Essential Design Criteria for Semiconductor Cleanrooms
2024.07.01
Essential Design Criteria for Semiconductor Cleanrooms
Semiconductors are integral to nearly every electronic device, from everyday items like smartphones and coffee makers to complex automobiles, defense equipment, and spaceships. Manufacturers produce semiconductors in specialized cleanrooms because the wafers are extremely sensitive to environmental contaminants.
In this article, we delve into the design requirements of semiconductor cleanrooms.
Semiconductor Cleanroom Design: Meeting Air Quality Standards
Semiconductor cleanrooms are controlled environments located within semiconductor foundries or fabs. They tightly regulate the following parameters:
- Temperature
- Humidity
- Airflow
- Temperature variation over time
- Noise
- Vibration
- Lighting
- Airborne particles
Maintaining these parameters is essential for achieving the highest air quality standards while optimizing productivity. Even a single dust particle can render a chip useless. A well-designed cleanroom must feature an efficient HVAC system that controls temperature, humidity, filtration, and other attributes to ensure the air quality remains within acceptable limits. Each machine may have individual exhaust systems to remove contaminated air and particulates. Cleanrooms must control particulate matter, static, outgassing, and equipment failures, which can lead to contamination events, such as power glitches, pressure malfunctions, fan motor failures, and wafer handling machine breakdowns.
Controlling Temperature, Humidity, and Airflow
Semiconductors exhibit an inverse relationship between temperature coefficient and resistance. When heated, semiconductor conductance increases, and resistance decreases. The outermost electrons separate from the atomic nucleus of the material compound, and as free electrons multiply, resistance drops accordingly. Therefore, maintaining a specific temperature range during semiconductor manufacturing is crucial to ensure the chips perform correctly in their applications.
Relative humidity in semiconductor cleanrooms should be between 30-50%, which is optimal for inhibiting bacterial growth and ensuring the comfort of cleanroom personnel. Airflow should follow vertical laminar flow, where air moves from the ceiling to the floor. The air enters vents in the floor, is purified by HEPA filters, regulated for temperature and humidity, and then recirculates into the room.
Cleanroom Classifications for Semiconductor Manufacturing
Semiconductor cleanrooms must meet ISO 14644-1 Class 5 or lower, which allows a maximum of 3,520 particles at 0.5µm or smaller per cubic meter of air. They must also comply with ISO 14644-2, which requires implementing a quality control system that meets stringent classification criteria.
Depending on the application, a semiconductor fabrication plant may also need to adhere to industry-specific regulations from the EPA, the SEMI Standards Program, various industry task forces, technical committees, and other regulatory bodies. These standards vary based on the type of fabrication process, wafer size, and line width, and are followed in conjunction with ISO to ensure the cleanroom environment is controlled 24/7, producing consistent and high-quality products.
Custom Environmental Control Solutions for Semiconductors
Our custom environmental control units (ECUs) provide precise temperature and humidity tolerances to meet even the most demanding requirements. Minor temperature differences during semiconductor scanning can result in false readings. Our ECUs control temperature variations within 0.02 °C, ensuring accurate readings. Other tolerances include:
- Airflow: up to 4000 CFM
- Humidity: ±0.5% relative humidity
- Setpoint temperature: 19°C – 23°C
- Temperature change: max of 1°C/5 minutes
- Humidity change: max of 1% relative humidity/3 minutes
Our team of skilled engineers can design and develop custom ECUs to meet almost any semiconductor manufacturing application or customer specification. We design our ECUs to fit inside or next to the fabrication environment and offer them in vertical or horizontal configurations.
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