Silicon carbide (SiC), a cornerstone of third-generation wide-bandgap semiconductors, is reshaping the landscape of power devices in new energy vehicles, 5G communications, rail transit, and beyond, thanks to its exceptional properties-wide bandgap, high critical breakdown field, and superior thermal conductivity. However, its extreme Mohs hardness of 9.2–9.3 and pronounced chemical inertness make wafer processing a critical bottleneck that directly impacts device performance and yield, presenting a notoriously "tough nut to crack." In conventional wafer fine polishing, colloidal silica (SiO₂) abrasives, though capable of delivering ultra-low surface roughness, are far softer than SiC and thus suffer from extremely low material removal rates. Diamond abrasives, on the other hand, are overly "aggressive," often leaving deep scratches and subsurface damage. Consequently, alumina (Al₂O₃), with its suitable hardness and stable physicochemical properties, has emerged as a leading candidate for SiC fine polishing abrasives. In particular, hundred-nanometer-scale (100–150 nm) alumina is becoming the workhorse in high-end SiC CMP (Chemical Mechanical Polishing) slurries, as it strikes an ideal balance between mechanical removal capability and surface defect control.
Why Hundred-Nanometer-Scale Alumina?
The choice of abrasive particle size is fundamentally governed by the trade-off between removal efficiency and surface quality. Micron-sized abrasives (>1 μm) can deliver higher mechanical removal rates but tend to cause fatal defects such as deep scratches and pits on the wafer surface, failing to meet the stringent requirement of atomic-scale planarity. Finer abrasives, conversely, are prone to agglomeration and lack sufficient cutting force, leading to a drastic drop in polishing efficiency and struggling to overcome the high hardness barrier of SiC. Hundred-nanometer alumina abrasives, in contrast, possess adequate momentum to perform effective mechanical grinding. Moreover, with proper morphology control, they can facilitate "rolling abrasion" under the constraint of the polishing pad, thereby minimizing the risk of scratching to a manageable level. This particle size range has now gradually become the mainstream technical pathway for state-of-the-art SiC fine polishing slurries.
Of course, beyond particle size, SiC fine polishing imposes the following additional requirements on abrasives:
(1) Particle Size Distribution: For hundred-nanometer alumina, monodispersity is no less critical than the absolute value of the average particle size. Even if the mean diameter is controlled within the hundred-nanometer range, a broad size distribution not only compromises polishing uniformity but also allows larger particles to induce deep scratches during polishing, directly leading to chip scrap.
(2) Morphology: Irregularly shaped alumina particles (e.g., platelets, needles, or angular fragments) are highly likely to gouge the wafer surface and generate scratches during polishing. In contrast, spherical or near-spherical particles tend to participate in material removal by rolling between the polishing pad and the wafer, effectively dispersing shear forces and markedly reducing defect density.
(3) Crystal Phase: Alumina exists in multiple crystalline phases (γ, δ, θ, α, etc.), among which α-Al₂O₃ is the thermodynamically most stable phase and also the hardest (Mohs hardness 9) and most chemically inert. During CMP, α-phase alumina provides sustained and stable mechanical cutting action without undergoing uncontrolled reactions with the acidic or alkaline media commonly found in polishing slurries.
(4) Ultra-High Purity: Metallic impurities must be controlled at exceptionally low levels; otherwise, they risk contaminating the wafer and degrading device performance.