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Views: 481 Author: Site Editor Publish Time: 2026-01-20 Origin: Site
In semiconductor manufacturing, chemical cleaning refers to removing harmful impurities and oils from the surfaces of semiconductors, metals, and tools. This process uses chemical reagents and organic solvents to dissolve or react with contaminants. Often, physical aids like ultrasonic cleaning, heating, or vacuuming are used to achieve a perfectly clean surface.
Semiconductors are extremely sensitive to impurities. Even one part per million (ppm) of a contaminant can alter the physical properties of a device. While we use controlled doping to create functionality, unintended contamination from tools, chemicals, or air can ruin an experiment. Chemical cleaning is essential to maintain the integrity of the silicon wafer.
Chemical cleaning covers three main areas:
Silicon Wafers: The substrate itself.
Metal Materials: Tungsten wires, molybdenum sheets, and aluminum alloys used in evaporation.
Tools and Vessels: Tweezers, quartz tubes, glassware, and graphite molds.
These include natural or synthetic oils, resins, and waxes. They often come from cutting/polishing lubricants, fingerprints, or photoresist residues.
Mechanism: These adhere via Van der Waals forces and electrostatic attraction.
Cleaning Challenge: Most are insoluble in water and create a hydrophobic surface. This prevents cleaning acids or bases from reaching the wafer surface. Therefore, removing these with solvents or surfactants is always the first step.
Common ions include K+, Na+, Ga2+, Fe2+, Cl-, and F-. These come from air, water, chemicals, and human perspiration.
Mechanism: These ions bond to the silicon surface through chemical forces. They act as "traps" for electrons or holes, severely affecting electrical performance. Because the bonding is strong, they are much harder to remove than molecular impurities.
Heavy metals like Gold (Au), Silver (Ag), and Copper (Cu) often adsorb onto the surface through substitution reactions in acidic etchants.
Mechanism: These have the strongest adsorption force. Since noble metals like Gold do not react with standard acids, reagents like Aqua Regia (a mixture of Nitric and Hydrochloric acid) are required to complex and dissolve them.
Based on the types of impurities, the standard procedure follows this logic:
Degreasing: Use surfactants or organic solvents to remove molecular oils. This "unmasks" the surface for the next steps.
Ion Removal: Use acid or alkaline solutions (often with hydrogen peroxide) to strip chemical ions.
Atomic Removal: Use Aqua Regia or acidic peroxide to dissolve residual metal atoms.
High-Purity Rinse: Final wash with deionized water.
Working with industrial cleaning agents requires strict safety protocols.
Solvents like Toluene, Acetone, and Ethanol are highly flammable and toxic.
Storage: Keep in cool areas away from fire.
Heating: Use water baths; never use direct flames.
Emergency: Use CO2 or foam extinguishers for fires. Always work in a fume hood to avoid toxic vapors.
Strong acids (Sulfuric, Hydrofluoric, Aqua Regia) and bases (NaOH, KOH) are highly corrosive.
Protection: Always wear rubber gloves and masks.
Dilution Rule: Always pour acid into water, never water into acid, to prevent explosive splashing.
Skin Contact: If splashed, rinse immediately with massive amounts of water and seek medical attention.
Gas cylinders (Hydrogen, Oxygen) are under high pressure (approx. 150 kg/cm ²).
Storage: Keep cylinders away from direct sunlight and heat.
Contamination: Ensure valves and wrenches are free from oil and grease to prevent spontaneous combustion.
Hydrogen: Always purge systems with inert gas before introducing hydrogen to prevent explosions.
Conduct all operations in a fume hood.
Treat all waste liquids before disposal.
Wash gloves thoroughly before removing them to avoid skin contact with residues.
