Application of air filter in semiconductor chip factory

24/07/2020

    Today, semiconductor chip factories are the most critical of the cleanliness of the production environment, and they have the most demanding requirements for air filters. The dust sticking to the chip may cause an open circuit or a short circuit and directly affect the yield.
    One of the indicators to measure the degree of chip integration is the "line width", that is, the width of the wires on the integrated circuit. In the age when the line width was calculated in micrometers, the manufacturing environment's restriction on the particle size of dust was less than 1/10 of the line width. As the line width continued to decrease, 1/10 became 1/4 and 1/2. In 2002, the line width of the P4 processor in ordinary microcomputers was reduced to 0.13 μm. At this time, any dust may damage the circuit, and the traditional comparison of particle size and line width is outdated.

    Application of air filter in a semiconductor chip factory
    The traditional form of ventilation in the chip factory is "large circulation". The entire ceiling of the workshop is covered with HEPA filters without partitions, and the entire floor is a return air grid. Now some workshops of chip factories use high-efficiency filter units (FFU, FanFilterUnits) with their own fans. Both large cycle and FFU forms can achieve sufficient cleanliness, but there are differences in operation management and energy consumption.
    High-efficiency filters and FFUs that can be squeezed into the chip factory must be scanned and tested one by one. The chip factory believes that the test dust used in the traditional inspection method is itself a source of pollution, so the chip factory does not buy the sodium flame method and the DOP method.
    The sea salt ions in the air are the enemy of all electronics industries, but the particles of sea salt dust are relatively large, and ordinary filters can remove them. Some people say that the ideal location for the electronics industry should be far from the coast, but the domestic chip factory is built in the economically developed coastal area, and it is enough to spend a little more money on the filter.
    Chip manufacturers are particularly concerned about possible trace volatile elements on the filter. In recent years, there has been a high-efficiency filter material of PTFE fiber. This material has no volatile matter, but it is static. The filtered air needs to be electrically neutralized to eliminate ions in the air. There is less hidden danger and more A trouble. At present, the price of PTFE high-efficiency filter materials is relatively high, and most high-efficiency filters still use traditional glass fiber filter paper. The possible volatiles on the high-efficiency filter mainly come from the binder, cleaning agent, test dust, auxiliary materials used in the manufacturing process, and the filter manufacturer that supplies the chip factory should work hard to avoid trace volatiles.
    However, when the line width of the chip is as small as 0.5 μm, it is found that chemical pollutants in the air become the main hazard affecting the yield. Therefore, the air conditioning system of the later chip factory is generally equipped with a chemical filter. The chemical filter mentioned by the chip factory is an activated carbon filter, and its principle and manufacturing process are not complicated.
    The sources of chemical pollutants are outdoor air, the craft itself, people, and decoration materials. In most cases, designers and field personnel can't tell the type and concentration of pollutants. Therefore, the chemical filter used in the chip factory should have two characteristics: broad-spectrum adsorption performance and sufficient activated carbon materials. The so-called broad-spectrum adsorption means that it can absorb more or less anything. The most traditional, cheapest, and uneven micropore size granular activated carbon can have this function. If the type of pollutant can be determined, targeted chemical treatment can be performed on the adsorption material to enhance the adsorption capacity of specific pollutants. Filter suppliers sometimes also provide corresponding on-site testing services to help users determine the use of chemical filters, which requires the suppliers to have experts in chemical filtration and have a close relationship with authoritative laboratories. Unfortunately, few domestic filter manufacturers have worked hard on it, so most of the chemical filters currently used by domestic chip factories are imported products.
    The semiconductor industry is not a "smoke-free industry", it also has environmental problems. The latest technology and materials are often used there, and some chemicals have been used in large quantities before their safety has been evaluated. In order to reduce environmental risks, the exhaust systems of some chip factories are also equipped with chemical filters.