Interface Reliability Research Articles

Effects of surface treatments for the adhesion improvement between Cu and SiCN in BEOL interconnect

This study focuses on the enhancement of interfacial reliability between Cu interconnects and silicon carbon nitride (SiCN) capping layers in semiconductor packaging structures through pre-deposition surface treatments. We compare three distinct treatments combined with H2 plasma, NH3 plasma, and SiH4 gas inflow, evaluating their effectiveness through quantitative measurement of interfacial adhesion energy using a double cantilever beam (DCB) fracture mechanics test. The results exhibit a remarkable adhesion energy improvement of over 1150 % with the addition of SiH4 gas treatment. Thorough investigations reveal that the mechanism of the exceptional adhesion enhancement is attributed to unique chemical bonding and fracture behavior. In other words, Si atoms in the SiH4 gas treatment incorporate onto Cu surfaces with specific crystallographic orientations, resulting in significantly stronger Cu–Si bonding in selective regions compared to other bondings. Moreover, the crystallographic-orientation-dependent bonding characteristic induces crack kinking at grain boundaries, dissipating the crack propagation energy. This work will provide crucial insight into enhancing the interfacial reliability and manufacturing yield of semiconductor devices.

Effects of Dielectric Curing Temperature on the Interfacial Reliability of Cu/Ti/PBO for FOWLP Applications

Effects of Dielectric Curing Temperature on the Interfacial Reliability of Cu/Ti/PBO for FOWLP Applications

Influence of samarium modification on the phase-change performance and phase structure of tin antimonide

This work presents the optimization of the crystallization behavior and reliability of Sn15Sb85 thin films by doping Sm element. The phase transition behaviors induced by thermal were investigated by in situ resistance measurement. With the addition of Sm element, Sn15Sb85 film exhibits the superior crystallization temperature (232 °C) and data conservation (172.32 °C for 10 years), larger activation energy of crystallization (4.91 eV) and crystalline resistance (∼103 Ω), which contributes to the increased thermal stability of the amorphous state and decrease in the programming energy. The Sm-doping can broaden the energy band gap from 0.55 to 1.07 eV. The amorphous Sm and Sn compositions could retard grain growth and refine grain size from 21.13 to 11.13 nm, combining with x-ray diffraction and x-ray photoelectron spectroscopy. The surface morphology of Sn15Sb85 film becomes smoother after Sm doping as determined by atomic force microscopy images, resulting in the improved interfacial reliability. Phase change memory devices based on Sm0.095(Sn15Sb85)0.905 films can successfully achieve the complete SET and RESET reversible operation process with high operating speed (200 ns) and low power consumption (1.6 × 10−10 J). The results suggest that doping the proper concentration of Sm element will be an effectual solution to adapt and optimize the crystallization properties of Sn15Sb85 phase change material.

Anti-CMAS corrosion mechanism of Al2O3 pore sealing and laser remelting on thermal barrier coatings

The sol-dip-coating method and surface laser remelting technology are applied to form an Al2O3 layer on a YSZ coating surface to effectively block the environmental sediment CMAS. The behaviour and mechanism for CMAS corrosion of the coating are investigated, and the interfacial reliability of the coating and matrix is calculated by using the Monte Carlo method. The bonding force between the Al2O3 sol and YSZ coating can be effectively improved by laser surface treatment. Samples subjected to a laser pretreatment and posttreatment (YL-AL) of the YSZ coating are found to show the best interfacial bonding strength between Al2O3 and YSZ. Furthermore, the YL-AL sample shows a higher CMAS resistance than the laser posttreatment (Y-AL) samples, which effectively combines the chemical resistance of Al2O3 to CMAS and the physical resistance of the laser re-melted densification layer against CMAS penetration.

A Conceptual Strategy toward High-Reliability Metal-Thermoplastic Hybrid Structures Based on a Covalent-Bonding Mechanism.

Metal-thermoplastic hybrid structures have proven their effectiveness to achieve lightweight design concepts in both primary and secondary structural components of advanced aircraft. However, the drastic differences in physical and chemical properties between metal and thermoplastic make it challenging to fabricate high-reliability hybrid structures. Here, a simple and universal strategy to obtain strong hybrid structures thermoplastics is reported by regulating the bonding behavior at metal/thermoplastic interfaces. To achieve such, we first researched and uncovered the bonding mechanism at metal/thermoplastic interfaces by experimental methods and density functional theory (DFT) calculations. The results suggest that the interfacial covalency, which is formed due to the interfacial reaction between high-electronegativity elements of thermoplastics and metallic elements at metal surfaces, dominates the interfacial bonding interaction of metal-thermoplastic hybrid structures. The differences in electronegativity and atomic size between bonding atoms influence the covalent-bond strength and finally control the interfacial reliability of hybrid structures. Based on our covalent-bonding mechanism, the carboxyl functional group (COOH) is specifically grafted on polyetheretherketone (PEEK) by plasma polymerization to increase the density and strength of interfacial covalency and thus fabricate high-reliability hybrid structures between PEEK and A6061-T6 aluminum alloy. Current work provides an in-depth understanding of the bonding mechanism at metal-thermoplastics interfaces, which opens a fascinating direction toward high-reliability metal-thermoplastic hybrid structures.

Modification of NASICON Electrolyte and Its Application in Real Na-Ion Cells

The low ionic conductivity of solid-state electrolytes (SSEs) and the inferior interfacial reliability between SSEs and solid-state electrodes are two urgent challenges hindering the application of solid-state sodium batteries (SSSBs). Herein, sodium (Na) super ionic conductor (NASICON)-type SSEs with a nominal composition of Na3+2xZr2–xMgxSi2PO12 were synthesized using a facile two-step solid-state method, among which Na3.3Zr1.85Mg0.15Si2PO12 (x = 0.15, NZSP-Mg0.15) showed the highest ionic conductivity of 3.54 mS∙cm−1 at 25 °C. By means of a thorough investigation, it was verified that the composition of the grain boundary plays a crucial role in determining the total ionic conductivity of NASICON. Furthermore, due to a lack of examination in the literature regarding whether NASICON can provide enough anodic electrochemical stability to enable high-voltage SSSBs, we first adopted a high-voltage Na3(VOPO4)2F (NVOPF) cathode to verify its compatibility with the optimized NZSP-Mg0.15 SSE. By comparing the electrochemical performance of cells with different configurations (low-voltage cathode vs high-voltage cathode, liquid electrolytes vs SSEs), along with an X-ray photoelectron spectroscopy evaluation of the after-cycled NZSP-Mg0.15, it was demonstrated that the NASICON SSEs are not stable enough under high voltage, suggesting the importance of investigating the interface between the NASICON SSEs and high-voltage cathodes. Furthermore, by coating NZSP-Mg0.15 NASICON powder onto a polyethylene (PE) separator ([email protected]), a 2.42 A∙h non-aqueous Na-ion cell of carbon|[email protected]|NaNi2/9Cu1/9Fe1/3Mn1/3O2 was found to deliver an excellent cycling performance with an 88% capacity retention after 2000 cycles, thereby demonstrating the high reliability of SSEs with NASICON-coated separator.

A novel thermal-mechanical model and the characteristics of interfacial stress in the laminated structure for flexible electronics

Flexible electronics have attracted rapidly growing interest owing to their great potential utility in numerous fundamental and emerging fields. However, there are urgent issues that remain as pending challenges in the interfacial stress and resulting failures of flexible electronics, especially for heterogeneous laminates of hard films adhered to soft polymer substrates under thermal and mechanical loads. This study focuses on the interfacial stress of a representative laminated structure, that is, the Si film is adhesively bonded to soft polydimethylsiloxane with a plastic polyethylene terephthalate substrate. An novel thermal-mechanical coupling model for this flexible structure is established in this paper, which presents the essential characteristics of interfacial shear stress. In addition, under thermal and mechanical loads, a typical case is investigated by combining an analytical solution with numerical results using the differential quadrature method. Furthermore, thermal and mechanical loads, material and geometry parameters are quantitatively explored for their influences on the interfacial shear stress. Targeted strategies for decreasing stress are also suggested. In conclusion, the thermal-mechanical model and application case analyses contribute to enhancing the design of interfacial reliability for flexible laminated structures.

Enhancing Interfacial Reliability of Metal–Thermoplastic Hybrid Joints via Adding Carbon Fiber and Adjusting Welding Heat Input

Interfacial structures govern the reliability of metal-thermoplastic hybrid joints used in the aerospace industry. The current work demonstrated by experimental methods and density functional theory (DFT) calculations that introduction of carbon fibers (CFs) enhanced the mechanical properties and weakened the corrosion resistance of polyamide 6 (PA6)/A6061-T6 (6061) joints. The bonding strength of typical PA6/6061 joints was increased by 33.70% with the introduction of CF. However, the differences in intrinsic work functions of the CF and various phases within 6061 led to the formation of serious cracks at CFRPA6/6061 interfaces and heavy corrosion on 6061 surfaces, corresponding to the decreased corrosion resistance of PA6/6061 joints. Herein, we present a potential solution to adjust the welding heat input to enhance metal/thermoplastic interfacial reliability. With a rotation speed of 400 mm/min during friction lap joining (FLJ), the fabricated CFRPA6/6061 joint could achieve a strong interface with high strength (bonding strength = 1.730 kN) and relative corrosion resistance (corrosion rate < 0.1 mm/a). The results provide a reliable explanation for the effect of CF on mechanical properties and corrosion resistance of CFRPA6/6061 joints. Furthermore, the knowledge gained in this work will benefit future research in the optimization of processes to improve the reliability of metal-thermoplastic hybrid structures.

Enhanced Interfacial Reliability and Mechanical Strength of CoSb3-Based Thermoelectric Joints with Rationally Designed Diffusion Barrier Materials of Ti-Based Alloys.

To achieve high-performance thermoelectric (TE) devices, constructing a good interfacial connection between TE materials and electrodes is as important as having high figure-of-merit TE materials. Although CoSb3-based TE devices have received great attention for power generation recently, the limited long-term service stability is the main obstruct for their applications. In this work, we have prepared two kinds of Ti-based alloys (Ti83.7Al10.7Si5.6 and Ti74Ni26) as the diffusion barrier layer of CoSb3-based TE joints by the spark plasma sintering method and have systematically investigated their interfacial behaviors during the aging process. The performances of contact resistivity and mechanical strength for Ti74Ni26/Yb0.4Co3.8Fe0.2Sb12 TE joints are good before aging treatment but gradually deteriorate during the aging process, which should be ascribed to the phase-transition-induced negative thermal expansion in Ti-Ni alloys. On the other hand, Ti83.7Al10.7Si5.6/Yb0.4Co3.8Fe0.2Sb12 TE joints show both low contact resistivity (<10 μΩ·cm2) and high mechanical strength (>20 MPa) before and after 16-day aging at 500 °C, which is originated from the matching of the coefficient of thermal expansion (CTE) and the formation of network structures in Ti-Al-Si alloys. We have also prepared an eight-couple TE module of p-Ge0.9Sb0.1TeB0.01/n-Yb0.4Co3.8Fe0.2Sb12 and have measured its corresponding device performance. Our work has demonstrated that the matched CTE and network structures in the Ti-Al-Si alloy are key to obtain high-performance CoSb3-based TE joints for long-term service.

The interfacial reliability of through-glass vias for 2.5D integrated circuits

PurposeGlass is a promising interposer substrate for 2.5 D integration; yet detailed analysis of the interfacial reliability of through-glass vias (TGVs) has been lacking. The purpose of this paper is to investigate the design and material factors responsible for the interfacial delamination in TGVs and identify methods to improve reliability.Design/methodology/approachThe interfacial reliability of TGVs is studied both analytically and numerically. An analytical solution is presented to show the dependence of the energy release rate (ERR) for interfacial delamination on the via design and the thermal mismatch strain. Then, finite element analysis (FEA) is used to investigate the influence of detailed design and material factors, including the pitch distance, via aspect ratio, via geometry and the glass and via materials, on the susceptibility to interfacial delamination.FindingsERR for interfacial delamination is directly proportional to the via diameter and the thermal mismatch strain. Thinner wafers with smaller aspect ratios show larger ERRs. Changing the via geometry from a fully filled via to an annular via leads to lower ERR. FEA results also show that certain material combinations have lower thermal mismatch strains, thus less prone to delamination.Practical implicationsThe results and approach presented in this paper can guide the design and development of more reliable 2.5 D glass interposers.Originality/valueThis paper represents the first attempt to comprehensively evaluate the impact of design and material selection on the interfacial reliability of TGVs.

The effect of finish layer on the interfacial cracking failure of Au[sbnd]Si bonding

The interfacial reliability of Au-Si bonding between Cu/MoCu/Cu (named as CPC) substrate and silicon chip is analyzed. The results of optical microscopy (OM) and conformal laser scanning microscopy (CLSM) revealed that the Au layer of the cracked sample has small roughness without any patterns on it. Furthermore, the results of scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD) and electron probe micro-analysis (EPMA) demonstrated that the void or crack initiated at the interface between a thin intermetallic compound (IMC) layer and the NiCo layer. It showed that the cracked sample had higher Ni content within NiCo layer and smaller size of Au layer. Moreover, the IMCs were characterized using transmission electron microscopy (TEM), which were identified as bulk-like dispersed NiSi2 and a thin continuous (Ni,Co)2Si layer. Based on the experimental results, the failure mechanism of Au-Si bonding is concluded coming from the unbalanced diffusion rate between Ni and Si during interfacial reaction. Higher Ni content of NiCo layer and small grain size of Au and (Ni,Co)2Si layer accelerate the diffusion of Ni, which also promotes the growth of interfacial Ni-contained IMC. As a result, the vacancy flows diffuse inversely towards the interface and form voids along the interface, which leads to the final crack failure.

Al-Si Alloy as a Diffusion Barrier for GeTe-Based Thermoelectric Legs with High Interfacial Reliability and Mechanical Strength.

To build high-performance thermoelectric (TE) devices for power generation, a suitable diffusion-barrier layer between the electrodes and the TE materials in a TE device is generally required for achieving good interfacial connection with high reliability, high mechanical strength but low electrical and thermal contact resistivities. GeTe-based materials have attracted great attention recently due to their high TE performance in the mid-temperature range, but studies on their TE devices are still limited. Here, we selected the Al66Si34 alloy as a diffusion barrier for GeTe-based TE legs based on the matching test of the coefficient of thermal expansion. The good connection between Al66Si34 and Ge0.9Sb0.1TeB0.01 is realized by the interfacial reaction, where the randomly distributed Al2Te3 and Ge precipitates are formed at the interface of the joint. The as-prepared interfacial electrical contact resistivity can be as low as 20.7 μΩ·cm2 and only slightly increases to 26.1 μΩ·cm2 after 16 days of aging at 500 °C. Moreover, the shear strength of the joints can be as high as 26.6 MPa and unexpectedly increases to 41.7 MPa after 16 days of aging. The thickness of the reaction layer tends to be stabilized after 8 days of aging and nearly does not change after further aging to 16 days, which may be ascribed to the drag effect from Si and the secondary Ge phases. These results demonstrate the great potential of the Al-Si alloy as a diffusion barrier for GeTe-based TE devices with high performance.

Rate dependent shear debonding between a highly stretchable elastomer and a rigid substrate: Delayed debonding and pre-stretch effect

In this paper, the interfacial shear debonding characteristics and mechanism between a highly stretchable acrylic tape and a rigid polycarbonate strip are explored systematically with three types of in-plane loading. An effective approach is proposed based on the findings to improve interfacial adhesive strength. The debonding energy solely dissipated by breaking the interfacial bonds is found to be closely related to the loading rate, which can be explained by the Chaudhury’s model. Rate dependent delayed debonding is repeatedly observed under various stretch levels. The threshold level of the driving force of delayed debonding is correlated with the intrinsic fracture energy of the interfacial molecular chains and expected to be rate independent. Shear debonding is significantly affected by the pre-existed defects at the interfacial crack front. An effective and easy-to-operate cyclic pre-stretch approach with a moderate amplitude and rate is proposed, which is capable of improving the interfacial reliability by diminishing the pre-existed defects. A quantitative model is also constructed to characterize the pre-stretch effect on the interfacial adhesion.

Interfacial Stress Analysis on Skutterudite-based Thermoelectric Joints under Service Conditions

In thermoelectric (TE) devices, the interfacial reliability greatly influenced devices’ durability and power output. For skutterudites (SKD) devices, TE legs and electrodes are bonded together with diffusion barrier layer (DBL). At elevated temperatures, DBL react with SKD matrix or electrode to generate complex interfacial microstructures, which often accompanies evolutions of the thermal, electrical and mechanical properties at the interfaces. In this work, a finite element model containing the interfacial microstructure characteristics based on the experimental results was built to analyze the interfacial stress state in the skutterudite-based TE joints. A single-layer model was applied to screen out the most important parameters of the coefficient of thermal expansion ( CTE ) and the modulus of DBL on the first principle stress. The multilayer model considering the interfacial microstructures evolution was built to quantitively simulate the stress state of the TE joints at different aging temperatures and time. The simulation results show that the reactive CoSb2 layer is the weakest layer in both SKD/Nb and SKD/Zr joints. And by prolonging the aging time, the thickness of the reaction layer continuously increased, leading to a significant raising of the interfacial stress. The tensile testing results of the SKD/Nb joints match the simulation results well, consolidating accuracy and feasibility of this multilayer model. This study provides an important guidance on the design of DBL to improve the TE joints’ mechanical reliability, and a common method to precisely simulate the stress condition in other coating systems.

Laser-Based Surface Modification of Microstructure for Carbon Fiber-Reinforced Plastics

Bonding repair is a powerful feature of carbon fiber-reinforced plastics (CFRP). Based on the theory of interface bonding, the interface adhesion strength and reliability of the CFRP structure will be directly affected by the microscopic features of the CFRP surface, including the microstructure, physical, and chemical characteristics. In this paper, laser-based surface modification was compared to Peel-ply, grinding, and polishing to comparatively evaluate the surface microstructure of CFRP. The surface microstructure, morphology, fiber damage, height and space parameters were investigated by scanning electron microscopy (SEM) and laser confocal microscopy (LCM). Relative to the conventional grinding process, laser modification of the CFRP surface can result in more uniform resin removal and better processing control and repeatability. This decreases the adverse impact of surface fiber fractures and secondary damage. The surface properties were significantly optimized, which has been reflected such things as the obvious improvement of surface roughness, microstructure uniformity, and actual area. The improved surface microstructure based on laser modification is more conducive to interface bonding of CFRP structure repair. This can enhance the interfacial adhesion strength and reliability of repair.

High-temperature reliability of low-temperature and pressureless micron Ag sintered joints for die attachment in high-power device

Micron Ag paste had a more affordable price, feasible large-scale synthesis, and longer storage life compared to nano Ag paste, thus it attracts much industrial interest for die attachment of high-power devices. However, the previous studies of high-temperature reliability were mainly focused on nano Ag joints, the research about reliability of micron Ag joints, especially low-temperature and pressureless, was very limited. Therefore, we evaluated high-temperature stability of low-temperature and pressureless micron Ag joint, involving in the changes of mechanical behaviors, evolution of microstructure and interfacial reliability. The average joint strength of micron Ag joints was independent of aging time and kept approximately 35 MPa after aging for 1000 h. The fracture of the micron joint was dominated by the ductile deformation of Ag grains during the fracture process. On the other hand, the microstructure of porous structure evolved greatly during aging process. Ag grains were oriented randomly before and after aging process, but the Ag grains increased slightly from 827.2 nm initially to 1178.4 nm after 1000 h aging. Meanwhile, the pores size in porous structure increased, the number decreased significantly, and the porosity also decreased slightly. Moreover, the barrier layers at interfaces of micron Ag joint remained stable and reliable during aging at 250 °C. The results would promote the large-scale application of the commercially available micron Ag paste in high-power devices.

Effects of Zn and Ga Additions to Suppress PdSn4 Growth at a Solder/Pd Interface Under Current Stressing

PdSn4 is the major phase formed in the interfacial systems of Pd with lead-free solders. In this study, we examined the interfacial behaviors of the Sn/Pd/Sn system under current stressing of 5000 A/cm2 at 180°C. The results revealed that the electromigration effect on the PdSn4 was insignificant. However, the PdSn4 growth was very fast, similar to that without current stressing. The thickness of the PdSn4 layer was ∼44 μm after only 6 h of current stressing, and further increased to be ∼83 μm after a 24-h test. The PdSn4 phase had a superior electromigration-resistance, but the fast growth was a major concern for the interfacial reliability of the solder joints. To suppress the PdSn4 growth, minor amounts of Zn or Ga were added into the Sn-based solder to investigate the solder/Pd couples under current stressing. Remarkably, only minor 0.5 wt.%Zn addition effectively inhibited the PdSn4 growth under current stressing. After 6 h of current stressing, the thickness of the PdSn4 layer was reduced to ∼17 μm. In addition, minor Ga addition had a similar inhibiting effect. In the Sn-0.5 wt.%Ga/Pd couple, the PdSn4 layer was only ∼12 μm thick even after current stressing of 24 h. The inhibiting effects of Zn and Ga on the PdSn4 growth under current stressing and the related possible reasons are further discussed.

Failure Mechanisms of SAC/Fe-Ni Solder Joints During Thermal Cycling

Thermal cycling tests have been conducted on Sn-Ag-Cu/Fe-xNi (x = 73 wt.% or 45 wt.%) and Sn-Ag-Cu/Cu solder joints according to the Joint Electron Device Engineering Council industrial standard to study their interfacial reliability under thermal stress. The interfacial intermetallic compounds formed for solder joints on Cu, Fe-73Ni, and Fe-45Ni were 4.5 μm, 1.7 μm, and 1.4 μm thick, respectively, after 3000 cycles, demonstrating excellent diffusion barrier effect of Fe-Ni under bump metallization (UBM). Also, two deformation modes, viz. solder extrusion and fatigue crack formation, were observed by scanning electron microscopy and three-dimensional x-ray microscopy. Solder extrusion dominated for solder joints on Cu, while fatigue cracks dominated for solder joints on Fe-45Ni and both modes were detected for those on Fe-73Ni. Solder joints on Fe-Ni presented inferior reliability during thermal cycling compared with those on Cu, with characteristic lifetime of 3441 h, 3190 h, and 1247 h for Cu, Fe-73Ni, and Fe-45Ni UBM, respectively. This degradation of the interfacial reliability for solder joints on Fe-Ni is attributed to the mismatch in coefficient of thermal expansion (CTE) at interconnection level. The CTE mismatch at microstructure level was also analyzed by electron backscatter diffraction for clearer identification of recrystallization-related deformation mechanisms.

A superior interfacial reliability of Fe–Ni UBM during high temperature storage

Ball shear test was conducted on the SnAgCu/Fe–Ni solder joints, as well as SnAgCu/Cu for comparison after reflow and 150 °C high temperature storage following the industrial JEDEC standards. According to microstructural observation, Fe–Ni UBMs show better diffusion barrier effect than Cu UBM, which form very thin FeSn2 or FeSn2+(Cu,Ni)6Sn5 layers at the interface without any Kirkendall voids. With such thin IMC layers, the shear strengths of Fe–Ni solder joints were comparable to Cu solder joints, which are in the range of 6.3–6.4 mg/μm2 after reflow and then fall into 4.7–5.1 mg/μm2 after 1000 h storage. Statistic observations revealed four kinds of fracture mode among failed solder joints, which are ductile fracture, brittle fracture, UBM fracture and pad lift respectively. The UBM fracture is the most common failure mode for Cu solder joint due to the fast consumption and low mechanical strength of Cu UBM, while the ductile failure takes the majority for Fe–Ni UBMs although it gradually turned into brittle fracture later as the aging time increased. The related mechanism of fracture behavior was also discussed concerning the physical properties of interfacial IMCs. Combining the low IMC growth rate, the comparable shear strength and the ductile fracture mode, Fe–45Ni UBM is superior to Cu UBM on the interfacial reliability of high temperature storage.

Effect of Temperature/Humidity Treatment on Interfacial Reliability on Screen-Printed Ag / Polyimide for Advanced Embedded Packaging Technologies

Abstract The effect of temperature/humidity treatment conditions on the interfacial adhesion energy between a screen printed Ag film and a polyimide substrate was evaluated by using a 90° peel test. The measured peel strength values decrease from 254.7 N/m to 59.3 N/m after the temperature/humidity treatment at 85°CC/85% relative humidity for 500 h. X-ray photoelectron spectroscopy analysis of the peeled surfaces indicates that peeling occurs cohesively inside of the polyimide, which is closely related to both the decrease in the interfacial adhesion energy and the polyimide degradation due to weak boundary layer formation.