Why should the relative humidity of the clean room be strictly controlled?

Poor control of relative humidity can degrade the overall performance of the clean room, and it will also bring a series of effects. 1. Bacterial growth. Bacteria and other biological contamination (mold, viruses, fungi, mites) can thrive in environments with relative humidity above 60%. Some flora can grow when the relative humidity exceeds 30%. The relative humidity in the range of 40% to 60% minimizes the effects of bacteria and respiratory infections. Therefore, the relative humidity of the clean room should be controlled within a certain range. 2. The clean room staff feel the comfortable range of room temperature. Humidity in the range of 40% to 60% is also a moderate range for human comfort. If the humidity in the clean room is too high, it will make people feel stuffy, and if the humidity is lower than 30%, it will make people feel dry, chapped skin, respiratory discomfort and emotional discomfort, which will affect the work. 3. The relative humidity of the clean room is not well controlled, and electrostatic charge occurs. Static charges begin to dissipate rapidly when the relative humidity exceeds 50%, but they can persist for long periods of time on insulators or ungrounded surfaces when the relative humidity is less than 30%. A cleanroom relative humidity of between 35% and 40% can be a satisfactory compromise, and semiconductor cleanrooms typically use additional controls to limit the build-up of static charge. 4. Poor relative humidity control can easily cause metal corrosion in the clean clean room modular. The rate of many chemical reactions, including corrosion processes, will increase with increasing relative humidity. All surfaces exposed to the ambient air of the cleanroom are quickly covered with at least a monolayer of water. When these surfaces are composed of thin metal coatings that can react with water, high humidity can speed up the reaction. Some metals, such as aluminum, can form a protective oxide layer with water and prevent further oxidation reactions; others, such as copper oxide, are not protective. In environments with high humidity, copper surfaces are more susceptible to corrosion. 5. Water vapor condensation. In pharma clean room environments with high relative humidity, capillary forces in the form of concentrated water form bonds between particles and surfaces, which can increase particle adhesion to siliceous surfaces. This effect, known as Kelvin Concentration, is not significant when the relative humidity is less than 50%, but becomes the dominant force for particle-to-particle adhesion when the relative humidity is around 70%. 6. Degradation of clean room lithography. The most pressing need for moderate control in semiconductor cleanrooms is the sensitivity of photoresist. Due to the extremely sensitive nature of photoresist to relative humidity, its control range of relative humidity is the most stringent. Relative humidity and temperature are critical for photoresist stability and precise dimensional control. Even under constant temperature conditions, the viscosity of the photoresist will drop rapidly as the relative humidity rises. Of course, changing the viscosity changes the thickness of the protective film formed by the fixed component coating. In addition, in high relative humidity environments, photoresist swelling is aggravated after bake cycles due to moisture absorption. Photoresist adhesion can also be negatively affected by higher relative humidity; lower relative humidity (about 30%) makes photoresist adhesion easier even without the need for polymeric modifiers such as hexamethyldisiloxane Azane (HMDS). 7. Water absorption. Poor relative humidity control will have a certain impact on the water absorption output of the clean clean room modular.

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