| HS Code | 379472 |
| Product Name | High selective SiN/SiO Etchant Electronic/EL Grade |
| Chemical Type | Phosphoric acid-based etchant with selective additives |
| Grade | Electronic/EL Grade |
| Physical State | Liquid |
| Appearance | Clear colorless solution |
| Density | About 1.69 g/cm3 at 20°C |
| Boiling Point | Approximately 155-160°C at use concentration |
| Solubility In Water | Completely miscible with water |
| Target Material | Silicon nitride (SiN) |
| Selectivity Sin To Sio2 | High selectivity, >200:1 |
| Silicon Nitride Etch Rate | Approximately 50-60 Å/min at 155°C |
| Operating Temperature | 150-160°C |
| Polarity Application | Designed for selective SiN etching over SiO2 |
As an accredited High selective SiN/SiO Etchant Electronic/EL Grade factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | High selective SiN/SiO Etchant, Electronic/EL Grade, packaged in 1 gallon HDPE bottle with secure sealing, ensuring purity and safe handling. |
| Container Loading (20′ FCL) | High selective SiN/SiO etchant, electronic grade, shipped as 20′ FCL in sealed drums/IBCs, ensuring safe, contamination-free container loading. |
| Shipping | This high-selectivity SiN/SiO₂ etchant, Electronic/EL Grade, ships as a corrosive, hazardous liquid in sealed, chemically compatible containers. Transport requires UN-compliant packaging, hazard labeling, and temperature-controlled, moisture-free handling. Ensure proper documentation, spill containment, and trained personnel during loading, transit, and delivery to preserve purity and safety. |
| Storage | Store in tightly sealed original HDPE container in a cool, clean, dry, well-ventilated area at 15–30°C. Keep away from moisture, direct sunlight, and incompatible substances such as strong bases, reactive metals, and oxidizers. Use secondary containment to prevent leakage. Ensure containers are clearly labeled and inspected regularly for damage or leaks. |
| Shelf Life | Shelf life is approximately six months from manufacture when stored unopened in original container. Protect from light, moisture, and air for optimal stability. |
Across front-end-of-line logic manufacturing, the high selective SiN/SiO etchant is deployed in immersion wet benches after spacer definition and liner removal. The chemistry is supplied as an electronic-grade phosphoric acid formulation released under SEMI C8 batch criteria, with critical metal cations such as iron, chromium, nickel, and copper specified below 10 ppb and particle counts below 10 counts/mL at 0.1 µm. A production bath processes 50-wafer cassettes in a quartz tank fitted with a reflux condenser, 0.05 µm PTFE recirculating filters, and three-point RTD temperature monitoring. The bath is controlled at 160 °C ± 0.5 °C. Blanket data from ellipsometric thickness measurements over 49-point maps show LPCVD silicon nitride etch rates of 40–70 Å/min, while thermal silicon dioxide loss runs below 2 Å/min, yielding a selectivity above 30:1. A 100:1 dilute HF pre-dip clears the native oxide before nitride etch; the subsequent rinse uses ultrapure water conforming to ASTM D5127 Type E-1. The principal process conflict on the line is water evaporation from the open acid surface. When reflux is interrupted, the acid concentration climbs and the thermal oxide etch rate increases by approximately 15% per 1 wt% H3PO4 shift; inline gravimetric density control adds deionized water when density deviates more than 0.005 g/cm³ from the setpoint. Production records also show that ammonium fluorosilicate residues carried from earlier dry-etch chambers can dissolve in the hot acid and increase surface roughness on exposed silicon if the pre-etch rinse is shortened below 5 min.
The limiting constraint in 3D NAND wordline replacement is not the bulk etch rate of stoichiometric silicon nitride but the transport of reactive acid through high-aspect-ratio slits after the tier stack has been opened. Typical slit openings are below 100 nm, while the alternating oxide/nitride stack can exceed 6 µm in height. Etch rate at the mid-tier falls 30–50% below the blanket monitor value because recirculation flow cannot penetrate the cavity and reaction products accumulate. Temperature is therefore held between 160 °C and 165 °C; operation above 165 °C accelerates water flash-off and thins exposed CVD oxide, while operation below 160 °C leaves silicon nitride residue in the mid-tier before endpoint. The oxide loss budget is tighter than in logic: tunnel oxide and gate dielectric are scaled below 10 nm, and a measured loss of 3 Å shifts threshold voltage distribution beyond retention criteria. The bath is maintained at 85–86 wt% H3PO4 by water refill loops and filtered at 0.05 µm. Dissolved silicon is controlled between 50 ppm and 120 ppm through a bleed-and-feed loop; below 50 ppm the oxide etch rate rises above 3 Å/min, while above 120 ppm silicic acid nucleates particles that clog slit openings. Post-etch acceptance uses scanning electron microscopy across 30 cross-sections per wafer, and a residual nitride bridge wider than 5 nm rejects the wafer.
| Parameter | Logic spacer | 3D NAND | DRAM hard mask | MEMS release |
|---|---|---|---|---|
| Bath temperature | 160 °C ± 0.5 °C | 160–165 °C | 155 °C ± 1 °C | 160 °C |
| Silicon nitride removal | 40–70 Å/min | Mid-tier 30–50% lower than blanket | 12–20 min cap removal | 20–40 Å/min for Si-rich nitride |
| Oxide allowance | <2 Å/min | <3 Å loss | <5 Å HDP oxide | 5–10 nm thermal oxide per 45 min |
| Main control variable | Reflux density control | Silicon loading 50–120 ppm | Doped-oxide concentration | Dummy-cassette bath pre-loading |
Cell nitride hard mask and sacrificial cap removal in DRAM places the selective SiN/SiO etchant in direct contact with borophosphosilicate glass and high-density plasma oxide. The doped oxides are more vulnerable to hot phosphoric acid than undoped TEOS, so DRAM-dedicated baths run at 155 °C ± 1 °C. A silicon-rich hard mask with refractive index 1.95–2.05 etches more slowly than stoichiometric LPCVD nitride; endpoint may be set by fixed etch time in batch mode, typically 12–20 min, or by trapped-charge decay in single-wafer spray processors. The underlying HDP oxide loss is held below 5 Å; selectivity to undoped TEOS is above 40:1, but selectivity to borophosphosilicate glass containing 3–5 wt% boron can be only half of that value. Bath segregation is mandatory because logic baths carrying titanium or tungsten residues from contact modules can locally increase doped-oxide attack through galvanic effects. After etch, the wafer is rinsed with hot ultrapure water at 70 °C to prevent silicic acid precipitation during cooling, then transferred to an IPA vapor dryer to avoid water marks in high-aspect-ratio capacitor holes.
When production wafers reach the MEMS release module, the selective SiN/SiO etchant encounters a silicon-rich low-stress LPCVD nitride composition that etches at less than half the rate of the stoichiometric logic film. Such films typically show a refractive index of 2.2–2.4, and their removal in the same 160 °C bath proceeds at 20–40 Å/min. The thermal oxide stop layer therefore receives a longer exposure, and a 250 nm thermal oxide film may lose 5–10 nm during a 45 min release etch. Because freshly prepared acid shows a transiently higher oxide etch rate, the bath is pre-loaded with a sacrificial silicon nitride dummy cassette for 2–3 h before production wafers are introduced. The etch endpoint is checked with infrared reflectance and witness-wafer ellipsometry rather than fixed time. Published data for the exact selectivity on silicon-rich nitride with aluminum-sealed substrates is limited, so qualification relies on witness-wafer measurements and post-release inspection. The MEMS wet bench is segregated from CMOS tools because residual phosphate and metal cations in a shared drain can corrode exposed aluminum electrodes if rinse is delayed beyond 10 min.
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Type HSN-EL85 high-selectivity silicon nitride/silicon dioxide etchant is supplied as an electronic/EL-grade liquid formulation for wet front-end processes. The product uses electronic-grade phosphoric acid as the bulk solvent and a silicate-based selectivity modifier that reduces thermal silicon dioxide dissolution during silicon nitride removal. It is intended for batch immersion and single-wafer spray systems; no hydrogen fluoride or fluoride salt is present. The product is filtered through 0.1 μm polytetrafluoroethylene membrane cartridges during final filling and is packaged in nitrogen-purged high-density polyethylene containers.
Lot release documentation includes trace-metal quantification by inductively coupled plasma mass spectrometry and particle counting by laser light scattering. The assigned electronic/EL grade reflects compliance with SEMI C5 liquid chemical specifications for phosphoric acid, with additional limits for chloride, nitrate, and sulfate imposed by ion chromatography. Application data in this document are representative values from qualification lots on 200 mm and 300 mm wet stations; published data for every device topography is limited, and final process qualification remains necessary.
For hot phosphoric acid chemistries, the silicon nitride etch rate follows an Arrhenius dependence with an apparent activation energy near 0.55 eV. The thermal silicon dioxide etch rate is lower but becomes acute above 168 °C, where selectivity degrades by more than 40% in water-deficient baths. Recirculated wet benches therefore maintain the bath at 160 ± 1 °C with immersion heaters controlled by proportional-integral-derivative loops. Heater surfaces are quartz-sheathed; exposed stainless steel contributes iron and nickel that deposit on wafer surfaces and reduce gate oxide dielectric strength. Viscosity increases from 42 mPa·s at 25 °C to approximately 57 mPa·s at 60 °C, but at process temperature the fluid remains pumpable through fluoropolymer filter housings.
Selectivity is controlled less by temperature than by dissolved silicon activity. During nitride dissolution, the bath accumulates orthosilicic acid, which suppresses oxide attack by reducing free water activity at the SiO₂ surface. HSN-EL85 is pre-spiked with a silicate-based modifier so that a new bath does not require 12–24 h of sacrificial nitride strip before production use. Without this conditioning, thermally grown SiO₂ loss can exceed 3 nm on the first 25-wafer lot because dissolved silicate is absent. The modifier concentration is verified at the 251.6 nm silicon emission line by inductively coupled plasma optical emission spectroscopy, with batch-to-batch variance controlled to ±0.02 wt% as SiO₂.
Table 1 consolidates representative certificate-of-analysis limits for the product. These values are not a substitute for user-specific qualification data.
| Parameter | Limit/Value | Test Method |
|---|---|---|
| H₃PO₄ assay | 85.0 ± 0.5 wt% | Titration, internal SOP aligned with SEMI C5 |
| Density at 25 °C | 1.685 ± 0.010 g/mL | ASTM D4052 |
| Viscosity at 25 °C | 42 ± 3 mPa·s | Rotational viscometer |
| Particles ≥ 0.2 μm | ≤100 counts/mL | Laser light-scattering, SEMI C5 |
| Particles ≥ 0.5 μm | ≤50 counts/mL | Laser light-scattering, SEMI C5 |
| Fe | ≤50 ppb | ICP-MS |
| Al | ≤50 ppb | ICP-MS |
| Ca, K, Mg, Na each | ≤50 ppb | ICP-MS |
| Total trace metals | ≤250 ppb | ICP-MS sum |
| Chloride | ≤1.0 ppm | Ion chromatography |
| Nitrate | ≤1.0 ppm | Ion chromatography |
| Sulfate | ≤1.0 ppm | Ion chromatography |
| Silicate modifier as SiO₂ | 0.35–0.55 wt% | ICP-OES at 251.6 nm |
Buffered oxide etch removes silicon dioxide rapidly but attacks silicon nitride slowly; selectivity is inverted relative to nitride strip requirements. Conventional electronic-grade 85% phosphoric acid etches Si₃N₄ at approximately 4.0 nm/min at 160 °C but also removes thermal SiO₂ at 0.35–0.60 nm/min, depending on bath age and silicon loading. HSN-EL85 is formulated to reduce thermal SiO₂ etch to ≤0.12 nm/min under the same temperature. Representative rates are measured by spectroscopic ellipsometry on 25 nm thermally grown SiO₂ and 100 nm LPCVD Si₃N₄ films before and after single-wafer spray processing.
Table 2 compares representative etch rates and selectivity for the product, a conventional phosphoric-acid reference, and a 7:1 buffered oxide etch reference. The comparison indicates that the product suppresses oxide dissolution rather than accelerating nitride removal. This suppression is achieved without adding fluoride species, which are known to create surface microroughness on SiO₂ and to complicate on-site waste treatment.
| Chemical system | Temperature | Si₃N₄ rate | SiO₂ rate | Selectivity Si₃N₄:SiO₂ |
|---|---|---|---|---|
| HSN-EL85 | 160 °C | 4.2 ± 0.4 nm/min | 0.12 ± 0.03 nm/min | 35:1 minimum |
| Conventional 85% H₃PO₄ | 160 °C | 4.0 ± 0.5 nm/min | 0.45 ± 0.10 nm/min | 9:1 |
| 7:1 BOE | 25 °C | 0.2 ± 0.1 nm/min | 90 ± 10 nm/min | 0.002:1 |
Single-wafer spray processors require dispense of the etchant at 70–80 °C to limit aerosol formation and concentration drift. The product is compatible with 0.05 μm fluoropolymer point-of-use filtration at these temperatures; higher dispense temperatures above 90 °C accelerate water evaporation and produce phosphoric acid mist that redeposits on wafer edges. On a 300 mm spray chamber, exhaust face velocity should be maintained at 0.8–1.2 m/s. Rotational speed is set between 300 rpm and 800 rpm, with edge rinse provided by ultrapure water of 18.2 MΩ·cm resistivity. Etch depth is checked by spectroscopic ellipsometry at 49 wafer points; within-wafer non-uniformity for blanket Si₃N₄ is ≤3% (1σ) when exhaust and dispense parameters are centered.
In batch immersion, a typical nitride strip process loads 50 wafers in a polytetrafluoroethylene cassette, maintains bath temperature at 160 °C, and strips 40 nm LPCVD Si₃N₄ in 10–12 min. The selectivity modifier keeps oxide loss below 1.5 nm in this window. Replenishment of volatiles is controlled by deionized water injection based on density or refractive index, not fixed time, because water evaporation rate varies with exhaust flow.
In nitride strip, trace metals partition preferentially onto exposed silicon dioxide surfaces, where they can degrade minority carrier lifetime and gate oxide integrity. The HSN-EL85 specification limits each major metal to ≤50 ppb and total trace metals to ≤250 ppb. Liquid chemical suppliers typically report these values by ICP-MS after 10,000× matrix dilution; the method detection limits for Fe, Ca, and Mg are below 5 ppb. Field data from recirculated wet benches show that bath metal accumulation is dominated by hot-plate corrosion, not by product replenishment. When a stainless steel heater is present, iron concentration rises from 2 ppb to 12 ppb within 72 h, even with continuous filtration. The product should therefore be used with quartz or perfluoroalkoxy heating surfaces.
Oxide loss budgeting for nitride strip must include both thermal SiO₂ removal and subsequent aqueous rinse. Residual silicate films can precipitate in pH-neutral rinse water and create particle defects. A two-step rinse protocol is recommended: first, ultrapure water at 25 °C for 120 s; second, a dilute hydrochloric acid rinse at 0.1 mol/L for 30 s to remove adsorbed silicates. The product is incompatible with ammonia-containing vapor prime systems, because ammonium phosphate solids can precipitate in exhaust lines. Mixing with hydrofluoric acid or fluoride salts should be avoided; the silicate modifier reacts with free fluoride to form fluorosilicic acid, which lowers selectivity and creates fume-handling complications.
Storage stability at 15–25 °C is 12 months in unopened nitrogen-purged high-density polyethylene containers. Bulk dispense systems should use 0.1 μm polytetrafluoroethylene filters and maintain positive nitrogen pressure above 2 kPa. Product that has been frozen or exposed to temperatures below 5 °C may precipitate silicate species; thawing does not fully restore selectivity and such material should not be used for gate-oxide-sensitive processes.
