| HS Code | 559396 |
| Chemical Name | Tetramethylammonium hydroxide |
| Common Abbreviation | TMAH |
| Chemical Formula | C4H13NO (equiv. (CH3)4NOH) |
| Cas Registry Number | 75-59-2 |
| Molecular Weight | 91.15 g/mol |
| Appearance | Clear, colorless to slightly yellowish liquid (aqueous product) |
| Odor | Ammonia-like / amine odor |
| Typical Supplied Concentration | 25 wt% aqueous solution (electronic/developer grade) |
| Density | Approx. 1.01 g/cm3 at 25°C for 25 wt% solution |
| Ph | Strongly basic; approx. 13 for 25 wt% solution |
| Ionization | Dissociates fully in water to (CH3)4N+ and OH- |
| Melting Freezing Point | Approx. -13°C for 25 wt% aqueous solution |
| Boiling Point | Approx. 100-105°C for 25 wt% aqueous solution |
| Solubility | Miscible with water; soluble in methanol and ethanol; essentially insoluble in nonpolar organic solvents |
| Thermal Decomposition | Decomposes above approx. 130°C, evolving trimethylamine and other degradation products |
| Flash Point | No flash point in dilute aqueous solution; avoid overheating concentrated residues |
As an accredited TMAH (Tetramethylammonium Hydroxide) Mitsubishi Chemical factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | TMAH (Tetramethylammonium Hydroxide) from Mitsubishi Chemical is supplied in 25 kg polyethylene drums with secure seals and hazard labeling. |
| Container Loading (20′ FCL) | 20′ FCL loading of TMAH (Mitsubishi Chemical) uses sealed drums/pails, secure bracing, and proper labeling for safe, compliant transport. |
| Shipping | Ship TMAH (tetramethylammonium hydroxide) as UN 1835, Class 8 corrosive, in properly sealed, UN-approved containers. Use hazard labels, corrosion-resistant packaging, and complete dangerous goods documentation. Ensure handlers wear full protective equipment, segregate from acids, and follow regulatory transport requirements to prevent exposure, leakage, or fatal contact. |
| Storage | Store TMAH (Tetramethylammonium Hydroxide) from Mitsubishi Chemical in tightly sealed, original containers in a cool, dry, well-ventilated area away from heat, direct sunlight, and incompatible materials such as strong acids and oxidizers. Ensure secondary containment to prevent leaks, and follow local regulations for corrosive and toxic chemical storage. |
| Shelf Life | Shelf life is typically one year when stored in a sealed container under cool, dry, well-ventilated conditions. |
In advanced-node logic and DRAM manufacturing, aqueous tetramethylammonium hydroxide is applied on 300 mm coater/developer tracks through PTFE/PFA pressure vessels, 0.05 µm capsule filters, and point-of-use conductivity sensors. The standard developer composition is 2.38 wt% TMAH in ultrapure water, equivalent to 0.261 N; concentration is held within ±0.02 wt% by automatic titration or density metering. The downstream lithographic sequence includes positive-tone chemically amplified resist spin-coating, soft bake, 193 nm or 248 nm exposure, post-exposure bake, puddle development for 45–90 s at 23.0 °C ± 0.5 °C, deionized water rinse at 20–25 °C, and spin dry. Temperature excursions outside the range alter linewidth by 0.8–1.5 nm/°C for dense contact-hole arrays; adequate point-of-use chilling and recirculation flow above 8 L/min per develop bowl are required. Compliance references include ISO 14644-1:2015 Table 1 for Class 3 airborne particle control, SEMI S2-0724 for equipment safety, and CLP Regulation (EC) No 1272/2008 for TMAH classification as Skin Corr. 1B, H314; transport is UN 3267, Class 8, Packing Group II. Equipment experience on production tracks shows that brass or aluminum fittings generate soluble metal contamination and develop residue, so wetted components must be PTFE, PFA, or electrophished stainless steel. Terminal products include advanced logic processors, DRAM and NAND memory, and CMOS image sensors on 300 mm wafers. TMAH is supplied by Mitsubishi Chemical as electronic-grade 25 wt% aqueous solution for dilution or as ready-to-use 2.38 wt% developer.
Anisotropic etching of single-crystal silicon with TMAH proceeds by hydroxide-mediated oxidation at {100} and {110} surfaces, while {111} planes etch slowly because of higher activation energy for dangling bond removal. Etchant bath composition is 5–25 wt% TMAH in deionized water at 75–90 °C; 25 wt% at 80 °C is common for cavity formation, whereas 5 wt% at 70–75 °C reduces pyramidal hillock formation but lowers {100} etch rate. In unagitated quartz or PTFE reflux reactors, hydrogen gas bubbles accumulate on horizontal surfaces and cause localized etch stop or roughness, so wafer flipping or bath agitation every 15–30 min is required. The process sequence includes RCA1 cleaning with NH4OH/H2O2/H2O, dilute HF native oxide removal, thermal SiO2 or LPCVD Si3N4 mask deposition, photolithographic mask opening, reactive ion etching of the mask, anisotropic TMAH etch, post-etch diluted HCl/H2O2/DI rinse, and V-groove depth metrology. Published data for spray tool configurations with recirculating TMAH are limited; batch-to-batch variation due to bath aging and dissolved silicon can shift {100} etch rate by up to 15%. Compliance references include ISO 14644-1:2015 Table 1 Class 5 for post-etch wafer cleanliness, SEMI S2-0724 for heated bath interlocks, and UN 3267 for transport of concentrated TMAH before dilution. Terminal devices are MEMS inertial sensors, pressure transducers, microfluidic channels, and inkjet printheads. TMAH must not be mixed with strong oxidizers or aluminum-containing wafer carriers, as hydrogen evolution becomes vigorous and aluminum dissolves.
| Parameter | Measured range | Process implication |
|---|---|---|
| Si(100) etch rate | 0.4–0.9 µm/min | V-groove formation at 54.7° to {111} planes |
| Si(110) etch rate | 0.7–1.2 µm/min | Faster cavity sidewall etching |
| Si(111) etch rate | 0.01–0.03 µm/min | Etch stop plane for diaphragm thickness control |
| Thermal SiO2 mask etch rate | 0.1–0.3 nm/min | Allows deep cavities with thin oxide masks |
| LPCVD Si3N4 mask etch rate | < 0.1 nm/min | Preferred hard mask for long etches |
Horizontal conveyorized developing equipment configured with TMAH-based developers operates at replenishment rates linked to dry film loading and exposed panel area. The working developer formulation contains TMAH at 0.8–1.2 wt%, a sodium-free carbonate/bicarbonate buffer maintaining pH 11.8–12.4, and defoamer at 0.01–0.05 g/L; no alkali hydroxide is added because sodium residues degrade electrical migration resistance in high-density interconnect substrates. Conveyor speed, spray pressure 1.8–2.5 bar, and developer temperature 29–32 °C are set so resist breakpoint occurs at 50–60% of developing chamber length; pH above 12.6 causes dry film adhesion loss at curved panel edges, while pH below 11.2 leaves inter-trace resist scum on 20–30 µm line/space patterns. The downstream process includes inner-layer lamination, dry film photoresist lamination with hot-roll laminators, UV exposure with laser direct imaging or phototools, developing in horizontal TMAH modules, cupric chloride or sulfuric-peroxide etching, and resist stripping. Compliance requirements are IPC-A-600J for acceptability, IPC-SM-840D for solder mask chemical resistance, IPC-4101E for laminate raw material, and ISO 14001:2015 for developer effluent neutralization prior to discharge. Terminal products are HDI PCB, IC packages, and flex-rigid multilayer boards with 25–50 µm fiducial line widths. Bath life is constrained by dissolved dry film loading; in-line conductivity and gravimetric solid monitoring are used to dose TMAH replenisher rather than timed bulk dumping.
Mobile sodium and potassium cations from inorganic developers shift threshold voltage in a-Si and IGZO thin-film transistors, causing mura and long-term non-uniform brightness in large-area displays. For this reason, array fabs specify TMAH-based developers with Na and K below 1 ppb by ICP-MS. The developer is prepared at 2.38 wt% TMAH with nonionic fluorosurfactant at 0.005–0.02 wt%; some Gen 8.5/10.5 ITO-based resists are developed at 1.19 wt% TMAH to reduce attack on indium tin oxide edges. Downstream production includes slit-coat photoresist application at wet thickness 1.5–2.0 µm, h-line or i-line exposure through multi-lens aligners, alkaline development at 23.0 °C ± 0.5 °C for 60–120 s, DI water rinse at 0.3–0.8 MPa nozzle pressure, and post-bake at 120–140 °C. Compliance references include ISO 14644-1:2015 Table 1 Class 5 for array photolithography cleanrooms, SEMI S2-0724 for developer supply systems, and IEC 62321-3-1:2013 for restricted substance screening of display modules under import/export compliance. Terminal products are TFT backplanes for LCD, OLED, and Mini-LED displays. Wetted developer lines must be constructed from PP, PTFE, or PVDF; acrylic and polycarbonate covers are not permitted due to stress cracking from TMAH vapor absorption.
In fan-out wafer-level packaging, thick chemically amplified positive photoresist layers of 5–120 µm are patterned for redistribution layers, copper pillar bumps, and through-silicon vias. TMAH is used at 2.38 wt% in ultrapure water; for resist coatings above 50 µm, development is split into multiple puddle cycles totaling 120–300 s at 23.0 °C ± 0.5 °C, with spin-dry between puddles to remove dissolved resist and reduce pattern collapse. The downstream process sequence includes wafer pre-cleaning, adhesion priming, thick resist coating, edge bead removal, exposure through mask aligners or reduction steppers, post-exposure bake, TMAH puddle development, DI rinse, plasma desum, and electroplating of copper or solder. Compliance references include SEMI S2-0724 for chemical supply, ISO 14644-1:2015 Table 1 Class 6 for wafer-level packaging cleanrooms, and JEDEC J-STD-020E for moisture/reflow sensitivity qualification of final molded devices. Terminal products are fan-out packages, 2.5D interposers, and flip-chip copper pillar interconnects. Bath life is limited by resist dissolution loading; recirculating filtration at 0.1 µm and developer refresh rates of 10–20% per wafer batch are required to maintain residue-free via openings below 10 µm diameter.
Photomask blank manufacturing for 248 nm, 193 nm, and EUV reticles uses TMAH development because the quaternary ammonium base dissolves exposed carboxylate-bearing positive photoresist while preserving chromium oxide and molybdenum silicide hard films within the process window. The developer is prepared as 2.38 wt% TMAH with Cr, Fe, Ni, and Cu below 0.1 ppb each to avoid printable mask defects. Development occurs in spin-spray processors at 23.0 °C ± 0.2 °C for 30–90 s, followed by DI water rinse and nitrogen spin dry. The full downstream production path includes quartz substrate cleaning, resist spin-coating, e-beam or 193 nm laser mask writing, post-exposure bake, TMAH development, post-develop inspection, chromium wet or dry etch, and resist strip. Compliance references are ISO 14644-1:2015 Table 1 Class 3, SEMI S2-0724, and REACH Regulation (EC) No 1907/2006 Annex II; reticle defectivity is measured with inspection systems operating at pixel sizes below 50 nm. Terminal products are binary masks, attenuated phase-shift masks, and reticle blanks for EUV patterning. TMAH developer must not be stored in borosilicate glass containers over long periods because alkaline attack can release silicon and boron into solution, increasing haze defects after spin dry.
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Tetramethylammonium hydroxide (TMAH) supplied by Mitsubishi Chemical is an aqueous quaternary ammonium base with CAS registry number 75-59-2, empirical formula C4H13NO, and molecular weight 91.15 g/mol. The product is used in semiconductor and display manufacturing as an alkali-metal-free photoresist developer, in microelectromechanical systems as a silicon anisotropic etchant, and in selected industrial processes as a strong organic base where sodium and potassium are excluded. Commercial designations TMAH-238 and TMAH-25 identify nominal concentrations of 2.38 wt% and 25 wt%, respectively. The 2.38 wt% grade is the standard positive photoresist developer for diazonaphthoquinone-novolac resists, with a hydroxide normality of 0.261 N. The 25 wt% grade has a nominal normality of 2.74 N and is used for point-of-use dilution or anisotropic silicon etching. Mitsubishi Chemical electronic-grade material is produced by quaternary ammonium salt electrolysis and subsequent purification, which reduces alkali-metal and chloride carryover relative to commodity TMAH.
The product is supplied as an aqueous solution rather than as an anhydrous solid because anhydrous TMAH is hygroscopic and has limited thermal stability. Specification control therefore concentrates on concentration, density, refractive index, carbonate content, metal cations, chloride, and particle burden. Table 1 lists nominal concentrations and derived normalities used in fabrication. Density values are for clear water-white solutions at 20°C; the assay window for electronic-grade developer is typically maintained within ±0.5% relative of nominal concentration, while industrial-grade material may have wider tolerances. Concentration is not controlled solely by pH because TMAH is a strong electrolyte and pH is an insensitive function of small normality changes in the 0.261 N region.
| Designation | TMAH concentration | Nominal hydroxide normality | Nominal density at 20°C | Primary application |
|---|---|---|---|---|
| TMAH-238 | 2.38 wt% | 0.261 N | 1.006 g/cm³ | Positive photoresist developer |
| TMAH-20 | 20 wt% | 2.19 N | 1.013 g/cm³ | Dilution stock and industrial alkaline processing |
| TMAH-25 | 25 wt% | 2.74 N | 1.011 g/cm³ | Silicon anisotropic etch, point-of-use dilution |
In positive photoresist development, the 2.38 wt% TMAH developer is dispensed through point-of-use filters rated at 0.1 µm or tighter before contacting the wafer. Development is performed by immersion, puddle, or spray methods, with developer temperature commonly controlled at 23 ± 0.5°C. The development rate of diazonaphthoquinone-novolac resists depends on TMAH normality, developer surfactant content, and resist formulation; fabs therefore monitor developer concentration by conductivity, refractive index, or acid-base titration against 0.1 mol/L hydrochloric acid. A drift in developer normality outside the supplier specification changes the dissolution rate of exposed resist and affects final critical dimension. The use of TMAH instead of sodium or potassium hydroxide is driven by the requirement to avoid mobile alkali-metal contamination in gate oxide and back-end dielectric stacks. After development, TMAH residues are removed by deionised water rinse; the organic base decomposes thermally without leaving a sodium or potassium residue.
Concentration control in the dispense loop is maintained by temperature-compensated conductivity or refractometry. A shift of 0.5% relative in TMAH concentration can alter exposed-resist dissolution rate enough to shift dense-line critical dimensions beyond the process window for advanced nodes. For this reason, point-of-use blending from TMAH-25 is preferred over long-term storage of dilute developer. Static mixers, nitrogen-blanketed daybeds, and final membrane filtration at 0.05 µm or 0.1 µm are typical. The filtration membrane must be polypropylene or PTFE-based because nylon and cellulose ester membranes degrade in 0.261 N hydroxide and can add extractable organic contamination.
Electronic-grade TMAH is controlled by trace metal and particle budgets rather than by bulk alkalinity alone. Under the SEMI C21 framework for TMAH photoresist developers, sodium and potassium are typically specified below 10 µg/L each; iron, aluminium, calcium, magnesium, copper, and zinc are normally held below 5 µg/L each for critical layers. Particulate specifications commonly require fewer than 100 particles/mL at 0.2 µm and larger. Mitsubishi Chemical electronic-grade TMAH-238 is filtered through 0.05 µm or 0.1 µm membrane filters and filled in cleanroom-compatible containers to maintain these budgets. Chloride is limited because residual chloride can promote aluminium pad corrosion and copper/low-k reliability defects; electronic-grade developer specifications frequently set chloride below 50 µg/L. Industrial-grade TMAH may carry higher metal and chloride loads and is not suitable for front-end lithography unless upgraded by filtration and ion exchange.
Certificate-of-analysis methods for electronic-grade TMAH commonly include ion chromatography for chloride, sulfate, nitrate, and bromide; inductively coupled plasma mass spectrometry for trace metals; acid-base titration for assay; and laser particle counting for particulate burden. A typical electronic-grade lot release reports assay, density, refractive index, Na, K, Fe, Al, Ca, Mg, Cr, Cu, Ni, Zn, chloride, sulfate, nitrate, and particle counts at 0.2 µm and 0.5 µm. The absence of a single universal specification reflects node-specific cleanliness requirements; the supplier provides lot-release criteria matched to the fab front-end process and analytical detection limits.
Material compatibility boundaries are fixed by the strongly alkaline character of the solution. TMAH attacks aluminium, zinc, magnesium, and borosilicate glass; storage and dispensing equipment is specified in high-density polyethylene, polypropylene, or fluoropolymer. Mixing with strong mineral acids is exothermic and may produce violent boiling; the acid should not be added to bulk TMAH. Strong oxidisers, including concentrated hydrogen peroxide, can decompose the quaternary ammonium cation and generate pressure in closed vessels. Personnel exposure is controlled by local exhaust ventilation and chemically resistant gloves because the solution is classified as corrosive to skin and eyes under GHS and CLP. For 25 wt% material, transport classification is UN 1835, Class 8, Packing Group II for most commercial consignment conditions.
Carbon dioxide absorption is a primary stability constraint for dilute and concentrated TMAH. Contact with ambient air converts hydroxide to tetramethylammonium carbonate and bicarbonate, reducing free hydroxide concentration and altering development rate. The effect is more serious in 2.38 wt% developer because a small normality loss is proportionally larger. Tanks and daybeds are therefore blanketed with nitrogen, and point-of-use dilution lines are sealed against back-diffusion of air. Online carbonate or conductivity monitoring is used where tight develop-rate control is required. If bulk developer is exposed to air for extended periods, the normal response is discarding or re-assay of the bath; replenishment based on pH alone is unreliable because carbonate-bicarbonate buffering masks the true free-base loss. Published data for the exact rate of carbon dioxide uptake in Mitsubishi Chemical TMAH are limited because uptake rate depends on surface-to-volume ratio, agitation, and ambient humidity.
Concentrated TMAH-25 is used in microelectromechanical systems fabrication as a metal-ion-free anisotropic etchant for single-crystal silicon. The hydroxide etches (100) silicon faster than (111) silicon, producing the characteristic anisotropic cavities used for diaphragms, cantilevers, and microfluidic structures. Reported etch rates for 25 wt% TMAH at 80°C typically fall between 0.3 µm/min and 1.5 µm/min, depending on dissolved silicon, oxygen, agitation, and additive package. Etch masks of LPCVD silicon nitride or silicon dioxide are used because TMAH attacks aluminium and may roughen silicon dioxide over time, though attack is generally less severe than with potassium hydroxide of equivalent pH. Compared with potassium hydroxide, TMAH etching yields lower sodium mobility and permits use in CMOS-compatible post-processing; the trade-off is lower thermal oxide selectivity and greater sensitivity to dissolved oxygen and silicate accumulation. The Mitsubishi Chemical concentrated grade is diluted with ultra-pure water of resistivity not less than 18 MΩ·cm before use; in-line blending and degassing reduce etch-rate drift associated with carbon dioxide and oxygen uptake.
The principal difference between Mitsubishi Chemical TMAH and commodity TMAH lies in the control of halide and metal impurities, the consistency of concentration, and packaging for cleanroom use. Commodity TMAH is often produced by electrolysis of tetramethylammonium chloride and may retain chloride at levels that are acceptable for organic synthesis but not for semiconductor lithography. Electronic-grade Mitsubishi Chemical material is specified for chloride, bromide, and metal levels compatible with front-end processing. In contrast to inorganic alkali-metal developers, TMAH provides equivalent or higher pH with no sodium or potassium residue. Compared with choline hydroxide, TMAH has a lower molecular weight and a higher hydroxide content per unit mass; compared with tetraethylammonium hydroxide, TMAH is more volatile in thermal residue testing and is the default quaternary ammonium developer for photoresist systems sensitive to larger organic cations. The surfactant package is not universally pre-mixed, allowing fabs to select wetting agents that match the resist stack rather than accepting a supplier-fixed formulation.
| Parameter | Value or reference |
|---|---|
| CAS registry number | 75-59-2 |
| GHS skin corrosion category | Skin Corr. 1A |
| EU CLP classification | Met. Corr. 1, Skin Corr. 1A, Eye Dam. 1 |
| Transport | UN 1835, Class 8, Packing Group II |
| Electronic-grade purity framework | SEMI C21 |
| EU regulation | REACH (EC) 1907/2006 |
| Dilution water quality | Resistivity ≥ 18 MΩ·cm at 25°C |
The concentrated product should not be stored in glass, aluminium, zinc, or unlined carbon steel. Container headspace should be kept minimal and dry nitrogen-blanketed. Published data for specific Mitsubishi Chemical TMAH performance in every resist or micromachining stack is limited; qualification for a specific process is therefore performed by measuring critical dimension, etch rate, surface roughness, particle counts, and metal contamination on the actual production tool.
