• Journal of the Korean institute of surface engineering
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• v.56 no.3
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• pp.180-184
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• 2023

Scholars have proposed wafer-level bonding and three-dimensional (3D) stacked integrated circuit (IC) and have investigated Cu-Cu bonding to overcome the limitation of Moore's law. However, information about quantitative Cu-Cu direct-bonding conditions, such as temperature, pressure, and interfacial adhesion energy, is scant. This study determines the optimal temperature and pressure for Cu-Cu bonding by varying the bonding temperature to 100, 150, 200, 250, and 350 ℃ and pressure to 2,303 and 3,087 N/cm². Various conditions and methods for surface treatment were performed to prevent oxidation of the surface of the sample and remove organic compounds in Cu direct bonding as variables of temperature and pressure. EDX experiments were conducted to confirm chemical information on the bonding characteristics between the substrate and Cu to confirm the bonding mechanism between the substrate and Cu. In addition, after the combination with the change of temperature and pressure variables, UTM measurement was performed to investigate the bond force between the substrate and Cu, and it was confirmed that the bond force increased proportionally as the temperature and pressure increased.

• Journal of the Microelectronics and Packaging Society
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• v.23 no.4
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• pp.69-77
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• 2016

We propose nano-scale Cu direct bonding technology using ultra-high density Cu nano-pillar (CNP) with for high stacking yield exascale 2.5D/3D integration. We clarified the joining mechanism of nano-scale Cu direct bonding using CNP. Nano-scale Cu pillar easily bond with Cu electrode by re-crystallization of CNP due to the solid phase diffusion and by morphology change of CNP to minimize interfacial energy at relatively lower temperature and pressure compared to conventional micro-scale Cu direct bonding. We confirmed for the first time that 4.3 million electrodes per die are successfully connected in series with the joining yield of 100%. The joining resistance of CNP bundle with $80{\mu}m$ height is around 30 m for each pair of $10{\mu}m$ dia. electrode. Capacitance value of CNP bundle with $3{\mu}m$ length and $80{\mu}m$ height is around 0.6fF. Eye-diagram pattern shows no degradation even at 10Gbps data rate after the lamination of anisotropic conductive film.

• Journal of Powder Materials
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• v.20 no.2
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• pp.114-119
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• 2013

In the DBC (direct bonding of copper) process the oxygen partial pressure surrounding the AlN/Cu bonding pairs has been controlled by Ar gas mixed with oxygen. However, the direct bonding of Cu with sound interface and good adhesion strength is complicated process due to the difficulty in the exact control of oxygen partial pressure by using Ar gas. In this study, we have utilized the in-situ equilibrium established during the reaction of $2CuO{\rightarrow}Cu_2O$ + 1/2 $O_2$ by placing powder bed of CuO or $Cu_2O$ around the Cu/AlN bonding pair at $1065{\sim}1085^{\circ}C$. The adhesion strength was relatively better in case of using CuO powder than when $Cu_2O$ powder was used. Microstructural analysis by optical microscopy and XRD revealed that the interface of bonding pair was composed of $Cu_2O$, Cu and small amount of CuO phase. Thus, it is explained that the good adhesion between Cu and AlN is attributed to the wetting of eutectic liquid formed by reaction of Cu and $Cu_2O$.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.5
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• pp.563-571
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• 2012

In 3D integration package using TSV technology, bonding is the core technology for stacking and interconnecting the chips or wafers. During bonding process, however, warpage and high stress are introduced, and will lead to the misalignment problem between two chips being bonded and failure of the chips. In this paper, a finite element approach is used to predict the warpages and stresses during the bonding process. In particular, in-plane deformation which directly affects the bonding misalignment is closely analyzed. Three types of bonding technology, which are Sn-Ag solder bonding, Cu-Cu direct bonding and SiO2 direct bonding, are compared. Numerical analysis indicates that warpage and stress are accumulated and become larger for each bonding step. In-plane deformation is much larger than out-of-plane deformation during bonding process. Cu-Cu bonding shows the largest warpage, while SiO2 direct bonding shows the smallest warpage. For stress, Sn-Ag solder bonding shows the largest stress, while Cu-Cu bonding shows the smallest. The stress is mainly concentrated at the interface between the via hole and silicon chip or via hole and bonding area. Misalignment induced during Cu-Cu and Sn-Ag solder bonding is equal to or larger than the size of via diameter, therefore should be reduced by lowering bonding temperature and proper selection of package materials.

• Journal of the Korean institute of surface engineering
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• v.54 no.5
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• pp.207-212
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• 2021

The mechanical and electrical characteristics can be improved in 3D stacked IC technology which can accomplish the ultra-high integration by stacking more semiconductor chips within the limited package area through the Cu direct bonding method minimizing the performance degradation to the bonding surface to the inorganic compound or the oxide film etc. The surface was treated in a ultrasonic washer using a diamond abrasive to remove other component substances from the prepared cast plate substrate surface. FE-SEM was used to analyze the bonding characteristics of the bonded copper substrates, and the cross section of the bonded Cu conjugates at the sintering junction temperature of 100 ℃, 150 ℃, 200 ℃, 350 ℃ and the pressure of 2303 N/cm² and 3087 N/cm². At 2303 N/cm², the good bonding of copper substrate was confirmed at 350 ℃, and at the increased pressure of 3087 N/cm², the bonding condition of Cu was confirmed at low temperature junction temperature of 200 ℃. However, the recrystallization of Cu particles was observed due to increased pressure of 3087 N/cm² and diffusion of Cu atoms at high temperature of 350 ℃, which can lead to degradation in semiconductor manufacturing.

• Journal of the Microelectronics and Packaging Society
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• v.20 no.1
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• pp.7-13
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• 2013

3D stacked IC is one of the promising candidates which can keep Moore's law valid for next decades. IC can be stacked through various bonding technologies and they were reviewed in this report, for example, wafer direct bonding and atomic diffusion bonding, etc. As an effort to reduce the high temperature and pressure which were required for high bonding strength in conventional Cu-Cu thermo-compression bonding, surface activated bonding, solid liquid inter-diffusion and direct bonding interface technologies are actively being developed.

• Korean Journal of Materials Research
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• v.2 no.4
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• pp.241-247
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• 1992

The direct bonding of Cu to $Al_2O_3$, employing the $Cu-Cu_2$O eutectic skin melt, is investigated. The bonding force and interface structure of samples prepared by oxidation at $1015^{\circ}C$ in $1.5{\times}10^{-1}$torr followed by bonding at 107$5^{\circ}C$ under $10_{-3}$ torr vacuum have been studied using peeling test, SEM, EDS and XRD. It has been found that the optimal strength is obtained for 3 minutes of oxidation while the adhesion force is decreased with oxidation shorter or longer than 3 minutes. The rupture occured at alumina-eutectic interface. Fractured surface of $Al_2O_3$covered with $Cu_2$O nodules pulled out of the Cu indicates that bonding strength is governed by $Cu-Cu_2$O interface and not by $Cu_2$O-A$l_2O_3$interface. The bonding force is slightly increased with bonding time and the reaction phases of CuA$l_2O_4$and $CuAlO_2$are formed at interface during the bonding.

• Transactions of Materials Processing
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• v.18 no.4
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• pp.342-346
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• 2009

Forming characteristics for the bundle extrusion of Cu-Ti bimetal wires are investigated, which can identify the process conditions for weak mechanical bonding at the contact surface during the direct extrusion of a Cu-Ti bimetal wire bundle. Bonding mechanism between Cu and Ti is assumed as a cold pressure welding. Then, the plastic deformation at the contact zone causes mechanical bonding and a new bonding criterion for pressure welding is developed as a function of the principal stretch ratio and normal pressure at the contact surface by analyzing micro local extrusion at the contact zone. The averaged deformation behavior of Cu-Ti bimetal wire is adopted as a constitutive behavior at a material point in the finite element analysis of Cu-Ti wire bundle extrusion. Various process conditions for bundle extrusions are examined. The deformation histories at the three points, near the surface, in the middle and near the center, in the cross section of a bundle are traced and the proposed new bonding criterion is applied to predict whether the mechanical bonding at the Cu-Ti contact surface happens. Finally, a process map for the direct extrusion of Cu-Ti bimetal wire bundle is proposed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.393-397
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• 2005

A process map has been developed, which can identify the process conditions for weak mechanical bonding at the contact surface during the direct extrusion of a Cu-Ti bimetal wire bundle. Bonding mechanism between Cu and Ti is assumed as a cold pressure welding. Then, the plastic deformation at the contact zone causes mechanical bonding and a new bonding criterion fur pressure welding is developed as a function of the principal stretch ratio and normal pressure at the contact surface by analyzing micro local extrusion at the contact zone. The averaged deformation behavior of Cu-Ti bimetal wire is adopted as a constitutive behavior at a material point in the finite element analysis of Cu-Ti wire bundle extrusion. Various process conditions for bundle extrusions are examined. The deformation histories at the three points, near the surface, in the middle and near the center, in the cross section of a bundle are traced and the proposed new bonding criterion is applied to predict whether the mechanical bonding at the Cu-Ti contact surface happens. Finally, a process map for the direct extrusion of Cu-Ti bimetal wire bundle is proposed.

• Journal of Welding and Joining
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• v.30 no.3
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• pp.26-31
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• 2012

Three-dimensional integrated circuit (3D IC) technology has become increasingly important due to the demand for high system performance and functionality. We have evaluated the effect of Buffered oxide etch (BOE) on the interfacial bonding strength of Cu-Cu pattern direct bonding. X-ray photoelectron spectroscopy (XPS) analysis of Cu surface revealed that Cu surface oxide layer was partially removed by BOE 2min. Two 8-inch Cu pattern wafers were bonded at $400^{\circ}C$ via the thermo-compression method. The interfacial adhesion energy of Cu-Cu bonding was quantitatively measured by the four-point bending method. After BOE 2min wet etching, the measured interfacial adhesion energies of pattern density for 0.06, 0.09, and 0.23 were $4.52J/m^2$, $5.06J/m^2$ and $3.42J/m^2$, respectively, which were lower than $5J/m^2$. Therefore, the effective removal of Cu surface oxide is critical to have reliable bonding quality of Cu pattern direct bonds.