Hybrid Bond Research Articles

(Invited) Hybrid Bonding-Based Interconnects: A Status on the Last Robustness and Reliability Achievements

I. INTRODUCTION and BACKGROUND 3D integration technologies have emerged less than 10 years ago as viable solutions for meeting IC requirements such as higher performance, increased functionality, lower power consumption, and a smaller footprint. Some examples of 3D integration in products are CMOS Image Sensors (CIS), memories and interposers. Through-Silicon-Vias (TSVs) are integrated in most of these products, because they allow die-level assembly, and simplify some aspects of test and packaging. However, TSVs disadvantage is the silicon device keep out zones combined with a Cu pillar pitch typically limited to ~40 µm. For some applications, such as CMOS image sensors and memories, smaller pitches (< 10 µm) are required for the vertical die-to-die connections; direct hybrid bonding (HB) is the solution of interest. While the first HB products are put on the market [1] few detailed studies are published from the robustness/reliability point of view. This paper reviews the robustness/reliability achievements and include previously published data related to the HB module (Wafer-to-Wafer [W2W] or Die-to-Wafer [D2W]). II. RESULTS Compared to standard microelectronics processes, the main difference of 3D integration consists in the addition of a wafer-bonding step. Due to the bonding tool alignment accuracy, from 200 nm to 1 µm respectively for W2W and D2W, misalignment could lead to an electrical yield loss. W2W-based studies demonstrated 100 %-yield [2, 3] where D2W ones still show lower yield (>90 %) [4] mainly due to more recent developments.Silicon dioxide can be hydrophilic, this tends to highlight a potential risk of moisture sensitivity of the HB module. By means of uHAST, Beillard and Gambino did not evidence any issue [3, 5].Because different materials are assembled, thermomechanical stress issue could arise. ST/CEA-LETI works demonstrated [2, 6] no particular impact at 7.2 and 1.44 µm-interconnect pitches after thermal cycling tests. For larger pitches, Gambino and Gao reached a similar conclusion [3, 7].Electromigration (EM)-induced degradation is another potential reliability issue. As demonstrated by ST/CEA-LETI [8], for a pitch of 7.2 µm, HB integration is immune to EM whatever the electron flow. The failure always occurs in the BEoL layers. For a smaller pitch (3.24 µm), IMEC highlights a potential risk to the HB module itself [9].Cu diffusion in silicon and silicon dioxide is a well-known issue in microelectronics and is solved by using diffusion barriers (TaN/Ta, Ti/TiN...). Despite the lack of a diffusion barrier at the bonding interface in their integration, ST/CEA-LETI [10, 11] demonstrated by electrical and chemical characterization (TVS/BTS, ToF-SIMS/TEM-EELS) that no copper diffusion is nevertheless detectable. Gambino and Kagawa, with different integrations, reached the same conclusion [3, 12].To conclude, in the light of the published works, even if HB module could raise specific robustness/reliability issues, all the lights are green for mass production with micrometric pitches, which is consistent with the fact that this approach, at these pitches, is found in some products [1]. On the contrary, for sub-micrometric pitches some questions remain topical (IMD reliability, Cu diffusion, electromigration). Acknowledgment This work was supported by the French National Research Agency (ANR) under the ”Investissements d’avenir” programs: ANR 10-AIRT-0005 (IRT NANO-ELEC).

On the fatigue properties of a third generation aluminium-steel butt weld made by Hybrid Metal Extrusion & Bonding (HYB)

The present investigation is concerned with the high-cycle axial fatigue behaviour of a third generation Al-steel butt weld made by Hybrid Metal Extrusion & Bonding (HYB). In this particular weld, metallurgical bonding is achieved by a combination of microscale mechanical interlocking and intermetallic compound (IMC) formation, where the IMC layer is in the sub-micrometre range (<1µm). During high-cycle axial fatigue testing this microstructure provides a high intrinsic resistance against interfacial cracking. In the as-welded condition, fatigue fracture typically initiates at the weld toe on the aluminium side of the joint due to the unfavourable effect of having a geometrical stress riser localised inside the soft heat-affected zone. Since the interfacial bond strength is not a limiting factor, the fatigue properties of the Al-steel HYB butt weld are seen to fully match those of corresponding Al-Al weldments produced by gas metal arc welding, laser beam welding and friction stir welding.

State-of-the-Art and Outlooks of Chiplets Heterogeneous Integration and Hybrid Bonding

AbstractIn this study, the recent advances and trends of chip-let design and heterogeneous integration packaging will be investigated. Emphasis is placed on the definition, kinds, advantages and disadvantages, lateral interconnects, and examples of chiplet design and heterogeneous integration packaging. Also, emphasis is placed on the fundamental and examples of hybrid bonding.

Impact of Bonding Sequence on Contact Resistance in Hybrid Bonding of Via-middle TSV Wafer

Abstract This study examines the impact of the bonding sequence on the contact resistance in the hybrid bonding of a via-middle Cu though-silicon via (TSV) wafer. Hybrid bonding was performed at room temperature via a surface-activated bonding method using an ultrathin Si film. Comparative study of various bonding sequences revealed that the (a) cleaning of the target Si, via-middle TSV, and Cu electrode wafers with an Ar fast atom beam (FAB), (b) transferring of the Cu electrode wafer into another chamber during cleaning of the via-middle TSV wafer, and (c) transferring of the via-middle TSV wafer to another chamber while cleaning the Cu electrode wafer were all effective in decreasing the oxygen atoms in the bonding interface (amorphous Si layer) and reducing the contact resistances between the TSVs and Cu electrodes.

State-of-the-Art and Outlooks of Chiplets Heterogeneous Integration and Hybrid Bonding

Abstract In this study, the recent advances and trends of chiplet design and heterogeneous integration packaging will be investigated. Emphasis is placed on the definition, kinds, advantages and disadvantages, lateral interconnects, and examples of chiplet design and heterogeneous integration packaging. Also, emphasis is placed on the fundamental and examples of hybrid bonding.

Corrosion behavior and interfacial conductivity of amorphous hydrogenated carbon and titanium carbide composite (a-C: H/TiC) films prepared on titanium bipolar plates in PEMFCs

In this work, amorphous hydrogenated carbon and titanium carbide composite (a-C: H/TiC) films are deposited on titanium bipolar plates which are used in proton exchange membrane fuel cells (PEMFCs). It was fabricated by high power pulsed magnetron sputtering (HiPIMS) with TiN and TiCN transition layers. The microstructure results indicated that the titanium element was introduced in the films with a form of titanium carbide, and the increasing ID/IG values imply the graphitization of films. Amorphous carbon with a large content of sp2 hybrid bonds leads to an excellent conductivity of 1.6 mΩ·cm2 at 1.4 MPa and improves the corrosion resistance by inhibiting the growth of columnar crystal. In addition, a number of sp2-riched clusters on the surface enhance the hydrophobicity of the film. The a-C: H/TiC films prepared in this work significantly improved the hydrophobicity, corrosion resistance and interfacial conductivity of titanium bipolar plates, showing a great potential for applications in PEMFCs.

Advancement of Chip Stacking Architectures and Interconnect Technologies for Image Sensors

Abstract Numerous technology breakthroughs have been made in image sensor development in the past two decades. Image sensors have evolved into a technology platform to support many applications. Their successful implementation in mobile devices has accelerated market demand and established a business platform to propel continuous innovation and performance improvement extending to surveillance, medical, and automotive industries. This overview briefs the general camera module and the crucial technology elements of chip stacking architectures and advanced interconnect technologies. This study will also examine the role of pixel electronics in determining the chip stacking architecture and interconnect technology of choice. It is conducted by examining a few examples of CMOS image sensors (CIS) for different functions such as visible light detection, single photon avalanche photodiode (SPAD) for low light detection, rolling shutter, and global shutter, and depth sensing and light detection and ranging (LiDAR). Performance attributes of different architectures of chip stacking are overviewed. Direct bonding followed by Via-last through silicon via (Via-last TSV) and hybrid bonding (HB) technologies are identified as newer and favorable chip-to-chip interconnect technologies for image sensor chip stacking. The state-of-the-art ultrahigh-density interconnect manufacturability is also highlighted.

Revealing the Al/L12-Al3Zr inter-facial properties: Insights from first-principles calculations

To uncover the mechanical performance and micro-structure of Al/L12-Al3Zr interface through density functional theory, four interface models are investigated considering two different terminations of L12-Al3Zr surfaces along the [001] direction. Results indicated stacking sequence and atom type between two phases influences the mechanical performance of the interface quite well. The interface consisting of four Al atom-terminated Al(001) slab as well as one Al and four Zr atom-terminated L12-Al3Zr(001) slab not only has relatively even charge distribution due to the same atomic arrangement as L12-Al3Zr bulk, but also enjoys the strong hybrid bonds between inter-facial Al and Zr atoms, gaining the best performer in the tensile test. However, it's the different situation for the model constructed by four Al-terminated Al(001) slab and four Al-terminated L12-Al3Zr(001) slab, the poorest performer. As for the other two interface models with the similar fracture energy and peak stress, one of them, though held together just through the relatively weak bonds of inter-facial Al, has the advantage of evenly-located inter-facial atoms which results in the even charge distribution, for the same atomic arrangement as Al bulk. The other, the inter-facial atoms of which are distributed unevenly, gets the benefit of the strong hybridization of inter-facial atoms.

Formation of metal–semiconductor nanowire heterojunctions by nanosecond laser irradiation

Laser nano-joining has emerged as a preferred technique for better device performance as it can result in stronger mechanical contacts and enhance the electrical properties between nanocomponents. It is often used to bond metallic nanostructures, but there is little information available on the applicability of the corresponding processes for creating hybrid bonds between metal and semiconductor nanomaterials. In this article, we show that Nd:YAG nanosecond (ns) laser irradiation is an effective tool for use in the nano-joining of metal–semiconductor nanowire (NW) combinations. We show that photothermal, electron–hole pair creation and plasmonic effects combine to facilitate nano-joining with Nd:YAG ns laser radiation, producing similar interfacial structures to those occurring under femtosecond laser irradiation. We find that Nd:YAG laser irradiation is effective in the production of bonds between Ag–TiO2 and Ag–CuO NW structures but that the detailed mechanism involved in the creation of these bonds depends on the bandgap energy of the semiconductor NW. Direct heating of the semiconductor through photoexcitation of excitons and electron transfer to the conduction band is significant in the Nd:YAG laser nano-joining of low bandgap materials such as CuO. Coupling of surface plasmon resonance energy to electrical carriers in the semiconductor NW at the Ag-semiconductor interface is found to be important in all hybrid systems, including those involving a wide bandgap material such as TiO2. Since the Nd:YAG ns laser is widely available, these results suggest that nano-joining of heterogeneous materials with ns laser pulses is a practical alternative to joining with ultrashort laser radiation.

Computational Intelligence-Based Prognosis for Hybrid Mechatronic System Using Improved Wiener Process

In this article, a fast krill herd algorithm is developed for prognosis of hybrid mechatronic system using the improved Wiener degradation process. First, the diagnostic hybrid bond graph is used to model the hybrid mechatronic system and derive global analytical redundancy relations. Based on the global analytical redundancy relations, the fault signature matrix and mode change signature matrix for fault and mode change isolation can be obtained. Second, in order to determine the true faults from the suspected fault candidates after fault isolation, a fault estimation method based on adaptive square root cubature Kalman filter is proposed when the noise distributions are unknown. Then, the improved Wiener process incorporating nonlinear term is developed to build the degradation model of incipient fault based on the fault estimation results. For prognosis, the fast krill herd algorithm is proposed to estimate unknown degradation model coefficients. After that, the probability density function of remaining useful life is derived using the identified degradation model. Finally, the proposed methods are validated by simulations.

Mechanism and Process Window Study for Die-to-Wafer (D2W) Hybrid Bonding

Room temperature hybrid bonding is a good candidate to replace thermal compression bonding due to its better resistance to Cu oxidation and its capability for large die integration. However, the bonding mechanism with Cu thickness non-uniformity and real dishing conditions has not yet been fully understood. To study the mechanism and to explore the window of annealing temperature for the void-free interface, finite element analysis (FEA) and auxiliary experiments with real process issues have been conducted. A Cu thickness variation of 6.6% across the whole wafer after electroplating causes a metal dishing between 4 and 16 nm during chemical mechanical planarization. The critical stress (78.1 MPa) of dielectric material gives the upper boundary of temperature, and the complete contact of metal limits the lower boundary for our FEA models. The window for the annealing temperature is then simulated to be within a range between 295 °C and 302 °C. This is the first time that FEA with a non-uniform process input has been implemented to generate a process window of die-to-wafer (D2W) hybrid bonding for real world application. This paper provides a deep understanding and practical guidance for D2W hybrid bonding.

Construction of the Fe3+-O-Mn3+/2+ hybrid bonds on the surface of porous silica as active centers for efficient heterogeneous catalytic ozonation

The Fe3+-O-Mn3+/2+ hybrid bonds were constructed on the surface of the amorphous and porous silica molecular sieve (MCM-41) by a three-step method that involved impregnation, hydrothermal incorporation, and annealing. The obtained FeMn-MCM-41 has an amorphous, less-ordered mesoporous structure with uniformly distributed Fe and Mn and a large specific surface area. It exhibits high activity, good recyclability, and wide pH applicable range for the heterogeneous catalytic ozonation (HCO). The TOC removal of methyl orange at high concentration of 327.5 ​mg ​L−1 is 78% on FeMn-MCM-41, which is not only much higher than the value of single ozonation (43%) but also much higher than the value on mixed catalysts of Fe-MCM-41 and Mn-MCM-41 (52%). We demonstrate that large amounts of the Fe3+-O-Mn3+/2+ hybrid bonds were created on the surface of porous silica, and the partial electron migration occurs in the hybrid Fe3+-O-Mn2+ (or Fe3+-O-Mn3+) bonds. As is well known, Fe3+ and Mn3+/2+ are very strong and weak Lewis acid sites in their oxides, respectively, and the partial electron migration lowers the acidity of Fe3+ sites and in the meantime increases the acidity of Mn3+/2+ sites, making both sites more suitable for catalytic production of free hydroxyl radicals (•OH). The synergetic effect of Fe3+ and Mn3+/2+ significantly improve the intrinsic activity of the FeMn-MCM-41 for HCO. This work may offer a new strategy for developing efficient mesoporous catalysts for catalytic ozonation.

Phase Formation and Wear Resistance of Carbon-Doped TiZrN Nanocomposite Coatings by Laser Carburization

Carbon-doped TiZrN nanocomposite coatings were investigated for phase formation and wear behavior. They were prepared by laser carburization using carbon paste, and the thermal energy of the pulsed laser was limited to the range of 20 to 50%. X-ray photoelectron spectroscopy analysis revealed that the ratio of carbide (TiC, ZrC) increased as the thermal energy of the laser increased. The sp2/sp3 ratio increased by approximately 16% when the laser thermal energy was raised from 30 to 40%, and the formation of amorphous carbon was confirmed in the carbon-doped TiZrN coatings. As a result of microstructural analysis, the carbon-doped TiZrN nanocomposite was formed by an increase of hybrid bonds in expanded localized carbon clusters. Wear resistance was evaluated using a ball-on-disc tester, which showed that the friction coefficient decreased from 0.74 to 0.11 and the wear rate decreased from 7.63 × 10−6 mm3 (Nm)−1 to 1.26 × 10−6 mm3 (Nm)−1. In particular, the friction coefficient and wear rate improved by 71 and 66%, respectively, owing to the formation of carbon-doped TiZrN nanocomposite with amorphous carbon while the thermal energy was increased from 30 to 40%.

Magnetic anisotropy in Co/phosphorene heterostructure

Magnetic anisotropy (MA) in magnetic multilayer structures plays a critical role in the design of future spintronic and magnetic devices. This property is more important for structures with a thickness of few angstroms, such as few-layer two-dimensional materials. Here, we determined the variation in the interface MA in mono- and bi-layer Co/phosphorene heterostructures via first-principles density functional theory calculations. We found that the MA of these structures was comparable to those of ferromagnet/heavy-metal interfaces, despite the small spin-orbit coupling strength of phosphorus atoms. The hybridization of the metal d and the phosphorene p orbitals is well manifested in the projected density of states of these systems. The strain dependence of the magnetic anisotropy energy (MAE) in bilayer Co/phosphorene heterostructures under uniaxial strains along zigzag and armchair directions of the phosphorene layer was investigated, indicating that the MAE of the system increases by more than 80% by applying the strain. More specifically, by utilizing the uniaxial tensile strain along the zigzag direction of this structure, we found that MA could vary from perpendicular to in-plane directions. Our findings indicate that interlayer hybrid bonds in two-dimensional layered materials can be a promising approach to tailoring the MA property.

Interface microstructure and tensile properties of a third generation aluminium-steel butt weld produced using the Hybrid Metal Extrusion &amp; Bonding (HYB) process

Abstract The Hybrid Metal Extrusion & Bonding (HYB) process is a patented solid state joining method for metals which utilizes filler material additions to consolidate the weld. In the present investigation the interface microstructure and tensile properties of a 4 mm thick joint, belonging to the third generation Al-steel HYB butt welds, are characterized. The mechanical testing shows that the HYB weld exhibits excellent tensile properties, displaying ultimate tensile strength values in the range from 238 to 266 MPa. Moreover, supplementary digital image correlation analysis of the strain evolution occurring during tensile testing reveals that all plastic deformation is localized to the soft heat-affected zone on the aluminium side of the joint, leading to necking and final fracture in the aluminium. Scanning and transmission electron microscopy examinations of the Al-steel interface show that bonding occurs by a combination of microscale mechanical interlocking and intermetallic compound formation. The intermetallic layer has a thickness varying between 0.1 and 1 μm and is composed of Al–Fe–Si crystals. This makes the butt joint highly resistant against interfacial cracking. The subsequent benchmarking against commercial fusion and solid state welding methods reveals that the tensile properties of the Al-steel HYB weld even surpass those reported for comparable friction stir welds. At the same time, the HYB process allows butt welding to be performed at much higher speeds compared to friction stir welding, without compromising the mechanical integrity of the weldment.

Effect of Annealing-Induced Tensions on the Mechanical Failure of Copper/Copper Interface in Wafer-to-Wafer Hybrid Bonding

The copper/copper (Cu/Cu) interface has an important role in wafer-to-wafer hybrid bonding for 3D integration applications. Reports indicate the possibility of the formation of post-bonding interfacial voids and cracks which must be avoided. Here, we use molecular dynamics simulations to investigate the effect of annealing-induced tensions on the strength and deformation mechanisms of Cu/Cu interfaces. We perform tensile tests on the pristine and defective Cu/Cu interfaces including a prototypical interfacial grain boundary in two defective limits: the presence of a single (isolated) void, and an array of multiple voids. The latter resembles interfacial nanoscale roughness as a result of weak sample preparation and bonding conditions. We show that in the limit of isolated voids, the strength of the system is lower than that of the pristine interface. The corresponding deformation mechanism is ductile and through dislocation activities which could be accompanied by void growth. In contrast, multiple interfacial voids lead to a ductile-to-brittle transition in the failure mechanism accompanied by a drastic reduction of the system strength. Our findings shed light on the importance of process control to assure the integrity and reliability of the bonded components.

First principles study on electronic structure, ferromagnetism and dielectric properties of α-Fe, FeSiAl and Fe3Si

Based on the plane-wave pseudo-potential theory, the first principle calculation was used to study the electronic structure, ferromagnetism and dielectric properties of α-Fe, FeSiAl and Fe3Si alloys. Results indicate that the Fe3Si has the strongest hybridization and covalent bond. And α-Fe has the most stable system structure. The PDOS shown that the peak for the imaginary part of dielectric constant in the low-energy region is due to the electronic transitions of the hybridized 3d spin-down Fe states above and below the Fermi level, and the high-energy peak of it is formed by the transitions from the broad 3d spin-down band in the valence band to the unoccupied 3d spin-down states. Compared with α-Fe and FeSiAl, the imaginary part of the dielectric constant of Fe3Si is larger, and the magnetic moment of Fe3Si alloy is the largest according to the electronic structure and magnetic analysis. Therefore, Fe3Si has better absorbing properties.

Cellular Response to Sol-Gel Hybrid Materials Releasing Boron and Calcium Ions.

Poly(dimethylsiloxane) (PDMS)-SiO2-CaO-based hybrid materials prepared by sol-gel have proved to be very promising materials for tissue engineering applications and drug-delivery systems. These hybrids are biocompatible and present osteogenic and bioactive properties supporting osteoblast attachment and bone growth. The incorporation of therapeutic elements in these materials, such as boron (B) and calcium (Ca), was considered in this study as an approach to develop biomaterials capable of stimulating bone regeneration. The main purpose of this work was thus to produce, by sol-gel, bioactive and biocompatible hybrid materials of the PDMS-SiO2-B2O3-CaO system, capable of a controlled Ca and B release. Different compositions with different boron amounts were prepared using the same precursors resulting in different monolithic materials, with distinct structures and microstructures. Structural features were assessed by Fourier transform infrared (FT-IR) spectrometry and solid-state nuclear magnetic resonance (NMR) techniques, which confirmed the presence of hybrid bonds (Si-O-Si) between organic (PDMS) and inorganic phase (tetraethyl orthosilicate (TEOS)), as well as borosiloxane bonds (B-O-Si). From the 11B NMR results, it was found that Ca changes the boron coordination, from trigonal (BO3) to tetrahedral (BO4). Scanning electron microscopy (SEM) micrographs and N2 isotherms showed that the incorporation of boron modifies the material's microstructure by increasing the macroporosity and decreasing the specific surface area (SSA). In vitro tests in simulated body fluid (SBF) showed the precipitation of a calcium phosphate layer on the material surface and the controlled release of therapeutic ions. The cytocompatibility of the prepared hybrids was studied with bone marrow stromal cells (ST-2 cell line) by analyzing the cell viability and cell density. The results demonstrated that increasing the dilution rate of extraction medium from the hybrids leads to improved cell behavior. The relationship between the in vitro response and the structural and microstructural features of the materials was explored. It was shown that the release of calcium and boron ions, determined by the hybrid structure was crucial for the observed cells behavior. Although not completely understood, the encouraging results obtained constitute an incentive for further studies on this topic.

Reliability of Cu Nanoparticles/Bi-Sn Solder Hybrid Bonding Under Cyclic Thermal Stresses

The influence of thermal cycle stress loading on hybrid bonding, which was formed by sintering a mixture of Cu nanoparticles and a eutectic Bi-Sn solder powder, has been investigated. A Si chip and a directly bonded aluminum (DBA) substrate were bonded using the hybrid bonding layer. The bonded sample was evaluated using a thermal cycle test (− 40°C and 250°C). The degradation process of the sample during the test was observed nondestructively using synchrotron radiation x-ray computed laminography. The thermal cycle stress loading had a minimal effect on the microstructure of the bonding layer, which has a high bonding strength owing to the liquid phase sintering and high decomposition melting temperature of the Cu-Sn compound formation. This property reduced the Al deformation of the DBA substrate caused by the thermal cycle loading, resulting in the suppression of the bonding layer degradation. Therefore, hybrid bonding can be instrumental in achieving the reliable operation of power modules at high temperatures.

Demonstration of Low-Temperature Fine-Pitch Cu/SiO₂ Hybrid Bonding by Au Passivation

Fine pitch Cu/SiO2 hybrid bonding has been successfully demonstrated at a low temperature of 120 °C, a breakthrough, using Au passivation method in this work. To explore the bonding mechanism of passivation structures for hybrid bonding in details, Cu-Cu direct bonding with Au passivation on both wafer-level and chip-level has been discussed, including analyses of AFM, SAT, TEM, electrical measurements, and reliability test. Cu/SiO2 hybrid bonding with the fine pitch structure with stable electrical performance can be achieved at low bonding temperature under an atmospheric environment. Accordingly, this Au passivation scheme for Cu/SiO2 hybrid bonding with excellent bonding quality, low thermal budget, and high reliability shows a great feasibility for the 3D IC and heterogenous integration applications.