Abrasive-Free Polymer Chemical–Mechanical Polishing for PI/Cu Hybrid Bonding: High-Rate Removal and an Atomistic Mechanism from Neural-Network-Potential Molecular Dynamics

Presented at the 2026 IEEE Hybrid Bonding Symposium, Jan 22-23, 2026 in Silicon Valley.  More information below.
(22:33) Dr. Teruo Hirakawa, Resonac America, Inc.
Summary: Hybrid bonding (HB) for fine-pitch 3D integration demands sub-nanometer roughness and a controlled Cu protrusion (80–230 nm). Conventional silica abrasive slurries remove polyimide (PI) or polybenzoxazole (PBO) only at a few tens of nm/min, whereas alumina can reach 500–700 nm/min but at the cost of scratches -— both unsuitable for HB surfaces. Here, we report an abrasive-free polymer CMP based on Fe3+ aqueous chemistry that combines high polymer removal with low Cu loss while avoiding particle-induced scratches. On 300mm blanket wafers, PI/PBO removal rates up to 800 nm/min were obtained, while Cu removal remained at ~8 nm/min, yielding ~40–100× polymer/Cu selectivity. On patterned test wafers, an as-deposited ~300 nm step in PI film was reduced to <30 nm in 60 s; continued polish produced PI/Cu HB surfaces with Cu protrusion ~100 nm and roughness Ra ? 0.2–0.5 nm on both PI and Cu, conforming to the general requirements for HB. To address whether material removal can proceed without abrasive particles, we performed comparative neural-network-potential molecular dynamics (NNP-MD) for the interfaces (silica-loaded, alumina-loaded, and an abrasive-free Fe3+ solution). In the abrasive interfaces, the simulations reproduce Si-O-C and Al-O-C linkages, with Al-O-C more persistent under load; by contrast, the Fe3+ solution exhibits Fe-O-C coordination to carbonyl and ether oxygen atoms in PI, weakening the imide/amide backbone and catalytically activating bond scission. This contrast provides a chemical rationale for the formation -— and hard-pad-stress-assisted removal -— of an Fe-weakened near-surface layer without particles, consistent with our wafer-level selectivity. Accordingly, we propose a three-step mechanism for abrasive-free polymer CMP: Fe3+ adsorption and coordination ? bond scission and near-surface softening ? stress-assisted removal of the weakened layer, explaining how abrasive?free CMP delivers high-rate, high-selectivity, HB-ready surfaces while mitigating particle-induced defects in chip-on-wafer flows.
Bio: Teruo Hirakawa is a Senior Researcher at Resonac America, Inc., specializing in chemical–mechanical planarization (CMP) and interfacial reaction chemistry. His work integrates ab initio molecular dynamics (AIMD/DFT-MD) and neural-network-potential molecular dynamics (NNP-MD) to elucidate reaction mechanisms in solution and at solid–liquid and solid–solid interfaces. He received a B.S. in Biotechnology and M.S. and Ph.D. in Engineering from Osaka University (Department of Precision Science & Technology, Graduate School of Engineering). Supervised by Prof. Yoshitada Morikawa, his doctoral research advanced first-principles molecular dynamics of aqueous reactions. Dr. Hirakawa focuses on translating atomistic insights into manufacturable CMP and hybrid-bonding process improvements.

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