1. Background and Challenges
Silicon carbide (SiC), renowned for its wide bandgap, exceptional hardness, and superior thermal stability, has emerged as a critical substrate material for next-generation power semiconductor devices. However, these very properties — high hardness and chemical inertness — make the precision polishing of SiC surfaces one of the most formidable challenges in the semiconductor industry. Chemical Mechanical Polishing (CMP) is currently the dominant process for achieving ultra-smooth SiC wafer surfaces, relying on oxidizing agents within the slurry to chemically soften the SiC surface, followed by mechanical material removal through abrasive action. Nevertheless, the atomic-level chemical interaction between oxidizing agents and the SiC surface has long remained poorly understood, significantly hindering the rational design and optimization of high-efficiency CMP slurry formulations.
2. Research Methodology: ReaxFF Reactive Force Field Molecular Dynamics Simulation
To uncover the microscopic removal mechanism in SiC CMP, researchers employed ReaxFF reactive force field Molecular Dynamics (MD) simulation. Unlike conventional force fields, ReaxFF is capable of dynamically describing the breaking and formation of chemical bonds in real time, making it particularly well-suited for investigating surface evolution processes involving chemical reactions.This approach enabled researchers to track, at the atomic scale, the following sequential processes: the adsorption and reaction of oxidant molecules with the SiC surface, including how oxygen atoms penetrate Si-C bonds and trigger bond rupture; the progressive formation and thickness evolution of the oxide layer, capturing the gradual transformation of the surface from SiC to an oxide layer dominated by SiO₂; and the detachment of oxidation products under mechanical force, revealing how abrasive particles strip the softened oxide layer from the substrate.
3. Core Mechanism: The Synergistic Oxidation–Removal Pathway
The simulation results clearly elucidate the microscopic material removal pathway in SiC CMP, which is fundamentally a two-step cyclic process driven by the synergistic interaction between chemical oxidation and mechanical abrasion.
The first step is the chemical oxidation stage. Oxidizing agents in the slurry react with the SiC surface, preferentially attacking Si-C bonds and progressively generating a transition oxide layer composed primarily of SiO₂ or SiOₓCᵧ. This oxide layer exhibits significantly lower hardness and mechanical strength compared to the SiC bulk, thereby achieving effective “chemical softening” of the surface material. The simulation further reveals that the growth thickness of the oxide layer follows a well-defined correlation with polishing process parameters, such as oxidant concentration, temperature, and contact pressure, providing a theoretical foundation for targeted process control.The second step is the mechanical removal stage. Under the shearing and indentation forces exerted by abrasive particles, the softened oxide layer is progressively detached from the SiC surface. The freshly exposed SiC surface then reacts again with oxidizing agents, initiating the next oxidation cycle. It is precisely this continuous cycle of “oxidation → softening → removal → re-oxidation” that constitutes the fundamental material removal mechanism in SiC CMP.
4. Implications for Slurry Formulation Design
The mechanistic insights gained at the atomic scale provide critical theoretical guidance for the formulation and optimization of SiC CMP slurries, with practical implications in the following areas:
Oxidant selection and concentration optimization: The reactivity of the oxidant directly governs the rate of oxide layer formation. An insufficient concentration leads to inadequate removal efficiency, while an excessive concentration may produce an overly thick oxide layer that abrasive particles cannot effectively strip away. An optimal balance between these two extremes must be identified.
Synergistic control of pH and temperature: The solution environment influences the effective activity of the oxidant and the phase composition of the resulting oxide layer, which in turn affects the ease of mechanical removal. Precise matching based on atomic-scale understanding is therefore essential.
Matched abrasive design: The hardness, particle size, and morphology of abrasives must be matched to the mechanical properties of the softened oxide layer, enabling efficient removal of the oxidized material while minimizing subsurface damage to the SiC bulk.
5. Conclusion
Through ReaxFF molecular dynamics simulation, researchers have systematically elucidated, for the first time at the atomic scale, the complete microscopic pathway of oxidation-based material removal in SiC CMP. This work not only fills a fundamental theoretical gap in SiC polishing mechanism research, but also lays a solid scientific foundation for the rational and targeted design of CMP slurry formulations. A thorough understanding and deliberate exploitation of the synergistic “chemical oxidation — mechanical removal” mechanism represents the key to overcoming the technical bottleneck of high-efficiency, high-quality SiC CMP.