Multiscale Mechanical Characterization of Hybrid-Bonding Copper: From Instrumented Indentation to AFM

Published

June 17, 2026

Author(s)

Gheorghe Stan, Yvonne Gerbig, Nicolas Alderete, Paresh Daharwal, Cristian Victor Ciobanu

Abstract

As transistor dimensions approach their physical scaling limits, advanced packaging has emerged as an effective solution to today's challenging demands. Hybrid bonding (HB), in particular, has become a disruptive enabler in this space. With interconnect pitches below 10 µm and trending submicron, the influence of length-scale effects cannot be overlooked as the behavior of metals at these scales deviates from that predicted by bulk properties. In this context, understanding, modeling, and optimizing HB-systems for reliability requires knowledge of elastoplastic mechanical properties at the micro- and nanoscale. Here, we present a framework for multiscale mechanical characterization of polycrystalline, electroplated copper (Cu) surfaces in HB-ready patterns under ambient conditions. At the microscale, we leveraged the instrumented nanoindentation technique (IIT) with spherical probes of 1 µm and 5 µm nominal radii, near the critical dimension of the metal pads. At the nanoscale, we employed contact resonance and indentation via atomic force microscopy (AFM) with spherical probe radii of less than 30 nm, enabling localized probing of nanoscale features. Using single-step indentation we first examined the stochastic, earliest onset of plastic deformation (i.e., incipient plasticity). In complement, we then harness multi-step indentation to derive indentation stress-strain (ISS) curves that reflect later stages of plasticity (i.e., developed plasticity) and from which indentation yield stress is obtained. Our experiments reveal a marked difference in the incipient plasticity of Cu, with AFM approaching the theoretical limit (τy ≈ 8.7 GPa), and IIT revealing lower strength limits (τy ≈ 0.75 GPa). ISS curves show an indentation yield stress of (σy ≈ 0.64-0.83 GPa), comparable to results from micropillar compression. Our findings emphasize the importance of length-scale relevant metrology, which is critical for modeling the response of Cu under different loading scenarios (e.g., nanoscopic contact at bonding, thermal warping). Moreover, our novel multimodal AFM methodology provides an effective approach for elastoplastic characterization aligned with the industry's drive for smaller pitches, in-situ testing, and the widespread availability of AFM technology. Concurrently, to facilitate the adoption of our framework, we introduce an open-source software for the analysis of micro- and nanoscale spherical indentation experiments.

Conference Dates

May 26-29, 2026

Conference Location

Orlando, FL, US

Conference Title

The 2026 IEEE 76th Electronic Components and Technology Conference

Pub Type

Conferences

Download Paper

https://doi.org/10.1109/ECTC51846.2026.00127

Local Download

Keywords

advanced packaging, hybrid bonding, microscale and nanoscale plasticity, size-effects, atomic force microscopy, nanoindentation

Citation

Stan, G. , Gerbig, Y. , Alderete, N. , Daharwal, P. and Ciobanu, C. (2026), Multiscale Mechanical Characterization of Hybrid-Bonding Copper: From Instrumented Indentation to AFM, The 2026 IEEE 76th Electronic Components and Technology Conference, Orlando, FL, US, [online], https://doi.org/10.1109/ECTC51846.2026.00127, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=961486 (Accessed October 9, 2026)

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