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Clean Room Application
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1. Clean Room / Aseptic Clean Room Clean Room is a room in which the concentration of airborne particles is controlled, and which is constructed and used in a manner to minimize the introduction, generation, and retention of particles inside the room, and in which other relevant parameters, e.g. temperature, humidity, and pressure, are controlled as necessary. Also, the illumination, hazardous steam, and airflow direction and its velocity are also defined. Aseptic Clean Room is a room where the Microorganisms such as bacteria or virus and biological particles are more strictly controlled. Industrial Clean Room ICR It is the Clean Room for industrial use, such as Precision industries, electric industries, etc. Biological Clean Room BCR 2. Features for Clean Room Air-conditioning I.Temperature and humidity requirements are higher than general air-con. The temperature requirement for general air-con is between 18°C and 26°C and the relative humidity is between 40% and 65%; while the temperature in Clean Room should be controlled between 22°C and 24°C and the humidity in it should be between 45% and 55%. II.Constant temperature and humidity control It is extremely temperature-sensitive for the semiconductor industry; therefore, the temperature and humidity should be controlled within ± 1°C and ± 3% in most of the Clean Room areas. III.More air needed to balance the air pressure in Clean Room A large amount of the chemicals and toxic gas will be required during the semiconductor production. Therefore, there will also be a huge amount of gas exhausted due to the volatile gas and exhaust gas. To maintain positive pressure inside the Clean Room, the air supply into the Clean Room is also relatively increased. IV.Twenty-Four Seven running and monitoring on Air-con system Part of the machines in the semiconductor production are highly sensitive to the temperature/humidity variation, such as the Stepper in Photo lithography area. A slight change of the temperature or humidity would affect the accuracy of the device. Moreover, the products like chips should be put in the environment with constant temperature and humidity. Therefore, the air-con system should be strictly monitored and managed. V.Air pressure inside the Clean Room in the semiconductor factories For the semiconductor factories, the air pressure in the Clean Room should be higher than the outside. Besides avoiding the influence from the temperature, humidity, and particles outside the Clean Room, it also helps extend the lifetime of the ULPA filter. However, the pressure difference should be constrained to avoid the cost increase from the increased out bounding air from Clean Room. VI.Airflow direction In order to remove the airborne particles inside the Clean Room, the air velocity shall reach the certain standard. Also, the airflow direction shall be controlled based on various levels of the Clean Room. 3. Clean Room System The Clean Room system would produce clean air that is conformed to the specification. The clean air shall be steadily and continuously supplied to the FAB. Generally speaking, the source for producing clean air is called OUTSIDE AIR. It will undergo various of processing units in the Clean Room to produce the clean air that conforms to the specification. The following is the simplified process: The Outside air goes into the Make-up Air Unit (or MAU) to pre-filter the particle and control the temperature/humidity. After that, the air goes to the Mech. Chase. Inside the Chase, the circular air in the Clean Room and the supplying air from the MAU are mixed, and Dry Cooling Coil will cool down the air inside the Mech. Chase to the requested temperature by the Clean Room specification. Then the Fan Filter Unit (or FFU) enables the airflow cycle in the Clean Room to remove the particles and heat. Last, the air will be supplied to FAB area after filtered by the Ultra-low penetration air (or ULPA Filter). 4. Definition of Cleanliness It means the capability for the Clean Room to effectively control the particle number in the specific room. To define the function of different types of the Clean Room, we define it based on the particles of “Specific Size” in “Specific Volume”. Take the particle diameter above 0.5μm for example:
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