How to define local cleaning requirements for semiconductor front-end equipment?

The cleanliness requirements of semiconductor front-end equipment cannot just be written in an industry name or an ISO level. The exposure status, sensitive particle size, transmission action and equipment boundaries of wafers in different processes are different, and the corresponding local cleaning requirements are also different. In addition to particles, conditions such as molecular contamination, temperature, static electricity and vibration may be involved.

To define local cleaning requirements, it is necessary to start from the wafer exposure path and confirm the protection objectives and equipment interfaces step by step. The following will start from the exposure path, particle sensitivity, pollution type, and equipment interface.

Identify critical areas along wafer exposure path

The exposed position of the wafer within the equipment determines the local cleaning requirements. The exposed links of the wafer should be identified step by step from loading, transportation, processing to caching.

Things that need to be confirmed include:

• Where the wafer is exposed to the internal environment of the device;

• how long the exposure was;

• What are the surrounding institutional movements at the time of exposure;

• Whether the exposed location is close to dust-generating parts;

• Is the exposure location close to equipment openings?

Mapping the wafer transfer path and exposure points can help clarify which areas require local protection and which areas can share the background environment. For airflow planning in closed equipment cavities, please refer to How to plan clean air supply for closed equipment cavities? , understand how internal airflow paths are organized.

Particle sensitivity determines filtration requirements

Different processes have different sensitivities to particles. In the front-end process, particles on the wafer surface may directly affect the yield, and the sensitive particle size may be smaller than that in the conventional clean area.

When confirming particle sensitivity, it should be clear:

• Sensitive particle size range;

• allowed particle levels;

• Detection capabilities and methods;

• Filter grade requirements.

Filters cannot be specified by ISO rating alone, but also in combination with sensitive particle size and background load. For the selection logic of HEPA and ULPA, please refer to How do HEPA and ULPA match cleanliness goals? , first confirm the filtering requirements and then set the level.

In addition to particles, other types of contamination need to be considered

The local cleaning requirements of semiconductor front-end equipment are often not just particle control. Also confirm:

• Molecular contamination (AMC) : Some processes are sensitive to gaseous molecular contamination;

• Temperature : Equipment and processes may have requirements for temperature stability;

• Static electricity : Wafers and mechanisms may be sensitive to static electricity;

• Vibration : Precision measurement and motion mechanisms are sensitive to vibration.

These conditions need to be confirmed separately, and one particle grade cannot cover all requirements. The control mechanisms of particle and molecular pollution are different. For details, please refer to Why are lithography-related equipment concerned about both particle and molecular contamination? , understand the difference between the two types of pollution.

Transmission actions and mechanism occlusion affect protection boundaries

During wafer transfer, robots, grippers, and cache locations change local airflow and protective boundaries. Movement status should be taken into consideration when defining cleaning requirements.

Need to confirm:

• Robot movement trajectory and speed;

• The residence time of the wafer in different positions;

• Whether the organization blocks the air supply;

• Whether movement produces particles;

• Whether equipment openings and door movements affect airflow.

For the impact of wafer handling robots on air flow, please refer to How can wafer handling robots be incorporated into airflow verification? , understand the verification method under motion.

Equipment boundary and interface conditions

Local cleaning requirements should be implemented on the equipment interface. Need to confirm:

• Installation space and equipment structure;

• The installation location of the EFU or air supply module;

• Air inlet and exhaust interface;

• Control linkage and communication interface;

• Maintenance access and filter replacement path.

Commonly used local protection on equipment side The EFU equipment-end fan filter unit can select a structure based on equipment space and air supply requirements. Please refer to the room background air supply FFU clean air supply products , the logic of division of labor between the two is The division of labor between device-side EFU and room FFU is explained in detail.

Transform requirements into verifiable conditions

Local cleanliness requirements must ultimately be translated into verifiable conditions. It should be clear:

• Detect position and height;

• Detection of particle size and sampling methods;

• test status (static or dynamic);

• Judgment criteria;

• Acceptance scope.

The location and height of the sampling point should cover the actual exposed position of the wafer, rather than just under the air supply port. Related methods can be found in Why can’t the sampling point be located just below the air supply outlet? and How does a change in working height affect the detection position?。

Project judgment example

In a certain semiconductor front-end equipment, the wafers are exposed for a long time in the transmission and buffering locations. The original plan only defined requirements based on ISO levels and did not differentiate between exposure links. Adjustment method: Confirm the protection targets segment by segment according to the wafer exposure path, and define cleanliness requirements for different areas. After adjustment, the local protection range is clear, and the verification conditions correspond to the exposure location.

Another project has manipulator movement inside the equipment, and the original plan only measured static airflow. Adjustment method: Incorporate the movement status of the manipulator into the verification to confirm the protection effect of the wafer path during movement. Protection under adjusted dynamic conditions was confirmed.

These two situations illustrate that the local cleaning requirements of semiconductor front-end equipment should be defined segment by segment along the wafer exposure path, and cannot be determined only by industry name or one level.

Key points for selection and acceptance inspection

Aili industrial equipment supporting support

The local cleaning requirements of semiconductor front-end equipment involve multiple aspects such as wafer exposure path, particle sensitivity, molecular contamination and equipment interfaces. Aili Industrial has collaborative capabilities in fans, motors, filters, control systems and complete machine assembly links. It can check the EFU configuration, filtration level, air supply direction and interface conditions based on the wafer exposure position, transmission action and equipment space, helping to transform local cleanliness requirements into executable equipment solutions, rather than selecting based on just one ISO level. You can view the equipment package EFU equipment end fan filter unit , please refer to the filter package. HEPA and ULPA filters , please refer to room air supply FFU clean air supply products。