How should gaseous contamination be prevented from crossing into the wafer transfer area?

To reduce the cross-entry of gaseous contamination in the wafer transfer area, it is necessary to simultaneously manage the source, door area and equipment airflow, and then configure appropriate chemical filtration. Only increasing local filter media capacity cannot compensate for all open boundaries or unreasonable air paths. The problem in the transfer area is often not the filter element itself, but where the air comes from and where it goes.

First identify the input paths of cross-contamination

The input of gaseous contamination into the wafer transfer area usually comes from three directions: air infiltration from adjacent process areas, releases carried by FOUP or carriers, and outgassing from materials and operating processes inside the equipment. The propagation methods of these three types of sources are different, and the corresponding control positions are also different. Infiltration into adjacent areas is mostly related to the door area pressure difference and door opening timing; the carrier follows the transfer path of the wafer cassette; when the internal gas release of the equipment occurs downstream of the filter section, no matter how strong the inlet filtration is, it cannot cover it. During the investigation, concentration changes at transmission nodes, adjacent areas and operating periods should be compared first to confirm the dominant path before deciding on measures. Regarding how to distinguish whether pollution comes from outside or inside, please refer toHow to distinguish whether workshop pollution comes from outside or inside?。

The door area and buffer structure determine how much air will flow in

The door opening frequency, pressure difference stability and buffer room settings between the transmission area and adjacent areas directly affect the amount of cross input. Qualifying the pressure difference does not mean that there is no instantaneous backflow under dynamic working conditions. Air flow exchange at the moment of opening the door, continuous leakage of the logistics channel, and exhaust fluctuations may cause short-term input. Common improvement directions include: stabilizing the pressure difference in the door area, setting up buffer sections, optimizing the door opening sequence, and maintaining directional airflow at key interfaces. What these measures reduce is 'how much polluted air comes in', while chemical filtration addresses 'whether the incoming gas has been treated.' The two cannot replace each other.

Localized chemical filtration should be placed upstream of the actual protected location

The position of the chemical filter section should cover the actual air path that the wafer passes through, rather than just being installed at the air supply outlet. There may be multiple micro-environments inside the transfer area: EFEM internal circulation, transfer chamber, temporary storage position and loading port, each with different air sources and protection objects. If the filter section only handles room air supply, and the contamination enters from inside the equipment or the moment the door is opened, the outlet test may still fail to meet the standards. A reasonable approach is to first draw an air path diagram and mark the nodes where pollution may enter, and then determine whether the filter section should be placed at the inlet, circulation loop, or local protection position. Regarding the correspondence between EFEM air inlet and equipment cleanliness requirements, please refer toHow does EFEM air inlet chemical filtration correspond to equipment cleanliness requirements?。

Filter material capacity cannot make up for airflow organization defects

When there are open boundaries or uncontrolled airflow, increasing the number of media layers or capacity often has limited success. The air in the unfiltered section will not be processed because the filter element becomes larger, and the cross-incoming contamination will not change its path due to the high media capacity. The control sequence of the transfer area is usually: first reduce uncontrolled input (door area, buffer, pressure difference), then ensure that the necessary air flow passes through the matching filter section, and finally check the capacity and replacement cycle of the filter material. If the order is reversed, it is easy to have a situation where 'the filter element is replaced more frequently, but the problem remains the same.' Regarding the division of labor between local filtration and room filtration, please refer toCan a chemical filter be used alone in a room?。

Aili industrial supporting equipment

For projects such as the wafer transfer area, we usually draw the air path with the customer first to confirm whether the pollution comes from the door area, the carrier or the inside of the equipment, and then determine where the filter section should be placed. If the location is EFEM or local circulation at the equipment end, compact filter elements and FFU are more commonly used; if it is a room or buffer section, box-type or V-shaped structures are more suitable. Aili Industry can provide FFU matching, box-type, flat-type and V-type chemical filtration products. The compact structure of the equipment can be adapted to non-standard configurations according to space and air volume. If the original system involves replacing imported filter elements, it can also be checked according to the interface size and media requirements. The manufacturing end covers motors, fans, control systems, sheet metal and complete machine assembly. The interfaces between the filter section and the air supply structure can be aligned in the same package. Products can be viewedChemical filter product series page, box-type matching can be referred toMAU box-type chemical filter , FFU integrated configuration can be referred toChemical Filter FFU page. The specific gas effect, applicable environment and replacement cycle still need to be verified based on the corresponding configuration data and on-site working conditions. The actual results are subject to on-site leak detection and gas detection results.

Related questions and answers

If the pressure difference in the transmission area is qualified, why is there still gas crossover?
The pressure difference manages the average flow direction, and short-term input may occur at the moment of opening the door, logistics channels and exhaust air fluctuations. Qualified pressure difference does not mean that there is no crossover under dynamic working conditions. It needs to be judged based on event records and key point detection.

Is it enough to just add a chemical filter to the air supply vent?
It depends on where the pollution enters. If the contamination comes from inside the equipment or when the door is opened, only treating the air supply may not cover it. The position of the filter section should be determined based on the actual air path.

Can Aili Industrial assist in the selection of local filtration in the transmission area?
The position and product form of the filter section can be checked based on the air path, installation space and target gas. The compact structure of the equipment can be adapted in a non-standard way. The specific configuration needs to be confirmed based on the corresponding product information and on-site conditions.

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