| HS Code | 767747 |
| Chemical Name | Aluminum etchant (alkaline aqueous solution) |
| Appearance | Clear, colorless liquid |
| Odor | Mild acrid |
| Ph | 12–14 (strongly alkaline) |
| Density | 1.1–1.3 g/mL at 20°C |
| Specific Gravity | 1.1–1.3 |
| Boiling Point | Approximately 100°C (212°F) |
| Melting Point | Approximately 0°C (32°F) |
| Viscosity | Similar to water (1–2 cP at 20°C) |
| Solubility In Water | Fully miscible |
| Flash Point | Non-flammable |
| Reactivity | Reacts with aluminum, releasing hydrogen gas |
| Storage Temperature | 15–30°C (59–86°F) |
| Shelf Life | 12 months from date of manufacture |
| Hazard Classification | Corrosive |
As an accredited Aluminum Etchant factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Aluminum etchant is packaged in a 5-gallon (19 L) high-density polyethylene pail with a secure, resealable lid and clear hazard labeling. |
| Container Loading (20′ FCL) | Aluminum etchant loaded in a 20′ FCL as a fully contained unit, with secure packaging, ventilation, and segregation for safe transport. |
| Shipping | Aluminum Etchant is a corrosive hazardous material requiring regulated shipping. It must be packaged in UN-approved containers, labeled with corrosive placards, and accompanied by a Safety Data Sheet and dangerous goods documentation. Transport via ground is preferred; air shipping is restricted. Ensure compliance with IATA, IMDG, and DOT regulations. |
| Storage | Store Aluminum Etchant in tightly sealed, clearly labeled containers made of compatible materials (e.g., polyethylene or glass). Keep in a cool, dry, well-ventilated area away from direct sunlight, heat sources, and incompatible substances like strong oxidizers or bases. Ensure secondary containment and emergency eyewash/shower access nearby. |
| Shelf Life | Typical shelf life is 12 months if stored tightly sealed in original containers, away from heat, moisture, and contaminants. |
The etching of Al-0.5%Cu and Al-1%Si-0.5%Cu films in back-end semiconductor redistribution is carried out in a fully exhausted wet bench charged with 75–80 wt% phosphoric acid, 4–6 wt% acetic acid, 4–6 wt% nitric acid, and 10 wt% deionized water. Bath temperature is controlled at 40 °C ± 2 °C by a fluoropolymer inline heater and a quartz-shell heat exchanger; the etch rate for a 1.0 µm Al-0.5%Cu film under low-pressure recirculation falls between 150 nm/min and 300 nm/min, with the upper value reached only when dissolved aluminum is below 15 g/L. Nitric acid oxidizes the aluminum surface to Al³⁺, while acetic acid passivates exposed TiW or TiN barrier layers and limits undercut. Selectivity to TiW remains above 10:1 until bath temperature exceeds 45 °C, at which point lateral etching accelerates and produces ragged barrier edges. Endpoint for films thinner than 2 µm is monitored by optical emission spectroscopy at 405 nm on the exhaust line or by sheet resistance mapping on sacrificial monitor wafers; production lines running 200 mm wafers at 45 nm minimum line/space require endpoint repeatability better than ±3 s. Withdrawal from the bath is followed by a cascade rinse in 18.2 MΩ·cm deionized water within 45 s; delay or rinse pH above 6.5 initiates post-etch galvanic attack at Cu-rich Al-Cu precipitates. The recirculation loop includes a 0.1 µm PTFE membrane filter and ultraviolet sterilization, holding particle counts below 50 particles/mL at 0.5 µm size. Bath-specific gravity is held between 1.45 and 1.55, and titrated aluminum concentration must not exceed 30 g/L because etch uniformity across the wafer degrades beyond ±5% when viscosity shifts. The module is interlocked according to SEMI S2-0718 for chemical exhaust, fire detection, and emergency rinse access.
Immersion chemical milling of 2024-T3 and 7075-T6 aerospace skins relies on an alkaline aluminum etchant containing 130–180 g/L sodium hydroxide and 15–30 g/L sodium sulfide held at 85–95 °C. Removal rate is diffusion-limited by migration of aluminate ions from the boundary layer, so the process responds to rack movement, air sparging, and bath viscosity rather than to acid concentration alone. Maskant-to-metal peel strength is maintained above 7.0 N/25 mm after 30 min immersion; failure of the maskant at a step edge produces undercut that exceeds the ±0.05 mm tolerance defined in the CAM file. Each production rack carries sacrificial coupons measured at three positions with a digital micrometer having 0.005 mm resolution; etch rate and taper ratio are calculated from the difference between mask-protected and exposed zones. Once dissolved aluminum in the bath exceeds 60 g/L, solution viscosity increases and the taper ratio degrades from 1.0:1 toward 1.4:1, forcing premature spiking or dumping of the etch solution. Hydrogen evolution at the metal surface must be disrupted by low-pressure oil-free air sparging; insufficient sparging creates gas-channel defects that appear as shallow dendritic grooves along the rolling direction. After etching, the skins are transferred to chilled water below 30 °C and then desmutted in 10–15 vol% nitric acid at 20–25 °C to remove copper-rich smut. Feedstock verification for clad sheet references ASTM B209 and AMS-QQ-A-250; pit morphology and intergranular attack are checked per ASTM E407 before the skin moves to fluorescent penetrant inspection.
In thin-film transistor array manufacturing, gate electrodes of 300 nm Al-2.0at%Nd capped with 50 nm Mo are wet-etched in a phosphoric-acetic-nitric mixture modified with a nonionic surfactant to lower surface tension and improve wetting inside 3–5 µm trench geometries. The bath operates at 38–45 °C, and the target etch rate for the Al-Nd layer is 60–100 nm/min; the Mo cap is removed by the same acid blend, but the line switches to a higher nitric-acid ratio when cap thickness exceeds 80 nm. Taper angle is held between 30° and 50° to ensure silicon nitride gate insulator step coverage; angles below 25° increase the risk of drain-source bridging, while angles above 55° create seams in the insulator and lower breakdown voltage. Bath temperature variation across the tank must remain within ±1 °C; otherwise taper angle shifts between center and edge of Gen 5.5 substrates. Etch endpoint is detected optically at 405 nm on Gen 5.5 or Gen 8.5 etch lines, with endpoint variation below 5 s required for uniform CD loss across the substrate. The primary defect is galvanic corrosion at the Al-Nd/Mo interface when deionized water rinse pH exceeds 6.0; production lines therefore use CO₂-sparged rinse water or a pH-adjusted intermediate rinse. Sulfate anion carryover from sulfuric acid cleaners must remain below 5 ppm, otherwise surface pitting appears in the Al-Nd film after etch. Wastewater from the etchant module is monitored for nitrate and fluorine compounds under local discharge permits; RoHS Recast 2011/65/EU does not restrict aluminum etchants themselves but applies to the finished display module if it contains cadmium or lead in connected components.
| Application class | Etchant composition / operating window | Removal range | Critical process variable |
|---|---|---|---|
| Semiconductor redistribution | 75–80% H₃PO₄, 4–6% CH₃COOH, 4–6% HNO₃, 40 °C ± 2 °C | 0.5–2.0 µm | dissolved aluminum <30 g/L |
| Aerospace chemical milling | 130–180 g/L NaOH, 15–30 g/L Na₂S, 85–95 °C | 0.25–12.7 mm | dissolved aluminum <60 g/L |
| TFT Al-Nd/Mo gate | phosphate-acetate-nitrate, 38–45 °C | 200–500 nm | taper angle 30–50° |
| Metallographic Keller’s | 2 mL HF, 3 mL HCl, 5 mL HNO₃, 190 mL H₂O, 20–25 °C | 10–20 s immersion | surface finish 0.05 µm |
For aluminum-cored metal-clad printed circuit boards used in LED lighting and insulated-gate bipolar transistor power modules, a shallow microetch of the 5052-H32 or 1050-H24 substrate is used before dry film lamination to generate a 2–3 µm mechanical tooth profile and remove rolling oil oxide. The sodium hydroxide-based aluminum etchant is sprayed at 50–55 °C for 20–30 s in a conveyorized spray chamber, followed by a hydrochloric acid desmut step and a final rinse with water below 10 µS/cm conductivity. If relative humidity in the lay-up room exceeds 60%, the etched substrates must be held in desiccated storage for no more than 4 h before dry film lamination; otherwise photoresist adhesion drops below the peel strength needed for 75 µm line/space patterning. The same etching step removes burrs around punched holes if the punch-to-etch queue time is kept below 8 h; longer queue times allow aluminum hydroxide to age into a hydrated oxide that resists uniform microetching.
Metallographic coupons cut from rotary-forged 7075-T6 wheels are prepared by mechanical polishing through 0.05 µm colloidal silica, then immersion-etched in Keller’s reagent consisting of 2 mL hydrofluoric acid, 3 mL hydrochloric acid, 5 mL nitric acid, and 190 mL distilled water at 20–25 °C for 10–20 s. The hydrochloric and nitric acids attack the aluminum matrix and secondary phases at different rates, while hydrofluoric acid removes the passive oxide layer, revealing grain boundaries and precipitate-free zones without the excessive pitting observed with straight NaOH macroetch. Etching time must be shortened when the sample temperature exceeds 30 °C because grain-boundary attack accelerates and obscures the fine grain structure defined in ASTM E112-13(2021). Immediately after etching, the coupon is rinsed in warm tap water followed by ethanol and dried under forced nitrogen at 0.5–1.0 bar; delayed rinsing produces chromium-rich stain films on 7075 due to copper and chromium redeposition. For grain-flow documentation in load-bearing aerospace components, the etched surface is photographed at 12.5× to 25× using a digital microscope calibrated against a stage micrometer; measurements of grain aspect ratio are then compared to the minimum values specified on the forging drawing.
Surface micromachined MEMS devices use a diluted phosphoric-acetic-nitric aluminum etchant to release 1–3 µm aluminum sacrificial layers without attacking polycrystalline silicon, silicon nitride, or thermal oxide. The release bath is held at 30–40 °C with a 50:1 to 100:1 dilution of the semiconductor-grade formulation, producing lateral release distances of 50–200 µm in 20–60 min on test structures. Hydrogen bubbles generated at the aluminum dissolution front can adhere to 5 µm gaps and cause under-release near anchor points; ultrasonic agitation is generally avoided because it fractures released membranes, so the bath uses bubble-reducing wetting agents or vacuum priming. Rinsing with isopropyl alcohol followed by supercritical CO₂ drying reduces stiction after release, but the exact cycle depends on the geometry and spring constant of the released structure. Published data for this specific configuration is limited; selectivity to passivation films must be validated on each device wafer lot because the etch rate of silicon nitride in hot phosphoric acid becomes measurable above 40 °C.
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Aluminum Etchant AE-PAN-80/5/5/10 is a phosphoric acid/nitric acid/acetic acid/water mixture specified for wet chemical removal of aluminum and aluminum alloy thin films in microelectronic patterning and for macrostructural examination of aluminum alloy specimens. The product designation encodes the nominal mass ratio of the active components: 80 wt% phosphoric acid, 5 wt% nitric acid, 5 wt% acetic acid, and 10 wt% deionized water. Phosphoric acid provides the primary solvation of aluminum to soluble aluminum dihydrogen phosphate, nitric acid maintains a controlled oxidizing condition that reduces pitting and hydrogen evolution, and acetic acid lowers interfacial tension and buffers free acid activity at the metal/resist boundary. The product is filled through 0.1 µm polypropylene cartridges and is intended for wet benches constructed with high-density polyethylene, polypropylene, or fluoropolymer wetted surfaces.
The dissolution reaction proceeds by initial oxidation of the aluminum surface by nitrate ion, followed by solvation of the oxidized aluminum by phosphoric acid. In an unstirred beaker, hydrogen evolution is suppressed relative to hydrochloric acid-based etches because the nitrate reduction path consumes protons; this shifts the mixed potential to a passive region and reduces grain boundary pitting. In recirculating wet benches, local depletion of phosphoric acid at the etch front creates a viscosity gradient that reduces mass transfer in high-aspect-ratio features. The result is an aspect-ratio-dependent etch rate for features below 0.5 µm width, which must be accounted for by overetch budget or ultrasonic agitation.
Etch rate on aluminum-1% silicon and aluminum-0.5% copper films is controlled by free phosphoric acid concentration, temperature, and local depletion of reactants within the diffusion boundary layer. A temperature set point of 40 °C with a control band of ±1 °C is selected in many production wet benches to balance linewidth loss against throughput.
At 40 °C, etch rates determined by stylus profilometry on 500 nm blanket aluminum films typically fall between 120 nm/min and 250 nm/min; values outside this range indicate bath aging, excessive water uptake, or incorrect make-up ratios. Nitric acid content below 4.0 wt% increases undercut and pitting, while nitric acid content above 6.0 wt% can oxidize the aluminum surface and suppress the clear-etch rate. Because published data for this specific configuration is limited, process release should be based on monitor wafers rather than supplier typical values alone.
At the photoresist interface, the etch front advances isotropically; lateral etch may reach 0.8 to 1.2 times the vertical etch for dense 1.0 µm line/space patterns. Overetch is normally limited to 30% of the clear-etch time to keep undercut below 0.15 µm per side for a 500 nm film.
The lot-specific certificate of analysis reports component assays, trace metal impurities, and particle counts. Table 1 lists representative acceptance limits for semiconductor-grade material. Density at 20 °C is between 1.60 g/cm³ and 1.68 g/cm³ depending on water content; viscosity is measured by Brookfield viscometer at 25 °C as an incoming quality check under ISO 9001:2015 documentation control.
Component ratios are controlled within the acceptance limits because nitric acid concentration controls oxidizing power and acetic acid concentration controls wetting and buffering. A low acetic acid level produces poor wetting and irregular undercut at the resist edge; a high acetic acid level can soften photoresist and reduce etch rate. Batch-to-batch variation of acid ratio is checked by titration and by a monitor wafer.
| Parameter | Acceptance range | Test method |
|---|---|---|
| Phosphoric acid (H3PO4) | 79.0–81.0 wt% | acid-base titration |
| Nitric acid (HNO3) | 4.5–5.5 wt% | redox titration |
| Acetic acid (CH3COOH) | 4.5–5.5 wt% | gas chromatography |
| Water (H2O) | 9.0–11.0 wt% | Karl Fischer titration |
| Iron (Fe) | ≤100 ppb | ICP-MS |
| Copper (Cu) | ≤50 ppb | ICP-MS |
| Sodium plus potassium (Na + K) | ≤200 ppb | ICP-MS |
| Particles at 0.5 µm | ≤100 particles/mL | laser particle counter |
For aluminum interconnect patterning, the product is dispensed into a recirculating bath containing a temperature-controlled fluoropolymer heat exchanger and 0.1 µm polypropylene filter cartridges. Cassettes holding 100 to 150 mm wafers are immersed with continuous agitation at a flow velocity of 0.2 to 0.5 m/s across the wafer surface. The etch sequence includes a deionized-water pre-rinse, main etch, overetch, and a two-stage overflow rinse. End point is determined by optical emission from the bath or by a timed overetch established from a monitor wafer for each bath.
Hard-baked positive photoresist or polyimide masking is required; soft-baked resist may lift due to acetic acid wetting and thermal stress above 45 °C. The bath must be covered to reduce water uptake and acetic acid evaporation. Water uptake from ambient humidity above 60% relative humidity can shift component ratios and increase etch rate drift by ±5% over an eight-hour shift.
Bath make-up uses the product as supplied; dilution with deionized water is not recommended except under laboratory supervision because the component ratios, not just total acid concentration, determine selectivity. The bath is allowed to reach set point before wafer insertion, and the first monitor wafer of a shift verifies clear-etch time and undercut. If the first monitor clear-etch time differs from the established mean by more than 10%, the bath is re-titrated and the filter cartridges and heat exchanger are inspected for salt deposition.
The principal alternative chemistries for aluminum etching are hydrochloric acid/hydrogen peroxide solutions and alkaline hydroxide/tetramethylammonium hydroxide solutions. Hydrochloric acid/hydrogen peroxide mixtures attack aluminum rapidly but generate chloride-containing residues, corrode exposed copper or copper-alloy underlayers, and produce variable adhesion to positive photoresist. Alkaline chemistries attack silicon and silicon dioxide, making them unsuitable for front-end-of-line aluminum gate or interconnect patterning on silicon substrates; potassium hydroxide additionally introduces mobile potassium ions that degrade transistor threshold stability.
Compared with hydrochloric acid/hydrogen peroxide, the PAN-type product leaves phosphate rather than chloride residues; this is an advantage on aluminum-copper alloys where chloride can accelerate galvanic corrosion at the Al-Cu interface. The trade-off is a narrower temperature range and more stringent rinse requirement. Compared with alkaline etchants, the PAN-type product does not attack silicon, but it requires post-etch residue removal with a mild alkaline or commercial stripper to dissolve aluminum phosphate films that are not water-soluble.
Table 2 compares the product against these alternatives on parameters relevant to semiconductor wet bench operation. The values are representative literature and supplier data ranges; lot-specific confirmation is required because published data for this specific configuration is limited.
| Parameter | AE-PAN-80/5/5/10 | HCl/H2O2 | KOH/TMAH |
|---|---|---|---|
| Typical operating temperature | 35–50 °C | 25–40 °C | 40–80 °C |
| Aluminum etch rate | 120–400 nm/min | 50–300 nm/min, ratio-dependent | >500 nm/min |
| Behavior on thermal SiO2 | moderate selectivity, bath-age dependent | variable; can attack exposed oxide in aged baths | poor selectivity; attacks SiO2 |
| Resist compatibility | post-baked positive resist | variable; soft-bake resist lifting reported | polymer masks preferred |
| Major restriction | aluminum loading and water balance | chloride residues, metal underlayer attack | silicon attack, mobile-ion contamination |
In metallographic laboratories, the same product is used at 20 °C to 25 °C as a macroetchant for aluminum alloy sections prepared according to ASTM E340-15. Immersion times from 5 s to 60 s reveal grain flow, weld fusion lines, and segregation in alloys such as 2024, 6061, and 7075. The product differs from Keller’s reagent, which contains hydrofluoric acid, hydrochloric acid, and nitric acid; the absence of hydrofluoric acid reduces silica attack and eliminates fluoride-containing waste in laboratories where silicon-containing phases are present.
Post-etch rinsing uses deionized water meeting ASTM D5127-13 Type E-1.2 or better, with total organic carbon below 5 ppb and particle counts below 100 counts/L at 0.1 µm. Residual phosphoric acid films left after an inadequate rinse hydrolyze to aluminum phosphate crusts; chloride traces from facility water can initiate pitting at grain boundaries. A two-stage overflow rinse, with the first stage at 25 °C and the second stage at 40 °C, reduces ionic carryover and prevents condensate formation on wafer surfaces.
Bath life is governed by aluminum loading and water balance. As aluminum concentration increases above 2–5 g/L depending on product grade, etch rate decreases, undercut increases, and precipitate formation on heater surfaces becomes measurable. Periodic density checks and acid titrations detect water uptake from humid air; a density drop below 1.60 g/cm³ at 20 °C generally indicates dilution beyond the operable range. Filtration through 0.1 µm polypropylene cartridges removes particle agglomerates but does not remove dissolved aluminum, so bleed-and-feed or complete bath replacement is required.
Aluminum Etchant AE-PAN-80/5/5/10 is corrosive and oxidizing; storage must be separated from strong bases, organic amines, and reducing agents. The safety data sheet reports classification under EC No 1272/2008 as skin corrosive and metal corrosive. Use of polyvinyl chloride, polycarbonate, or stainless steel for storage or transfer is contraindicated; wetted parts must be high-density polyethylene, polypropylene, or fluoropolymer. Spent etchant contains phosphoric acid, acetic acid, nitric acid, and dissolved aluminum; neutralization with lime or sodium hydroxide slurry must be carried out under continuous pH control to avoid exothermic release. The product is supplied under EC No 1907/2006 registration where applicable, and users must verify local discharge limits for phosphate and nitrate.
Technical-grade aluminum etchants with higher trace metal tolerances are used in metal finishing and routine metallography, whereas semiconductor-grade product is filtered and controlled for particles and mobile ions. The distinction between grades is not the active acid ratio but the trace metal and particle burden; technical-grade material may contain iron above 1 ppm and particle counts above 1000 counts/mL, which can produce defects in submicron interconnect lines or unstable etch rates on thin films.
