Why does EFU need a matching chemical filter?

EFU (Equipment Fan Filter Unit) is usually installed inside the equipment or in a local area of ​​the equipment to provide clean air supply to the wafer transfer area, optical inspection station, and precision assembly position. Its standard configuration is a fan plus particle filter, which is responsible for controlling particulate matter in the air.

However, the particle filter cannot handle the gaseous pollution inside the equipment. Wafers, optical lenses, sensors, precision metal surfaces, these sensitive objects are not only afraid of particles, but may also be afraid of certain gases. Acid gases may corrode metal circuits, alkaline gases may affect photoresist, and organic vapors may form a thin film on the surface. If the EFU only controls particles, these gases will enter the equipment with the supply air and cause adverse effects at critical locations. For specific differences, please refer to Discussion of the difference between chemical filters and HEPA filters .

Where does gaseous pollution at the equipment end come from?

In the area served by EFU, gaseous pollution may come from several directions.

Release of material inside the device. Seals, lubricants, cables, plastic structural parts, and adhesives may release trace amounts of organic matter at operating temperatures. These releases are usually not in high concentrations, but the internal space of the equipment is closed and pollutants are easy to accumulate. For specific investigation methods, please refer to whether to do air sampling before choosing a chemical filter . Discuss

Process release. Some processes inherently generate or use gaseous substances. For example, the photolithography process may involve alkaline components, and the cleaning process may use organic solvents. If these substances diffuse inside the equipment, the EFU air supply may bring them to sensitive areas.

external input. The air inlet to the EFU may come from the clean room environment around the equipment, or may be introduced from the outside through pipelines. If there is gaseous pollution in the clean room itself, or if there are emission sources near the fresh air outlet, the external input will also affect the inside of the equipment.

Personnel maintenance operations. When replacing materials, cleaning equipment, and performing maintenance operations, gaseous pollution may be introduced or generated for a short period of time.

Only by clarifying these sources can we determine whether the EFU needs a chemical filter section and where the filter section should be placed. For specific configuration, please refer to Discussion on why MAU needs to configure chemical filtration section .

Selection around device protection objects

Whether the EFU is equipped with a chemical filter depends on the sensitive objects inside the device.

Semiconductor equipment. During the transportation, storage, and processing of wafers, the surface may be affected by gaseous contamination. Acidic gases, alkaline gases, organic vapors, and dopants may cause problems in different processes. The equipment is equipped with a chemical filtration section, which can reduce the target gas concentration in the local environment.

Optical inspection equipment. If organic matter or corrosive components are deposited on the surfaces of lenses, filters, and photoelectric sensors, the light transmittance or detection accuracy may be affected. EFU supporting chemical filtration can deal with this type of gaseous pollution.

Precision assembly equipment. Some metal contacts and precision mechanisms are sensitive to corrosive gases. Gaseous contamination inside the device may cause changes in contact resistance or surface oxidation.

Not all EFUs require chemical filters. If there are no gaseous pollution sources inside the equipment and the external input is well controlled, only the particle filter section can meet the requirements. Whether to configure it depends on the sensitivity of the equipment, the source of pollution and the actual detection data.

Matching structure and fan

Device-side space is often tight. When installing a chemical filtration section to EFU, several conditions need to be checked.

Installation space. The available height, depth and width inside the EFU are limited. The thickness, shape and interface of the chemical filtration section must match the EFU structure. Ultra-thin EFU is equipped with a chemical filter layer, which may require special design. Please refer to the specific structure Discussion on whether ultra-thin EFU can also be equipped with a chemical filter layer .

Resistance and fan margin. Chemical filtration sections increase system resistance. Whether the EFU fan can maintain the target air volume needs to be calculated based on the working point after adding resistance. If the margin is insufficient, it may be necessary to adjust the fan configuration or optimize the filter section structure. For specific accounting methods, please refer to Discussion of how much the added resistance of the chemical filter will increase the fan's electricity consumption .

Seal and bypass. The EFU space on the equipment side is compact, and the sealing structure must be reliable. Frame bypass allows untreated air to bypass the filter material, affecting the outlet concentration. For specific inspection methods, please refer to Discussion on how to check frame bypass after chemical filter installation .

Maintain path. The chemical filter section may have a different replacement cycle than the particle filter. The internal space of the equipment is limited, and the operation space and disassembly and assembly path for filter element replacement must be confirmed during the design stage. involving The overall solution, interface and maintenance method of the fan filter unit at the EFU equipment end need to be checked together during the planning stage.

Filter segment order and coordination

When there are both a particle filtration section and a chemical filtration section in the EFU, the order needs to be confirmed.

A common sequence is the chemical filtration section before the particle filtration section. In this way, the particle filter section can intercept trace amounts of dust that may be generated by chemical media and protect the quality of the terminal air supply. But this order is not absolute. If the chemical medium is sensitive to dust, the particles can also be pre-filtered first and then go through the chemical filtration section.

The powder loss and outgassing of chemical media must be confirmed. Some chemical filter materials may generate dust or release trace components during operation. If the chemical section is placed after the particle filter, this part of the dust will directly enter the inside of the equipment. When selecting, confirm the clean compatibility of the media. For specific verification methods, please refer to Discussion on how to verify the low outgassing requirements of ULPA .

Both properties are verified separately. The efficiency and sealing of the particle filter are confirmed according to corresponding standards; the target gas outlet concentration of the chemical filtration section is independently tested. You can’t just do one type of testing. For specific sampling methods, please refer to Discussion of sampling points for chemical filter performance verification .

Project judgment example

There is a wafer transfer mechanism inside a certain semiconductor equipment. After running for a period of time, unknown defects were found on the surface of some wafers.

The particle control was checked to be normal. Later, it was found that there was a trace amount of organic vapor inside the equipment. The source was the lubricant and sealing material inside the equipment. Particle filters do not have the ability to handle this type of gas.

Adjustment plan: Add a chemical filtration section for organic gases on the air supply path of the equipment EFU. Before installation, the internal space of the EFU, fan margin and maintenance access were checked, and a thin chemical filtration structure was selected. After installation, the organic vapor concentration inside the equipment and the wafer surface condition were detected to confirm that the improvement was obvious.

This case shows that gaseous pollution at the equipment end requires targeted filtration solutions, which cannot be solved by particle filters. involving For the configuration of the chemical filter product series , it is recommended that the equipment structure, target gas and operating conditions be provided to the supplier for verification.

Key points for selection and acceptance inspection

About Aili Industrial’s EFU chemical filtration package

The core of the EFU supporting chemical filter is to match the equipment end pollution characteristics, space conditions and protection objectives, and then select the matching media and structure.

Aili Industrial has independent manufacturing capabilities in filters, motors, fans, control systems and sheet metal processing, and can provide chemical filter product series and supporting air supply equipment. For equipment-side projects, we can assist in checking the configuration and interface of the chemical filtration section based on the equipment structure, target gas, air volume and maintenance requirements. When the filter is matched with EFU, FFU and other equipment, the resistance, maintenance methods and sampling points can be uniformly confirmed.

Related products:Chemical filter product series、FFU matching chemical filter、MAU box chemical filter . Provide equipment structure, target gas and system conditions when inquiring to help confirm the appropriate filtration solution. The specific selection is subject to the technical documents and test results confirmed by the project.