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Semiconductor plant clean workshop construction and environmental technical requirements
2024/12/3
With the establishment of China's "core" plan, the state has introduced various policies to support the development of the domestic semiconductor industry, the development of third-generation semiconductors, and the localization of ten new infrastructure, detonating the strong demand for chips and demonstrating the strong power and potential of chips. The production environment and equipment requirements of semiconductors and chips are extremely high, so what are the environmental requirements of semiconductor and chip clean areas?
Because electronic products in the manufacturing, production process of the indoor air environment and quality requirements are extremely strict, mainly to control particles and dust as the main object, but also to the temperature and humidity of the environment, the amount of fresh air, noise and so on have made strict regulations.
Indoor noise level (empty state) : should not be greater than 65dB(A). Vertical flow clean room full ratio should not be less than 60%, horizontal unidirectional clean room should not be less than 40%, otherwise it is local unidirectional flow. The static pressure difference with the outdoor should not be less than 10Pa, and the static pressure difference between the clean area and the unclean area with different air cleanliness should not be less than 5Pa. The amount of fresh air in the clean room should be the maximum of the following two items. The sum of the amount of fresh air required to compensate the indoor exhaust air volume and maintain the indoor positive pressure value. Ensure that the supply of fresh air per person per hour in the clean room is not less than 40m3. Clean the air conditioning system heater, should be set up fresh air, overtemperature power off protection, if the use of point humidification should be set up no water protection, cold areas, fresh air system should be set up anti-freeze protection measures, clean room air supply volume.
Complex design and construction and high construction costs
Electronic chip clean workshop has strict cleanliness requirements, it can be imagined that its design and construction is also quite complex. In addition, the higher the cleanliness, the higher the construction cost. For example, a 100-level unidirectional flow clean room, only the construction cost of interior decoration and air conditioning cleaning system will be 10,000 yuan or more per square meter. Coupled with fire protection, waste, power supply and distribution and automatic control systems, the construction cost will be higher.
After the completion of the construction of the electronic chip clean workshop, it must go through three aspects of acceptance, namely: empty acceptance, static acceptance and dynamic acceptance, and only after completion of acceptance can it be put into daily use. Therefore, it faces huge technical risks, as well as the pressure of subsequent operation, maintenance, debugging and testing.
The target value of relative humidity in a semiconductor clean room is approximately controlled in the range of 30% to 50%, allowing a narrow range of error of ±1%, such as in the lithography zone - or even less in the far ultraviolet treatment zone - while elsewhere it can be relaxed to the range of ±5%.
Because relative humidity has a series of factors that can reduce the overall performance of clean rooms, including: bacterial growth. Staff feel comfortable in room temperature range. A static charge appears. Metal corrosion. Condensation of water vapor. Degradation of lithography. Water absorption. Bacteria and other biological contaminants (molds, viruses, fungi, mites) can thrive in environments with relative humidity of more than 60%. Some bacterial communities can grow at relative humidity of more than 30%. Humidity should be controlled in the range of 40% to 60% to minimize the effects of bacteria and respiratory infections.
Relative humidity in the range of 40% to 60% is also a moderate range for human comfort. Too much humidity can make people feel stuffy, while humidity below 30% can make people feel dry, chapped skin, respiratory discomfort and emotional unhappiness.
The high humidity actually reduces the accumulation of electrostatic charges on the cleanroom surface - a desired result. Low humidity is ideal for charge accumulation and a potentially damaging source of electrostatic discharge. When the relative humidity exceeds 50%, the electrostatic charges begin to dissipate rapidly, but when the relative humidity is less than 30%, they can persist for a long time on an insulator or an ungrounded surface. Relative humidity between 35% and 40% can be used as a satisfactory compromise, and semiconductor clean rooms generally use additional controls to limit the accumulation of electrostatic charges. The speed of many chemical reactions, including corrosion processes, will increase with the increase of relative humidity. All surfaces exposed to the air around the clean room are quickly covered with at least one single molecular layer of water. When these surfaces are composed of thin metal coatings that can react with water, high humidity can speed up the reaction. Fortunately, some metals, such as aluminum, can form a protective oxide with water and prevent further oxidation reactions; But the other case is that copper oxide, for example, is not protective, so in a high humidity environment, the copper surface is more susceptible to corrosion. In addition, in the high relative humidity environment, due to the absorption of water, the expansion of the photoresist after the baking cycle is increased. Photoresist adhesion can also be negatively affected by higher relative humidity; The low relative humidity (about 30%) makes photoresist adhesion easier, even without the need for polymeric modifiers. Controlling relative humidity in a semiconductor clean room is not arbitrary. However, as time has changed, it is good to review the causes and foundations of common and generally accepted practices.
