issues of electrochemical migration and void formation seen in AMB substrates, offering a reliable bonding interface for power electronic substrates.

Design of metamaterial perfect absorbers in the long-wave infrared region.

We designed a narrow-band metamaterial absorber (NMA) and an ultra-broadband metamaterial perfect absorber (UMPA) based on the impedance matching theory. The narrow-band metamaterial absorber mainly consists of Si3N4 cylinders with Si3N4 and Ti substrates. Numerical analysis shows that the absorption peak of the NMA is about 99.9% and the absorption bandwidth with more than 90% absorption is about 4.8 μm (9.5-14.3 μm). To further extend the absorption bandwidth, an ultra-broadband absorber was designed by integrating a Ti hyperbolic rectangle into the Si3N4 cylinder of the NMA. Numerical analysis shows that the absorption bandwidth of the UMPA is up to 10 μm (7-17 μm) with an average absorption rate of 96.6%. The designed UMPA has polarization insensitive properties with wide-angle absorption characteristics, and the average absorption can reach 85% and 76% in transverse magnetic (TM) and transverse electric (TE) modes, respectively, at 60° oblique incidence. The high absorption and wide band are mainly dominated by localized surface plasmon resonance, Fabry-Perot resonance and inter-resonance interactions. The designed absorber achieves excellent absorption in the long infrared wavelength band, which has potential applications in energy absorption, infrared sensing and other fields.

Copper bonding silicon nitride substrate using atmosphere plasma spray

Silicon nitride (Si3N4) is an excellent engineering ceramic with high strength, fracture toughness, wear resistance, and good chemical and thermal stability. Recently, the enhanced thermal conductivity enables Si3N4 to have potential application prospects in the electronic and orthopedic fields. Metal bonding with Si3N4 is often the key to these applications. Here we report a facile approach for the titanium-activated Cu bonding on Si3N4 substrates using an atmosphere plasma spray (APS) process. With X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) observation, it was shown that the interaction between the pre-bonded Ti (by APS) on Si3N4 promoted the adhesion and high bonding strength of APS Cu on Si3N4. The interfacial structure and phases were characterized, and tensile strength, electrical resistivity, thermal conductivity, and residual stress of Cu bonded Si3N4 were measured accordingly. The APS deposited Cu layer is dense, has a high purity, and is joined firmly with Ti pre-bonded Si3N4 substrate. The maximum tensile strength between Cu and Si3N4 is as high as 89.4 MPa. The Si3N4 substrate bonded with highly dense Cu demonstrates a low surface resistivity of 8.72 × 10−4 Ω∙mm, and high thermal conductivity of 98.12 W/m·K, which shows potential applications in electronic devices.

Highly Sensitive Phototransistors Based on Partially Suspended Monolayer WS2

Two-dimensional (2D) materials have attracted tremendous interests because of various advantages, such as high carrier mobility, favorable band gap, strong light-matter interaction, and flat dangling-bond-free surface. However, the photodetection performance of the pristine monolayer 2D materials is not competitive with that of their bulk counterpart due to the atomic thickness. Here, we demonstrated the direct growth of monolayer WS2 on the Si3N4 substrate by chemical vapor deposition. The porous morphology is formed at the surface of the Si3N4 substrate during the growth process, and therefore, the as-grown WS2 is partially suspended on porous Si3N4. The phototransistor based on as-grown monolayer WS2 exhibits a high responsivity of 1.58 × 105 A/W and a fast response speed of 40 ms. Because of light resonant scattering of the porous Si3N4 substrate, the absorption coefficient of monolayer WS2 is enhanced from finite element analysis. In addition, biaxial tensile strain distribution in the partially suspended WS2 induces a built-in in-plane electric field and less carrier mass from first-principles calculations. Therefore, we attributed the high performance of the phototransistor to the hybrid structure of partially suspended monolayer WS2 on the porous substrate. Our present work paves a way to achieve high-performance monolayer photodetector from substrate morphology engineering.

Substrate-Induced Changes on the Optical Properties of Single-Layer WS2.

Among the most studied semiconducting transition metal dichalcogenides (TMDCs), WS2 showed several advantages in comparison to their counterparts, such as a higher quantum yield, which is an important feature for quantum emission and lasing purposes. We studied transferred monolayers of WS2 on a drilled Si3N4 substrate in order to have insights about on how such heterostructure behaves from the Raman and photoluminescence (PL) measurements point of view. Our experimental findings showed that the Si3N4 substrate influences the optical properties of single-layer WS2. Beyond that, seeking to shed light on the causes of the PL quenching observed experimentally, we developed density functional theory (DFT) based calculations to study the thermodynamic stability of the heterojunction through quantum molecular dynamics (QMD) simulations as well as the electronic alignment of the energy levels in both materials. Our analysis showed that along with strain, a charge transfer mechanism plays an important role for the PL decrease.

Structure-Dependent Electrical Conductance of DNA Origami Nanowires.

Exploring the structural and electrical properties of DNA origami nanowires is an important endeavor for the advancement of DNA nanotechnology and DNA nanoelectronics. Highly conductive DNA origami nanowires are a desirable target for creating low-cost self-assembled nanoelectronic devices and circuits. In this work, the structure-dependent electrical conductance of DNA origami nanowires is investigated. A silicon nitride (Si3 N4 ) on silicon semiconductor chip with gold electrodes was used for collecting electrical conductance measurements of DNA origami nanowires, which are found to be an order of magnitude less electrically resistive on Si3 N4 substrates treated with a monolayer of hexamethyldisilazane (HMDS) (∼1013 ohms) than on native Si3 N4 substrates without HMDS (∼1014 ohms). Atomic force microscopy (AFM) measurements of the height of DNA origami nanowires on mica and Si3 N4 substrates reveal that DNA origami nanowires are ∼1.6 nm taller on HMDS-treated substrates than on the untreated ones indicating that the DNA origami nanowires undergo increased structural deformation when deposited onto untreated substrates, causing a decrease in electrical conductivity. This study highlights the importance of understanding and controlling the interface conditions that affect the structure of DNA and thereby affect the electrical conductance of DNA origami nanowires.

Effect of microstructures on dielectric breakdown strength of sintered reaction‐bonded silicon nitride ceramics

AbstractSilicon nitride (Si3N4) was prepared from silicon by a sintered reaction‐bonded silicon nitride method using yttria and magnesia as sintering additives. Post‐sintering (PS) of nitrided compacts was carried out at 1850°C under a nitrogen pressure of 1 MPa. Effect of PS time on microstructure and dielectric breakdown strength (DBS) of the prepared Si3N4 ceramics was evaluated. The DBS was measured using specimens with four different thicknesses (0.30, 0.20, 0.10, and 0.05 mm) in order to examine the thickness dependence. The porosity of the sintered Si3N4 decreased by prolonging the PS time, and the full density could be achieved at the PS time of over 6 h. After full densification, rod‐like β‐Si3N4 grains grew up, and their maximum grain size increased from 45.1 to 154.7 μm by prolonging the PS time from 6 to 48 h. The DBS of the thick Si3N4 substrates (0.30 mm) showed little variation from 35.4 to 47.0 kV/mm, regardless of the PS time. On the other hand, that of the thin ones (0.05 mm) dramatically decreased from 99.5 to 9.8 kV/mm with increased the PS time from 6 to 48 h. Because the DBS sharply decreased at the thin substrate sintered for longer time in which some large‐elongated grains might span the substrate thickness‐wise throughout, it was inferred that the interface between β‐Si3N4 grains and grain boundary phase/intergranular glassy films might be a path of the dielectric breakdown.

A facile approach towards Wrinkle-Free transfer of 2D-MoS2 films via hydrophilic Si3N4 substrate

Two-dimensional (2D) transition-metal dichalcogenides (TMDs) have been widely explored as next-generation semiconductor materials owing to their attractive electrical and optical properties. Currently, high-performance 2D-TMD-based electronic devices are obtained by transferring growth substrates onto target substrates. In practice, however, transfer-induced wrinkles and structural deformation on the target substrate pose a significant challenge. Herein, we successfully demonstrated a wrinkle-free transfer method that could facilely control the wrinkles of MoS2 thin films on hydrophilic Si3N4 substrates. Owing to the high wettability of the Si3N4 substrate, the residual water droplets between the MoS2 thin film and the target substrate were effectively removed, minimizing unexpected wrinkles and structural deformation. By simply adjusting the wetting properties of the target substrate, the device performance improved to a field-effect mobility of ∼ 0.756 cm2/(V·s), which is six times higher than that of the SiO2 substrate. Furthermore, the standard deviation of the electrical characteristics of the 50 2D-field-effect transistors was reduced by the Si3N4 substrate. In addition, the intrinsic characteristics of the MoS2 FET were evaluated by suppressing the effect of charge trapping through pulsed I-V measurements. Facilely-controlled wrinkles in MoS2 thin films can be used in various electronic devices, sensors, optoelectronic devices, and neuromorphic devices.

Residual stress, microstructure and corrosion behavior in the 316L/Si3N4 joint by multi-layered braze structure-experiments and simulation

In this study, Mo interlayer of different shapes were designed for relieving the residual stress in a Si3N4/316L joint by finite element model simulation. It was found that the Mo interlayer designed by half-cylindrical slotting could reduce the residual stress of Si3N4 substrate in the joint by shifting the maximum residual stress from Si3N4 to the 316L substrate. The formation of Ag based solid solution in the seam could further reduce the maximum residual stress of Si3N4 due to the low yield strength of Ag. Ultimately, the maximum residual stress of Si3N4 in the joint was decreased significantly. Furthermore, the microstructure and corrosion behavior of the Si3N4/316L joint were also studied in detail. When Mo/Ag was inserted into the seam as a composite interlayer, the corrosion resistance of the Si3N4/316L joint was improved by the change in corrosion mechanism from pitting of Cu-rich phase to the uniform corrosion of both 316L and Mo.

Site-specific preparation of plan-view samples with large field of view for atomic resolution STEM and TEM studies of rapidly solidified multi-phase Al Cu thin films

The present work describes application of a method for site-specific plan-view sample preparation for atomic column resolution scanning transmission and transmission electron microscopy (STEM and TEM) from free-standing thin films of multi-phase Al-alloys after laser irradiation induced rapid solidification (RS). The electron-transparent multilayer thin film samples (amorphous Si3N4 substrate plus metal alloy layer) had a total initial thickness of ≈ 130–200 nm. At such large total sample thickness frequently multiple grains of the same or different phases overlap along the electron beam path in the RS microstructures of the alloys. Consequently, accurate atomic resolution images in TEM and STEM mode, and composition sensitive analytical data of the metastable microstructural features presenting in the RS microstructures cannot be obtained with confidence. Using low-energy concentrated Ar ion beam milling, locally thinned regions with thickness of 20–30 nm with large fields of view ≥ (30 μm)2 suitable for high-resolution TEM/STEM studies have been created with micron-scale site-specificity. As example application, atomic scale resolution TEM/STEM imaging has been performed of the banded grain regions of the RS microstructure established in multi-phase AlCu alloy thin films. The sample preparation strategy described here appears to be readily applicable to freestanding thin film specimens in general.

Wettability and Spreading Behavior of Sn–Ti Alloys on Si3N4

The purpose of this study was to investigate the wetting behavior and interfacial reactions of Sn-Ti alloys, which has been widely applied to join ceramics with metals, on Si3N4 substrates. The isothermal wetting process of Sn-xTi alloys (x = 0.5, 1.0, 1.5, 2.0 and 2.5 wt.%) on Si3N4 was systematically studied from 1223 K to 1273 K through sessile drop methods. The microstructures of the interface were characterized by X-ray diffraction (XRD) and microscope (SEM). The active Ti element remarkably enhanced the wettability of Sn-xTi melts on Si3N4 substrates because of the formation of metallic reaction layers (Ti5Si3 and TiN). With the Ti content rising, thicker Ti5Si3 layer formed on the TiN phase inducing a lower equilibrium contact angle. The value of the lowest contact angle was 6°, which was obtained in the Sn-2.0Ti/Si3N4 system at 1273 K. Larger Ti5Si3 grains were found in Sn-2.5Ti melt and a higher final contact angle was obtained. Lower temperature increased the final contact angle and slowed down the spreading rate. The formation of reaction products was calculated thematically, and the spreading kinetics was calculated according to the reaction-driven theory. The spreading behavior of Sn-Ti alloy on Si3N4 ceramic was composed of rapid-spreading stage and sluggish-spreading stage. The calculated activity energy of spreading was 395 kJ/mol. Eventually, the wetting process of Sn-2.0Ti/Si3N4 system was successfully elucidated. These results provide significant guidance information for the brazing between metals and Si3N4 ceramic.

A low-damage copper removal process by femtosecond laser for integrated circuits

To develop a low-damage, low-cost, high-precision copper (Cu) removal process is conducive to promoting the development of integrated circuits in the direction of three-dimensional integration. In this study, a Cu film removal process without damage to the underlying substrate for integrated circuits by femtosecond (fs) laser was proposed. Theoretically, the feasibility of removing Cu film without damaging the substrate by fs-laser was demonstrated by studying the laser energy absorption and coupling, and temperature transient response of Cu/SiC bilayer material under fs-laser irradiation. Experimentally, fs-lasers were used to remove Cu films on SiC, SiO2, and Si3N4 substrates commonly used in integrated circuits. The experimental results show that the fs-laser with suitable fluence can effectively remove the Cu film without damaging the substrate, which is due to the nonlinear absorption of laser fluence by Cu film and the thermal resistance at the metal-nonmetal interface. Moreover, compared with the high-fluence fs-laser, the low-fluence multi-pulse fs-laser is more suitable for the effective removal of Cu film without damage to the substrate. Finally, the application of fs-laser in the preparation of an on-chip filter demonstrates the great potential of fs-laser in the fields of ICs and electronic device processing.

Effect of Ti concentration on the wetting of molten Cu-8.6Zr-xTi alloys on Si3N4 substrate

This paper investigated the wettability of molten Cu-8.6Zr-xTi (x = 0, 10, 15, 20 at.%) alloys on Si3N4 substrate using a modified sessile drop method at 1100 °C. In situ examinations of contact angles, and normalized contact radii indicated liquid Cu and Cu-8.6Zr alloy could not wet Si3N4. Excellent wetting of molten Cu-Zr-Ti on Si3N4 substrate was induced by adding Ti and further the TiN, Ti segregation layer, and Ti-Zr-Si compounds presented at the solid/liquid interface. On the other hand, spreading dynamics were determined mainly by the interaction of molten alloys and solid ceramic at the interface and appeared in two periods, which correspond to the decomposition of Si3N4 and the precipitation of the Ti-nitride reaction layer, respectively. Besides, the adsorption of active element Ti at the interface improved the wettability to some extent.