Surfactant-Free Hydrothermal Synthesis Creates Size-Tunable Monodisperse CeO2 CMP Abrasives

Cerium oxide (CeO₂) is a cornerstone abrasive in chemical mechanical polishing (CMP), where precise surface planarization is essential for advanced semiconductor fabrication. Its effectiveness is tied to the Ce³⁺/Ce⁴⁺ redox pair and the abundance of oxygen vacancies, which together support efficient material removal and smooth surface formation. Yet, many conventional CeO₂ synthesis routes struggle to deliver reliable morphology and straightforward scalability for semiconductor-grade use.

A new report in Engineering Chemical Engineering describes a simple, surfactant-free hydrothermal method to produce spherical CeO₂ abrasives with tightly controlled particle size. By tuning the water volume during synthesis, the researchers achieved particle sizes spanning 32 to 531 nm while maintaining strong sphericity and good dispersity—traits that are crucial for consistent pad–particle–wafer interactions.

The study also connects structure formation to reaction chemistry. GCMS analysis and thermodynamic calculations indicate that nitrate acts as an oxidant, converting Ce³⁺ to Ce⁴⁺ while generating NO and NO₂ gases. Ce⁴⁺ subsequently reacts with acetate to precipitate CeO₂, releasing CH₄ and CO₂. Although the oxidation steps alone are thermodynamically unfavorable, coupling them to CeO₂ precipitation drives the overall process forward.

Mechanistic insight extends to particle-size control: increasing water volume dilutes ethylene glycol and acetic acid, weakening their capping and structure-directing roles. This reduces the nucleation rate, leading to fewer nuclei and enabling enhanced growth into larger spheres.

Structural verification comes from XRD, which confirms the fluorite CeO₂ phase with diffraction peaks matching JCPDS No. 340394. HRTEM further shows lattice fringes consistent with (111) and (200) planes, supporting the high crystallinity of the synthesized particles across the full size distribution.

Importantly for CMP, the abrasive performance shows a clear particle-size trend: maximum material removal rate (MRR) rises to 73.7 nm·min⁻¹ at a median particle size of 343 nm, while surface roughness (Ra) stays remarkably stable at 0.3–0.4 nm for 32–531 nm. The advantage is attributed to the uniform spherical geometry, which distributes contact forces more evenly than irregular or polydisperse morphologies.

The researchers then optimized abrasive loading and found that 0.5 wt% CeO₂ provides the best tradeoff between removal efficiency and surface quality. Under these conditions, Ra drops from 1.93 nm (untreated) to 0.31 nm, an 84% improvement. Higher concentrations (≥1.0 wt%) introduce abrasive residue and degrade roughness.

Finally, time-dependent polishing revealed Ra decreasing with polishing duration, reaching a minimum of 0.30 nm at 15 minutes. When compared with commercial CeO₂ (81 nm), the synthesized abrasives (65 nm) delivered lower roughness at both 5 and 15 minutes, while maintaining comparable or slightly higher MRR. The results highlight size uniformity and spherical morphology as key drivers of smooth, defect-minimizing CMP outcomes.

The work establishes a scalable, low-complexity route to tailor CeO₂ abrasives for precision surface processing, linking reaction chemistry to particle formation and, ultimately, to measurable wafer-quality gains.

Keywords

Chemistry; CeO₂; hydrothermal synthesis; CMP; particle size control; fluorite structure; HRTEM; MRR; surface roughness