| HS Code | 952815 |
| Appearance | White, homogeneous slurry |
| Particle Shape | Spherical |
| Alumina Crystal Phase | Alpha (α) phase |
| Alumina Purity | ≥ 99.99% (4N) |
| Average Particle Size D50 | 0.3–0.5 μm |
| Particle Size Distribution D90 D50 | ≤ 1.5 |
| Solid Content | 20–40 wt% |
| Ph At 25 C | 7.0–8.0 |
| Specific Gravity | 1.2–1.3 |
| Viscosity At 25 C | 20–100 mPa·s |
| Trace Metal Impurity Content | Na, K, Fe, Cu, Ni, Zn each ≤ 1 ppm |
| Dispersion Stability | > 6 months without sedimentation |
As an accredited Spherical Alumina Polishing Slurry Electronic/EL Grade factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Spherical Alumina Polishing Slurry Electronic/EL Grade is supplied in a 5 kg HDPE container with tamper-evident seal, ensuring purity and safe handling. |
| Container Loading (20′ FCL) | Spherical alumina slurry loaded in sealed drums, palletized, secured, and blocked in 20' FCL to prevent leakage and contamination. |
| Shipping | Spherical Alumina Polishing Slurry (Electronic/EL Grade) ships in sealed, corrosion-resistant containers to prevent contamination. Transport requires proper labeling as a chemical; avoid extreme temperatures. Standard ground freight is typical, with hazmat documentation if applicable. Ensure upright handling, spill containment, and compliance with local regulations during transit. |
| Storage | Store in a tightly sealed container in a cool, dry, well-ventilated area, away from direct sunlight and extreme temperatures. Avoid freezing; keep at 5–30°C. Protect from dust and contamination. Do not allow slurry to dry out. Mix gently before use, and follow manufacturer’s specified shelf life. |
| Shelf Life | Shelf life is 6 months from manufacture when stored sealed, at 5–30°C, protected from freezing and contamination. |
Sapphire wafer planarization for C-plane LED epitaxy is performed on single-sided rotary polishing equipment with hard polyurethane pads, typically at platen speeds of 30 rpm to 60 rpm and head downforces from 13.8 kPa to 41.4 kPa (2 psi to 6 psi). The electronic-grade spherical alumina slurry is supplied at a flow rate of 20 mL/min to 60 mL/min across a 4-inch wafer; larger wafers require proportional ramping of flow to prevent drying at the pad leading edge. In this application the abrasive load is commonly held between 5 wt% and 20 wt%, with D50 specified by ISO 13320:2020 laser diffraction in the 0.30 µm to 0.80 µm range. The pH is maintained at 10.0 to 11.5 because the alumina surface remains sufficiently charged to avoid gelation while the alkaline carrier weakens the sapphire surface through hydroxylation. A drop below pH 9.0 moves the system toward the alumina isoelectric point and produces hard agglomerates that create crescent-shaped pits; a rise above pH 12.0 increases the concentration of soluble aluminate species and narrows the active abrasive population. Material removal for C-plane sapphire is generally reported in the 1 µm/h to 5 µm/h range under these conditions, but published data for this specific spherical alumina grade is limited and must be verified by lot-specific pad-wafer friction measurement. Final epi-ready wafers are inspected by atomic force microscopy over a 10 µm × 10 µm scan window, with roughness for LED-grade C-plane material controlled below 0.25 nm Ra after 2 µm to 5 µm of subsurface damage removal. Production-scale failure modes include pad glazing, edge fast polish, and iron staining. Pad glazing appears as a brown hydrophobic film on the pad land area and can be traced to slurry drying when flow drops below 15 mL/min or when exhaust airflow across the platen exceeds 0.5 m/s. Edge fast polish is accelerated by backing film wear; replacing the backing film at 40-hour intervals avoids a characteristic W-shaped total thickness variation profile. Iron contamination above 10 µg/L in the slurry loop is sufficient to create haze after high-temperature annealing because iron diffuses into the sapphire surface; PP, HDPE, or PTFE wetted parts are required. The slurry should not be frozen because ice crystal growth fractures spherical alumina into angular fragments that increase scratch density even after remixing. Dilution is performed with 18 MΩ·cm deionized water to prevent cation-induced bridging. No stabilizer package based on amine chemistry should be added without full compatibility testing because amine-based additives adsorb onto polyurethane pads and change the friction coefficient by more than 20%.
On 4H-SiC (0001) silicon-face substrates intended for power metal-oxide-semiconductor field-effect transistors, planarization after diamond lapping is performed on dual-axis polishers with hard polyurethane pads having Shore D hardness of 55 to 65 and radial grooves. The spherical alumina slurry is typically loaded at 2 wt% to 5 wt% because higher concentrations raise scratch counts without proportionally increasing removal rate. Platen speed is set between 40 rpm and 80 rpm, downforce between 20.7 kPa and 41.4 kPa (3 psi to 6 psi), and slurry flow between 30 mL/min and 80 mL/min for 150 mm wafers. Si-face 4H-SiC is chemically inert under most slurry formulations; the alumina abrasive mechanically activates the surface and transmits energy to a thin silicon oxide layer that is regenerated by oxidizers. The alkaline carrier helps remove the resulting silicate species, but pH drift above 11.0 changes the dissolution equilibrium of the spherical alumina itself. Hydroxyl ion attack at the particle surface converts part of the abrasive into soluble aluminate ions, releasing irregular fragments that are no longer captured by the slurry filtration loop. These fragments become embedded in the pad and generate microscratches on the Si-face; the damage is visible under Nomarski microscopy as light streaks along the polishing direction. For this reason the pH is typically controlled within 9.5 to 10.8 when the slurry contains only alumina abrasive. If the pH must be raised further for oxidation rate reasons, the abrasive should be pretreated and the working bath filtered through a 0.5 µm absolute filter to remove fragments before they reach the pad. Material removal rate for 4H-SiC using alumina alone is commonly cited in the 0.1 µm/h to 0.8 µm/h range, which is significantly lower than when the slurry is modified with transition-metal oxide additives; however, such additives may introduce metal contamination and are not suitable for all device fabs. Final roughness after SCI cleaning is measured by atomic force microscopy; production targets for epi-ready SiC surfaces are generally below 0.3 nm RMS over a 5 µm × 5 µm scan area. Routine thickness removal is monitored by capacitance-based full-wafer thickness mapping rather than single-point measurements. The slurry loop must be free of calcium and magnesium above 5 µg/L because divalent cations interact with dissolved silicates and precipitate as adherent pad scales. Published data for this exact spherical alumina grade on SiC is limited, so initial process qualification requires removal-rate mapping and defect metrology on each incoming lot.
Second-step barrier chemical mechanical polishing on copper damascene wafers separates the removal of the Ta/TaN barrier layer from the copper metal and the interlayer dielectric. Spherical alumina is used at low abrasive loading, commonly 0.1 wt% to 1.0 wt%, because the copper surface is soft and conventional angular alumina at high solids increases dishing and metal line damage. The slurry is formulated at pH 9.0 to 10.5 with a corrosion inhibitor such as benzotriazole or 5-aminotetrazole; the inhibitor passivates the copper surface during barrier clearing. On 200 mm rotary polishers, the process window is summarized below. Pad conditioning is a critical variable: in situ diamond conditioning is performed continuously at 0.5 kg to 1.5 kg downforce to regenerate the pad texture and remove embedded alumina before it agglomerates. Without conditioning, the coefficient of friction rises within 10 min and the removal rate selectivity shifts from barrier-dominated to dielectric-dominated removal. The removal rate of TaN under these conditions is typically 30 nm/min to 100 nm/min, while the copper removal rate is held below 20 nm/min to limit dishing; the resulting selectivity ratio is therefore approximately 1.5:1 to 5:1. Published values vary with pad type, pH buffering capacity, and linewidth, and no single selectivity number is transferable between fabs. Post-CMP inspection of 0.18 µm line-space test structures commonly requires copper dishing below 20 nm and dielectric erosion below 30 nm measured by high-resolution stylus profilometry. The high-purity spherical alumina slurry must not contain chlorine-containing oxidizers if the fab prohibits chloride because residual chloride above 10 µg/L accelerates copper corrosion after cleaning. Amine-based pH buffers must be evaluated for compatibility with the interlayer dielectric; low-k materials with k value below 3.0 can absorb amine species and shift dielectric constant upward by 0.1 to 0.3. Cleaning after barrier CMP uses double-sided brush scrubbers and 18 MΩ·cm deionized water; incomplete cleaning leaves alumina particles at the copper line edges and increases electrical leakage across comb test structures.
| Parameter | Typical range |
|---|---|
| Abrasive concentration | 0.1 wt% – 1.0 wt% |
| pH | 9.0 – 10.5 |
| Platen speed | 50 rpm – 90 rpm |
| Head downforce | 10.3 kPa – 20.7 kPa (1.5 psi – 3.0 psi) |
| Slurry flow | 100 mL/min – 200 mL/min |
| Pad conditioning downforce | 0.5 kg – 1.5 kg |
For fired 96% alumina and aluminum nitride ceramic substrates used in power modules and radio-frequency packages, planarization before direct copper bonding is accomplished by uniform removal of surface waviness and grain-boundary pull-out defects. The electronic-grade spherical alumina slurry is diluted with 18 MΩ·cm deionized water to an abrasive concentration of 5 wt% to 15 wt%. Polishing is carried out on single-sided rotary plate machines with composite pads of medium hardness; platen speed is controlled from 20 rpm to 50 rpm, and applied pressure from 10 kPa to 35 kPa. Under these conditions, surface roughness measured by ISO 4287 profilometry can be reduced from lapping-level 0.5 µm Ra to below 0.05 µm Ra while maintaining flatness below 0.05 mm over a 100 mm length. Aluminum nitride substrates are sensitive to alkaline hydrolysis; the slurry pH should not exceed 10.0 because ammonia and alkali metal hydroxides attack exposed AlN grain boundaries and form aluminum hydroxide precipitates that increase surface porosity. Metallic cross-contamination from previous copper or silver polishing operations is not permitted; a dedicated dispensing loop and pad set must be used because residual metal particles above 1 µm can become embedded at ceramic grain boundaries and degrade dielectric breakdown voltage. Cleaning after planarization uses immersion rinsing and megasonic agitation at 40 kHz to dislodge alumina residues from pores. The cleaned substrate is dried under filtered hot air below 100 °C to avoid thermal stress cracking. Batch-to-batch variance in slurry particle size affects the removal of grain-boundary pull-out features more than centerline average roughness; this is why the slurry supplier should maintain D50 within ±0.05 µm and report particle size by ISO 13320:2020. Published data for this specific electronic-grade spherical alumina slurry on AlN is limited, and initial process validation should include dielectric breakdown test coupons rather than roughness alone.
Aluminum alloy disk substrates plated with electroless nickel containing 11.5 wt% to 12.5 wt% phosphorus are polished on double-sided planetary machines that remove 1 µm to 3 µm of NiP per side. The process requires a hard closed-cell polyurethane pad, an acidic alumina slurry, and continuous filtration. When spherical alumina replaces irregular alumina, the surface defect density can be reduced because spherical particles do not expose sharp contact points that create deep narrow scratches. Slurry D50 for this operation is normally specified between 0.10 µm and 0.35 µm by ISO 13320:2020; oversized particles above 0.8 µm are controlled to fewer than 0.01% by number because they produce defects that exceed the magnetic head fly-height budget. The process is typically run at 20 rpm to 50 rpm platen speed and 10 kPa to 25 kPa pad pressure, with slurry flow from 100 mL/min to 300 mL/min per side through a 0.5 µm absolute filter. pH is held between 2.5 and 4.5 to dissolve NiP polishing by-products and prevent the formation of nickel hydroxide films. If pH is allowed to drift above 4.5, phosphate complexes precipitate on the pad surface and produce a load-bearing glaze that reduces removal rate by more than 30%. Surface quality is quantified by atomic force microscopy with a 10 µm × 10 µm scan field; production hard disk substrates are commonly required to show roughness below 0.2 nm Ra and waviness below 0.5 nm after polishing and cleaning. The polishing slurry must be free of sodium and calcium above 5 µg/L because these ions are electrochemically active and can create ionic residues at the disk surface after lubricant treatment. The aqueous slurry should not be stored beyond 48 hours after dilution at room temperature because microbial growth and slow dissolution of alumina can shift pH and particle charge. Direct comparison to irregular alumina is summarized below.
| Metric | Irregular alumina | Spherical alumina |
|---|---|---|
| Scratch density post-polish | 2 – 5 defects/cm² | 0.5 – 1.5 defects/cm² |
| Average roughness Ra | 0.15 – 0.25 nm | 0.10 – 0.20 nm |
| Removal rate | 0.4 – 0.8 µm/min | 0.3 – 0.6 µm/min |
| Pad glazing onset pH drift | >4.0 | >4.5 |
Edge and facet polishing of GaN-on-sapphire LED dies after singulation is performed to remove microcracks and improve light extraction from sidewalls. Spherical alumina slurry at 1 wt% to 3 wt% abrasive loading is metered onto chemical-resistant low-nap pads; the die array is mounted on a rigid carrier and processed at pad pressure between 0.5 psi and 2.5 psi. The material removed is typically less than 1 µm per facet, and the main objective is defect smoothing rather than thickness reduction. Removal rate does not increase linearly with pad pressure in this configuration. When pressure exceeds 2.5 psi, the spherical alumina particles are forced into the pad surface, reducing the effective contact area and causing a transient removal-rate plateau or decline. This mechanical embedment is not reversed by slurry flow alone; the pad must be conditioned or replaced after 20 batches to restore the original friction signature. At the same time, high pressure increases chipping at the die corners because the rigid carrier transmits localized stress through the adhesive tape. Published data for this specific configuration is limited, and process settings should be revalidated when die size falls below 200 µm × 400 µm because the ratio of facet perimeter to area changes. Slurry pH is held near 7.0 to 9.0 to avoid attack on exposed GaN edge planes; strongly alkaline media above pH 11.0 can produce facet roughening rather than smoothing. The slurry must be free of sodium above 5 µg/L because sodium residues at the exposed sidewall can alter the surface potential and interfere with subsequent conformal dielectric deposition. Filtration through a 0.5 µm absolute filter is used to remove any agglomerates before the slurry contacts the die frontside. After polishing, the die carrier is transferred to a megasonic rinse bath at 40 kHz to remove alumina particles from the facet-pad contact zone; residual particles can shadow the sidewall during atomic layer deposition of passivation layers.
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Spherical Alumina Polishing Slurry Electronic/EL Grade is supplied as an aqueous dispersion of high-purity α-Al₂O₃ with controlled spherical morphology and a narrow particle size distribution. The product line is designated EL-SAS-0.3, EL-SAS-0.5, and EL-SAS-1.0, where the numeric suffix denotes median particle size. Sphericity factor exceeds 0.90 as measured by dynamic image analysis per ISO 13322-1:2014, and particle size distribution is measured by laser diffraction per ISO 13320:2020. The electronic/EL grade differs from lapping-grade alumina slurry in its lower alkali metal and transition metal content and in its controlled pH and zeta potential for chemical mechanical planarization of hard electronic substrates.
Typical manufacturing specifications are provided in Table 1. Viscosity is measured with a Brookfield RV rotational viscometer using spindle 2 at 60 rpm and 25°C per ASTM D2196-20. pH is determined with a glass electrode per ASTM E70. Metallic impurities are quantified by ICP-MS per ASTM D5673. The span, defined as (D90−D10)/D50, is controlled at ≤0.90 for the 0.30 µm grade, ≤1.0 for the 0.50 µm grade, and ≤1.2 for the 1.00 µm grade. Oversize particles greater than 3 µm are not detected by wet sieving per ISO 3310-1:2016.
| Parameter | EL-SAS-0.3 | EL-SAS-0.5 | EL-SAS-1.0 |
|---|---|---|---|
| D50 median particle size (µm) | 0.30 ± 0.03 | 0.50 ± 0.04 | 1.00 ± 0.08 |
| D90 particle size (µm) | ≤0.65 | ≤1.0 | ≤2.0 |
| Solid content (wt%) | 20.0 ± 1.0 | 25.0 ± 1.0 | 30.0 ± 2.0 |
| pH at 25°C | 10.5 ± 0.5 | 10.8 ± 0.4 | 10.0 ± 0.5 |
| Viscosity at 25°C, 60 rpm (mPa·s) | ≤5.0 | ≤8.0 | ≤10.0 |
| Sodium (ppm) | ≤5 | ≤8 | ≤10 |
| Iron (ppm) | ≤10 | ≤15 | ≤20 |
The product uses deionized water with resistivity ≥18.0 MΩ·cm at 25°C. The abrasive concentration is selected to balance removal rate and suspension stability; the 0.30 µm grade is intended for final polish and surface finish below 1 nm Ra on sapphire and aluminum nitride, while the 1.00 µm grade is used for stock removal after sawing or lapping. The 0.50 µm grade is an intermediate formulation for silicon carbide and for two-step sapphire processing.
On a single-side rotary polisher with a 380 mm grooved polyurethane pad and 20–35 kPa downforce, the 0.30 µm grade removes c-plane sapphire at 1.2–1.8 µm/h when platen speed is 55–65 rpm and slurry flow rate is 15–25 mL/min. These values require continuous in situ pad conditioning with a diamond conditioner for 10 s every 5 min; when conditioning is omitted, removal rate decays by 20–30% within 30 min because alumina particles and sapphire swarf fill pad pores and promote glaze formation. Total thickness variation across a 100 mm wafer remains below ±0.5 µm under these conditions, with edge exclusion of 3 mm.
On a production-scale double-side polishing line for 4-inch sapphire, the main defect source was not removal rate decay but micro-scratch generation after pH drift in the return line. A stainless steel pH electrode in the slurry return and a dilute potassium hydroxide dosing loop restored zeta potential and reduced scratch counts to below 3 scratches per 100 cm² under dark-field inspection at 50× magnification. This indicates that pH control at the point of use is as critical as nominal particle size for defect-free epitaxial substrates. Material removal follows Prestonian behavior over the specified downforce range; above 40 kPa the exponent deviates because abrasive particle fracture occurs on hard sapphire surfaces.
Silicon carbide wafer finishing with the 0.50 µm grade is typically conducted after diamond mechanical polishing. Under 25–30 kPa downforce and 50 rpm platen speed, removal rates on the Si-face of 4H-SiC range from 0.3 to 0.8 µm/h when an oxidizing additive is present. Without the additive, removal rate falls by 40–50% because alumina abrasion alone cannot overcome the chemical inertness of silicon carbide. Published data for this specific configuration is limited to single-wafer runs and should not be treated as a full production baseline. For 6-inch semi-insulating silicon carbide, the 0.50 µm grade is used with a harder polyurethane pad of Shore D 60–70 to maintain wafer flatness. The polishing temperature should remain below 35°C; above this threshold evaporation increases ionic strength and reduces zeta potential, causing drying artifacts on the pad and higher micro-scratch counts. Post-polish cleaning follows an RCA SC-1 step and dilute hydrofluoric acid; the acidic step removes residual aluminum from the SiC surface. The product is not recommended for final silicon wafer polishing; colloidal silica remains the reference abrasive in that application because residual aluminum on silicon can degrade gate oxide integrity.
Electronic/EL grade designation imposes lower mobile-ion limits than conventional lapping-grade alumina slurries. Sodium is ≤5 ppm for the 0.30 µm grade, potassium ≤5 ppm, iron ≤10 ppm, copper ≤2 ppm, and total transition metals ≤20 ppm when determined by ICP-MS per ASTM D5673. Chloride and sulfate are limited to ≤10 ppm and ≤20 ppm, respectively. Zeta potential magnitude measured by electrophoretic light scattering exceeds 35 mV at pH 10.0–11.0; this maintains electrostatic repulsion and prevents agglomeration in stagnant slurry lines. If the pH drifts below 9.0 through atmospheric carbon dioxide absorption, zeta potential magnitude decreases and micro-scratches increase. Recirculating systems therefore require closed-loop pH control and carbon dioxide-free nitrogen blanketing. The slurry should not be diluted with water containing calcium or magnesium above 10 ppm, because divalent cations compress the electrical double layer and induce flocculation.
Storage in sealed containers at 5–35°C is required; freeze-thaw cycles cause irreversible aggregation. Shelf life is 12 months from date of manufacture under these conditions. The formulation is supplied in 20 L and 200 L high-density polyethylene containers. Drums should be purged with nitrogen during dispensing to limit carbon dioxide uptake. Slurry transferred to day tanks should be recirculated continuously at a flow rate sufficient for at least 5 tank turnovers per hour; static storage in lines is not acceptable because settled particles can be reintroduced as agglomerates during tool start-up.
The composition is formulated to meet RoHS 2011/65/EU Annex II maximum concentration values for lead, mercury, cadmium, hexavalent chromium, PBB, and PBDE. REACH candidate-list SVHC content is below 0.1 wt%. The product is free of halogenated solvents when assessed by EN 14582:2016.
Comparative performance data for c-plane sapphire polishing are summarised in Table 2. The values are specific to a 380 mm grooved polyurethane pad, 30 kPa downforce, 60 rpm platen speed, and 20 mL/min slurry flow rate. Surface roughness was measured by atomic force microscopy over 10 × 10 µm scan areas per ISO 25178-2:2021, and subsurface damage depth was evaluated by cross-section transmission electron microscopy.
| Abrasive system | D50 (µm) | Removal rate (µm/h) | Post-polish Ra (nm) | Subsurface damage depth (µm) |
|---|---|---|---|---|
| Spherical α-Al₂O₃ electronic/EL grade | 0.30 | 1.2–1.8 | 0.20–0.35 | <0.5 |
| Irregular calcined α-Al₂O₃ | 0.30 | 1.0–1.5 | 0.45–0.80 | 1.0–2.0 |
| Colloidal silica | 0.08 | 0.1–0.4 | 0.08–0.20 | <0.2 |
Spherical morphology reduces brittle fracture by distributing normal load over a larger effective contact area; irregular calcined particles generate angular contacts and localized stress concentrations that increase subsurface damage. The hardness differential between α-Al₂O₃ and amorphous silica explains the higher removal rate of spherical alumina on sapphire but also requires a polyurethane pad with Shore D hardness 45–60 and in situ conditioning to prevent particle embedding and pad glazing. Subsurface damage depth is a critical metric for GaN-on-sapphire LED manufacturing. Transmission electron microscopy cross-sections show that spherical alumina produces a damaged layer below 0.5 µm under the stated conditions, whereas irregular calcined alumina generates deeper lateral fractures along the c-axis. Colloidal silica produces the lowest subsurface damage but its removal rate on sapphire is too low for bulk stock removal in high-volume LED production; a two-step sequence using spherical alumina for bulk removal and colloidal silica for final finish is therefore specified for some high-brightness LED wafers. Compared with polycrystalline diamond slurries, spherical alumina produces lower stock removal but lower Ra and less edge chipping, making it suitable for substrates that will receive epitaxial deposition.
For GaN-on-sapphire LED substrates, the 0.30 µm grade is specified after a 1.00 µm stock removal step. The final surface must exhibit low haze and no sub-surface damage because residual damage acts as non-radiative recombination centers after GaN epitaxy. Production wafers are typically sampled at 5 points per wafer using AFM per ISO 25178-2:2021; full-wafer haze is quantified by dark-field scattering. When haze exceeds the process limit, the root cause is usually large-particle contamination from the polishing pad or from a pH drift in the slurry line, not the primary particle size distribution.
For power semiconductor substrates such as 4H-SiC, the spherical alumina grade is used as an intermediate step after diamond mechanical polishing. The final CMP step may use colloidal silica or a mixed-abrasive slurry to achieve the required 0.1–0.3 nm Ra on the Si-face. The electronic/EL grade is compatible with such sequential processes if the equipment is rinsed thoroughly between steps; cross-contamination of alumina into the final silica step increases residual aluminum on the wafer surface and can shift threshold voltage in metal-oxide-semiconductor devices.
Aluminum nitride substrates are processed in a two-step sequence using the 1.00 µm grade followed by the 0.30 µm grade. The first step removes saw damage and planarizes the as-fired surface; the second step reduces RMS roughness below 1 nm when measured by AFM over 2 × 2 µm scan areas per ISO 25178-2:2021. On a 200 mm single-side polisher with a 300 mm vacuum carrier, the transition between grades requires a 10 min deionized water rinse; without this rinse, carryover of coarse particles produces crescent-shaped scratches at the wafer edge. Final polish is typically performed at 20 kPa downforce and 50 rpm platen speed for 60–90 min.
The pH is maintained at 10.5 ± 0.3. A drop below 9.5 causes measurable agglomeration and increases micro-scratch density. An oxidizing additive is not required for aluminum nitride because the material hydrolyzes slowly in alkaline aqueous media to form a soft aluminum oxyhydroxide layer that is removed mechanically. Post-polish cleaning uses dilute citric acid at pH 3.5 ± 0.2 followed by megasonic deionized-water rinse. Dark-field inspection should show fewer than 5 particles per 2-inch wafer; higher counts indicate incomplete cleaning or flocculation in the recirculation loop. The slurry should not be combined with amine-based additives because certain amines complex aluminum ions and alter zeta potential, causing redeposition of aluminum-containing species on the substrate surface.
