Surface Energy Characterization for Die-Level Cu Hybrid Bonding

Advanced packaging technology has become more and more important in the semiconductor industry because of the benefits of higher I/O density compared to conventional soldering technology. In advanced packaging technology, copper–copper (Cu-Cu) bonding has become the preferred choice due to its excellent electrical and thermal properties. However, one of the major challenges of Cu-Cu bonding is the high thermal budget of the bonding process caused by Cu oxidation, which can result in wafer warpage and other back-end-of-line process issues in some cases. Thus, for specific applications, reducing the thermal budget and preventing Cu oxidation are important considerations in low-temperature hybrid bonding processes. This paper first reviews the advancements in low-temperature Cu-based bonding technologies for advanced packaging. Various low-temperature Cu-Cu bonding techniques such as surface pretreatment, surface activation, structure modification, and orientation control have been proposed and investigated. To overcome coplanarity issues of Cu pillars and insufficient gaps for filling, low-temperature Cu-Cu bonding used, but it is still challenging in fine-pitch applications. Therefore, low-temperature Cu/SiO2, Cu/SiCN, and Cu/polymer hybrid bonding have been developed for advanced packaging applications. Furthermore, we present a novel hybrid bonding scheme for metal/polymer interfaces that achieves good flatness and an excellent bonding interface without the need for the chemical mechanical polishing (CMP) process.

Interfacial fracture toughness of vacuum-plasma-sprayed coatings

This study investigates the adhesion properties of polycarbonate (PC) and liquid silicone rubbers (LSR) through surface activation using ultraviolet C (UVC) radiation. While self-adhesive LSRs adhere easily to certain thermoplastic composites such as polybutylene terephthalate (PBT) and polyamides (PAs), bonding to PC typically requires surface treatment due to the lack of compatible functional groups. Previous methods like plasma or flame treatment have been effective, but the use of UVC radiation for surface activation remains unexplored. Through experiments, it was found that UVC surface activation, particularly with ozone-generating lamps, significantly enhances the peel strength between PC and self-adhesive LSRs. The study evaluates the impact of different irradiation times and lamp configurations on peel resistance, surface energy, and composite stability. Results show that UVC/ozone (wavelengths 254 nm and 185 nm) activation increases peel resistance, with distinct differences observed between LSR types. Additionally, the study examines the stability of UVC activation over time and under various storage conditions, highlighting its effectiveness for up to 36 months at room temperature. Furthermore, the relationship between surface energy and peel strength is analyzed, finding that UVC/ozone activation increases surface energy but does not consistently correlate with improved adhesion. The study concludes with a comparison of UVC/ozone activation to alternative surface treatment methods, emphasizing its advantages such as cost-effectiveness and stability while considering limitations regarding substrate compatibility and occupational safety aspects. Overall, UVC/ozone surface activation presents a promising approach for enhancing adhesion in PC-LSR composite systems and holds potential for applications across various industries.

The surface energy of a polished amorphous carbon (a-C) wafer spin-coated with fullerene derivatives is evaluated by the contact angle measurements of test liquids. The contact angles of the epoxy prepolymer droplets are also measured to investigate the effects of fullerene derivatives on the adhesiveness between the epoxy resin and the a-C wafer surface. A marked increase in surface energy is observed when the wafer is spin-coated with the fullerene derivatives having a polar group. The three surface energy components, dispersive, polar, and hydrogen bonding forces, are determined from the contact angles by an expanded Fowkes method. The total surface energy thus obtained varies from 36.2 to 50.4 mN/m, depending on the nature of fullerene derivatives. The major factor, which increases the surface total energy, is found to be the polar component of the fullerene derivatives. Microscopic structures of the thin films of fullerenes on the wafer have no essential effects on the surface energy and the wettability between the a-C wafer and the epoxy resin. In the present study, we demonstrate that the fullerene derivative with a polar group acts as an adhesive in the fixation between the epoxy resin and the a-C wafer: a polar group of the fullerene derivative has large affinity to the epoxy resin, and the fullerene core, to the a-C surface.

A radio-frequency (RF) plasma/glow discharge surface polymerization process which significantly decreases the amount of physical cell outgrowth on poly(methyl methacrylate) (PMMA) squares has been studied. A statistically significant reduction in cell attachment, adhesion and spreading of bovine lens epithelial or rabbit corneal endothelial cells onto RF-plasma modified PMMA intraocular lenses (IOLs) compared to standard, commercial (as received) PMMA intraocular lenses (IOLs) in cell culture has also been shown. The surface modification process utilizes an argon RF-plasma "non-polymer forming" surface activation as well as a RF-plasma polymerization surfacing technique. The RF-plasma surface polymerization process decreases the amount of cell outgrowth and cell attachment, adhesion and spreading on the RF-plasma modified PMMA substrates. The final RF-plasma modified PMMA substrates are also microscopically smoother and/or have improved surface energy characteristics as compared to the unmodified PMMA squares and unmodified PMMA IOLs manufactured using the currently available mechanical, tumble polishing techniques. The RF-plasma surface polymerization process can generate the same chemical surface composition as the PMMA substrates, using RF-plasma polymerized methyl methacrylate, or can have the potential of changing the surface chemistry on the PMMA substrates using various RF-plasma polymerized hydrophilic or hydrophobic organic monomers. The irregular, semi-smooth hydrophobic PMMA substrates were surface grafted and exhibited an ultrasmooth, pinhole free surface with the same surface chemistry and energy using special RF-plasma polymerization techniques by covalenting bonding RF-plasma polymerized MMA. The PMMA substrates also exhibited a relatively smoother surface finish combined with different surface chemistry and energy characteristics by covalently bonding RF-plasma polymerized hydrophilic acrylic acid or ethylenediamine and hydrophobic hexamethyldisiloxane organic monomers. This research has shown that the modified surface of the RF-plasma polymerized PMMA IOLs showed a statistically significant decrease in the amount of cell attachment, adhesion and spreading as compared with extensive cell attachment, adhesion, and spreading on the unmodified PMMA IOLs. Therefore, due to the reduced amount of cell activity, secondary opacification, pseudophakic precipitates, and synechiae, are less likely to occur on the RF-plasma modified IOLs after surgical implantation.

A pre-wafer-bonding remote-plasma treatment is presented as a route to hydrophilic elevated temperature wafer bonding. This particular remote plasma technique was used as a non-etching surface activation technique. We report a post anneal surface energy of 2,250 mJ/m2 using remote plasma activation which is higher than other reported results. Furthermore, the trend in increasing surface energy with increased with plasma exposure time showed no tail-off. The surface damage present in other plasma techniques is avoided and as a consequence exposure times could be extended. An increase in pre-bonding remote plasma treatment times resulted in increased surface energy, this held true for; initial pre-anneal bonding where van der Waals forces hold the wafers together, for ambient covalent bonding, and, for elevated temperature covalent bonding. It also held true for homo and hetero-wafer bonding. Increased surface energy was evident over a variety of bonding and annealing conditions. Surface energies or more descriptively, bonding energies result are reported for Si to Si and Si to quartz bonding and compared with various other pre-bonding treatments. Attention is focused on results obtained by varying different plasma parameters; exposure time, gas species, etc., and their effect on the surface energy of bonded pair. For silicon to quartz, we report an annealing temperature of 200°C without de-bonding, which is an extension of 50°C over previously reported values. Pre- and post plasma surface roughness measurements were made using an atomic force microscope while bond interface was characterized using scanning acoustic microscopy.

Interfacial energy effects and the evolution of pore size distributions during quartz precipitation in sandstone

Hybrid bonding, with wafer level bonding to form oxide-oxide bonds and Cu-Cu bonds is a promising technology for 3D integrated circuits. In this paper, the impact of various process parameters on the wafer-level bond quality of fusion (direct) and hybrid bonding have been evaluated. Investigated process parameters include: TEOS based oxide (Tetra-Ethyl-Ortho-Silicate) process deposition temperature, oxide densification annealing conditions, plasma conditions for wafer surface activation, chemical mechanical polishing (CMP) process conditions and post-bonding annealing conditions. In addition to these process parameters, design parameter such as Cu pad density is also critical. For fusion/hybrid bonding, surface properties are very critical. This includes surface roughness, bow and warpage, flatness and edge roll-off. Thus, all these surface properties were continuously monitored during the wafers fabrication. Bond quality was characterized by scanning acoustic microscopy (SAM) images. Bonding energy was calculated using Maszara model, where the crack length is measured from the SAM micrographs. Target objective of this study is to determine optimum process conditions in order to achieve eventual bonding energy > 1J/m2, which is a pre-requisite for 3D multi-wafer stacking without any delamination.

A chemo-mechanical fracture model for the welding interface of vitrimers

This aims to establish design rules for the influence of complex polymer matrices on the surface properties of small molecules. Here, we consider the dependence of the surface behaviour of some model additives on polymer matrix hydrophobicity. With stoichiometric control over hydrolysis, we generate systematic changes in matrix chemistry from non-polar, hydrophobic PVAc to its hydrolysed and hydrophilic analogue, PVA. With the changing degree of hydrolysis (DH), the behaviour of additives can be switched in terms of compatibility and surface activity. Sorbitol, a polar sugar-alcohol of inherently high surface energy, blooms to the surface of PVAc, forming patchy domains on surfaces. With the increasing DH of the polymer matrix, its surface segregation decreases to the point where sorbitol acts as a homogeneously distributed plasticiser in PVA. Conversely, and despite its low surface energy, octanoic acid (OA) surprisingly causes the increased wettability of PVAc. We attribute these observations to the high compatibility of OA with PVAc and its ability to reorient upon exposure to water, presenting a hydrophilic COOH-rich surface. The surfactant sodium dodecyl sulfate (SDS) does not show such a clear dependence on the matrix and formed wetting layers over a wide range of DH. Interestingly, SDS appears to be most compatible with PVAc at intermediate DH, which is consistent with the amphiphilic nature of both species under these conditions. Thus, we show that the prediction of the segregation is not simple and depends on multiple factors including hydrophobicity, compatibility, blockiness, surface energy, and the mobility of the components.

One of the methods used for the evaluation of coating adherence consists of determining an apparent interfacial fracture toughness through interfacial indentation in the cross-section of the coated system. In the present paper the interfacial crack propagation in a thermal spray coated system, during interfacial indentation test, was studied by finite element method. A Vickers indenter was applied at the coating/substrate interface to perform indentation test. In order to simulate the cracking, an initial semi-circular crack lying at the interface between the substrate and the coating was considered. Since the cracks resulting from interfacial indentation test have been reported to have a semi-circular shape, the crack was forced to advance by a uniform distance normal to the crack front in the plane of interface at each step of calculation. In these conditions it was shown that the interfacial crack has a mixed fracture mode. An apparent interfacial fracture energy Jca was calculated by this method to evaluate the interfacial adhesive toughness. The model was applied to study the crack propagation at the interface between a Cr3C2-NiCr HVOF coating and a grey cast iron substrate. A reasonable agreement between the calculation results and reported experimental data was found.

Application of nanotechnology in oil and gas industry has received great attention from many researchers. This is due to two features of nanoparticles that make them unique which are their size and the ability to adjust their behaviour. Nanoparticles are very active and energetic materials with a high tendency to form nano textured surfaces in combination with surfactants, and causing a major change in the system’s interfacial properties. Surface energy of surfactants can be significantly increased by the interaction of nanoparticle and surfactant and more adsorption on the rock surface occurs with higher surface energy. The objective of this study is to investigate the effectiveness of Al2O3 and ZrO2 nanoparticles to alter oil-wet dolomite rock to more water wet condition. In this study, nanoparticle was dispersed in three different surfactants namely cetyltrimethylammonium bromide, CTAB (cationic), sodium dodecyl sulphate, SDS (anionic) and TX-100 (non- ionic). Critical micelle concentration of the surfactant was determined by measuring its surface tension (SF). The CMC value of the surfactant was established at the inflection point of the curve. The IFT was determined after the addition of nanoparticles. The results revealed that there is significant reduction of IFT after addition of nanoparticles. Reduction of IFT indicates the ability of the solution to decrease capillary forces and increase mobility of the oil in pore throat. Initial wettability of the dolomite substrate was determined and then was submerged in different nanofluids at different concentration. Contact angle of the rock surface was measured as quantitative method to determine the wettability of the system. The experiment was further investigated by evaluating adsorption of the surfactant on the rock surface. Isotherm adsorption of the surfactant was studied and the result revealed that ionic surfactant has higher adsorption capacity. This is mainly because the charged group on solid surface strongly influences the adsorption of surfactant at solid-liquid interface.

Electrode reaction of ferrocene in a nitrobenzene+water emulsion

Surface sites and unrelaxed surface energies of tetrahedral silica polymorphs and silicate

Surface energy characterization is important to design the fabrication process of reliable electronic devices. Surface energy is influenced by various factors such as surface functionality and morphology. Owing to the high surface-to-volume ratio, surface energy at the nanoscale can be different from that of the bulk. However, the conventional methods for characterization of surface energy such as a sessile drop or Washburn methods cannot be used for nanoscale samples, owing to the limited volume for characterization. Recently, surface energy characterization on the nanoscale using atomic force microscopy (AFM) with Peak Force-Quantitative Nanomechanical Mapping (PF-QNM) imaging mode has been proposed. The nanoscale AFM tips measure the adhesion forces at the nanoscale, which are converted into surface energy through pre-calibrated curves. Successful surface energy characterization of nanoscale metal samples using AFM with the PF-QNM method has been reported previously. This mini-review discusses the recent progress on surface energy characterization at the nanoscale using AFM with the PF-QNM method. The fundamentals of the PF-QNM mode are introduced, and the results of surface energy characterization are summarized. Consequently, the future research direction for surface energy characterization at the nanoscale is discussed.