Can the wafer come into contact with compressed air? Why?

Wafer during manufacturingAvoid direct contact with ordinary compressed air, clean compressed air that has been strictly processed needs to be used. The following are the specific reasons and specifications:

1. Why can’t I come into contact with ordinary compressed air?

1. pollution risk：

• oil pollution: Ordinary compressed air may contain trace amounts of oil, and even a small amount will adhere to the wafer surface, affecting the adhesion of photoresist and the accuracy of circuit patterns.
• moisture condensation: Undried compressed air can easily condense into water in low-temperature pipes, causing moisture on the wafer or equipment corrosion.
• particle scratch: Solid particles such as dust and metal chips may scratch the wafer surface, causing irreversible defects.

2. process affects：

• Lithography accuracy declines: Impurities may contaminate the lithography mask with pollutants, resulting in deviation in chip pattern reproduction.
• The etching uniformity deteriorates: Impurity gases change etching chemical reaction conditions and affect line edge control.
• Doping concentration fluctuations: Impurities interfere with the doping process, resulting in inconsistent transistor performance.

3. equipment damage：

• Corrosion of precision parts: Compressed air containing corrosive gases can accelerate equipment aging.
• pipe blockage: Particulate matter may block gas nozzles or vacuum pumps, increasing the risk of downtime.

2. Specifications for the use of clean compressed air

1. Quality level requirements：

• oil-free: Oil residual content ≤0.01 mg/m³ (some process requirements ≤0.1 ppm).
• dryness: Pressure dew point ≤-40℃ (some processes need ≤-70℃).
• particle filtration: The filtration efficiency of particles ≥0.01 μm is ≥99.995%.
• pressure stability: The fluctuation range is controlled within ± 0.01MPa.

2. Gas supply system design：

• Independent gas supply room: The compressed air generator must be independent of the clean room to avoid the effects of heat radiation and vibration.
• multi-stage filtration: Equipped with oil-water separator, activated carbon absorber and ultra-precision filter in turn.
• pipe material: Use 316L stainless steel or electropolishing the inner wall of the pipe to reduce particulate matter shedding.

3. Usage Scenario Restrictions：

• Direct contact is prohibited: During wafer transfer, cleaning and other links, compressed air is only used to drive equipment (such as air cylinders) and does not come into direct contact with the wafer.
• positive pressure protection: Maintain positive pressure in the clean room to prevent external air from penetrating.

3. Alternative plans and emergency measures

1. Nitrogen substitution: Using high-purity nitrogen in critical process steps, such as wafer transfer, is more costly but safer.
2. Fluorine oil test method: In the high-voltage testing process, fluorine oil immersion is used instead of compressed air insulation. After testing, the fluorine oil is easy to volatilize and has no residue.
3. electrostatic protection: If compressed air must be used to purge the equipment, static electricity must be eliminated first through an ionization device.

conclusion: Wafer manufacturing has extremely strict quality requirements for compressed air. Impurities in ordinary compressed air may directly lead to wafer scrapping or equipment failure. Through oil-free air compressors, multi-stage filtration systems and strict dew point control, compressed air can be ensured to meet Class 1 standards (ISO 8573 – 1) to meet semiconductor process requirements.