Which process of high purity compressed air is used in semiconductor factory

High-purity compressed air is mainly used in the following key process links in semiconductor manufacturing plants, and its application is closely related to the stringent requirements of chip manufacturing for cleanliness and process stability:

1. Wafer Surface Treatment Process

1. wafer cleaning
   • after chemical mechanical polishing (CMP), the wafer surface is purged with high-purity compressed air to remove residual chemicals and particles (particle size <0.1 μm).
   • The purge pressure needs to be accurately controlled between 0.2 MPa and 0.3MPa to avoid air flow impact damage to the wafer surface.
2. photoresist coating
   • before coating the photoresist, high-purity air is used to blow off static electricity and fine dust on the surface of the wafer to ensure uniform adhesion of the photoresist.
   • Air cleanliness shall meet ISO 1 level (particles with particle size> 0.1μm <10/m & sup3;).

2. Vapor Deposition and Etching Process

1. chemical Vapor Deposition (CVD)
   • as a carrier gas to transport reaction precursors (such as silane, ammonia), it is necessary to control the water content <1ppm to avoid the reaction of water vapor with the precursor to generate particles.
   • Airflow stability shall be controlled within ± 1% to ensure the uniformity of film thickness.
2. plasma etching
   • as an auxiliary gas to participate in plasma excitation, it is necessary to control the oil content <0.001 mg/m & sup3; to prevent oil pollution reaction chamber.
   • The air flow pressure fluctuation should be <± 0.005MPa to avoid over-engraving or under-engraving caused by uneven plasma distribution.

3. packaging and testing process

1. wire bonding
   • before gold wire ball welding, use high purity air to blow away dust in the bonding area to improve the welding yield (>99.9%).
   • The air dew point shall be ≤-60 ℃ to prevent virtual welding caused by water vapor condensation.
2. Chip Testing
   • in the high temperature reverse bias (HTGB) test, the chip is cooled with high purity air to avoid oil contamination of the test socket.
   • The air velocity shall be precisely controlled at 0.5-1.0 m/s to ensure temperature uniformity <± 2 ℃.

4. environment control system

1. clean room positive pressure maintenance
   • continuous air supply to the clean room through high-purity air to maintain indoor positive pressure (5-10Pa) to prevent external pollution from invading.
   • The air supply volume needs to be dynamically adjusted according to the clean room level (e. g. ISO level 5 requires 240 air changes per hour).
2. Exhaust gas treatment
   • in the waste gas incinerator (Burner), high-purity air is used as a combustion gas to ensure that toxic gases (such as SiHalready) are completely oxidized.
   • The oxygen content of the air should be stabilized at 20.9±0.1% to avoid secondary pollution caused by incomplete combustion.

5. Quality Assurance Requirements

1. purity Standard
   • high purity air for semiconductor plant shall meet the following requirements:
     • particulate matter (>0.1 μm):<1/m & sup3;
     • oil content:<0.003 mg/m & sup3;
     • water content: dew point ≤-70 ℃
2. supply System Design
   • stainless steel pipe (BA grade polished), inner wall roughness ≤ Ra0.4μm.
   • Configure automatic drain valve and particulate filter, and perform pipeline wipe inspection every 6 months.

High-purity compressed air plays the role of "invisible process gas" in semiconductor manufacturing, and its quality directly affects chip yield and reliability. The daily consumption of high-purity air in a typical 12-inch fab can reach 50,000m & sup3;, and the system investment accounts for 8-10% of the total cleanroom investment. It is suggested that semiconductor factories should establish an on-line air quality monitoring system to collect particles, oil, humidity and other parameters in real time, and to provide early warning of potential pollution risks through trend analysis.