| HS Code | 731618 |
| Productname | Buffered Oxide Etch / BOE Electronic/EL Grade |
| Chemicalsystem | Ammonium fluoride (NH4F) buffered hydrofluoric acid (HF) |
| Componentcasnumbers | HF: 7664-39-3; NH4F: 12125-01-8 |
| Appearance | Clear colorless liquid |
| Physicalstate | Liquid |
| Odor | Sharp pungent acid odor |
| Ph | Approximately 4 to 5, ratio-dependent acidic buffer |
| Specificgravity | Approximately 1.10 to 1.20 at 20°C |
| Density | Approximately 1.10 to 1.20 g/cm3 at 20°C |
| Boilingpoint | Approximately 100°C for aqueous solution |
| Freezingpoint | Approximately -30°C to -15°C |
| Vaporpressure | Approximately 23 mmHg at 20°C |
| Solubility | Fully miscible in water |
| Hydrofluoricacidcontent | Typically 6-10 weight percent |
| Ammoniumfluoridecontent | Typically 25-40 weight percent |
| Bufferratio | Common ratios are 6:1, 7:1, or 10:1 NH4F:HF |
| Etchrateonthermaloxide | Approximately 500-1500 Å/min at 25°C depending on ratio and conditions |
| Selectivity | High selectivity for SiO2 over Si and Si3N4 |
| Puritygrade | Electronic/EL grade with low ppb metallic impurities and particulate control |
As an accredited Buffered Oxide Etch /BOE Electronic/EL Grade factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | BOE Electronic/EL Grade is packaged in a 4 L fluorinated HDPE container with secure sealing, labeled for safety and traceability. |
| Container Loading (20′ FCL) | 20′ FCL container of Buffered Oxide Etch (BOE), Electronic/EL grade, packed in sealed drums, secured and loaded for safe transport. |
| Shipping | Buffered Oxide Etch (BOE Electronic/EL Grade) ships as a corrosive, toxic liquid under UN1790, Hydrofluoric Acid Solution, Class 8 (6.1). It requires compliant packaging, hazard labeling, and ground/air transport restrictions. Handle only with specialized PPE; spills require immediate fluoride-specific emergency response. Ensure temperature-controlled storage and segregation from incompatible materials. |
| Storage | Store Buffered Oxide Etch (BOE Electronic/EL Grade) in tightly sealed, original HF-compatible containers, preferably polyethylene or PTFE. Keep in a cool, dry, well-ventilated area, away from direct sunlight and incompatible materials. Use secondary containment to prevent spills. Do not store in glass or metal containers. Ensure area is clearly labeled and access is restricted to trained personnel. |
| Shelf Life | For BOE Electronic/EL Grade, shelf life is typically 6–12 months from manufacture, stored sealed at room temperature away from moisture. |
Before gate oxidation or epitaxial deposition in front-end wafer fabrication, sacrificial pad oxide and native oxide removal from silicon surfaces is performed with buffered oxide etch blended from 40% ammonium fluoride and 49% hydrofluoric acid. Common volumetric working ratios are 10:1 and 20:1 NH4F:HF; the 10:1 formulation is frequently qualified for thermal oxide etch rates in the range of 80–120 nm/min at 25±0.5 °C, although oxide density, dopant content, bath loading, and throughput alter the measured value. The etch is performed on recirculated PFA wet benches with 0.1 µm point-of-use filtration, in-line conductivity measurement, and high-efficiency exhaust. After timed immersion or single-wafer spray processing, the wafers are rinsed with ultrapure water and dried through an isopropyl alcohol Marangoni dryer to reduce watermarks. The chemical reaction consumes ammonium fluoride and generates fluosilicate species; bath replenishment is triggered by free HF titration, with control limits usually held within ±0.2 wt% of the target value to stabilize etch rate and photoresist compatibility. Lot qualification for semiconductor use requires raw HF and NH4F certified to SEMI C5 and SEMI C28 grade limits, metal impurity control for Fe, Cu, Ni, Cr and alkali elements below supplier CoA limits of 10 ppb each by ICP-MS, and cleanroom handling under ISO 14644-1:2015 Class 3 conditions. In this application, BOE removes sacrificial oxide prior to LPCVD silicon nitride, rapid thermal processing, or epitaxial growth; it is not used for bulk silicon removal because the etch rate of silicon in NH4F-buffered HF is negligible. The processed wafers continue to transistor fabrication for DRAM, NAND flash, and logic devices. Wafers with exposed aluminum or copper metallization are excluded from the same bath because dissolved metal cross-contamination degrades minority carrier lifetime and causes defect formation in downstream thermal processing.
Thin-film transistor liquid-crystal display and active-matrix organic light-emitting diode backplanes use silicon oxide as a gate insulator or interlayer dielectric that must be opened over contact pads or patterned before subsequent deposition. For large-area glass substrates, BOE is run at more dilute ratios such as 15:1 and 20:1 to reduce the isotropic etch rate and hold undercut beneath hardened photoresist within acceptable sidewall limits. Conveyorized spray etchers or multi-tank immersion tools with linear recirculation process Gen 6 substrates of 1,500 mm × 1,850 mm and Gen 8.5 substrates of 2,200 mm × 2,500 mm. In a 15:1 bath at 25 °C, deposited silicon oxide etch rate is typically controlled below 75 nm/min; the resulting lateral undercut under photoresist is commonly held between 1.0 µm and 2.5 µm per side, depending on resist adhesion promotion with hexamethyldisilazane and post-bake temperature. Bath make-up uses EL grade BOE lot-certified against SEMI C5 and SEMI C28 raw-material metal limits, but the TFT line supplements bulk purities with ion chromatography to track fluoride, ammonium, and dissolved silicon in working baths. Operator and tool safety is managed under SEMI S2 / SEMI S8 equipment environmental and safety guidelines, with HF sensors interlocked to exhaust scrubbers. After oxide etch, rinsing through counter-flow ultrapure water and air-knife drying prevents silica residue from redepositing on indium tin oxide contact regions. The patterned substrates proceed to thin-film transistor array testing and cell assembly, with terminal displays for television, desktop monitor, automotive instrument cluster, and mobile panel applications. Published data for sidewall etch profiles in specific Gen 8.5 spray tools is limited because etch rate and undercut are strongly dependent on glass temperature uniformity and conveyor speed; therefore pilot lot qualification on sacrificial glass is standard before mass production.
| BOE working ratio (NH4F:HF) | Bath temperature | Deposited SiO2 etch rate | Photoresist undercut per side | Primary process monitor |
|---|---|---|---|---|
| 15:1 | 25 °C | 55–75 nm/min | 1.0–2.5 µm | Ion chromatography and free HF titration |
| 20:1 | 25 °C | 40–60 nm/min | <1.5 µm | Conductivity and pH trending |
Surface-micromachined MEMS fabrication depends on the removal of sacrificial silicon dioxide or phosphosilicate glass from beneath polycrystalline silicon, amorphous silicon, or silicon nitride structural layers. BOE release is performed at volumetric ratios of 7:1 or 10:1 for PSG and 20:1 for thermal or CVD oxide, with bath temperature maintained at 20–25 °C in low-particle immersion tanks. The etch is isotropic, so release distance is controlled by diffusion through narrow gaps; for channels below 2 µm, megasonic agitation reduces the boundary layer and prevents local depletion of fluoride species. Because sacrificial film thickness varies across a wafer, etch progress is monitored by wafer curvature, white-light interferometry, or sacrificial test features rather than fixed immersion time alone. The permissible over-etch window is frequently limited to approximately ±10% of the nominal cleared time because the BOE solution attacks densified low-stress silicon nitride hard masks and may widen anchor regions. After release, the wafers are moved through ultrapure water dilution, isopropyl alcohol displacement, and supercritical CO2 drying to eliminate capillary-force stiction of compliant cantilevers, membranes, or interdigitated fingers. Compliance in this segment emphasizes equipment safety performance under SEMI S2 and SEMI S10 chemical handling criteria, while the EL grade buffered oxide supply provides low alkali metal content that would otherwise drift onto electrostatic actuator surfaces during release. Terminal MEMS products include inertial sensors for automotive airbag and electronic stability control, gyroscopes for navigation, capacitive pressure sensors, and micromirror arrays for projection. The process is not applied to stacks with exposed aluminum or copper metallization because the etchant attacks aluminum and can contaminate shared baths; vapor-phase HF is preferred when liquid release produces chronic stiction failures in extremely long or thin structural elements.
After rejected device wafers and monitor wafers are depackaged and stripped of photoresist or organic films, reclaim service providers introduce BOE to remove thermal oxide, TEOS-based CVD oxide, or high-density plasma oxide without heavily attacking the underlying single-crystal silicon. The buffered chemistry is selected when residual oxide thickness exceeds 500 nm and when a faster concentrated HF etch would create excessive surface pitting or uncontrolled silicon consumption. Reclaim immersion systems use polypropylene tanks with exhaust hoods, temperature control from 30–35 °C, and cassette agitation to move spent etchant from wafer-center regions. After dielectric removal, the wafers enter an SC1 solution of NH4OH/H2O2/H2O at 70–80 °C to remove particles and organic residues, followed by an SC2 solution of HCl/H2O2/H2O at 70–80 °C to remove metals and less soluble contaminants. Reclaimed-wafer quality is measured against SEMI M1 polished wafer parameters for diameter, flatness, total thickness variation, bow, and warp; particle counts are verified by dark-field laser scanning, and trace metal residues are checked by secondary ion mass spectrometry on periodic lot samples. The end product is a reclaimed monitor wafer or test wafer used for furnace qualification, particle counting, implant setup, or lithography send-ahead checks. Operational boundary: wafers originating from copper metallization lines are quarantined from the BOE reclaim bath because dissolved copper can reduction-deposit on silicon surfaces and severely reduce carrier lifetime.
Physical failure analysis and construction analysis on integrated circuits use BOE as a controlled dielectric delayering solution when silicon oxide must be removed selectively from copper or tungsten interconnect structures and when exposed aluminum is not present in the region of interest. The etchant is prepared at 10:1 or 20:1 NH4F:HF and held at 25±0.5 °C in a laboratory wet station with local exhaust. Analysts apply the liquid by micro-pipette to localized oxide regions or immerse the die in timed increments of 15–30 s; depth is checked with optical interference color charts, scanning electron microscopy, or focused ion beam cross-sections. For copper/low-k integrated circuits, BOE removes silicon oxide quickly but may not provide adequate selectivity to all carbon-doped oxide or organosilicate glass dielectrics; published data for specific dielectric stacks is limited, so sacrificial units are processed before the device of interest. This step exposes contact plugs, via chains, and transistor contacts for subsequent imaging or energy-dispersive X-ray spectroscopy. Electrostatic discharge protection for the failing units follows ANSI/ESD S20.20, and laboratory air monitoring keeps airborne HF below the ACGIH TLV-TWA of 0.5 ppm. The terminal output of this application is not a production wafer but a prepared cross-section or delayered die that supports fault isolation reports and root-cause identification.
Quartz crystal resonator blanks are chemically trimmed in BOE baths to adjust resonance frequency before metal electrode deposition and final sealing. The buffered etchant attacks synthetic quartz on exposed faces and is run at a volumetric ratio such as 6:1 or 7:1 NH4F:HF; the bath is held at 45–55 °C because the quartz etch rate at 25 °C is much lower than that of thermal silicon dioxide and would slow production. Blanks are mounted in mesh trays and etched for calculated intervals based on pre-etch frequency or motional capacitance; a subset of blanks is measured in a test fixture compliant with IEC 60444-1 to track frequency shift in parts per million. When the target frequency is reached, the bath is flooded with ultrapure water to quench the reaction, and blanks proceed to electrode metallization and hermetic packaging. Effluent from the trim bath is neutralized with calcium hydroxide or calcium chloride to precipitate fluoride, while waste streams are controlled under national discharge permits and RoHS process chemical restrictions. Terminal products include quartz crystal units and clock oscillators used in automotive engine control units, wireless transceivers, and microcontroller clock circuits. Process limitations include non-uniform attack at etched blank edges and the need to remove insoluble residue before sealing; published data for specific crystallographic etch anisotropy in production trim baths is limited.
Competitive Buffered Oxide Etch /BOE Electronic/EL Grade prices that fit your budget—flexible terms and customized quotes for every order.
For samples, pricing, or more information, please contact us at +8615365186327 or mail to admin@ascent-chem.com.
We will respond to you as soon as possible.
Tel: +8615365186327
Email: admin@ascent-chem.com
Flexible payment, competitive price, premium service - Inquire now!
Buffered Oxide Etch (BOE) Electronic/EL Grade is a filtered aqueous mixture of 40 wt% ammonium fluoride (NH4F) and 49 wt% hydrofluoric acid (HF), supplied in volumetric ratios of 5:1, 6:1, 7:1, 10:1, and 20:1. Model designations include BOE 5:1 EL, BOE 6:1 EL, BOE 7:1 EL, BOE 10:1 EL, and BOE 20:1 EL; the first number denotes the volume ratio of 40 wt% NH4F to 49 wt% HF. The Electronic/EL designation indicates low trace-cation and particle specifications intended for semiconductor and microelectronic wet processing. In production wet benches, the product is dispensed from high-density polyethylene or fluoropolymer containers through 0.1 µm or 0.05 µm point-of-use filters. Lot certification commonly includes ICP-MS trace-metal data, particle counts, and assay. Individual metal maxima for Fe, Na, K, Ca, Mg, and Zn are commonly supplied in the range of 10 ppb to 50 ppb, depending on supplier and grade; actual values must be read from the lot certificate of analysis. The product is used in immersion tanks, recirculating etch baths, and single-wafer spray processors for controlled removal of thermally grown or deposited silicon dioxide layers. Packaging is normally performed in cleanroom environments meeting ISO 14644-1:2015 Class 5 or better, with fluoropolymer or high-density polyethylene bottles and drum liners.
Etch rate is governed by the equilibrium concentration of the bifluoride ion, HF2−, and by the pH established through the NH4F/HF buffer pair. In a 6:1 BOE mixture, the higher NH4F fraction maintains a stable pH and supplies fluoride species as HF is consumed during SiO2 etching. Typical etch rates for thermally grown SiO2 at 25 °C in 6:1 BOE are reported near 100 nm/min; 5:1 and 7:1 formulations bracket approximately 80 nm/min to 120 nm/min, depending on oxide density, anneal history, and bath age. Deposited oxides etch faster than thermal oxide due to lower film density; plasma-enhanced CVD oxide may require a reduced immersion time or a higher dilution ratio such as 10:1 or 20:1. Temperature control is a critical parameter. Recirculating wet benches should maintain bath temperature within ±0.5 °C of the qualified set point because etch rate shifts with temperature. Bath turnover, spiking, and replacement schedules are established by etch-rate monitors rather than fixed calendar days. Published data for LPCVD silicon nitride etch rate in BOE varies with film stoichiometry and should be obtained from the specific lot application note rather than treated as a universal selectivity value.
| Volume ratio NH4F 40 wt% : HF 49 wt% | NH4F 40 wt% volume fraction | HF 49 wt% volume fraction |
|---|---|---|
| 5:1 | 83.3% | 16.7% |
| 6:1 | 85.7% | 14.3% |
| 7:1 | 87.5% | 12.5% |
| 10:1 | 90.9% | 9.1% |
| 20:1 | 95.2% | 4.8% |
On high-volume lines, particle contamination is controlled by point-of-use filtration and by restrictions on wetted materials. PFA, PTFE, PVDF, and polypropylene are accepted for recirculation loops; borosilicate glass and polymethyl methacrylate are incompatible because HF attack releases leachables and degrades the bath. Bath life is limited by evaporation losses of HF and by accumulation of dissolved silicon species. Process baths are spiked or exchanged when etch rate falls outside the qualified range, not solely when visual clarity changes. Rinse after etch uses overflowing ultrapure water with resistivity ≥18.2 MΩ·cm at 25 °C; water quality should conform to ASTM D5127-18 for electronic-grade water. Particle counts at ≥0.5 µm are commonly specified below 10 particles/mL; ≥0.2 µm counts may be specified below 50 particles/mL in some supplier specifications. Actual limits vary by supplier and should be confirmed against the lot certificate. Anion concentrations are measured by ion chromatography; lower reporting limits for chloride, sulfate, and nitrate are typically at or below 100 ppb. The absence of non-volatile additives in some EL formulations reduces post-etch residue, but this property depends on the specific grade and must be verified before use in gate-level processes.
| Parameter | Typical acceptance criterion | Test method |
|---|---|---|
| Fe | ≤20 ppb | ICP-MS |
| Na, K, Ca, Mg | ≤20 ppb each | ICP-MS |
| Cu, Ni, Cr, Zn | ≤10 ppb each | ICP-MS |
| Particles ≥0.5 µm | ≤10 particles/mL | optical particle counter |
| Point-of-use filtration | 0.1 µm or 0.05 µm | filter integrity test |
Substrate compatibility and rinse-drag-out constraints determine whether BOE Electronic/EL Grade can be inserted into an existing wet process. The product is intended for silicon dioxide films and is not a bulk silicon etchant at typical process conditions; however, the presence of free HF attacks glass, quartz, and some metal films. Etching of thermal SiO2 on silicon wafers requires a timed process or endpoint detection because selectivity to silicon is finite. For sacrificial oxide release in MEMS, the same bath chemistry is used with longer immersion and periodic agitation; release times must account for etch-rate loss due to dissolved silicon accumulation. Spray-tool use requires PFA or PVDF nozzles and collection lines; stainless steel components are not compatible unless passivated and isolated from the etch stream. Production wet-bench data indicate that drag-out increases with viscosity at higher NH4F ratios; 10:1 and 20:1 formulations can exhibit higher drag-out than 5:1, increasing rinse-water load. Facilities should evaluate rinse-water neutralization capacity when changing ratio. Storage should be maintained between 15 °C and 25 °C. Avoid combination with ammonia-based cleaning agents in the same process line due to exothermic neutralization and potential HF vapor release; segregated exhaust and drench equipment are required.
Differences from other wet etch products are defined by buffer content, etch rate, and application. Unbuffered 49 wt% HF shows higher initial SiO2 etch rates, often above 800 nm/min at 25 °C for thermal oxide, but rate falls as fluoride is consumed. BOE Electronic/EL Grade commonly limits oxide etch rate to 50 nm/min to 120 nm/min, improving thickness control for thin films. Dilute HF at 100:1 or 200:1 in water is used for native oxide removal and particle removal in pre-diffusion cleans; BOE is selected for thicker sacrificial oxide or mask oxide etching. Vapor HF anhydrous tools are not a direct substitute because chamber materials, condensation control, and selectivity management differ. BOE is not a photoresist stripper and will not dissolve organic films; it is inserted after solvent strip or ashing when oxide etching is required.
In immersion stripping of sacrificial or mask oxide, BOE Electronic/EL Grade is selected when wafer-to-wafer thickness uniformity must be kept tighter than with unbuffered 49 wt% HF. Recirculating baths for immersion stripping are typically configured with fluoropolymer filters, PFA immersion heaters, and temperature sensors in the return line. Process data from production wet benches show that etch-rate drift is lower for BOE than for unbuffered HF over the first 50 wafer cassettes of bath life, provided the bath is spiked with fresh BOE according to etch-rate monitor output. The oxide etch is not self-limiting; over-etch can occur if wafers remain in the bath after endpoint. For a 6:1 EL bath, a qualified process may remove 100 nm of thermal oxide in approximately 60 s at 25 °C; this timing must be re-qualified for each tool and film type. Endpoint is often determined by film thickness before and after etch rather than visual de-wetting. Spray processors require component-level compatibility because aerosol formation can increase HF exposure risks. Installation should include exhaust interlocks and leak detection on recirculation lines. Published data for this specific configuration is limited for sub-10 nm films; process development relies on blanket wafer split-lot tests.
Batch-to-batch variance in Electronic/EL Grade BOE is controlled by blending ratio tolerances and trace-metal lot release. Etch rate can shift by ±5 nm/min when the HF assay moves within the supplier tolerance; therefore incoming chemical qualification often includes a 100 nm thermal oxide coupon etch test on a PFA wafer cassette. Metrology uses optical ellipsometry before and after etch. The measured etch rate is compared with the supplier lot value; a deviation greater than ±10% triggers bath spiking or supplier review. This is a production equipment behavior observed on recirculating wet benches with load sizes of 25 wafers per cassette. Lot certification from ICP-MS should be distributed to the process owner rather than retained only in logistics. For facilities converting from unbuffered HF to BOE, the rinse-water neutralization loop must be resized for both fluoride and ammonium content. Published data for this specific configuration is limited for mixed acid waste streams; waste treatment design should be evaluated with site-specific ion load data.
Supplier qualification should include an audit of purification, blending, and packaging. The purification path for EL grade typically begins with raw HF that has been distilled and NH4F that has been recrystallized or treated by ion exchange. Blending is performed with sparge-grade nitrogen to avoid carbonate contamination. Filling is conducted in cleanrooms meeting ISO 14644-1:2015 Class 5; container closures are fluoropolymer-lined. Shipment lot documentation should include the actual batch analysis for each metal, not only pass/fail. These controls are necessary because trace metal contamination at greater than 20 ppb can change gate dielectric integrity in front-end processing. The product specification is therefore meaningful only when paired with the certificate of analysis and the wafer-level qualification coupon data.
Filtration and dispense systems for BOE EL require attention to bubble entrainment and pump cavity design. Diaphragm pumps with PTFE bellows or magnetically levitated centrifugal pumps are used to avoid metal ion shedding from stainless steel. Filter cartridges should be hydrophilic PTFE or PFA, rated at 0.1 µm absolute; filter change intervals are set by differential pressure rise above 0.7 bar at 25 °C. Elevated differential pressure can create particle shedding and reduce flow. Point-of-use spiking with fresh BOE should be done through a dosing pump into the return line, not by manual pouring into the tank, because localized high HF concentration at the liquid surface increases vapor formation. Bath level sensors and temperature interlocks are expected on production tools. These components are part of the wet bench rather than the product itself, but their material and operating limits determine whether the product meets its specification at the wafer surface.
Selectivity data for BOE against silicon nitride, polycrystalline silicon, and aluminum are not universal. Thermal SiO2 etch rate is often used as the process control metric, while the etch rate of other films is measured on the same wet bench. For LPCVD nitride deposited at 780 °C to 820 °C, BOE etch rate is generally below 10 nm/min but can rise with film oxygen content. Aluminum films are attacked by BOE; therefore aluminum pads must be protected by photoresist or removed from the process flow before immersion. Copper compatibility is poor in HF-containing solutions; copper lines require barrier protection or dedicated single-wafer processing. These process limitations are independent of the Electronic/EL grade purity and must be verified with the specific film stack.
