| HS Code | 171186 |
| Appearance | Clear, colorless to very pale yellow liquid |
| Physical State | Liquid at room temperature |
| Odor | Pungent acidic odor |
| Chemical Type | Acidic selective wet etchant for IGZO film |
| Water Solubility | Fully miscible with water |
| Boiling Point | > 100 °C |
| Specific Gravity 25 C | 1.10 ± 0.02 |
| Ph As Supplied | < 1.0 |
| Vapor Pressure | Essentially similar to water |
| Viscosity 25 C | 1.5 – 2.5 cP |
| Ionic Impurity Content Na K Fe Cu | ≤ 0.1 ppm each |
| Non Volatile Residue | ≤ 0.001 wt% |
| Particle Count | ≤ 50 particles/mL at ≥ 0.5 µm |
| Igzo Etch Rate | 80 – 120 nm/min at 25 °C |
| Etch Selectivity Vs Sio2 Sinx | > 100 : 1 |
As an accredited IGZO Etchant Electronic/EL Grade factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Packaged in a 1 L HDPE bottle, IGZO Etchant Electronic/EL Grade ensures high purity, safe handling, and reliable etching performance. |
| Container Loading (20′ FCL) | 20′ FCL: IGZO etchant (Electronic/EL grade) loaded in secure, leak-proof drums/pails, with proper segregation and labeling for safe transport. |
| Shipping | IGZO Etchant (Electronic/EL Grade) ships as a hazardous, corrosive liquid. Packaged in sealed, chemical-resistant containers to prevent leakage, it requires ground transport only, with proper hazard labeling and documentation. Avoid air freight. Ensure compliance with local regulations and handle with protective equipment during loading and unloading. |
| Storage | Store IGZO Etchant (Electronic/EL Grade) in its original, tightly sealed container in a clean, cool, dry, well-ventilated area, away from direct sunlight, heat, and incompatible chemicals. Maintain stable temperatures to preserve purity; avoid moisture and contamination. Ensure secondary containment, proper labeling, and restricted access. Follow manufacturer’s specifications and local regulations. |
| Shelf Life | Shelf life is typically 6 months from manufacture when stored unopened in original containers at recommended temperatures. |
For amorphous IGZO backplane fabs running Gen 8.5 glass, EL-grade etchants are introduced in the array wet etch module after source-drain metal deposition. The working chemistry is normally oxalic-acid-based, with free acid maintained between 0.8 wt% and 1.2 wt% at 35 °C. Etch rates for sputtered a-IGZO in this window fall between 40 nm/min and 90 nm/min, depending on film density, gallium fraction, and post-deposition anneal condition. Bath temperature is controlled within ±0.5 °C using inline heat exchangers, and spray pressure on flat-panel wet processors is set from 0.15 MPa to 0.25 MPa to prevent puddle formation on 2200 mm × 2500 mm substrates. The process window is constrained by two competing failure modes: incomplete oxide removal leaves residual channel material and raises TFT leakage current, while overetch beyond 60 s produces undercut at Mo/Al/Mo or Cu/Mo source-drain edges. Selectivity to underlying SiOx etch-stop layers must remain above 100:1 to avoid gate insulator erosion; molybdenum selectivities above 30:1 are preferred to control sidewall attack. Lot release of EL-grade material includes cation impurity limits below 10 ppb for each of Na, K, Fe, and Cu when analyzed by ICP-MS according to EPA 6020B. Particle counts above 0.1 µm are held below 10 particles/mL by an optical particle counter calibrated to ISO 21501-4:2018. Production-scale experience indicates that bath aging shifts etch rate by −8% to −15% per 100 glass substrates due to dissolved indium and gallium loading. Endpoint detection and supplemental acid dosing are therefore interlocked with carrier count rather than fixed process time.
| Parameter | Acceptance limit | Analytical method / standard |
|---|---|---|
| Free acid as oxalic acid | 0.8–1.2 wt% | acid-base titration |
| Na, K, Fe, Cu each | 10 ppb maximum | EPA 6020B |
| Zn | 5 ppb maximum | EPA 6020B |
| Chloride | 50 ppb maximum | ISO 10304-1:2009 |
| Sulfate | 50 ppb maximum | ISO 10304-1:2009 |
| Nitrate | 50 ppb maximum | ISO 10304-1:2009 |
| Particles at 0.1 µm | 10 particles/mL maximum | ISO 21501-4:2018 |
On Gen 10.5 copper/molybdenum source-drain stacks, the dominant yield limit is not the bulk IGZO etch rate but the interfacial sidewall attack at the Cu/Mo boundary during post-etch rinse and dwell. The EL-grade formulation must maintain pH between 2.3 and 2.8 and free peroxide below 0.2 wt% to minimize galvanic coupling. Molybdenum lines exposed to dissolved copper ions can suffer local CD widening of 0.3–0.7 µm after a 45 s etch step when peroxide is present. Etch loading curves flatten after 180–220 panes per 300 L bath, at which point bath drainage and re-spiking with fresh acid are required to restore CD uniformity across the 2940 mm × 3370 mm substrate. Conductivity and ORP sensors integrated into the recirculation loop trigger spiking at ±10 mS/cm deviation rather than relying on fixed carrier count alone. Critical dimension metrology uses CD-SEM on 5-point patterns, with within-glass range held below 0.5 µm for a 4 µm channel length. Selectivity to copper must exceed 200:1 when measured by profilometry on blanket films; selectivity to molybdenum must exceed 40:1. Because the etchant attacks exposed ITO only weakly but can roughen it, pixel contact vias are protected with photoresist before the wet etch step. Published data for this specific configuration is limited; fabs using Gen 10.5 Cu/Mo IGZO backplanes typically perform design-of-experiments on each sputter target lot to adjust etch time for lot-specific oxide density.
| Film stack / condition | Etch rate | Selectivity to IGZO | Assessment method |
|---|---|---|---|
| a-IGZO, 0.8 wt% oxalic acid, 35 °C | 40–80 nm/min | — | profilometry |
| SiOx etch-stop layer | <0.5 nm/min | >100:1 | ellipsometry |
| Molybdenum source-drain layer | <1 nm/min | >40:1 | profilometry |
| Copper source-drain layer | <0.2 nm/min | >200:1 | four-point probe |
| Ti/Al/Ti pixel electrode | <0.5 nm/min | >50:1 | cross-section SEM |
When the active layer is transferred to a polyimide substrate for foldable OLED production, the post-deposition anneal is capped below 250 °C to limit substrate shrinkage and outgassing. This low thermal budget produces a less dense IGZO film that etches 30–50% faster than comparable glass-deposited films. To maintain the same critical dimension, the bath temperature is reduced to 30 °C and free acid concentration is cut to 0.5–0.7 wt%. Process control relies on sheet resistance and optical thickness measurements rather than time alone, because polyimide substrate lots vary in surface energy. Polyimide immersion compatibility is validated by weight gain below 0.2% after 30 min exposure per ASTM D570-22 and by elongation retention above 90% in tensile testing per ASTM D882-18. Acidic etchant contact with exposed polyimide edges can cause microcracking if the film is not pre-baked at 150 °C for 30 min after photoresist developer. Residual alkaline developer neutralizes the etchant at the edge and raises local pH enough to precipitate aluminum hydroxide on Al-sourced metal lines. Batch-to-batch variance in polyimide surface hydrophilicity shifts etch wetting; inline plasma treatment at 100–200 W with Ar/O2 feed gas before photoresist coating is used to stabilize adhesion. The terminal foldable display stack uses a channel etch-stop process, so selectivity to PECVD SiOx above 100:1 remains non-negotiable. A single process lot showing SiOx loss above 5 nm after 90 s immersion is rejected.
Processing of flat-panel X-ray detector arrays differs from display fabs primarily in leakage-current control and pixel electrode compatibility. The etchant is applied after IGZO photoconductor deposition on readout structures, and residual metal cations in the etched film must remain below 1×1010 atoms/cm² at the backchannel to prevent dark current drift. EL-grade formulation with cation impurity ceilings of 5 ppb for Na, K, Fe, Cu, and Zn per EPA 6020B supports this requirement. Etch rate is limited to 25–45 nm/min at 28 °C to preserve the amorphous network, while post-etch rinse in ultrapure water with total organic carbon below 10 ppb is mandatory. The detector industry rejects panels if X-ray image lag exceeds 1.5% after 60 s exposure; process deviations from low-temperature etch reduce this margin by altering oxygen vacancy concentration. Selectivity to the indium tin oxide pixel contact must exceed 100:1, because ITO exposure occurs at the pixel via perimeter and excessive attack increases contact resistance by 10–20%. Detector fabs routinely qualify etchant lots by measuring leakage current on gate-biased structures at ±5 V, with acceptance based on lot-to-lot drift below 5 pA. Airborne particle control is maintained at ISO 14644-1:2015 Class 4 in the wet etch bay to limit point defects in large-area detector panels.
Active-matrix mini-LED backplanes using IGZO drive transistors require the etch step to preserve a Ti/Al/Ti pixel electrode already deposited on the glass. Dilute oxalic acid formulations are preferred because they show negligible titanium attack at pH above 2.0, whereas hydrochloric-acid-based mixtures can create pitting on titanium adhesion layers at 35 °C. The process is run at 30–35 °C with etch time shortened to 20–35 s because the IGZO film is typically only 20–40 nm thick. Aluminum lines require inhibitor buffering; dissolved aluminum above 15 mg/L in the bath increases the risk of metal-organic residue formation on the panel surface when molybdenum is present from source-drain layers. Bath filtration through 0.05 µm polytetrafluoroethylene membranes at 20 L/min prevents particle-related point defects, which for mini-LED pixel pitches below 500 µm translate into visible dark spots. Selectivity of IGZO to Ti/Al/Ti must exceed 50:1; selectivity to SiNx passivation must exceed 100:1. The final active-matrix substrate drives 500–2000 zones in high-dynamic-range LCD backlights and automotive displays.
In under-display optical fingerprint sensor arrays, IGZO transistors are processed on 150 mm or 200 mm wafers rather than display glass. The wet etch step must create a backchannel with roughness below 1 nm RMS to keep electron mobility above 10 cm²/V·s. Purely time-based etch is not reliable; etch depth is monitored by spectral reflectance on monitor wafers. Alkali and transition metal contamination must remain below 2 ppb for Na and Fe because the device operates at subthreshold current below 1 pA. The etchant is diluted with ultrapure water containing total organic carbon below 10 ppb. Etch rate is set to 15–30 nm/min at 25 °C to preserve steep sidewall profiles. Any micro-masking particle larger than 0.2 µm creates point defects. Wafers are processed in quartz tanks to avoid boron leaching from borosilicate, and post-etch rinse includes CO2-diluted ultrapure water to suppress electrostatic charge. Metal selectivity to Ti/Au contacts must exceed 500:1. Production-scale failure analysis shows that skipping the CO2 rinse increases gate oxide micro-arc defect density by more than 0.05 defects/cm² on 200 mm wafer lots.
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IGZO Etchant Electronic/EL Grade is an aqueous mixed-acid formulation intended for wet patterning of amorphous indium–gallium–zinc oxide (a-IGZO) channel layers in active-matrix liquid crystal display and oxide thin-film transistor backplanes. The product identification used in this document is IGZ-EL; container suffixes denote packaging volume such as 20 L, 200 L, and 1000 L. The product is supplied ready to use, not as a concentrate, and is filtered at point-of-use through a 0.1 µm rated PTFE capsule filter before contact with the substrate. The base acid system contains nitric, phosphoric, and acetic acids; the exact acid concentration profile is supplier-confidential, but the lot certificate of analysis reports free-acid normality, density, pH, particle burden, and trace-metal content. The etching mechanism is not identical to conventional indium-tin-oxide etchants because the a-IGZO film contains gallium and zinc oxide domains that dissolve at differing rates. In the EL-grade formulation, nitric acid oxidizes indium and gallium sites, phosphoric acid moderates dissolution of zinc-rich domains, and acetic acid buffers free-acid activity to reduce unwanted attack on molybdenum and aluminium source/drain metallisation. The buffered free-acid activity also lowers the galvanic couple between the a-IGZO film and underlying barrier metals during spray etching with a 0.2–0.4 MPa double-fluid nozzle array.
The dissolution of a-IGZO proceeds through an acid–oxidative pathway. In the absence of chloride, nitrate ions are reduced at the film surface while indium and gallium oxides are converted to soluble nitrate and acetate complexes. Zinc oxide dissolution is primarily acid–base: zinc oxide reacts with phosphoric acid to form zinc phosphate or zinc hydrogen phosphate species, which must remain dissolved or suspended until the final rinse. Acetic acid acts as a weak ligand and viscosity modifier, reducing the diffusivity of the dissolving cations so that the boundary-layer thickness increases and the etch front becomes more uniform. This role is similar to that of acetic acid in buffered oxide etchants used for silicon dioxide, but the phosphoric acid component specifically suppresses zinc phosphate precipitation and reduces the risk of post-etch residue. The product is chloride-free except for trace chloride from raw materials, and the trace chloride concentration is reported on the certificate of analysis because chloride can promote pitting on copper and aluminium interconnect layers. Dilution with site-generated deionized water is not required for standard spray or immersion processes; if dilution is performed for a specific tool, the water should meet ASTM D5127-13(2020) Type E-1 quality and the bath should be re-qualified for pH shift and trace-metal pickup.
For backplane manufacturing, the limiting contamination of a wet etchant is not total metal content but the concentration of mobile alkali and transition metal cations that can adsorb onto the IGZO channel during the rinse step. Sodium and potassium are particularly critical because they migrate into the back-channel interface and shift threshold voltage. The lot-release table below is representative for electronic/EL grade material; a supplier certificate of analysis may report tighter internal limits. The analytical methods are selected to be compatible with an acidic matrix containing phosphoric acid. Trace metal analysis by inductively coupled plasma mass spectrometry uses collision or reaction cell technology to reduce spectral interferences from phosphorus-based polyatomic species, and the method is adapted from ISO 17294-2:2016 with matrix-matched calibration.
| Parameter | Value/Specification | Test Method |
|---|---|---|
| Appearance | Colorless to pale yellow clear liquid | Visual inspection against backlight |
| Density at 20 °C | 1.08–1.12 g/mL | ASTM D4052 |
| pH | 0.2–0.8 | ASTM E70 |
| Sodium, potassium, iron | each ≤ 5 µg/L | ICP-MS, ISO 17294-2:2016 |
| Copper, nickel, chromium, zinc | each ≤ 2 µg/L | ICP-MS, ISO 17294-2:2016 |
| Particles ≥ 0.2 µm | ≤ 50 counts/mL | Optical particle counter, ISO 21501-4:2018 |
| Total chloride | ≤ 1 mg/L | Ion chromatography, EPA Method 300.1 |
The particle specification at 0.2 µm is relevant because a Gen 8.5 immersion bath can recirculate several thousand litres per hour; a defect rate of 1 particle/mL above background can create visible pixel defects if the particle deposits in the channel region before the passivation layer is formed. Point-of-use filtration with a 0.1 µm hydrophobic PTFE membrane and periodic filter integrity testing according to ASTM F838-20 is recommended. The etch module and storage containers should be dedicated to EL-grade acids; cross-contamination from general-purpose wet benches has been observed to raise iron and zinc background by an order of magnitude. Because the product is opened and filtered in an ISO Class 5 cleanroom according to ISO 14644-1:2015, any transfer hardware must be rinsed with Type E-1 water and dried with filtered nitrogen before use. The GHS classification includes corrosive to metals, category 1; storage and piping must follow local chemical handling codes for acidic oxidiser mixtures.
On production spray tracks, the etchant is typically heated to 35 ± 1 °C and delivered through 20–24 dual-fluid nozzles at a liquid pressure of 0.2–0.4 MPa and an air or nitrogen atomization pressure of 0.05–0.15 MPa. The substrate conveyor speed is adjusted so that the clear-to-endpoint time for a 30 nm a-IGZO film is 45–90 s; these figures are representative process windows and must be re-qualified after any change in deposition tool, film density, or post-deposition anneal. The bath endpoint is not determined visually in production; it is detected by a reflectance sensor that monitors the disappearance of the IGZO thin-film interference colour. Overetch is normally limited to 10–20% of clear-to-endpoint time to control critical dimension loss. Higher overetch levels may be required for high-density film edges, but this increases the risk of back-channel surface roughening and threshold voltage instability.
Immersion tooling is used for smaller substrates, coupons, or rework processing. The etch bath is agitated by nitrogen bubbling through a 0.2 µm sparger at 0.5–1.0 L/min per litre of bath. Without agitation, zinc oxide-rich residues can remain on the surface and form a boundary layer that slows the final removal of gallium-rich regions. Wetted parts must be PVDF, PTFE, or natural unpigmented polypropylene; stainless steel and titanium are incompatible because the mixed acid system and trace fluoride impurities create pitting and release cations into the bath. The recirculation loop should include a 0.1 µm capsule filter and a non-metallic heat exchanger with temperature control of ±0.5 °C. The product is not recommended for ultrasonic tanks above 40 kHz because cavitation can accelerate erosion of the filter housing and generate particles.
Bath life is controlled by acid titration and by the accumulation of dissolved indium, gallium, and zinc. At a total dissolved metal concentration above approximately 10–20 mg/L, the etch rate may shift and precipitation of metal phosphates can occur on the substrate edge. The operational boundary is therefore set by daily ICP-MS metal monitoring and by free-acid titration. If the bath is held at 40 °C for more than 8 h, acetic acid evaporation increases and the free-acid ratio drifts unless a sealed or condensing bath cover is used. The product should not be mixed with hydrogen peroxide, ammonia, or amine-based strippers because redox and pH changes can generate heat and precipitate metal hydroxides. Storage should be in vented high-density polyethylene or fluoropolymer containers at 10–30 °C; unopened shelf life is typically 12 months from the blending date.
The principal difference between the EL-grade IGZO etchant and a conventional ITO etchant is the selectivity to the source/drain metallisation. Indium tin oxide etchants based on hydrochloric/nitric acid mixtures are aggressive to copper and aluminium and can produce undercutting when the IGZO channel is patterned before metal deposition. In a back-channel-etched thin-film transistor, the IGZO layer is often in contact with molybdenum or a molybdenum/copper stack. The EL-grade formulation uses a buffered acid system that maintains the open-circuit potential of the molybdenum below the transpassive dissolution region in the mixed-acid environment. The galvanic corrosion current between IGZO and molybdenum, measured in a three-electrode cell with a Ag/AgCl reference electrode according to ASTM G59-97(2020), is lower than that observed with hydrochloric-acid-containing ITO etchant because the redox potential is controlled by the nitric/phosphoric acid ratio. Published data for this specific configuration is limited; each film stack should be qualified by electrochemical testing before production release.
The dissolution selectivity also affects sidewall profile. A fast zinc dissolution component that is not balanced by a gallium/indium dissolution rate leads to tapered or overhung profiles. The buffered acetic acid component raises the viscosity and reduces the boundary-layer depletion rate, producing a more gradual concentration gradient across the etch front. This is observable as a sidewall angle of 30–50° after 30% overetch in a single-wafer spin processor when measured by scanning electron microscopy. The specification is not universal; it depends on the underlayer and on the etch-tool uniformity. Lot-to-lot variation of the etchant density and free-acid normality is controlled within the table window to avoid a shift in the sidewall angle. The redox potential of the bath should be monitored with platinum and Ag/AgCl electrodes; for molybdenum protection, the oxidation-reduction potential is typically maintained below +450 mV vs Ag/AgCl. If the bath is over-sparged with air, the redox potential rises and molybdenum attack increases.
For bottom-gate TFT structures, loss of the etch-stop layer is the most process-limiting defect. The EL-grade formulation is designed to minimize attack on silicon oxide or silicon nitride etch-stop films. The etch rate on thermally grown silicon oxide should be checked by ellipsometry after each bath make-up; if the oxide loss exceeds 2 nm for a 30 nm IGZO clear-to-endpoint time, the bath free-acid ratio has drifted outside the control window and the bath should be adjusted or recharged. This threshold is derived from the maximum allowable reduction in gate dielectric thickness for a 100 nm etch-stop layer. Published data for this specific configuration is limited, but the numerical bound is used as an internal process control limit. The product differs from technical-grade IGZO etchants in that the technical-grade materials may carry iron concentrations above 100 µg/L and particle counts above 500 counts/mL; the EL grade reduces these burdens by one to two orders of magnitude, which is necessary for stable oxide TFT threshold voltage and low pixel defect density.
Transferring a general-purpose ITO etchant to IGZO patterning without reformulation typically produces three failure modes. First, the zinc oxide component of the IGZO film may dissolve too rapidly relative to indium and gallium, leaving a zinc-depleted surface layer that causes non-uniform line-edge roughness. Second, chloride-containing ITO etchants can initiate pitting on aluminium or copper source/drain electrodes if the passivation layer is not perfectly aligned or if the etch time exceeds the clear endpoint. Third, the particle and cation specifications of a technical-grade ITO etchant are not compatible with oxide TFT backplane requirements because sodium, potassium, and iron at even 10–100 µg/L can alter the back-channel interface. The EL-grade IGZO etchant differs by using a chloride-free acid system, by controlling trace metals to the table limits, and by maintaining a lower redox potential to protect molybdenum.
The substitution risk is particularly high on large-format Gen 8.5 and Gen 10.5 processing lines, where the bath volume is large and the surface area of the substrate is high. A batch that is not filtered to 0.1 µm can accumulate particles from the substrate edge and from the conveyor, and these particles can be redistributed across the active area. The EL-grade product is therefore supplied with a filter compatibility statement and a recommended recirculation rate of 5–10 bath turnovers per hour. In high-humidity cleanrooms above 60% relative humidity, the product should be stored in sealed containers to prevent moisture uptake and acid vapour loss; an open container can absorb water and change the etch rate by 5–15% over a shift. These are operational boundaries derived from wet-bench mass balance, not from single-lot observations.
The product is not intended for aluminium-dominant source/drain stacks without a molybdenum or titanium barrier layer. In such stacks, the galvanic couple between IGZO and aluminium can generate local pH changes at the metal edge and create notch defects. A separate layer-specific qualification is required when the underlayer is changed from molybdenum to titanium or from silicon oxide to aluminium oxide. If the process requires a common etchant for both ITO and IGZO layers on the same line, the supplier should be consulted with the stack cross-section and the gate dielectric thickness; a split-lot test on production material is preferable to extrapolation from laboratory dip tests.
