Tetramethylammonium hydroxide solution 334901Sigma

Tetramethylammonium Hydroxide Solution 25 wt. % in Methanol (Sigma-Aldrich Cat. # 334901)

Tetramethylammonium Hydroxide Solution (Catalog Code: 334901) by Sigma-Aldrich is a high-purity quaternary ammonium hydroxide solution formulated at 25 wt. % in electronic-grade methanol. Known widely as TMAH, this strong organic base serves as a premium metal-ion-free anisotropic etchant for monocrystalline silicon in microelectromechanical systems (MEMS) fabrication, semiconductor processing, and as a specialized reagent in the advanced sol-gel synthesis of catalytic nanomaterials.

Technical Specifications & Chemical Parameters

Core Applications & Industrial Uses

1. Anisotropic Silicon Etching (MEMS & Microfabrication)

TMAH is the primary industrial alternative to alkaline metal hydroxides for wet chemical etching of single-crystal silicon.

• Crystallographic Selectivity: Delivers high etch-rate ratios between silicon crystalline planes (e.g., {100}\{100\}{100} and {110}\{110\}{110} versus {111}\{111\}{111}), enabling the creation of precise V-grooves, cantilevers, membranes, and micro-cavities.
• CMOS Compatibility: Being an organic, metal-ion-free base, TMAH eliminates alkali-metal ion contamination (such as K+K^+K+ or Na+Na^+Na+), making it fully compatible with complementary metal-oxide-semiconductor (CMOS) integration lines.
• Passivation Selectivity: Exhibits exceptional etch selectivity over silicon dioxide (SiO2SiO_2SiO2​) and silicon nitride (Si3N4Si_3N_4Si3​N4​) masking layers.

2. Sol-Gel Synthesis & Catalytic Materials

• Zirconium Oxide (ZrO2ZrO_2ZrO2​) Synthesis: Applied in modified sol-gel preparation routes for tailoring the mesoporous structure and surface morphology of zirconia nanoparticles.
• CO Hydrogenation Catalysts: Serves as a structure-directing agent and basic catalyst precursor in synthesizing high-surface-area transition metal oxide supports dedicated to carbon monoxide hydrogenation and syngas conversion.

3. Organic Synthesis & Surface Cleaning

• Functions as a phase-transfer catalyst, organic base in methylation reactions, and precision developer/stripper in photolithographic processing.

Technical Comparison: TMAH vs. Potassium Hydroxide (KOH) for Silicon Etching

Packaging Options & Order Codes

Safety, Handling & Storage Guidelines

CRITICAL SAFETY ADVISORY (GHS / Hazcom): Tetramethylammonium hydroxide is an acutely toxic, highly corrosive substance capable of rapid transdermal absorption. Solutions in methanol are also toxic via inhalation/ingestion and represent a severe flammability hazard.

• Engineering Controls: Handle strictly inside an ISO-certified chemical fume hood with local exhaust ventilation.
• Personal Protective Equipment (PPE): Utilize heavy-duty chemical-resistant gloves (butyl rubber or silver shield recommended; thin nitrile is inadequate for extended contact), splash goggles, full face shield, and chemical-resistant aprons.
• Storage Requirements: Keep tightly sealed in a cool, dry, well-ventilated flammable storage cabinet (+15 °C to +25 °C). Keep isolated from strong oxidizers, mineral acids, and ignition sources.

Frequently Asked Questions (FAQ)

What makes TMAH 25% in methanol preferred over aqueous solutions for sol-gel processes?

The methanolic matrix reduces uncontrolled hydrolysis rates during alkoxide precursor condensation, allowing precise control over particle nucleation, crystal phase transitions, and pore distribution during the synthesis of metal oxides like ZrO2ZrO_2ZrO2​.

How should waste containing TMAH and methanol be disposed of?

Dispose of the solution through an authorized hazardous waste contractor as toxic, flammable, organic alkaline waste. Never neutralize with strong concentrated acids without controlled dilution and temperature cooling.

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