Tetramethylammonium hydroxide

Product Details

CasNo： 75-59-2

MF： C4H13NO

Appearance： liquid

Delivery Time： 15 days

Packing： 200kg/drum

Purity： 99%

1. Basic Information

• CAS No.: 75-59-2
• Molecular Formula: C4​H13​NO
• Molecular Weight: 91.15
• Appearance: Typically a colorless to pale yellow aqueous solution (the most common commercial form); has an ammonia-like odor and exhibits strong alkalinity. Anhydrous TMAH (rarely used directly) is a white crystalline solid, but it is highly hygroscopic and difficult to store.
• Density: 1.016 g/mL (for 25% aqueous solution, at 20℃; density increases with higher concentration, e.g., 1.040 g/mL for 40% solution).
• Boiling Point: 102–110℃ (at 760 mmHg, for 25% aqueous solution; boiling point rises slightly with increasing concentration due to reduced water content).
• Flash Point: >100℃ (for 25% aqueous solution; non-flammable in dilute form, but high-concentration solutions or anhydrous solids may pose fire risks when in contact with combustible materials).
• Refractive Index: 1.3806 (for 25% aqueous solution, at 20℃; used to verify solution concentration and purity).

2. Physical and Chemical Properties

• Hygroscopicity: Highly hygroscopic—absorbs moisture rapidly from the air, causing aqueous solutions to dilute and solid forms to deliquesce (dissolve in absorbed moisture).
• Reactivity with CO₂: Reacts quickly with carbon dioxide (CO2​) in the air to form tetramethylammonium carbonate/bicarbonate, reducing alkalinity and purity. Sealed storage is therefore mandatory.
• Thermal Decomposition: Decomposes at 130℃ into methanol (CH3​OH) and trimethylamine ((CH3​)3​N)—a key consideration for high-temperature applications (e.g., semiconductor processing, where temperature must be controlled below 120℃).
• Alkalinity: A strong base with equivalent strength to caustic soda (NaOH) or potassium hydroxide (KOH). A 1% (wt) aqueous solution has a pH of 12.9, capable of dissolving organic matter and reacting with acids to form salts.
• Solubility: Miscible with water in all proportions; soluble in polar organic solvents such as methanol and ethanol, but insoluble in non-polar solvents like benzene and hexane.

3. Product Quality Standards

TMAH is primarily classified into industrial grade and electronic grade (the most demanding category), with strict specifications for purity and impurities—especially for electronic applications requiring ultra-low metal ion content:

4. Core Applications

4.1 Electronics Industry (Primary Use)

TMAH is irreplaceable in semiconductor and liquid crystal display (LCD) manufacturing, mainly for:

• Silicon Wafer Etching: As an anisotropic etchant, it selectively etches silicon (especially single-crystal silicon) along specific crystal planes (e.g., the (100) plane), forming precise microstructures (e.g., trenches, vias) for integrated circuits (ICs). Unlike strong inorganic acids/bases, it avoids metal ion contamination of wafers.
• Cleaning Agent: Removes photoresist residues, organic contaminants, and oxide layers from wafer surfaces, ensuring the cleanliness of semiconductor components and improving device performance.
• Positive Photoresist Developer: In lithography processes, it dissolves the exposed areas of positive photoresist (where the photoresist polymer breaks down), transferring the circuit pattern from the photomask to the wafer.

4.2 Organic Synthesis

• Strong Organic Base: Used to prepare TMAH-derived salts (e.g., tetramethylammonium bicarbonate, tetramethylammonium fluoride) and as a catalyst for alkylation, acylation, and condensation reactions—promoting deprotonation of reactants and accelerating reaction rates.
• Phase Transfer Catalyst: Facilitates the transfer of reactants between aqueous and organic phases (e.g., in nucleophilic substitution reactions), improving reaction efficiency and yield without requiring harsh conditions.

4.3 Chemical Analysis

• Polarographic Analysis Reagent: Used in polarography (an electrochemical analysis method) to determine the concentration of trace metals (e.g., lead, cadmium) and organic compounds in solutions, thanks to its strong alkalinity and low interference.
• Acid Titrant: Ideal for titrating weak organic acids (e.g., carboxylic acids, phenols) in non-aqueous systems, as its strong alkalinity ensures complete neutralization and sharp end-point detection.

5. Manufacturing Methods

5.1 Traditional Silver Oxide Method (Obsolete)

• Process: Tetramethylammonium chloride ((CH3​)4​NCl) reacts with silver oxide (Ag2​O) in an aqueous solution to form TMAH and silver chloride (AgCl precipitate). The precipitate is filtered out, and the filtrate is concentrated to obtain TMAH solution.
• Disadvantages: High cost of silver oxide, complex process, and residual silver ions in the product—making it unsuitable for electronic-grade applications. It is now only used in small-scale laboratory synthesis.

5.2 Modern Electrolysis Method (Mainstream)

• Process:
  1. Aqueous tetramethylammonium chloride (or bromide) is used as the electrolyte in an electrolytic cell with a cation exchange membrane (to separate anode and cathode chambers).
  2. During electrolysis, chloride ions (Cl−) are oxidized at the anode to form chlorine gas (Cl2​, which is collected and treated), while water is reduced at the cathode to generate hydroxide ions (OH−).
  3. Tetramethylammonium cations ((CH3​)4​N+) migrate through the cation exchange membrane to the cathode chamber, combining with OH− to form TMAH.
• Advantages: Low cost, high product purity (ultra-low metal ion content), and continuous production capability—meeting the strict requirements of the electronic industry.

6. Safety Information

6.1 Toxicity

• Highly Toxic:
  • Subcutaneous LD₅₀ (mouse): 19 mg/kg (severe toxicity via skin absorption).
  • Intravenous LD₅₀ (rabbit): 1 mg/kg (extremely toxic via injection, causing rapid systemic damage).
• Long-Term Exposure Risks: Even low concentrations can cause cumulative damage to the nervous system, liver, and kidneys.

6.2 Hazardous Properties

• Corrosiveness: Causes severe chemical burns to the skin and cornea—skin contact leads to redness, blistering, and tissue necrosis; eye contact may result in permanent vision loss if not rinsed immediately.
• Incompatibility: Reacts violently with strong oxidants (e.g., hydrogen peroxide, potassium permanganate) and strong acids (e.g., sulfuric acid, hydrochloric acid), releasing heat and potentially causing splashing or explosion.
• Fire Risk: High-concentration TMAH solutions (≥50%) or anhydrous solids are flammable—combustion releases toxic gases including carbon monoxide (CO) and nitrogen oxides (NOₓ).

6.3 Protective Measures

• Personal Protection: Wear nitrile rubber gloves (latex is permeable to TMAH), a full-face chemical splash shield, a chemical-resistant apron, and a respirator with organic vapor cartridges (in poorly ventilated areas).
• Emergency Response:
  • Skin Contact: Immediately rinse with plenty of flowing water for 20+ minutes, then apply a neutralizing agent (e.g., dilute acetic acid) and seek medical attention.
  • Eye Contact: Hold eyelids open and flush with sterile normal saline for 15+ minutes; do not rub—seek emergency medical care immediately.
  • Inhalation: Move to fresh air, keep the airway open, and administer oxygen if breathing is difficult.
• Storage/Handling: Store in a sealed, corrosion-resistant container (e.g., HDPE or Teflon-lined drums) in a cool, dry, well-ventilated area; avoid contact with acids, oxidants, and combustible materials. Label clearly with "Highly Toxic," "Corrosive," and "Flammable" warnings.