What contaminants should be focused on with chemical filters in the lithography area?

The sensitivity of the photolithography process to the environment is relatively prominent in semiconductor manufacturing. Particle control is usually tight, but air molecular contamination (AMC) can also affect exposure and image quality.

The AMC that needs attention in the lithography area is not just a general 'gas'. Different components affect the photolithography process in different ways and have different control objectives. When selecting, you must first confirm what the key pollutants are, and then select the corresponding chemical filter media. Please refer to the specific classification Discussion of what AMC pollution in the air refers to .

Starting from equipment requirements

The starting point for the configuration of chemical filters in the lithography area is the specific requirements of the lithography equipment and process.

The sensitive objects of different process systems may be different. Deep ultraviolet (DUV) lithography, extreme ultraviolet (EUV) lithography, and electron beam lithography have different sensitivity to AMC and components of concern. The project should use corresponding equipment specifications and on-site inspection data, and cannot copy the configuration of other production lines.

Ordinary air deodorization goals cannot replace low-concentration process protection. The concentration levels of concern in the photolithography area are usually well below the human olfactory threshold, and detection methods and filtration schemes suitable for the target concentration need to be used. For specific differences, please refer to Discussion on why chemical filters should be selected according to the target gas .

Photoresists and coating materials are also released. Photoresists, anti-reflective coatings, thinners, and developers may release organic vapors during use. This part of the release source is inside the equipment or near the coating station, and needs to be evaluated in conjunction with the air flow path.

Key pollutant categories

According to common sensitive objects in the photolithography process, the following types of contaminants deserve special attention.

alkaline gas. Alkaline components such as ammonia and amines are one of the most common AMCs in the photolithography area. Trace amounts of alkaline substances may neutralize the photoacid in the photoresist, affecting the pattern resolution after exposure. The molecular properties of ammonia and different amines are different, and the suitability of the medium needs to be checked separately. For specific differences, please refer to How to choose chemical filters and filters for amine gas pollution Discussion of whether chemical filters can remove ammonia from the air .

Acid gas. Acidic components such as sulfur dioxide, hydrogen chloride, and nitrogen oxides may corrode or contaminate equipment optical components, photoresist, or wafer surfaces. External industrial emissions, processes or cleaning agents may be introduced. For specific differences, please refer to Discussion of the conditions for use of hydrogen chloride gas filtration that need to be paid attention to .

Organic vapor. Organic components such as solvent volatiles, plasticizers, and siloxanes may be deposited on the surface of optical lenses or wafers to form thin films, affecting light transmittance or subsequent processes. Photoresist, cleaning agents, and developers used in the photolithography area are common sources. For specific selection methods, please refer to Discussion on how to choose an air chemical filter for toluene pollution .

Dopants. Compounds of dopants such as boron and phosphorus may exist in trace amounts in the air in the photolithography area, affecting the electrical properties of the device. Such ingredients often require specialized detection methods and filter media.

List these types of pollutants separately, and then determine the priorities based on the process area and detection data. Not every lithography zone needs to control all categories simultaneously.

Methods to identify key pollutants

The configuration of the chemical filter in the photolithography area cannot be just based on experience and apply the list.

Test first. Take samples in the photolithography area and its fresh air inlet to detect target components such as alkaline, acidic, organic matter and dopants. Sampling points should cover the vicinity of key equipment, return air areas and fresh air inlets. For specific methods, please refer to whether to do air sampling before choosing a chemical filter . Discuss

Check equipment specifications. Lithography equipment manufacturers usually provide sensitive components and concentration requirements for AMC. The project documentation should translate these requirements into inputs for chemical filter selection.

Distinguish between external input and internal release. If the main source is fresh air brought in, focus on the fresh air section; if the main source is internal release of equipment, circulation filtration or equipment end protection needs to be considered. For specific differences, please refer to Why does MAU need to configure the chemical filter section and Discussion of what local contamination FFU plus chemical filter can handle .

Detection capabilities must match. The concentration level of concern in the photolithography area may be lower, and the detection limit of the detection method must meet the requirements. For details, please refer to Discussion of why chemical filter performance reports list specific target gases .

Filtration scheme and system coordination

After identifying the key pollutants, the corresponding chemical filtration section can be configured.

Fresh air section treatment. When external input is the main source, set up a chemical filtration section in the fresh air unit. Filter media type is selected based on the contaminants detected. For specific configuration, please refer to Description of MAU Box Chemical Filter .

Circulation filtering. When internal releases or external inputs accumulate in the clean area, a chemical filtration section can be set up on the return air or FFU circulation path. For details, please refer to Instructions for chemical filters provided with FFU .

Device-side protection. Lithographic equipment interiors are sensitive to AMC and may require independent localized chemical filtration. For device-side applications, please refer to Discussion on why EFU needs supporting chemical filters .

System resistance needs to be accounted for. Adding a chemical filtration section will increase the total resistance of the system. It is necessary to check the fan margin to confirm that the air supply volume meets the requirements. For specific methods, please refer to Discussion of how much the added resistance of the chemical filter will increase the fan's electricity consumption .

Multiple contaminants may require combined configurations. If alkaline gas and organic vapor are present at the same time, different media may need to be layered, or composite filter materials may be used. For specific differences, please refer to The clean room is contaminated by acid gas and solvent at the same time. Discussion on how to combine filtration solutions .

Running trace

The effect of chemical filters in the photolithography area requires long-term tracking.

Outlet concentration trends are more important than single readings. The efficiency of new filter material is usually high when it is first put in. As the running time increases, the outlet concentration may increase. Check the outlet regularly, and determine the timing of replacement based on the operating time and inlet load. For specific life assessment, please refer to Discussion of how long chemical filters last .

You cannot judge by just pressing the difference. The resistance of a chemical filter may not change much over its lifetime, but the gas handling capacity may have declined. A normal pressure difference does not mean that the outlet is up to standard. For specific differences, please refer to Discussion on whether the chemical filter can be replaced based on the pressure difference .

Record operating conditions and replacement history. Inlet concentration, air volume, operating time, and reasons for replacement should be recorded. If the effect changes later, it can help determine whether it is media consumption, front-end problems or changes in working conditions.

Project judgment example

After the equipment was running for a period of time in a certain photolithography area, it was found that the resolution of some batches of graphics fluctuated.

The particle control was checked to be normal and there was no significant change in equipment and process parameters. Further testing of air components revealed that the concentration of ammonia near the lithography equipment was relatively high, and the source was related to the surrounding cleaning process and external fresh air input.

Adjustment direction: Add a chemical filtration section for alkaline gases in the fresh air section, and set up auxiliary filtration on the return air path of the lithography equipment. Before configuring the filter section, the ammonia concentration, air volume, and temperature and humidity conditions were rechecked. After adjustment, the ammonia concentration decreased and the graphics resolution fluctuations were reduced.

This case illustrates that the key pollutants of the chemical filter in the photolithography area need to be determined based on process sensitive objects and detection data. involving When selecting chemical filter product series , it is recommended to provide equipment requirements, test data and system conditions to the supplier for verification.

Key points for selection and acceptance inspection

About Aili Industrial’s chemical filtration package for the photolithography area

The core of the configuration of chemical filters in the photolithography area is to match the sensitive objects of the equipment, sources of pollutants, and system conditions.

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 photolithography area projects, equipment specifications, target gases, concentration ranges, air volumes, and installation spaces can be combined to assist in checking the filter material type and structural configuration. 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、MAU box chemical filter、FFU comes with chemical filter . Providing a list of target contaminants, concentration ranges, and system conditions when requesting a quote can help confirm the appropriate filtration solution. The specific selection is subject to the technical documents and test results confirmed by the project.