I. Introduction
The airflow speed/air exchange frequency of the clean room has always been a concern in the design of the clean room. With the increase of the control effect of the clean room pollution source and the improvement of the efficiency of the final filter, the relevant specifications and guidelines are proposed. Whether the recommendation or reference value is conservative, there have been many discussions; the problems of noise and damage maintenance that FFU is worried about in application have been solved in practice. With the continuous improvement of FFU, whether to adopt FFU return air system It is also a hot spot: the control of suspended molecular pollution (AMC) has been increasingly mentioned on the agenda in the microelectronics and IC industries. The following summarizes and analyzes the situation of these issues separately.
Air flow speed
2.1 Application of recommendation or reference value
The determination of the airflow speed under certain cleanliness in the clean room varies with the specific conditions of the clean room. It is affected not only by the amount of dust generated indoors but also by the efficiency of the filter. In the case of industrial clean rooms, the degree of cleanliness is affected. And the factors that select the airflow speed are mainly:
(1) Indoor pollution sources: building components, personnel quantity and operation activities, process equipment, process materials and process processing itself are all sources of dust particles, which vary greatly depending on the specific conditions;
(2) Indoor airflow pattern and distribution: Unidirectional flow requires uniform and equal flow lines, but it will be affected by disturbances in process equipment layout and position changes and personnel activities to form local eddy currents; Avoid dead angles and temperature stratification;
(3) Control requirements for self-cleaning time (recovery time): the release of accidents in the clean room or the interruption of pollutants or air flow or the intermittent convection airflow during normal operation or the movement of people and equipment may cause deterioration of cleanliness. The self-cleaning time to restore the original cleanliness is determined by the airflow speed; the control requirement for the self-cleaning time depends on the ability to withstand the quality of the product and the yield of the product within the time frame (due to the deteriorated cleanliness);
(4) Efficiency of the final filter: In a certain indoor dust generation, a higher efficiency filter can be used to reduce the air flow speed; for energy saving, a higher efficiency filter should be considered, and the air flow speed should be reduced, or Use a lower efficiency filter and use a higher airflow speed to find that the product of flow and drag is small;
(5) Economic considerations: excessive airflow speed causes an increase in investment and operating costs. The appropriate airflow velocity is a reasonable combination of the above factors. Too large is often unnecessary and does not necessarily have an effect;
(6) For clean rooms with low cleanliness requirements, the number of air changes may be determined by the indoor heat removal requirements.
The above factors are difficult to quantify and can only be analyzed and compared. Therefore, in engineering applications, the airflow speed of the clean room is often referred to the recommended or reference values ​​of relevant specifications, guidelines, etc., and then the above factors are estimated according to the specific circumstances for comprehensive consideration.
The airflow speed is used for the unidirectional flow clean room; the non-unidirectional flow clean room should be used for the number of air changes, because the airflow speed is difficult to measure; it is also reflected by the final filter fullness rate, and can be used for various airflow patterns. Clean room, generally 100% full rate relative to flow rate 0.5m / s (100fpm), 25% relative to 0.125m / s (25fpm). The current recommended or reference values ​​for specifications, guidelines, etc. are shown in Table 1.
Note: 1. ISO14644-4 is clearly used as reference material for airflow speed/air exchange times. The list is only applicable to microelectronics and IC factories; for pharmaceutical plants, only ISO5 airflow speed is >0.2m/s, Reference values ​​are not listed in ISO 6-8.
2. (M) refers to a mixed flow, N refers to a non-unidirectional flow; * refers to a clean area where effective isolation measures have been taken against the source of pollution.
The recommended or reference values ​​for airflow speed and number of air changes in Table 1 should be said to be a reflection of experience. Values ​​such as those set forth in ISO/DIS 14664-4 are clearly applicable to that type of clean room; the recommended value of IEST is also considered by some authorities to be applicable only to semiconductor factories. Due to the large changes in specific conditions, some experience values ​​may not be suitable for the current indoor dust source control measures and filter efficiency improvement.
2.2 Discussion of recommendations or reference values
In recent years, many people have thought through experiments that these recommendations or reference values ​​are too conservative, and their arguments can be summarized as:
(1) The lateral diffusion of the airflow in the clean room is only possible at very low flow rates. The unidirectional flow is under a reasonable airflow structure, and the flow rate is 0.05-0.1 m/s, which is enough to carry away the pollutants. The diffusion performance of the particles is much lower than the convective performance; while the gas flow rate of more than 0.36 m/s is easily tens of millions of eddy currents, causing re-entanglement of contaminants. Therefore, the ideal self-cleaning time of the clean room Tr = volume / flow rate, after a certain value, due to the re-entanglement of the contaminants, and then increase the air flow speed, the actual Tr is no longer significantly reduced.
(2) The effect of the efficiency of the final filter on the cleanliness is worthy of attention. Some airflow speed/ventilation times are recommended or reference values ​​are often not considered for the efficiency of the final filter. The current HEPA/ULPA efficiency is selectable from 99.67%, 99.99%, 99.999%, 99.9995% up to 8 9 or more. In addition to the above mentioned effects of efficiency on the airflow velocity, the following aspects are also worthy of attention. In the case of non-unidirectional flow, the stability formula of the dust concentration in the clean room according to the principle of balanced release can be obtained:
(a) When the indoor dust generation is high, the change in the efficiency of the final filter has little effect on the cleanliness, so in this case, excessive filtration efficiency is unnecessary.
(b) In the case where the amount of dust generated indoors is low, the influence of the transmission change of the final filter efficiency at a low air flow rate increases the cleanliness.
The above can be seen in Figures 1a to 1c which can be cited.
Drawing related data:
The dust concentration before the fresh air enters the final filter is 1.75×106/m3
Indoor occurrence: G1=350/m3.min
G2=3500/m3.min
G3=35000/m3.min
G4=350000/m3.min
The ratio of fresh air volume to total air volume is 0.03
At present, some IC factories have ISO5 (0.3μm) clean rooms, adopt FFU system, with ULPA (99.9995%, 0.12μm), export wind speed is 0.38m/s, and the full rate is 25%, so the indoor average airflow The speed is 0.095 m/s at the lower limit of each relevant recommendation or reference value. The processing of this clean room is less in the clean room in the micro-environment, and it can be considered that the clean room is lower, in which case it may be desirable to use a low air flow rate.
According to reports, IEST currently has a lower limit on the recommended value of clean room airflow speed, such as:
≤ ISO5 level: air flow speed 0.2 ~ 0.5m / s;
ISO6 or 5 (non-unidirectional flow); air exchange times > 200 times / h;
ISO7 level: the number of air changes is 20~200 times/h;
ISO8 level: 2 to 20 times of air exchange / h;
III. Application of FFU system
3.1 Current FFU situation
FFU has proven to be unwarranted in terms of service life and maintenance. The current improvements are mainly:
(1) Adopting measures of current sharing and noise reduction, the noise can be within 50db;
(2) The motor adopts DC/EC (electronic rectifying motor), which saves nearly 50% compared with the original AC motor. Because the small-capacity (power <1/2HP) AC motor used by the small fan is generally capacitive phase-separated or Hidden pole, its efficiency is only about 40%, and the efficiency of DC/EC motor can reach 75-80%; in the speed control, each individual filter can be controlled by step-down filter to save energy, but the current investment The payback period is long and not widely used. Generally, group group control or full group control is commonly used.
(3) However, the static pressure at the exit of the FF flap cannot be too large. Generally, the exit wind speed is 0.38 m/s, and the static pressure is generally within 250 Pa.
3.2FFU return air system advantages compared to other methods
3.2.1 General evaluation
advantage:
(1) Great flexibility and easy to transform;
(2) less space occupied by buildings;
(3) The clean indoor air pressure is greater than the return air static pressure chamber, and the possibility of contamination of the clean room by the static pressure chamber is excluded.
Disadvantages:
(1) Require all the resistance of the return air passage (including perforated floor, grille and air duct), dry table cooler resistance and the resistance of the final filter (at the initial resistance), the total should be controlled at about 165Pa to meet the operation. When Zui has a large resistance of less than 250Pa. Therefore, the heat transfer area of ​​the dry surface cooler is larger, the size of the return air passage is larger, and the resistance of the porous floor and the grille is small. The general practice is to control the resistance of the dry surface cooler to about 50 Pa, and return to the air passage. The resistance is within 15Pa, otherwise it will be necessary to add a pressurized fan system, which is to reduce the overall advantages of the FFU system.
(2) After using DC/EC motor, the energy consumption per unit air volume may be lower than that of the current centralized system of large centrifugal fans, but studies have indicated that the energy consumption of the return air system of the large-scale axial fan is improved. Still high. Therefore, it is necessary to pay attention to the improvement of the efficiency of the large axial flow fan and the reduction of the resistance of the system.
(3) In general, the FFU system has a large energy consumption per unit of air volume, so the cooling load of the clean room is also increased accordingly.
3.2.2 Evaluation under specific circumstances
(1) When FFU is used to transform an old building into a clean room, its comprehensive economy is generally desirable.
(2) Clean room with strict cleanliness requirements. When the final filter is 100% full, it is uneconomical to use FFU for large systems; it is meaningful to compare small systems.
(3) For clean rooms where the cleanliness requirements are not strict, when the final filter has a full coverage of ≤40%, the overall system economy is similar, but the flexibility of the FFU system is important for the IC factory. Therefore, when the current IC factory has a filter coverage rate of ≤ 40%, it is common to use an FFU system.
4. Suspended Molecular Pollution (AMC)
4.1 AMC classification and control requirements
As a concern of the IC factory, AMC was first proposed by the Japanese 20 years ago. In recent years, the diameter of IC production has reached φ300mm, and the processing size (line width) has been less than 0.15μm, in some processing steps and processes. AMC has become a serious problem affecting the yield rate in the transfer and storage environment of the film. It has been clearly recognized that the control of AMC has been transferred from discussion to implementation.
For IC production, AMC is divided into four categories: A, B, C, and D, namely:
A - acidic substances such as Hcl;
B - alkaline substances such as NH3;
C—Substances whose boiling point is higher than room temperature and which can condense on the smooth surface, mainly hydrocarbons, and water vapor in some process environments also needs to be considered;
D——Doping substance, which can adsorb or interact with the surface of the wafer, such as arsenic, boron, phosphorus, etc.
AMC has a lot of potential pollution to current IC production than particle pollution. Particle pollution control only needs to determine the particle size and number, but for AMC control, in addition to the variation of chip line width, it is subject to process, The influence of process equipment, process materials and wafer transfer systems, etc., and even the use of various process materials (chemicals, specialty gases, etc.) for a certain process. In many cases, trace amounts of molecules are likely to be used for the next process. It is a pollutant, and the processing of the wafer has more than 300 independent processes at present, and the determination of the AMC control index is more complicated. Therefore, IC production control of AMC, different products, different processes, different processes and different process materials will have different requirements, the requirements for various pollutants, the current general statement is controlled in sub-pptm ~ 1000pptm between.
4.2 Implementation of AMC Control
For the production of ICs with a line width of 0.25 μm, activated carbon filters are often used in fresh air treatment; for key processes and the transfer and storage of wafers between processes, some manufacturers adopt AMC control, and some manufacturers do not. Control is mainly based on the measurement of economic effects. Reports on specific control requirements and measures are rare. It may be due to confidentiality, but it is certain that control can only be carried out in a local environment.
In order to meet the processing requirements of φ300mm wafers and <0.15mm line width, in recent years, AMC control has focused on the following three aspects:
(1) Accurate measurement techniques and establishment of standard test methods. Because this is the basis for mastering AMC control, it must be done first;
(2) According to the production requirements of ICs in the future, the equipment of the production line is isolated by micro-environment, and the transfer of the wafers between the equipments is carried out by using a front-open standard film box (FOUPs) system to isolate the wafers. Therefore, the materials used in equipment, FOUPs and micro-environments have not been required to release and adsorb the problems related to suspended molecular pollutants, and the removal measures for this pollutant have been developed and continuously improved;
(3) Control the filter of the AMC.
In recent years, especially in the past two to three years, there has been little progress in the development and introduction of controlled AMC filters;
A. HEPA/ULPA that does not release AMC substances;
a. Low boron ultra-fine glass fiber filter, which is now used in IC factories in Asia and Europe;
b. Porous polytetrafluoroethylene (ePTFE) filter, which is a film structure, and the price is about ten times higher than a. There are not many currently used, and the next generation is being developed.
B. Chemical filter
The chemical filters that have been introduced are mainly:
a. Activated carbon filter, most of which are grain-shaped, have disc type, honeycomb type, etc.; also have activated carbon fiber filter, which has the characteristics of high adsorption speed, high price; there are already crystal grains and fibers. Adhesive filter.
b Non-woven synthetic fabric is impregnated with various functional grains (such as activated carbon, activated aluminum, but mainly activated carbon) to adsorb AMC substances.
So far, it has been reported that in addition to the two test production lines, φ300mm wafer processing has four production lines (one in Germany, one in the United States, and two in Taiwan). The control of AMC is of course unknown, but the clean room environment is ISO5-6. Level, the design of the clean room is simpler. It can be seen that in the future IC production, the pollution control focus of its production environment will inevitably shift to the research and development and manufacturing of process equipment and wafer transfer and storage systems.
( Source: China Pharmaceutical Technology Alliance )
The airflow speed/air exchange frequency of the clean room has always been a concern in the design of the clean room. With the increase of the control effect of the clean room pollution source and the improvement of the efficiency of the final filter, the relevant specifications and guidelines are proposed. Whether the recommendation or reference value is conservative, there have been many discussions; the problems of noise and damage maintenance that FFU is worried about in application have been solved in practice. With the continuous improvement of FFU, whether to adopt FFU return air system It is also a hot spot: the control of suspended molecular pollution (AMC) has been increasingly mentioned on the agenda in the microelectronics and IC industries. The following summarizes and analyzes the situation of these issues separately.
Air flow speed
2.1 Application of recommendation or reference value
The determination of the airflow speed under certain cleanliness in the clean room varies with the specific conditions of the clean room. It is affected not only by the amount of dust generated indoors but also by the efficiency of the filter. In the case of industrial clean rooms, the degree of cleanliness is affected. And the factors that select the airflow speed are mainly:
(1) Indoor pollution sources: building components, personnel quantity and operation activities, process equipment, process materials and process processing itself are all sources of dust particles, which vary greatly depending on the specific conditions;
(2) Indoor airflow pattern and distribution: Unidirectional flow requires uniform and equal flow lines, but it will be affected by disturbances in process equipment layout and position changes and personnel activities to form local eddy currents; Avoid dead angles and temperature stratification;
(3) Control requirements for self-cleaning time (recovery time): the release of accidents in the clean room or the interruption of pollutants or air flow or the intermittent convection airflow during normal operation or the movement of people and equipment may cause deterioration of cleanliness. The self-cleaning time to restore the original cleanliness is determined by the airflow speed; the control requirement for the self-cleaning time depends on the ability to withstand the quality of the product and the yield of the product within the time frame (due to the deteriorated cleanliness);
(4) Efficiency of the final filter: In a certain indoor dust generation, a higher efficiency filter can be used to reduce the air flow speed; for energy saving, a higher efficiency filter should be considered, and the air flow speed should be reduced, or Use a lower efficiency filter and use a higher airflow speed to find that the product of flow and drag is small;
(5) Economic considerations: excessive airflow speed causes an increase in investment and operating costs. The appropriate airflow velocity is a reasonable combination of the above factors. Too large is often unnecessary and does not necessarily have an effect;
(6) For clean rooms with low cleanliness requirements, the number of air changes may be determined by the indoor heat removal requirements.
The above factors are difficult to quantify and can only be analyzed and compared. Therefore, in engineering applications, the airflow speed of the clean room is often referred to the recommended or reference values ​​of relevant specifications, guidelines, etc., and then the above factors are estimated according to the specific circumstances for comprehensive consideration.
The airflow speed is used for the unidirectional flow clean room; the non-unidirectional flow clean room should be used for the number of air changes, because the airflow speed is difficult to measure; it is also reflected by the final filter fullness rate, and can be used for various airflow patterns. Clean room, generally 100% full rate relative to flow rate 0.5m / s (100fpm), 25% relative to 0.125m / s (25fpm). The current recommended or reference values ​​for specifications, guidelines, etc. are shown in Table 1.
Note: 1. ISO14644-4 is clearly used as reference material for airflow speed/air exchange times. The list is only applicable to microelectronics and IC factories; for pharmaceutical plants, only ISO5 airflow speed is >0.2m/s, Reference values ​​are not listed in ISO 6-8.
2. (M) refers to a mixed flow, N refers to a non-unidirectional flow; * refers to a clean area where effective isolation measures have been taken against the source of pollution.
The recommended or reference values ​​for airflow speed and number of air changes in Table 1 should be said to be a reflection of experience. Values ​​such as those set forth in ISO/DIS 14664-4 are clearly applicable to that type of clean room; the recommended value of IEST is also considered by some authorities to be applicable only to semiconductor factories. Due to the large changes in specific conditions, some experience values ​​may not be suitable for the current indoor dust source control measures and filter efficiency improvement.
2.2 Discussion of recommendations or reference values
In recent years, many people have thought through experiments that these recommendations or reference values ​​are too conservative, and their arguments can be summarized as:
(1) The lateral diffusion of the airflow in the clean room is only possible at very low flow rates. The unidirectional flow is under a reasonable airflow structure, and the flow rate is 0.05-0.1 m/s, which is enough to carry away the pollutants. The diffusion performance of the particles is much lower than the convective performance; while the gas flow rate of more than 0.36 m/s is easily tens of millions of eddy currents, causing re-entanglement of contaminants. Therefore, the ideal self-cleaning time of the clean room Tr = volume / flow rate, after a certain value, due to the re-entanglement of the contaminants, and then increase the air flow speed, the actual Tr is no longer significantly reduced.
(2) The effect of the efficiency of the final filter on the cleanliness is worthy of attention. Some airflow speed/ventilation times are recommended or reference values ​​are often not considered for the efficiency of the final filter. The current HEPA/ULPA efficiency is selectable from 99.67%, 99.99%, 99.999%, 99.9995% up to 8 9 or more. In addition to the above mentioned effects of efficiency on the airflow velocity, the following aspects are also worthy of attention. In the case of non-unidirectional flow, the stability formula of the dust concentration in the clean room according to the principle of balanced release can be obtained:
(a) When the indoor dust generation is high, the change in the efficiency of the final filter has little effect on the cleanliness, so in this case, excessive filtration efficiency is unnecessary.
(b) In the case where the amount of dust generated indoors is low, the influence of the transmission change of the final filter efficiency at a low air flow rate increases the cleanliness.
The above can be seen in Figures 1a to 1c which can be cited.
Drawing related data:
The dust concentration before the fresh air enters the final filter is 1.75×106/m3
Indoor occurrence: G1=350/m3.min
G2=3500/m3.min
G3=35000/m3.min
G4=350000/m3.min
The ratio of fresh air volume to total air volume is 0.03
At present, some IC factories have ISO5 (0.3μm) clean rooms, adopt FFU system, with ULPA (99.9995%, 0.12μm), export wind speed is 0.38m/s, and the full rate is 25%, so the indoor average airflow The speed is 0.095 m/s at the lower limit of each relevant recommendation or reference value. The processing of this clean room is less in the clean room in the micro-environment, and it can be considered that the clean room is lower, in which case it may be desirable to use a low air flow rate.
According to reports, IEST currently has a lower limit on the recommended value of clean room airflow speed, such as:
≤ ISO5 level: air flow speed 0.2 ~ 0.5m / s;
ISO6 or 5 (non-unidirectional flow); air exchange times > 200 times / h;
ISO7 level: the number of air changes is 20~200 times/h;
ISO8 level: 2 to 20 times of air exchange / h;
III. Application of FFU system
3.1 Current FFU situation
FFU has proven to be unwarranted in terms of service life and maintenance. The current improvements are mainly:
(1) Adopting measures of current sharing and noise reduction, the noise can be within 50db;
(2) The motor adopts DC/EC (electronic rectifying motor), which saves nearly 50% compared with the original AC motor. Because the small-capacity (power <1/2HP) AC motor used by the small fan is generally capacitive phase-separated or Hidden pole, its efficiency is only about 40%, and the efficiency of DC/EC motor can reach 75-80%; in the speed control, each individual filter can be controlled by step-down filter to save energy, but the current investment The payback period is long and not widely used. Generally, group group control or full group control is commonly used.
(3) However, the static pressure at the exit of the FF flap cannot be too large. Generally, the exit wind speed is 0.38 m/s, and the static pressure is generally within 250 Pa.
3.2FFU return air system advantages compared to other methods
3.2.1 General evaluation
advantage:
(1) Great flexibility and easy to transform;
(2) less space occupied by buildings;
(3) The clean indoor air pressure is greater than the return air static pressure chamber, and the possibility of contamination of the clean room by the static pressure chamber is excluded.
Disadvantages:
(1) Require all the resistance of the return air passage (including perforated floor, grille and air duct), dry table cooler resistance and the resistance of the final filter (at the initial resistance), the total should be controlled at about 165Pa to meet the operation. When Zui has a large resistance of less than 250Pa. Therefore, the heat transfer area of ​​the dry surface cooler is larger, the size of the return air passage is larger, and the resistance of the porous floor and the grille is small. The general practice is to control the resistance of the dry surface cooler to about 50 Pa, and return to the air passage. The resistance is within 15Pa, otherwise it will be necessary to add a pressurized fan system, which is to reduce the overall advantages of the FFU system.
(2) After using DC/EC motor, the energy consumption per unit air volume may be lower than that of the current centralized system of large centrifugal fans, but studies have indicated that the energy consumption of the return air system of the large-scale axial fan is improved. Still high. Therefore, it is necessary to pay attention to the improvement of the efficiency of the large axial flow fan and the reduction of the resistance of the system.
(3) In general, the FFU system has a large energy consumption per unit of air volume, so the cooling load of the clean room is also increased accordingly.
3.2.2 Evaluation under specific circumstances
(1) When FFU is used to transform an old building into a clean room, its comprehensive economy is generally desirable.
(2) Clean room with strict cleanliness requirements. When the final filter is 100% full, it is uneconomical to use FFU for large systems; it is meaningful to compare small systems.
(3) For clean rooms where the cleanliness requirements are not strict, when the final filter has a full coverage of ≤40%, the overall system economy is similar, but the flexibility of the FFU system is important for the IC factory. Therefore, when the current IC factory has a filter coverage rate of ≤ 40%, it is common to use an FFU system.
4. Suspended Molecular Pollution (AMC)
4.1 AMC classification and control requirements
As a concern of the IC factory, AMC was first proposed by the Japanese 20 years ago. In recent years, the diameter of IC production has reached φ300mm, and the processing size (line width) has been less than 0.15μm, in some processing steps and processes. AMC has become a serious problem affecting the yield rate in the transfer and storage environment of the film. It has been clearly recognized that the control of AMC has been transferred from discussion to implementation.
For IC production, AMC is divided into four categories: A, B, C, and D, namely:
A - acidic substances such as Hcl;
B - alkaline substances such as NH3;
C—Substances whose boiling point is higher than room temperature and which can condense on the smooth surface, mainly hydrocarbons, and water vapor in some process environments also needs to be considered;
D——Doping substance, which can adsorb or interact with the surface of the wafer, such as arsenic, boron, phosphorus, etc.
AMC has a lot of potential pollution to current IC production than particle pollution. Particle pollution control only needs to determine the particle size and number, but for AMC control, in addition to the variation of chip line width, it is subject to process, The influence of process equipment, process materials and wafer transfer systems, etc., and even the use of various process materials (chemicals, specialty gases, etc.) for a certain process. In many cases, trace amounts of molecules are likely to be used for the next process. It is a pollutant, and the processing of the wafer has more than 300 independent processes at present, and the determination of the AMC control index is more complicated. Therefore, IC production control of AMC, different products, different processes, different processes and different process materials will have different requirements, the requirements for various pollutants, the current general statement is controlled in sub-pptm ~ 1000pptm between.
4.2 Implementation of AMC Control
For the production of ICs with a line width of 0.25 μm, activated carbon filters are often used in fresh air treatment; for key processes and the transfer and storage of wafers between processes, some manufacturers adopt AMC control, and some manufacturers do not. Control is mainly based on the measurement of economic effects. Reports on specific control requirements and measures are rare. It may be due to confidentiality, but it is certain that control can only be carried out in a local environment.
In order to meet the processing requirements of φ300mm wafers and <0.15mm line width, in recent years, AMC control has focused on the following three aspects:
(1) Accurate measurement techniques and establishment of standard test methods. Because this is the basis for mastering AMC control, it must be done first;
(2) According to the production requirements of ICs in the future, the equipment of the production line is isolated by micro-environment, and the transfer of the wafers between the equipments is carried out by using a front-open standard film box (FOUPs) system to isolate the wafers. Therefore, the materials used in equipment, FOUPs and micro-environments have not been required to release and adsorb the problems related to suspended molecular pollutants, and the removal measures for this pollutant have been developed and continuously improved;
(3) Control the filter of the AMC.
In recent years, especially in the past two to three years, there has been little progress in the development and introduction of controlled AMC filters;
A. HEPA/ULPA that does not release AMC substances;
a. Low boron ultra-fine glass fiber filter, which is now used in IC factories in Asia and Europe;
b. Porous polytetrafluoroethylene (ePTFE) filter, which is a film structure, and the price is about ten times higher than a. There are not many currently used, and the next generation is being developed.
B. Chemical filter
The chemical filters that have been introduced are mainly:
a. Activated carbon filter, most of which are grain-shaped, have disc type, honeycomb type, etc.; also have activated carbon fiber filter, which has the characteristics of high adsorption speed, high price; there are already crystal grains and fibers. Adhesive filter.
b Non-woven synthetic fabric is impregnated with various functional grains (such as activated carbon, activated aluminum, but mainly activated carbon) to adsorb AMC substances.
So far, it has been reported that in addition to the two test production lines, φ300mm wafer processing has four production lines (one in Germany, one in the United States, and two in Taiwan). The control of AMC is of course unknown, but the clean room environment is ISO5-6. Level, the design of the clean room is simpler. It can be seen that in the future IC production, the pollution control focus of its production environment will inevitably shift to the research and development and manufacturing of process equipment and wafer transfer and storage systems.
( Source: China Pharmaceutical Technology Alliance )
Vitamins are organic compounds and vital nutrients that an organism requires in limited amounts. An organic chemical compound (or related set of compounds) is called a vitamin when the organism cannot synthesize the compound in sufficient quantities, and it must be obtained through the diet.
Your body needs them to work properly, so you grow and develop just like you should. They are essential for the normal growth and development of a multicellular organism. Once growth and development are completed, vitamins remain essential nutrients for the healthy maintenance of the cells, tissues, and organs that make up a multicellular organism; they also enable a multicellular life form to efficiently use chemical energy provided by food it eats, and to help process the proteins, carbohydrates, and fats required for respiration.
Antioxidant Vitamins,Natural Vitamins,Essential Vitamins,Anti Aging Vitamins
SINOCHEM PHARMACEUTICAL CO., LTD , http://www.sinochemnutrition.com