Automatic temperature and humidity control
The temperature and humidity of the clean room are mainly determined according to the process requirements, but under the condition that the process requirements are met, the human comfort should be taken into consideration. With the increase in air cleanliness requirements, there is a trend that the process has more and more stringent requirements on temperature and humidity.
As the machining accuracy is getting finer and finer, the requirements for the temperature fluctuation range are getting smaller and smaller. For example, in the lithography exposure process of large-scale integrated circuit production, the difference between the thermal expansion coefficient of glass and silicon wafer as the material of the diaphragm is required to be smaller and smaller. A silicon wafer with a diameter of 100μm will cause a linear expansion of 0.24μm when the temperature rises by 1 degree. Therefore, it must have a constant temperature of ±0.1 degrees. At the same time, the humidity value is generally required to be low, because after a person sweats, the product will be polluted, especially For semiconductor workshops that are afraid of sodium, this kind of clean workshop should not exceed 25 degrees.
Excessive humidity causes more problems. When the relative humidity exceeds 55%, condensation will occur on the wall of the cooling water pipe. If it occurs in a precision device or circuit, it will cause various accidents. It is easy to rust when the relative humidity is 50%. In addition, when the humidity is too high, the dust on the surface of the silicon wafer will be chemically adsorbed by the water molecules in the air to the surface, which is difficult to remove. The higher the relative humidity, the more difficult it is to remove the adhesion, but when the relative humidity is lower than 30%, the particles are also easily adsorbed on the surface due to the action of electrostatic force, and a large number of semiconductor devices are prone to breakdown. The best temperature range for silicon wafer production is 35~45%.
