1. Temperature and humidity control in clean room

The temperature and humidity of clean space is mainly determined according to the process requirements, but under the condition of meeting the process requirements, the sense of comfort should be taken into account. With the improvement of air cleanliness requirements, there is a trend that the process of temperature and humidity requirements are more and more strict.
The specific process of the temperature requirements will be listed later, but as a general principle, because of the processing precision is more and more fine, so the temperature fluctuation range requirements are smaller and smaller. For example, in the photolithographic exposure process of large-scale integrated circuit production, the difference between the thermal expansion coefficient of glass and silicon wafer as mask plate material is becoming smaller and smaller.
The diameter of 100 um silicon wafer, the temperature rises 1 degree, causes 0.24um linear expansion, so there must be a constant temperature of ±0.1 degree, and the required humidity value is generally low, because people sweat, there will be pollution to the product, especially the semiconductor workshop afraid of sodium, this workshop should not exceed 25 degrees.

Too much humidity causes more problems. When the relative humidity exceeds 55 percent, condensation can form on the wall of the cooling water pipe, which can cause various accidents if it occurs in sophisticated devices or circuits. Relative humidity at 50% is easy to rust. In addition, when the humidity is too high, the dust attached to the surface of the silicon wafer will be chemically adsorbed on the surface through the water molecules in the air.
The higher the relative humidity is, the harder it is to remove the adhesion. However, when the relative humidity is lower than 30%, the particles are easy to adsorb on the surface due to the effect of electrostatic force, and a large number of semiconductor devices are easy to breakdown. The optimum temperature range for silicon wafer production is 35 -- 45%.

2. Air pressure regulation in clean room

For most clean Spaces, the internal pressure (static pressure) needs to be kept higher than the external pressure (static pressure) in order to prevent the invasion of external contamination. The maintenance of pressure difference should generally comply with the following principles:

（1）The pressure in clean space is higher than that in unclean space.

2. The pressure of the space with high cleanliness level is higher than that of the adjacent space with low cleanliness level.

3. The door connecting the clean room should be opened to the room with high cleanliness level.

The maintenance of the pressure difference depends on the fresh air volume to compensate for the air leakage through the gap at this pressure difference. So the physical meaning of the pressure difference is the resistance of the leakage (or penetration) air volume through various gaps in the clean room.