Why SiC and GaN CMP Lines Replace Colloidal Silica with Zirconia in Alkaline Buffered Slurries

In 150 mm and 200 mm silicon carbide wafer planarization, the addition of electronic/EL grade nano-zirconia abrasive powder as the solids component in a ready-to-use CMP slurry is held at 0.8–2.5 wt% for Si-face 4H-SiC and 0.5–1.5 wt% for C-face 4H-SiC when the oxidizer system contains 1.5–3.0 wt% hydrogen peroxide. The powder must satisfy ZrO2+HfO2 ≥ 99.9%, Fe2O3 ≤ 0.005%, Na2O ≤ 0.005%, and Cl− ≤ 0.005% because trace transition metals alter the SiC oxidation rate and induce leakage-current defects in the final device. Downstream production uses a single-wafer CMP tool with a perforated polyurethane pad, an in-situ diamond conditioning disk, and a 150–200 mL/min slurry flow rate. Platen speed is maintained at 55–70 min⁻¹, carrier speed at 60–75 min⁻¹, wafer backpressure at 0.8–1.2 psi, and pad temperature at 20–25 °C. Terminal finished products include 650 V and 1200 V SiC MOSFET wafers, GaN HEMT epitaxial wafers, and RF GaN-on-SiC wafers. Compliance anchors include ISO 14644-1:2015 Class 5 cleanroom packaging, ISO 13320:2020 particle size distribution verification, RoHS Directive 2011/65/EU Annex II, and REACH Regulation (EC) No 1907/2006 SVHC screening.

Process conflicts centre on the high-shear dispersion history of the slurry. At ZrO2 loadings above 3.0 wt%, the suspension viscosity increases and pump cavitation occurs in the slurry delivery line; at loadings below 0.5 wt%, the active particle density at the pad-wafer interface cannot sustain chemical-mechanical erosion, and the removal rate collapses. Batch-to-batch D50 movement from 120 nm to 160 nm has been observed to raise within-wafer non-uniformity by more than 15% unless the powder is pre-dispersed in a high-shear rotor-stator mixer at 3,000 min⁻¹ for 45 min and then filtered through a 0.5 µm PFA filter before entering the day tank. The pH window of 9.5–10.5 is critical; at pH below 9.0, the zeta potential of ZrO2 approaches the isoelectric point and agglomeration increases scratch counts, while pH above 10.5 promotes pad glazing. The formulation is incompatible with amine-based buffering agents at high pH because amine adsorption suppresses hydroxyl radical generation from hydrogen peroxide, reducing SiC oxidation. Published numeric removal-rate data for this exact electronic/EL grade is limited; equipment-specific removal rates must be established by on-tool coupon tests for each lot.

Yttria-tetragonal zirconia polycrystal ferrules in LC, SC, FC, and MPO connectors are planarized in the final end-face step with a 5–12 wt% nano-zirconia aqueous slurry buffered to pH 10.5–11.5 with potassium hydroxide. The downstream process is a multi-step polishing sequence: diamond lapping film at 9 µm, 3 µm, and 1 µm removes ferrule apex pre-damage, after which the zirconia slurry on a 0.6–0.8 mm hardness polyurethane pad creates the final physical-contact surface. A fixture holds 8 or 12 connectors; applied pressure is 0.8–1.2 psi, platen rotation is 60–120 min⁻¹, and per-batch polishing time is 60–120 s. Terminal finished product types are LC, SC, FC, and MPO single-mode and multimode fiber optic connectors. Compliance for the assembled connector is tested to Telcordia GR-326-CORE and IEC 61755-3-2, with end-face cleanliness verified by 200× Nomarski microscopy. The upper solids boundary is 15 wt%; above this level, the slurry produces scratches that degrade return loss below 45 dB. Polishing beyond 120 s per connector batch undercuts the zirconia ferrule relative to the silica fiber, creating a recess that shifts the physical contact geometry and increases back-reflection variability. The powder must be free of cerium and iron contamination above 10 mg/kg, as such residues generate end-face absorption centers under optical time-domain inspection.

When Zirconia Loadings Exceed 3 wt% in Sapphire Final Polishing, Pad Glazing and Edge Non-Uniformity Shift

Above 3.0 wt% nano-zirconia loading in a pH 10.0–11.0 final polishing slurry, the removal rate on c-plane sapphire stops increasing and pad glazing accelerates because zirconia particles accumulate in the polyurethane pad pores. The addition ratio is held at 2.0–3.0 wt% ZrO2 solids, with 0.3–0.8 wt% colloidal silica as a co-abrasive to moderate surface charge build-up. Downstream production uses a double-side planetary polisher for 100 mm or 150 mm sapphire wafers, with pad pressure 250–350 g/cm², platen speed 45–55 min⁻¹, and slurry flow 80–120 mL/min. The process removes 0.2–0.5 µm of subsurface damage left by diamond lapping and yields an epi-ready surface with Ra < 0.3 nm measured per ISO 4287:1997. Terminal product types are epi-ready sapphire wafers for blue and ultraviolet LED, micro-LED, and laser diode manufacturing. Compliance for the powder grade includes ISO 13320:2020 for D50 verification, IEST-STD-CC1246E Level 100 for packaging cleanliness, RoHS Directive 2011/65/EU Annex II, and REACH Regulation (EC) No 1907/2006 SVHC screening. The lower pH boundary is 9.0; at pH below this value, zeta potential of ZrO2 approaches the isoelectric point, causing rapid agglomeration and scratch defects above 0.5 µm in diameter. The co-abrasive ratio must not exceed 0.8 wt% silica, because silica dominates the surface charge at higher levels and suppresses the mechanical contribution of the zirconia particles, reducing removal rate at the wafer edge below the center by more than 20%.

Sintered aluminum nitride and low-temperature co-fired ceramic substrates are planarized with nano-zirconia abrasive to remove fired surface waviness and expose internal conductor pads. The lapping suspension is prepared at 10–20 wt% ZrO2 solids in deionized water with a polyacrylate dispersant at 0.1–0.3 wt%; final polishing uses 3–8 wt% solids on a polyurethane pad. The production process is a single-sided or double-sided lapping platform with a cast iron plate, followed by a polyurethane polishing platen; slurry is delivered at 60–100 mL/min per plate, and surface flatness is checked with a laser interferometer after each batch. Terminal finished products include AlN power module substrates, LTCC multilayer modules, and thick-film electronic substrates. Compliance is verified against ISO 4287:1997 for Ra control, IEC 62474:2018 for declarable substances, REACH Regulation (EC) No 1907/2006 SVHC screening, and RoHS Directive 2011/65/EU. The boundary condition: iron contamination from cast iron plates must be kept below 10 mg/kg in the recirculated slurry; above this level, residual iron diffuses into the AlN grain boundary phase during firing and increases surface leakage current. In addition, the slurry pH must not fall below 8.5; acidic conditions dissolve the polyacrylate dispersant and cause particle settling in the recirculation loop.

Electrostatic Chuck Polishing Alpha-Particle Control and Metrology Limits for Semiconductor Chamber Components

The final polishing sequence for an alumina electrostatic chuck begins with fixed-abrasive diamond conditioning, after which a 8–15 wt% nano-zirconia slurry removes subsurface dressing damage on a dedicated CNC polisher. The slurry pH is maintained at 9.0–10.0 to keep the zeta potential below −35 mV, avoiding re-agglomeration in the recirculation loop. Downstream process parameters include a 0.5–1.0 psi polishing pressure, spindle speed 800–1,200 min⁻¹, and sequential metrology with white-light interferometry for flatness and contact profilometry for Ra. Terminal components include electrostatic chucks, ceramic edge rings, and chamber liners for dielectric etch and deposition tools. Compliance requires ISO 14644-1:2015 Class 5 packaging, IEST-STD-CC1246E Level 100 surface cleanliness, and low-alpha emission qualification where uranium plus thorium content is controlled to < 50 µg/kg in the powder; RoHS Directive 2011/65/EU Annex II and REACH Regulation (EC) No 1907/2006 apply as material restrictions. Boundary conditions: polishing slurry must not be shared with stainless steel equipment due to chrome oxide pickup; if chromium exceeds 5 mg/kg in the slurry, it becomes a mobile contaminant in plasma etch chambers and shifts the electrostatic chuck leakage current after 500 h of radio-frequency operating life.

A Near-Neutral pH Zirconia Sol Produces Lower Edge Roll-Off in Glass Memory Disk Planarization

A near-neutral pH 8.5–9.5 zirconia sol with 1–5 wt% solids is employed in double-side planetary polishing of 65 mm and 95 mm glass memory disks to suppress edge roll-off. Compliance for the powder includes ISO 13320:2020 for particle size distribution, ISO 14644-1:2015 Class 5 packaging, IEC 62474:2018 for declarable substance reporting, and IEST-STD-CC1246E Level 100 for finished substrate cleanliness. The production process uses a double-side planetary polisher with polyurethane pads, pad pressure 0.5–1.0 psi, platen rotation 30–60 min⁻¹, and slurry flow 100–150 mL/min; post-polish cleaning includes megasonic deionized water and forced air. Terminal finished products are glass substrates for perpendicular magnetic recording hard disk drives. The processing boundary is strict: iron-bearing particulate above 1 mg/kg in the slurry becomes embedded in the glass surface during polishing, causing magnetic domain defects after sputtering because the embedded iron particle distorts the perpendicular anisotropy field.