| HS Code | 465589 |
| Product Name | Buffered Oxide Etchant (BOE) Electronic/EL Grade |
| Chemical Composition | Mixture of hydrofluoric acid (HF), ammonium fluoride (NH4F), and deionized water |
| Grade | Electronic/EL grade with high purity and low metallic impurities |
| Appearance | Clear, colorless liquid |
| Odor | Sharp, pungent, acrid |
| Hf Content | Typically 6-7% by weight |
| Nh4f Content | Typically 34-36% by weight |
| Nh4f To Hf Ratio | 6:1 standard; other ratios such as 7:1 available |
| Density | Approximately 1.15-1.18 g/cm3 at 20°C |
| Ph | Approximately 3-5 at 20°C |
| Etch Rate Sio2 | About 100 nm/min for thermal oxide at 25°C using 6:1 BOE |
| Solubility | Fully miscible in water |
| Vapor Pressure | Low, but tends to increase with temperature due to HF volatility |
| Storage Temperature | 15-25°C in original sealed container |
| Safety Hazard | Toxic and highly corrosive; causes severe skin and eye burns |
As an accredited Buffered Oxide Etchant (BOE) Electronic/EL Grade factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Buffered Oxide Etchant (BOE) Electronic/EL Grade is packaged in clean, sealed HDPE bottles, available in 1-liter quantities for precise use. |
| Container Loading (20′ FCL) | 20′ FCL: BOE electronic grade loaded in sealed, compatible containers, securely braced, labeled corrosive, segregated from incompatible materials. |
| Shipping | Buffered Oxide Etchant (BOE) Electronic/EL Grade is a hazardous, hydrofluoric-acid-based corrosive. It ships via ground transportation only under DOT hazmat regulations. Required packaging includes compliant, sealed containers with proper labeling. An additional hazmat fee applies. Air, international, and some residential deliveries are restricted. Handle with trained personnel and proper PPE. |
| Storage | Store Buffered Oxide Etchant (BOE) Electronic/EL Grade in its original, tightly closed high-density polyethylene (HDPE) container. Keep in a cool, dry, well-ventilated area away from sunlight, heat, and moisture. Use secondary containment. Never store in glass, metal, or near incompatible bases, oxidizers, or reactive metals. Keep segregated from other chemicals. |
| Shelf Life | Shelf life is typically 6–12 months when stored sealed in HDPE containers, away from heat and light. |
Advanced logic and memory front-end integration routes require oxide removal before selective epitaxy, silicide formation, or contact metallization. In production wet stations, electronic/EL-grade BOE is supplied as a volumetric blend of 40 wt% ammonium fluoride and 49 wt% hydrofluoric acid at ratios of 6:1, 10:1, or 20:1; the 6:1 composition is dispensed neat or diluted 1:1 v/v with ultrapure water in single-wafer spin processors. Bath temperature is maintained at 20–25 °C because thermal silicon dioxide etch rate increases by a factor of roughly 1.4–1.6 per 10 °C rise depending on bath age and ammonia loss. Compliance for the etchant rests on SEMI C36 for metal, anion, and particle limits, while rinse water must conform to ASTM D5127-13 Type E-1; the production envelope is typically an ISO 14644-1:2015 Class 3 cleanroom with local laminar flow. Endpoint detection in immersion tools is not direct for clear oxide layers; rather, process windows are established by measured etch rate and film thickness, with spectral reflectometry on monitor wafers after fixed-time removal. The chemical reaction consumes hydrofluoric acid and generates hexafluorosilicic acid: SiO₂ + 6 HF → H₂SiF₆ + 2 H₂O. In NH₄F-buffered systems the HF₂⁻ concentration is stabilised, so free fluoride activity remains more constant across bath loading than in unbuffered HF. Wetted surfaces must be PTFE, PFA, or HDPE; borosilicate glass plumbing, fritted spargers, and unprotected aluminium sensors are incompatible. Production-scale failure modes include ammonium fluoride crystallisation in unheated dead-legs below 18 °C, ammonia volatilisation from open recirculation tanks shifting pH and etch rate, and point-of-use filter blinding by silicate-laden precipitates. Terminal product types include advanced logic integrated circuits, DRAM, 3D NAND, and analog/mixed-signal devices where contact pre-clean or sacrificial pad oxide removal is required.
Sacrificial silicon dioxide release in MEMS capacitive inertial sensor production requires a lower-attack wet chemistry than concentrated 49% HF when thin polysilicon membranes, silicon nitride etch stops, or exposed aluminium bond pads are present. In these flows, a 20:1 electronic/EL-grade BOE is typically selected; it is dispensed undiluted or diluted 1:1 v/v with ultrapure water for stiction-sensitive structures. The as-supplied volumetric ratio refers to 40% NH₄F to 49% HF. Etchant quality is governed by SEMI C36, and the finished automotive MEMS devices are qualified under AEC-Q100 stress conditions, though the etchant itself is not the stress sample. The sacrificial film is commonly TEOS or PECVD silicon dioxide deposited over a sacrificial layer between polysilicon and the substrate; the oxide is removed through release holes, producing an isotropic undercut that must be timed to avoid attacking device anchors. Immersion tanks with megasonic agitation at 0.8–1.2 MHz can reduce etch time, but excessive acoustic power fractures released beams and comb fingers. Etch rate of PECVD oxide in 20:1 BOE at 25 °C varies with deposition temperature and silanol content, so lot-specific rate verification is required; published data for a specific deposition configuration is limited. After release etch, wafers are rinsed with ultrapure water and transferred through low-surface-tension liquid or supercritical CO₂ drying to prevent capillary stiction. This application produces inertial measurement units, gyroscopes, capacitive pressure sensors, and microphones.
Buffer ratio selection in thin-film transistor array processing is governed by the need to open silicon oxide passivation layers without excessive galvanic attack on aluminium or molybdenum source-drain metallization. A 10:1 or 20:1 blend of 40% NH₄F and 49% HF is used in horizontal spray etch chambers on Gen 8.5 and Gen 10.5 glass substrates. The etchant is recirculated through 0.1 μm PTFE cartridge filters, and bath temperature is controlled at 22 ± 1 °C because line undercut at the metal-selective edge increases with temperature due to electrochemical potential differences. Chemical train compliance references SEMI C36, and the cleanroom environment is held to ISO 14644-1:2015 Class 5; finished display modules are subject to RoHS 2011/65/EU for lead-free terminations. Spray processing uses multiple etch stages with intermediate deionized-water rinses; fixed-time etching is used because oxide thickness and bath etch rate must be correlated with the specific PECVD deposition tool, since RF power and pressure alter film density. Etch rate of PECVD silicon oxide in 10:1 BOE at 22 °C is commonly in the range of 30–60 nm/min, but it must be verified rather than assumed. Production experience shows edge-to-center nonuniformity arising from nozzle clogging by crystallised NH₄F when exhaust plenum relative humidity drops below 30%, and particle counts rise after bath age exceeds 72 h unless partial refresh is performed. The process produces active-matrix liquid-crystal display panels and OLED backplanes.
Quartz crystal resonator frequency adjustment after mechanical lapping uses controlled wet etching in a 4:1 to 10:1 NH₄F/HF buffered oxide bath heated to 60–80 °C. The bath is held at elevated temperature because crystalline quartz etches much more slowly than amorphous thermal oxide at ambient temperature; vessel and heater wetted surfaces must be PFA or PTFE, and immersion heater jackets must not create local hot spots that alter etch anisotropy. Chemical purity is bounded by SEMI C36, and the finished quartz crystal unit is qualified under IEC 60122-1. The process etches AT-cut quartz blanks in agitated immersion tanks, with monitor blanks removed at intervals for frequency measurement; thickness removal per pass is typically in the 0.1–1.0 μm range depending on crystallographic orientation and bath age. Dimensional etch rate varies across wafer sectors, so production tooling rotates wafers through the bath and uses frequency sorting after rinse to assign blanks to finishing lapping steps. Field data show bath etch rate drift upward as ammonium fluoride decomposes in heated conditions, while silicate accumulation reduces surface quality. The terminal products are quartz crystal resonators, TCXO/OCXO frequency references, and crystal filters used in communications equipment.
In crystalline silicon solar cell manufacturing, the phosphosilicate glass layer formed during POCl₃ tube diffusion is stripped after diffusion. Concentrated HF formulations are widely used; however, a buffered 6:1 or 7:1 BOE may be selected when a more stable HF₂⁻ concentration reduces etch-rate variation on lightly doped emitters and limits attack on transport rollers or exposed front-surface dielectrics. As-supplied BOE is typically diluted 1:5 v/v with ultrapure water before inline spray application. Chemical purity is controlled under SEMI C36, and European supply chains apply REACH (EC) 1907/2006 for hazardous substance communication; finished modules are qualified under IEC 61215. The wafers pass through a horizontal inline etch tool with spray bars above and below the wafer for simultaneous front and backside glass removal; residence time is set between 30–60 s according to PSG thickness and bath activity. After etching, wafers enter a cascading deionized-water rinse and heated nitrogen air-knife dryer. Bath life is limited by dissolved silicate loading; when silicon concentration exceeds several thousand ppm, rinsing residues and emitter redeposition increase. Edge nonuniformity appears where roller shadowing reduces spray impingement, so nozzle overlap at wafer entry and exit zones must be adjusted. This process produces monocrystalline and polycrystalline silicon solar cells, including PERC and TOPCon architectures.
Glass-based lab-on-a-chip devices are patterned with chromium-gold masks and wet etched in 6:1 to 10:1 BOE to form channel networks. The 10:1 composition is preferred over concentrated HF because the buffered bath reduces etch-rate variation and produces smoother sidewalls in borosilicate glass, although the etch remains isotropic. Channel depth is controlled by etch time and bath temperature; a 20 μm mask opening in 10:1 BOE at 25 °C produces an undercut of approximately 1.0–1.2 × the vertical depth on standard borosilicate glass. Chemical process compliance is derived from SEMI C36; finished in vitro diagnostic cartridges are manufactured under ISO 13485:2016, and material biocompatibility is assessed under the ISO 10993 series where applicable. The photomask must be pinhole-free because BOE penetrates mask defects and creates etch pits; patterned wafers are immersed in fluoropolymer tanks with continuous agitation to refresh etchant at the glass surface. Etch-rate monitoring uses sacrificial glass substrates from the same material batch, because boron oxide and alkali content shift local etch rate. The process produces microfluidic diagnostic cartridges, lab-on-a-chip devices, and microreactors. The isotropic nature limits minimum channel width to roughly twice the etch depth plus the mask opening; vertical sidewalls are not achievable without dry etch or alternative substrate processing.
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Buffered Oxide Etchant (BOE) Electronic/EL Grade is a wet-etch chemistry composed of electronic-grade ammonium fluoride solution and electronic-grade hydrofluoric acid in controlled volumetric ratios, commonly 5:1, 6:1, 7:1, 10:1, and 20:1. The 7:1 product is frequently specified for isotropic removal of thermally grown or deposited silicon dioxide in front-end semiconductor fabrication, where the ammonium fluoride component maintains a dissolved fluoride equilibrium that stabilises etch rate over bath life. The Electronic/EL designation is supply-chain and analytical-panel controlled; it indicates that trace metal contamination has been reduced to parts-per-billion levels, usually with individual alkali, alkaline earth, and transition metal cations certified at ≤25 ppb and critical mobile-ion species such as sodium and potassium at ≤10 ppb depending on the manufacturer’s certificate of analysis. The product is supplied in high-density polyethylene or fluoropolymer-lined containers because free hydrofluoric acid attacks borosilicate glass.
In unbuffered 49% hydrofluoric acid, consumption of HF during silicon dioxide dissolution progressively lowers free fluoride activity and changes the etch rate. BOE formulation changes the equilibrium by providing a large reservoir of ammonium fluoride, which dissociates into ammonium and fluoride ions and drives the formation of bifluoride according to the equilibrium HF + F⁻ ⇌ HF₂⁻. The primary etching of silicon dioxide can be represented by SiO₂ + 4HF → SiF₄ + 2H₂O, with subsequent conversion of SiF₄ to H₂SiF₆ in the presence of excess HF. Because ammonium fluoride supplies fluoride ion, the bath remains buffered against local depletion in high-aspect-ratio features and across recirculated production baths. The resulting pH window for BOE 7:1 at 25 °C is ordinarily 3.2–4.0, compared with a much lower and less stable pH in unbuffered HF. Published datasheets from electronic chemical suppliers list nominal thermal SiO₂ etch rate at 25 °C in BOE 7:1 as 75–100 nm/min, while 10:1 product typically runs 55–75 nm/min and 20:1 30–45 nm/min. Etch-rate drift across a bath life of 48–72 h is commonly held below ±5% when concentration and temperature are controlled.
Electronic/EL grade BOE 7:1 is released after ion chromatographic and inductively coupled plasma mass spectrometry panels. Assay of the major components is performed by acid-base titration and by ion chromatography for fluoride and ammonium. Anion contamination is measured by EPA Method 300.1, and cation contamination is measured by ICP-MS following EPA Method 6020B. The product is not a single universally standardised grade; fab-specific purchase specifications may be tighter than the values shown in Table 1.
Table 1. Representative BOE Electronic/EL Grade formulation windows and nominal etch-rate ranges published for semiconductor wet benches.
| Volumetric ratio | NH4F concentration (wt%) | HF concentration (wt%) | Nominal thermal SiO₂ etch rate at 25 °C (nm/min) |
|---|---|---|---|
| 6:1 | 32.0–35.0 | 6.3–7.4 | 90–120 |
| 7:1 | 33.0–36.0 | 5.8–6.7 | 75–100 |
| 10:1 | 34.5–37.5 | 4.1–5.0 | 55–75 |
| 20:1 | 36.0–39.0 | 2.0–2.7 | 30–45 |
Density at 25 °C for BOE 7:1 is approximately 1.11 g/cm³, and vapor pressure is dominated by hydrofluoric acid. The product is free of surfactants and photoresist strippers unless otherwise specified, which distinguishes standard Electronic/EL Grade BOE from formulated pad etchants that may contain acetic acid or ethylene glycol.
Wet-process tools for BOE Electronic/EL Grade use wetted components of polypropylene, polyethylene, PTFE, or PFA. Borosilicate glass, quartz, titanium, and stainless steel are not acceptable for long-term contact because free HF etches silicon dioxide and can corrode metals. Production-scale recirculating baths on 200 mm and 300 mm wafer lines are typically equipped with 0.05–0.1 µm PTFE or PFA point-of-use filters, overflow filtration, and temperature control at 22 ± 0.5 °C or 25 ± 0.5 °C. Temperature control tighter than ±1 °C is required for etch-rate repeatability because the thermal oxide etch rate changes approximately 10–15% per °C in the operating range. Bath life is normally limited by dilution from drag-out and by accumulated silicon and ammonium fluosilicate, not solely by fluoride depletion. In high-volume manufacturing, spiking with fresh BOE and bleed-and-feed operation are used to keep etch rate within the process window; batch-to-batch concentration variation from the manufacturer is usually specified at ±1% absolute for HF and NH₄F. Immersion tanks are exhausted and provided with acid-gas scrubbers; nitrogen blanketing is sometimes used to reduce moisture uptake and carbonate contamination.
In wafer fabrication, BOE Electronic/EL Grade is used in immersion tools for pad oxide removal, sacrificial oxide wet strip, native oxide removal before selective epitaxy, and oxide release steps in MEMS. A 100 nm thermal oxide film in BOE 7:1 at 25 °C is normally cleared in 60–120 s with overetch allowance; endpoint is rarely used in batch immersion, so process control is based on time and temperature. Spray tools and single-wafer tools use higher dilution ratios or lower temperature to reduce etch rate for thin films. Uniformity across a 300 mm wafer in an immersion bath with megasonic agitation at 800–1200 kHz is generally better than ±5% for oxide films thicker than 50 nm, while thinner films may show larger relative nonuniformity if the rinse step is not optimised. After etching, substrates are rinsed with ultrapure water to 18.2 MΩ·cm resistivity and dried under nitrogen or isopropyl alcohol vapor.
In high-aspect-ratio contact and trench cleaning, BOE 7:1 without surfactant may exhibit slower effective etch rate at feature bottoms due to diffusion limitation. Published data for this specific configuration is limited, but wetting is generally improved by adding a compatible fluorosurfactant or by physical agitation. For standard Electronic/EL Grade product, the absence of organic additives avoids carbon contamination in subsequent plasma or thermal steps. If wetting is insufficient, the fab may employ dilute BOE 100:1 or a formulated pad etchant; each substitution requires requalification because etch selectivity to photoresist and silicon nitride changes.
Commercial model designations are typically of the form BOE 7:1 EL or BOE 10:1 EL, where the ratio is the volume ratio of 40% ammonium fluoride solution to 49% hydrofluoric acid. A BOE 5:1 EL product has higher HF content and a faster etch rate; BOE 20:1 EL has lower HF activity and is used for controlled oxide thinning. Some suppliers append container size and trace-metal grade to the product code, for example BOE 7:1 EL-25L. The selected model is determined by the process etch rate requirement, the thermal oxide thickness to be removed, and the permitted silicon nitride or metal etch loss.
Differentiation from non-electronic grades is quantified in the analytical panel rather than in the etch chemistry itself. The same volumetric ratio of technical-grade BOE may etch SiO₂ at a comparable rate, but it can introduce mobile-ion contamination that shifts threshold voltage or degrades gate oxide integrity. Table 2 compares typical release limits for Electronic/EL Grade BOE 7:1, technical BOE, and reagent-grade hydrofluoric acid. The values are representative of industrial product literature and may vary by supplier.
| Parameter | Electronic/EL Grade BOE 7:1 | Technical/Industrial BOE | Reagent HF |
|---|---|---|---|
| Individual transition metals (Fe, Cu, Ni, Cr) | ≤5–25 ppb | 0.1–5 ppm | ≤5 ppm |
| Sodium and potassium | ≤10 ppb | up to 1 ppm | not specified |
| Anions (chloride, sulfate, nitrate) | ≤500 ppb each | ≤10 ppm | ≤5 ppm |
| Particles ≥ 0.2 µm | ≤100 counts/mL | not controlled | not controlled |
| Application | front-end oxide etch | glass and metal cleaning | general chemical analysis |
Replacement of unbuffered 49% HF with BOE Electronic/EL Grade is appropriate when the process requires stable pH, reduced photoresist lifting, and lower particle generation over long bath life. Unbuffered HF etches SiO₂ rapidly but pH shifts with depletion; BOE maintains a fluoride reservoir that reduces etch-rate falloff. For front-end oxide strip, BOE 7:1 is preferred over BOE 20:1 when faster removal is required without excessive metal attack; BOE 20:1 is used where slower, controlled oxide removal is needed. Compared with technical-grade BOE, the electronic grade reduces sodium, potassium, calcium, and iron contaminants by a factor of 100–1000×, as shown in Table 2. This contamination reduction is relevant for gate oxide formation, high-k dielectric deposition, and silicide formation. Compared with formulated pad etchants, standard BOE Electronic/EL Grade does not contain acetic acid or organic surface tension modifiers. This avoids carbon residue after dry processing but may provide inferior wetting in high-aspect-ratio trenches; chemically inert fluorosurfactant-free formulations are therefore used only where geometry permits adequate mass transport. Published data for direct device-yield comparisons between BOE EL grade and technical BOE are limited because contamination effects are process integration dependent.
Certificate-of-analysis data are typically generated by ICP-MS after preconcentration. Direct aspiration of high-fluoride matrices can damage quartz torches, so laboratories use PFA sample-introduction systems and matrix-matched calibration. Incoming inspection in wafer fabs may repeat cation analysis by EPA Method 6020B, anion analysis by EPA Method 300.1, and particle counts by liquid-borne optical particle counters. Packaging for Electronic/EL Grade is leached and tested to ensure no release of sodium, potassium, iron, or organic carbon. Common container sizes are 1 L, 5 L, 25 L, and 200 L high-density polyethylene drums with fluoropolymer inner caps; some manufacturers supply 5-gallon and 55-gallon containers for larger wet benches. Cleanroom filling under ISO 14644-1:2015 Class 5 conditions limits environmental particle and microbial contamination during packaging.
Operational boundaries are determined by the hazardous nature of hydrofluoric acid. BOE Electronic/EL Grade must be stored above 5 °C and below 30 °C in sealed polyethylene or fluoropolymer containers; freezing can precipitate ammonium fluoride, and elevated temperatures increase HF vapor pressure. The product is incompatible with strong bases, concentrated sulfuric acid, oxidising agents, and materials containing silica. Transport classification is typically UN 1790, Hydrofluoric acid solution, or UN 2817, Ammonium bifluoride solution, depending on exact composition and regulatory interpretation; the safety data sheet must be reviewed before use. For personnel handling, acid-resistant PPE, calcium gluconate gel, and local exhaust ventilation are specified. Rinse water from BOE processes requires fluoride treatment and pH neutralisation before discharge under local discharge permits. In semiconductor fabs, point-of-use pumping systems should be constructed of perfluoroalkoxy or polytetrafluoroethylene, and no metallic fittings should contact the process liquid.
Release documentation for Electronic/EL Grade BOE is also aligned to the hazard communication obligations of REACH Regulation (EC) No 1907/2006 and the classification, labelling, and packaging requirements of CLP Regulation (EC) No 1272/2008. Incompatibility with borosilicate glass, quartz, silicon dioxide, calcium compounds, concentrated alkalis, and strong reducing agents must be reflected in both storage segregation and tool design. The product attacks titanium, aluminum, and stainless steel at different rates; passivated stainless steel may be used only for secondary containment with fluoropolymer liners. BOE Electronic/EL Grade should never be mixed with sulfuric acid or nitric acid unless the tool is specifically designed for mixed acid processes because thermal runaway and hazardous gas release can occur.
