| HS Code | 423307 |
| Product Name | Indium Tin Oxide Etchant |
| Etchant Type | Acidic corrosive liquid |
| Main Composition | Hydrochloric acid, nitric acid, and deionized water |
| Appearance | Clear pale yellow to colorless solution |
| Acid Concentration | 10-30% by weight |
| Ph | <1 |
| Density | 1.05-1.15 g/cm3 at 20°C |
| Etch Rate | 20-50 nm/min at 40-50°C |
| Application Method | Immersion or spray etching |
| Operating Temperature | 40-50°C |
| Selectivity | High selectivity for ITO over glass and photoresist |
| Storage Conditions | Store in sealed HDPE container in cool, dry, ventilated area |
| Shelf Life | 6-12 months from manufacture date |
| Safety Hazard | Corrosive; causes skin and eye burns, harmful if inhaled |
As an accredited Indium Tin Oxide Etchant factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Packaged in a 125 mL HDPE bottle with secure cap, labeled for hazards, ready for safe use. |
| Container Loading (20′ FCL) | 20′ FCL: Indium Tin Oxide etchant packed in sealed drums/IBCs, secured and labeled, ready for safe transport. |
| Shipping | Indium Tin Oxide Etchant is a corrosive acidic solution requiring hazardous-material shipping. It must be packed in leak-proof, UN-approved containers, labeled as Corrosive Liquid (UN3264), and accompanied by SDS and dangerous-goods documentation. Ship via ground freight only unless air transport is pre-approved; segregate from bases, metals, and oxidizers to ensure safety. |
| Storage | Store Indium Tin Oxide etchant in its original, tightly sealed container in a cool, dry, well-ventilated area away from direct sunlight and incompatible materials such as bases, oxidizers, or reactive metals. Use corrosion-resistant secondary containment, preferably plastic or glass. Keep the container upright and clearly labeled. Ensure the storage area is secure and accessible only to trained personnel. |
| Shelf Life | Shelf life is typically 6 months when stored tightly sealed, at room temperature, away from light and moisture. |
In TFT-LCD array fabrication, the blanket indium tin oxide layer is deposited by DC magnetron sputtering onto alkali-free glass substrates at film thicknesses of 40–70 nm and then patterned after gate, source, and drain metallization. The wet etch process is integrated into a multi-chamber spray etcher with programmable nozzle pressure, exhaust control, and point-of-use dosing of hydrochloric acid, nitric acid, and deionized water. Bath temperature is maintained at 40±1 °C because the etch rate of as-deposited amorphous ITO shifts significantly when the HNO₃ fraction varies by more than 0.5 vol%. Supplier datasheets and production line audits document etch rates between 30 and 80 nm/min for HCl:HNO₃:H₂O systems when the bath is aged less than 8 h; beyond that interval, drag-out and acid volatilization cause undercut and residue variability. The isotropic chemistry produces lateral undercut of approximately 1× film thickness per side, so a 50 nm pixel electrode line loses 100–120 nm in total linewidth after the 15–20% overetch required to clear SnO₂-rich micro-islands. Endpoint detection is performed by optical transmission at 550 nm, with automatic shutoff when transmittance returns to the glass baseline. Residual cation contamination is limited to <10 ppb for Na, K, and Fe because mobile ions shift thin-film transistor threshold voltage under bias thermal stress. Sheet resistance after patterning is verified by four-point probe method ASTM F1711-20, and linewidth uniformity across Gen 8.5 substrates is held within ±5% by controlling etch bath oxidation-reduction potential and specific gravity.
On rigid touch sensor glass, indium tin oxide films are sputtered at 20–30 nm thickness to achieve sheet resistance of 100–150 Ω/sq, and the projected capacitive pattern is defined by photolithography followed by a puddle-type acid etch. The dominant limitation is bath temperature ripple across the cassette; a ±1 °C gradient creates variation in etch rate that is directly visible as bridge resistance spread because line widths of 25–50 µm are within the same order as the lateral undercut. For glass substrates, HCl-HNO₃ mixtures are used at 35–40 °C, with etch time set between 60 and 120 s depending on film crystallinity; crystallized ITO requires the HNO₃ fraction to be raised from 0.5 vol% to 1.5 vol%. For PET or PEN film-based touch sensors, the processing window changes sharply because the substrate is attacked by hydrochloric acid at concentrations above 1 N; oxalic acid solutions at 3–5 wt% and 45–60 °C are substituted, with measured etch rates of 5–20 nm/min, which delays web throughput by a factor of five compared with glass lines. Optical inspection with automated optical inspection equipment flags opens, shorts, and line edge roughness after resist stripping. Adhesion of the patterned ITO trace is checked by cross-cut tape test method ASTM D3359-23, with acceptance at class 5B on glass and 4B on PET because PET surface hydrolysis reduces interfacial adhesion. Sheet resistance stability after 85 °C/85% RH aging for 100 h is verified according to ASTM F1711-20; drift above 10% indicates residual etchant ions at the trace edge.
Table 1. Comparative behavior of two industrial ITO etchant classes used in display and touch sensor lithography.
| Parameter | HCl-HNO₃-H₂O system | Oxalic acid system |
|---|---|---|
| Substrate compatibility | Alkali-free display glass, quartz, heat-stabilized glass | PET, PEN, polycarbonate, polyimide webs |
| Operating temperature | 35–45 °C | 40–60 °C |
| Reported ITO etch rate | 30–80 nm/min | 5–20 nm/min |
| Etch profile | Isotropic; undercut approximately 1× film thickness per side | Isotropic; slower attack on crystallized ITO reduces edge roughness |
| Primary residue risk | Chloride and nitrate residues; elevated dark spot risk in OLED | Oxalate residues; lower ionic conductivity after rinse |
Across the anode plane of an organic light-emitting diode stack, the indium tin oxide layer is deposited at 100–150 nm to reach sheet resistance below 30 Ω/sq, and the subsequent wet etch must produce a tapered edge rather than a vertical undercut profile. The etch bath is operated in an ISO 14644-1:2015 Class 5 cleanroom because particulate defects as small as 0.2 µm become dark spots after organic materials are deposited. Process specifications for rigid OLED lines commonly require post-etch surface roughness below 1.5 nm Ra on the anode surface, measured by contact profilometry over a 500 µm scan length; higher roughness concentrates electrical field at the hole injection interface. The hydrochloric acid-based etchant is buffered with nitric acid at low concentration to maintain tin oxide dissolution without attacking the glass substrate, and etch time is trimmed until the ITO edge angle measured by scanning electron microscopy falls between 30° and 60°. An edge steeper than 60° produces poor step coverage of the hole injection layer, while an edge shallower than 30° consumes excessive device aperture and can create leakage paths along the bank. After etching and photoresist stripping, the substrate is subjected to a 10-min deionized water overflow rinse and UV-ozone treatment, because chloride residue above 5×10¹² atoms/cm² measured by time-of-flight secondary ion mass spectrometry accelerates device dark spot growth in accelerated lifetime testing.
In silicon heterojunction photovoltaic cells, a low-temperature indium tin oxide layer is sputtered over intrinsic and doped amorphous silicon passivation stacks, usually at 80–100 nm thickness and sheet resistance of 40–100 Ω/sq. Wet patterning is not universally applied because the a-Si:H layer is sensitive to acid penetration through pinholes and edge microcracks, but when busbar isolation or rework demands a chemical etch, the bath is formulated at lower acid strength and held below 30 °C. Under these conditions, the etch rate falls to 10–25 nm/min, and the process window is governed by the etch selectivity between ITO and amorphous silicon; a selectivity below 10:1 causes passivation damage that is measurable as an increase in carrier recombination under 1-sun open-circuit voltage decay. Equipment configuration uses single-wafer immersion or meniscus coating rather than batch spray because the fragile cell wafer must be wet on one side only. Post-etch inspection includes mapping of sheet resistance by ASTM F1711-20, and photoluminescence imaging is used to identify parasitic damage regions. Published data for this specific configuration is limited, and production lines therefore qualify each etchant lot by cross-sectional transmission electron microscopy of the ITO/a-Si:H interface on witness wafers.
Transparent conductive windows and resistive heater films often use ITO at 100–200 nm thickness with sheet resistance from 5 to 20 Ω/sq. The wet etch step defines large-area grid lines or removes edge regions after screen-printed resists, using tank or spray equipment with dimensions above 2 m for architectural glass. Because the substrate is tempered or chemically strengthened glass, the etch bath temperature is kept below 35 °C to avoid thermal shock; line speed is adjusted so that total acid contact does not exceed 180 s. Optical performance after patterning is verified according to ISO 9050:2003, with luminous transmittance retained above 85%. Sheet resistance uniformity across the aperture is measured by ASTM F1711-20, and the typical acceptance criterion is ±5% because resistive heating uniformity scales linearly with local sheet resistance. Failure modes on architectural-scale etchers include puddle stagnation at the bottom edge of vertical cassettes and non-uniform rinse water cascades that leave dilute acid films, producing visible contrast variation in the patterned ITO.
On flexible printed sensor webs, ITO patterning is performed in roll-to-roll immersion or spray systems where web tension, bath agitation, and drying temperature are coupled to etch time. The web is a heat-stabilized PET or polyimide film with sputtered ITO thickness of 20–50 nm and sheet resistance of 30–80 Ω/sq. Oxalic acid-based chemistries are preferred over HCl-HNO₃ because the polyester surface hydrolyzes under strong acid and the resulting haze increase exceeds 1.5% at 550 nm when measured by ASTM D1003-21. The etch bath is operated at 40–50 °C, and line speed is set so the dwell time in the etch module remains between 30 and 120 s; longer immersion produces visible attack at the ITO edge and reduces flexural endurance of the sensor trace. After the cascade deionized rinse, the web passes through infrared drying at 70–80 °C with air velocity above 5 m/s to prevent water spotting. Electrical verification is continuous, with in-line four-point probe heads recording sheet resistance per ASTM F1711-20; a recorded deviation above ±8% across the web width triggers automatic bath replenishment. The patterned web is then qualified for dynamic bending by cyclic flex test according to IEC 62715-5-1, with resistance change held below 10% after 100,000 cycles at a 5 mm bend radius.
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Indium Tin Oxide Etchant, designated ITO-200, is a pre-blended aqueous acidic solution intended for selective removal of indium tin oxide transparent conductive films from glass, quartz, and selected polymer substrates. The product contains hydrochloric acid and nitric acid as the primary reactive species; free chloride is controlled at 3.10–3.40 mol/L, free nitrate at 0.70–0.90 mol/L, and oxidation-reduction potential at 850–950 mV versus Ag/AgCl at 25 °C. The liquid is colorless to pale yellow with density 1.085–1.115 g/cm³ at 20 °C measured by ASTM D4052-18a. It is applied in immersion, spray, and puddle-based wet stations to pattern transparent conductive films with thicknesses typically between 90 nm and 150 nm in display, photovoltaic, and touch-sensor manufacturing.
The product is supplied as a single-component liquid, which distinguishes it from in-situ mixed aqua regia substitutes that require operator blending of concentrated mineral acids. Premixed delivery reduces batch-to-batch variation and lowers heat release during make-up. Each production lot is released against the specification limits in Table 1.
| Parameter | Representative control range | Test procedure |
|---|---|---|
| Density at 20 °C | 1.085–1.115 g/cm³ | ASTM D4052-18a |
| Free chloride | 3.10–3.40 mol/L | potentiometric titration with standardized silver nitrate after 0.45 µm PTFE filtration |
| Free nitrate | 0.70–0.90 mol/L | ion chromatography after dilution |
| Oxidation-reduction potential | 850–950 mV versus Ag/AgCl at 25 °C | ASTM D1498-14 |
| Fluoride | ≤10 ppm | ion-selective electrode |
| Iron | ≤5 ppm | inductively coupled plasma–optical emission spectrometry after acid digestion |
| Aluminum | ≤10 ppm | inductively coupled plasma–optical emission spectrometry after acid digestion |
| Shelf life in unopened container | 12 months at 10–25 °C | retention study |
The dissolution mechanism is an oxidative dissolution of In₂O₃ and SnO₂ in which nitrate acts as the oxidizer and chloride stabilizes soluble indium(III) and tin(IV) complexes. On a 110 nm sputtered indium tin oxide film with sheet resistance 10–15 Ω/sq, fresh-bath immersion at 40 °C typically removes 4–8 nm/s. The rate is strongly temperature-dependent; a decrease from 40 °C to 30 °C can lower etch rate by 30–50% in immersion tanks. Endpoint is verified by four-point probe sheet-resistance measurement after rinse and by optical transmission at 550 nm.
For a 100 nm film cleared at 5 nm/s, a 20% over-etch corresponds to 4 s of additional etching and an estimated lateral undercut of 0.02 µm per edge under isotropic conditions. Production lines that require tight critical dimensions typically use endpoint detection on a monitor substrate and limit over-etch to ≤20%.
Novolac-diazonaphthoquinone photoresists with a final thickness of 1.0–2.5 µm withstand immersion at 40 °C for up to 5 min without measurable lifting when adhesion is tested by ASTM D3359-17 cross-hatch tape pull. Resist systems with low crosslink density may soften beyond 10 min; published data for this specific configuration is limited, and each photoresist stack should be qualified on patterned test coupons. Silicon nitride passivation and silicon oxide hard masks show no measurable thickness loss after 10 min immersion at 35 °C, but aluminum and aluminum-copper metallization are aggressively attacked and must be masked or not present during ITO-200 processing.
Substrate preparation strongly influences etch uniformity. Glass substrates entering the wet bench should be free of particulate, organic, and alkali residues. A pre-clean sequence of alkaline detergent immersion at 40 °C, deionized water rinse at 18 MΩ·cm, and a dehydration bake at 120 °C for 10 min is used prior to indium tin oxide coating and again after photoresist development. Residual moisture before etching can dilute the etchant at the indium tin oxide–resist interface and create a local rate reduction at pattern edges; production lines therefore hold substrates in a loading buffer maintained at ISO 14644-1 Class 5 particle cleanliness and 23 ± 2 °C.
Film crystallinity and deposition method influence the required etch time. Dense crystalline indium tin oxide deposited at substrate temperatures above 200 °C tends to etch more slowly than room-temperature amorphous indium tin oxide; a post-deposition anneal at 250 °C in air may reduce fresh-bath etch rate by 20–40% on some lines. Process qualification coupons should therefore replicate the same sputter tool, deposition temperature, and oxygen partial pressure as the production film.
In conveyorized spray tools processing 370 mm × 470 mm glass substrates, bath temperature is maintained at 35–40 °C with a control band of ±2 °C, spray pressure set between 0.20 MPa and 0.35 MPa, and belt speed adjusted to achieve a total etch time of 60–120 s for 100–150 nm indium tin oxide. Production experience on high-volume display lines shows that non-uniformity across the substrate increases if nozzle filters are not replaced at the 10 µm pore-size specification; filter loading reduces spray impact at the edges and produces a center-to-edge sheet-resistance gradient. Megasonic excitation is not recommended for line/space features below 10 µm because acoustic cavitation can lift resist edges and amplify undercut.
Spent etchant accumulates dissolved indium and tin as indium(III) and tin(IV) chloro/nitrato complexes. In an immersion bath used for successive 100 mm square substrates, etch rate remains stable until indium concentration reaches approximately 500 mg/L; above this value, endpoint time extends by 10–30% and tin oxide residue may remain on the substrate if temperature is not raised. Process control uses inductively coupled plasma–optical emission spectrometry after dilution to track indium and tin. When indium exceeds 1000 mg/L, the bath is typically replenished or replaced because oxidation-reduction potential can fall below 850 mV versus Ag/AgCl and etch rate becomes too sensitive to load variation for stable production.
Replenishment is not a simple dilution. Make-up additions of concentrated nitric acid and hydrochloric acid can restore free-acid concentration, but excessive nitrate addition raises the risk of photoresist attack and fuming. Operator procedures therefore use a two-point titration for free chloride and free nitrate, with additions based on the calculated deficit from the release ranges in Table 1. Oxidation-reduction potential is used only as a secondary check because the signal is not specific to a single acid species.
Free-acid titration must not be performed on unfiltered bath samples because dissolved solids and resist particles interfere with silver nitrate titration endpoints. The recommended sample preparation is filtration through a 0.45 µm PTFE syringe filter, followed by cooling to 20 °C. For chloride, the sample is titrated with standardized silver nitrate using a silver billet electrode; for nitrate, ion chromatography after dilution is preferred because acid-base titration is not selective in the presence of metal chlorides.
Relative to oxalic acid-based indium tin oxide etchants, ITO-200 exhibits higher fresh-bath etch rate and does not leave tin oxalate precipitates when rinse is delayed. Relative to hydrobromic acid-based systems, ITO-200 has lower vapor pressure at equivalent acid normality and can be used in standard PVC-lined wet stations because free-bromine content is below detection. Relative to dry plasma etching with CH₄/H₂/Ar or Cl₂/BCl₃, ITO-200 produces an isotropic profile and is better suited to large-area panels where vacuum tool throughput is insufficient. The primary limitation is attack on exposed aluminum; process flows that use aluminum gate or source/drain metallization must sequence indium tin oxide etching before aluminum deposition or protect the metal with an overlying barrier. Table 2 summarizes the main distinctions.
| System | Active chemistry | Typical indium tin oxide removal rate at 40 °C | Residue or sidewall profile | Main process constraint |
|---|---|---|---|---|
| ITO-200 | HCl/HNO₃ aqueous | 4–8 nm/s | isotropic; low oxide residue if rinse follows | attacks exposed aluminum |
| Oxalic acid type | 5–10 wt% C₂H₂O₄ | 0.5–2.0 nm/s | isotropic; delayed rinse can leave tin oxalate residue | lower throughput; may require heated rinse |
| Hydrobromic acid type | HBr/Br₂ aqueous | 8–15 nm/s | isotropic; high tin solubility | higher vapor pressure and vent scrubbing demand |
| Dry plasma | CH₄/H₂/Ar or Cl₂/BCl₃ | 0.2–1.0 nm/s equivalent film removal | anisotropic; polymer deposition possible | vacuum tool throughput; chamber cleaning |
ITO-200 should not be confused with general-purpose chromium etchant, aluminum etchant, or copper etchant. Chromium etchant based on ceric ammonium nitrate may remove indium tin oxide but produces cerium-containing precipitates and is more costly. Phosphoric acid-based aluminum etchants typically leave tin oxide residues on indium tin oxide films. Cupric chloride copper etchants remove indium but do not readily dissolve the tin oxide component. ITO-200 is balanced to dissolve both indium oxide and tin oxide at comparable rates, preventing conductive tin oxide islands from remaining in patterned areas.
Waste treatment for spent ITO-200 and first-rinse effluent consists of neutralization with sodium hydroxide or lime to pH 8–9, which precipitates indium hydroxide and tin hydroxide; the slurry is dewatered with a filter press. The clarified liquid must be checked for residual nitrate and chloride before discharge under local sewer limits. Because the product contains nitric acid, storage tanks and piping should be constructed of high-density polyethylene or polyvinyl chloride, and pumps should use PTFE or PVDF wetted parts. Process baths require local exhaust ventilation to remove nitrogen oxide vapors generated during etching.
Do not combine ITO-200 with hydrogen peroxide, reducing agents, amines, or cyanide-containing waste streams. Mixing with organic solvents can generate heat and may form nitrogen-containing decomposition products; therefore, organic strippers must be rinsed from substrates before indium tin oxide etching. Handling requires impervious gloves made of butyl rubber or polyvinyl alcohol, face shield, and acid-resistant apron. Spills are contained with inert absorbent and neutralized slowly with sodium carbonate or limestone; rapid neutralization with concentrated alkali can generate heat and splatter.
