Control of humidity in dust free workshop purification

Significance: humidity control is an important condition for the production of dust-free workshop, and relative humidity is a common environmental control condition in the operation of dust-free workshop and clean room.

      The target value of typical relative humidity in semiconductor dust-free workshop and clean room is controlled in the range of 30% to 50%, and the allowable error is less than 0 ± Within a narrow range of 1%, for example, in the photolithography area or in the far ultraviolet treatment (DUV) area, it is even smaller, while in other places it can be relaxed to 1% ± Within 5%.

        In recent years, there are a series of factors that may reduce the overall performance of the clean room by maintaining the relative humidity in the process of handling air in these specified ranges, including:

      1. Bacterial growth;

      2. The comfortable range of room temperature for staff;

      3. Static charge appears;

      4. Metal corrosion;

      5. Water vapor condensation;

      6. Degradation of lithography;

      7. Water absorption.

      Bacteria and other biological pollution, mold, virus, fungi, mites in the relative humidity of more than 60% of the environment can actively reproduce. Some flora can grow when relative humidity exceeds 30%. When the relative humidity is between 40% and 60%, the influence of bacteria and respiratory tract infection can be reduced to Zui. Relative humidity in the range of 40% to 60% is also the moderate range of human comfort. High humidity can make people feel stuffy, while humidity below 30% can make people feel dry, skin rupture, respiratory tract discomfort and emotional discomfort.

        High humidity actually reduces the accumulation of static charge on the surface of dust-free workshop and clean room, which is the desired result. Low humidity is more suitable for the accumulation of charge and becomes a potential source of destructive electrostatic discharge. When the relative humidity exceeds 50%, the static charges begin to dissipate rapidly, but when the relative humidity is less than 30%, they can persist on the insulator or ungrounded surface for a long time.

        Relative humidity between 35% and 40% can be regarded as a satisfactory compromise. Semiconductor dust-free workshop and clean room generally use additional control devices to limit the accumulation of static charge. The rate of many chemical reactions, including the corrosion process, will increase with the increase of relative humidity. All surfaces exposed to the air around the dust-free workshop and clean room are quickly covered with at least one layer of water. When these surfaces are composed of thin metal coatings that can react with water, high humidity can accelerate the reaction. Fortunately, some metals, such as aluminum, can form a protective oxide layer with water and prevent further oxidation reaction. However, in another case, such as copper oxide, it is not protective. Therefore, in high humidity environment, copper surface is more vulnerable to corrosion.

        From this, it can be seen that the dust-free workshop has strict or even harsh requirements on humidity, and the dehumidifier can solve this problem in terms of humidity control, and the dehumidifier can fundamentally solve the strict requirements on temperature and humidity in the dust-free workshop.