Copper Bonding Technology in Heterogeneous Integration

Hybrid bonding has emerged as a promising 3D integration technology for the next generation stacking devices with advantages of higher performance and smaller form factor. As for the future devices with fine-pitch (sub-μm level) copper (Cu) interconnects, however, there are critical issues to consider for a successful application of hybrid bonding processes; (1) Cu diffusion with scaled Cu pads and (2) Cu re-sputtering and chamber contamination during plasma surface activation step that lead to fatal device failure (e.g. electrical shorts) even with a small amount. Here, we demonstrated robust connections for 0.4 to 0.7 μm-sized Cu pads of fine-pitch with wafer-to-wafer (W2W) Cu/SiCN hybrid bonding scheme through N2 plasma development and present comprehensive analyses for surface activation process. A computational work carried out by reactive molecular dynamics (MD) simulations was employed to propose an optimal N2 plasma condition that can enhance SiCN-SiCN bonding characteristics. The optimized N2 plasma condition reproduces SiCN-SiCN bonding strength of above 2.0 J/m 2 while suppressing oxidation of Cu pads below 2 nm. Cu/SiCN hybrid bonding characteristics using N2 plasma were confirmed to be void-free, well Cu-Cu interdiffused, and mechanically well aligned from the assessment involving SAT, TEM/EDS and FIB-SEM/EBSD analyses. Moreover, our optimal plasma condition meets the contamination- free criteria indicating that it is a preferable surface activation scheme without contaminating the plasma chamber regardless of continuous operations. The methodologies demonstrated in this work suggest that hybrid bonding can be applied to future fine- pitch device applications for successful 3D integration.

Contamination-Free Cu/SiCN Hybrid Bonding Process Development for Sub- μm Pitch Devices with Enhanced Bonding Characteristics

Hybrid bonding enables the commercialization of ultra-fine pitch high-density 3D packages. Cu/SiO2 hybrid bonding is the standard packing interface recently introduced in the industry. Here, the Cu/polymer hybrid bonding interface beyond Cu/SiO2 is proposed in order to have high compatibility for additional processes in the future. Ideally, polymers can provide excellent bonding strength and low permittivity, enabling high-speed signal transmission with high reliability. To realize it, optimum polymer and additives selection and polymer bonding processing development are needed to get the desired packaging interface. Therefore, detailed materials and processing challenges are discussed to realize the successful Cu/polymer hybrid bonding. Then, the authors’ preliminary results are suggested to supplement the feasibility of the emerging bonding technology. 

Advanced Cu/Polymer Hybrid Bonding System for Fine‐Pitch 3D Stacking Devices

With hybrid bonding pitch reduction, many challenges are arising especially the ones related to Cu-Cu connections with submicron Cu pads. A methodology is presented here to achieve submicron hybrid bonding pitch starting from single Cu pad thermomechanical behavior study to quantifying Cu-Cu contact resistivity. Depending on the single crystal Cu orientation, several nanometers difference in total deformation is obtained. The Cu dishing limit should be restricted with respect to the lowest deformation. Contact resistivity studies allow to further refine the Cu dishing to get a contribution of contact resistivity below <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$10^{-11}\ \Omega.\text{cm}^{2}$</tex> . By respecting these criteria, a 100 % yield was achieved down to 0.81 µm Cu/SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> hybrid bonding pitch. A successful method for the capacitance increase compensation with pitch reduction is also presented based on the adaptation of the geometric parameters of the hybrid bonding interconnects.

Sub $1\ \mu \mathrm{m}$ Pitch Achievement for Cu/SiO2 Hybrid Bonding

Fluidic-chemical characteristics of electroless copper deposition of ordered mass-fabricated pillars in a microchannel for chip packaging applications


 This paper reviews the most significant qualification and reliability achievements obtained, over the last 6 years, by the scientific community for hybrid bonding-based interconnects (HB) also called Cu-Cu or Cu/SiO2 bonding. First, the definition of words qualification, robustness and reliability are given to avoid misunderstanding about the published results. Second, the five potential threats (moisture ingress, thermomechanical stresses,electromigration, Cu diffusion, dielectric breakdown) are presented. Finally, the publications of six industrials or research and technology organizations are summarized and discussed. Most of the published data are related to qualification results (pass or fail). Few studies published in-depth studies, mainly on electromigration (Black’s parameters extraction and failure analysis) and copper diffusion (electrical and analytical characterizations). To conclude, once the manufacturing issues (surface preparation, alignment…) have been solved, this technology is robust and reliable at pitches > 1 μm as it reacts, roughly, like a conventional back-end of line (BEoL) interconnect.

Review—Hybrid Bonding-Based Interconnects: A Status on the Last Robustness and Reliability Achievements

/pdf/in-situ-characterization-of-thermomechanical-behavior-of-3v4yq71z.pdf

In-situ characterization of thermomechanical behavior of copper nano-interconnect for 3D integration

Investigation into Cu diffusion at the Cu/SiO2 hybrid bonding interface of 3D stacked integrated circuits

With hybrid bonding (HB) pitch reduction, many challenges are arising. One of them is related to the reliability of HB-based interconnects and in particular their electromigration performances as electromigration (EM)-related degradation is intimately linked to the electrical current in addition to temperature and mechanical stresses. This study highlights a change in the failure modes for EM-related failures in HB-based interconnects when decreasing the interconnect pitch from 6.84 down to 1.44 µm. The weakest link moves from the BEOL levels to hybrid bonding ones but without affecting the projected performance under use conditions. Additional studies done on design aspects do not evidence any negative impact on the electro migration resistance of the HB brick.

Recent Advances on Electromigration in Cu/SiO2 to Cu/SiO2 Hybrid Bonds for 3D Integrated Circuits

Hybrid Bonding (HB) is progressing as the major solution for 3D integrated-circuit with pitch reduction becoming the key. Reliability needs to be studied with HB pitch reduction for possible evaluation of new failure mechanisms and modes. In this paper, we developed a new methodology to study Time-Dependent Dielectric Breakdown (TDDB) at HB level that accounts wafer-to-wafer (W2W) overlay variations. Application of this method to a 1.44 µm-pitch 3D stacked test vehicle demonstrates its accuracy. TDDB at Cu/SiO2 HB interface follows the 1/E model at low electric fields for all studied temperature suggesting that the role of Cu in breakdown is negligible. The acceleration parameter and the activation energy dependence on the electric fields are studied. The cuprous oxide layer which may act as a barrier to Cu diffusion previously highlighted at the Cu/SiO2 HB interface does not exist for Cu/SiN interfaces as evidenced by EELS study. This might explain the difference in the TDDB acceleration models between HB level and BEoL ones.

New Method to Perform TDDB Tests for Hybrid Bonding Interconnects

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