Why do semiconductor clean rooms distinguish between particle and AMC control?

In the design and acceptance of semiconductor cleanrooms, particle control is usually a priority. The data measured by the particle counter directly reflects whether the clean room grade meets the standard. However, in actual operation, we sometimes encounter a situation: the particle indicators are qualified, but the product still has defects or fluctuations in yield.

After investigation, it is often found that the problem is not particles, but air molecular pollution (AMC). The two types of pollution are different in form, mode of transmission and filtration mechanism, as well as different control methods and detection methods. If they are managed together, it is easy to miss one of them. For specific differences, please refer to Discussion of the difference between chemical filters and HEPA filters .

The two types of pollution have different forms and impacts

The essential difference between particles and AMC determines their different ways of affecting the process.

Particles are solid or liquid particles suspended in the air, ranging in size from a few nanometers to tens of microns. Its impact is mainly physical: forming defects on the wafer surface, blocking photolithography exposure, or affecting the uniformity of film deposition.

AMC is a molecular level gaseous pollutant, including acid gas, alkaline gas, organic vapor, dopant, etc. Its impact is more subtle - it may change the surface properties of the material through chemical reactions, or it may be adsorbed on the wafer surface to form a thin film, affecting subsequent processes. For specific sources and categories, please refer to Discussion of what AMC pollution in the air refers to .

Particle contamination can be removed by surface cleaning, but the effects of AMC may have altered the material surface. The two have different risk windows and response methods in the process.

Detection methods cannot be mixed

The detection methods of particles and AMC are completely different, which is one of the reasons why they must be managed separately.

Particle detection uses a particle counter to sample the air and count the number of particles of different sizes. The test result is the particle concentration, usually in particles/cubic meter. The detection method is relatively mature and can read in real time.

AMC detection requires gas sampling and analysis. Commonly used methods include laboratory analysis after enrichment of sampling tubes, online gas analyzers, specific gas sensors, etc. The detection result is the concentration of the target gas, and the unit may be ppb or μg/m³. The sampling methods, analysis conditions and detection limits of different gases are different and need to be selected based on the components of concern. For specific sampling methods, please refer to whether to do air sampling before choosing a chemical filter . Discuss

Particle counters do not measure AMC, and gas analyzers do not reflect particle levels. The two sets of data answer different questions respectively and cannot be substituted for each other.

Different filtering mechanisms

Controlling particulates and AMC requires different filtration equipment.

Particle control relies on HEPA or ULPA filters. They intercept particles through fiber or membrane media, with filtration efficiency graded by particle size and standard. System design focuses on air volume, face velocity, sealing and leak detection. Can be referenced Description of HEPA high efficiency filter .

AMC control relies on chemical filters. They remove gaseous pollutants through adsorption or reaction media. Selection should focus on target gas type, concentration, temperature and humidity conditions and medium capacity. For specific principles, please refer to Discussion on why chemical filters should be selected according to the target gas .

Increasing the HEPA rating does not enhance AMC processing capabilities. Likewise, adding a chemical filtration section does not reduce particle control requirements. The two types of filters undertake different tasks in the system and need to be configured and accepted separately.

Different process sensitive objects

Different process areas have different sensitivities to particles and AMC, and the focus of control is also different.

The photolithography area is sensitive to alkaline gases (such as ammonia), and trace amounts of alkaline components may affect photoresist performance. At the same time, there are also strict requirements for particles. The control scheme needs to consider both particle filtration and chemical filtration for alkaline gases. For details, please refer to Discussion on how to choose chemical filters for amine gas contamination .

Etched and film deposition areas may be sensitive to acidic gases, organic vapors, or dopants. Different process steps require different AMC control objectives.

Wafer transfer and storage areas may be of greater concern for particles, but the need for localized chemical filtration also needs to be evaluated if AMC sources are present in the surrounding area. Device-side applications such as The discussion on why EFU needs supporting chemical filters can be used as a reference.

Therefore, the same control standard cannot be set for the entire clean room. The control targets for particles and AMC need to be determined separately by process area.

Control means need to be coordinated

AMC control cannot be solved by a single measure and requires the cooperation of multiple means.

Source control. Select low-outgassing materials, improve processes, and strengthen local exhaust to reduce AMC generation from the source. This is often more economical than terminal processing.

Fresh air treatment. Externally input AMC needs to be processed in the fresh air section. MAU is equipped with a chemical filtration section to reduce the load entering the clean area. For details, please refer to Discussion on why MAU needs to configure chemical filtration section .

Circulation filtering. AMC released indoors can be filtered through return air or FFU circulation. Please refer to the specific applicable conditions Discussion of what localized contamination can be treated by FFU plus chemical filter .

Device-side protection. Sensitive devices may require independent localized chemical filtration, handling releases within the device or external inputs.

Particle control also needs to be maintained simultaneously. The efficiency, sealing and leak detection of terminal HEPA or ULPA cannot be reduced by adding AMC control. The two types of control measures need to be co-designed rather than replacing each other.

Project judgment example

The particle counter data of a certain semiconductor factory showed that the cleanliness was up to standard, but unknown defects appeared on the surface of the wafers in a certain process.

Troubleshooting the particle system found no problems. Further testing of air components revealed trace amounts of organic vapor and alkaline gases, the sources of which were related to equipment and process materials. These AMC components deposit or react on the wafer surface, causing defects.

Adjustment direction: Add a chemical filtration section for organic gases and alkaline gases in the return air section of the clean room, and strengthen AMC treatment in the fresh air section. The particle filtration system remains unchanged and continues to be maintained to original standards. After adjustment, the defect rate dropped and the particle index was not affected.

This case shows that qualified particles do not mean that AMC meets the standards. Both need to be detected and controlled separately. involving When selecting chemical filter product series , it is recommended to provide process sensitive objects and test data to the supplier for verification.

Key points for selection and acceptance inspection

About Aili Industrial’s semiconductor clean package

For particle control and AMC control in semiconductor clean rooms, the two types of requirements need to be confirmed separately during the planning stage, and then uniformly checked at the system level.

Aili Industrial has independent manufacturing capabilities in filters, motors, fans, control systems and sheet metal processing, and can provide HEPA/ULPA filter and chemical filter product series. For projects involving both particle and AMC control, the process area, sensitive objects, detection data and system conditions can be combined to assist in checking the filter section configuration and division of labor. When the filter is matched with MAU, FFU, EFU and other equipment, the resistance, interface and maintenance methods can be confirmed uniformly.

Related products:Chemical filter product series、HEPA high efficiency filter、MAU box chemical filter . A list of particle control targets and AMC targets are provided during the inquiry to help confirm the appropriate combination solution. The specific configuration is subject to the technical documents and test results confirmed by the project.