Why do relevant equipment focus on both particle and molecular contamination?

The photolithography process is very sensitive to defects. Particles on the wafer surface may directly affect pattern quality, while certain gaseous molecular contamination may also affect photoresist, optical components or sensitive materials. Particle control and molecular contamination control are two different types of problems that need to be designed and verified separately.

The air particle level is qualified, which does not prove that molecular pollution meets the requirements. Mixing the two types of pollution together may miss the real risk.

The mechanisms of particulate and molecular pollution are different

Particle contamination refers to the deposition of solid particles in the air on the wafer surface or optical components, forming defects. Sources of particles include equipment dust, personnel activities, material introduction and filter bypass.

Molecular contamination (AMC) refers to gaseous or vaporous contaminants in the air that may come from material releases, process exhaust, the external environment or cleaning agents. Molecular contamination may affect sensitive surfaces through chemical reactions, adsorption, or condensation.

Particles and molecules have different physical forms, as well as different modes of propagation and control. Filters trap particles, but molecular contamination requires chemical filtration or air supply control.

Air particle levels do not cover molecular pollution

Cleanliness levels describe the concentration of particles in the air. Molecular contamination is usually measured as the concentration or surface residue of a specific contaminant, which are different indicators.

Even if air particle levels are acceptable, molecular contamination may still exceed standards. To determine whether molecular contamination meets the requirements, target contaminants should be detected separately rather than replaced by particle data.

For the difference between control methods of particulate and molecular pollution, please refer to How do HEPA and ULPA match cleanliness goals? , first understand the functional boundaries of the filter.

Sensitive objects of lithography equipment

Among lithography-related equipment, those that are sensitive to contamination usually include:

• Photoresist and rubberized surfaces;

• optical lenses and lenses;

• reticles and graphics surfaces;

• Precision motion mechanisms and sensors.

These objects differ in their sensitivity to particulate and molecular contamination and need to be evaluated separately. Some materials are more sensitive to specific gases or vapors and require individual confirmation.

Common sources of molecular contamination

Molecular contamination can come from:

• Equipment material and lubricant release;

• process exhaust and vacuum systems;

• external ambient air;

• Cleaner and solvent residues;

• Personnel activities and materials brought in.

To control molecular pollution, we need to start from several aspects: source control, ventilation elimination and chemical filtration. Some processes also require control of the concentration of specific gases or vapors.

Design and verify two types of controls separately

Particle control and molecular contamination control should be designed separately:

• Particle control: filter rating, air supply method, sealing and airflow organization;

• Molecular contamination control: chemical filters, air supply, exhaust and material management.

Verification should also be done separately:

• Particle detection: sampling according to particle size, location and state;

• Molecular contamination detection: sampling by target contaminant and method.

The sampling methods, instruments and judgment standards of the two types of tests are different and cannot be substituted for each other. For the selection of sampling location, please refer to Why can’t the sampling point be located just below the air supply outlet? , understand the representative layout ideas.

Chemical filtration and system resistance

When using a chemical filter in combination with a particle filter, the total resistance and fan capacity need to be checked. The resistance of the chemical filter media will affect the system operating point, so particle filters cannot be considered only when selecting.

For local protection on the equipment side, please refer to The fan filter unit at the EFU equipment end can be configured according to space and resistance selection. Filter products available HEPA and ULPA filters , check particle filtration efficiency and installation sealing. If airflow in the equipment cavity is involved, please refer to How to plan clean air supply for closed equipment cavities? , understand the internal airflow organization.

Two types of data are recorded separately during verification

Verification records for lithography equipment should include:

• Particle data: particle size, location, concentration;

• Molecular pollution data: target pollutants, concentrations, methods;

• Equipment operating status and process conditions;

• Filter and chemical filter media status.

The two types of data correspond to their respective evaluation ranges and cannot be mixed together for judgment. The cleanliness level must indicate the particle size and state. Please refer to the specific reasons. Why must the particle size be indicated in the cleanliness grade?。

Project judgment example

A certain photolithography equipment station passed the particle inspection, but the process still had defects. The investigation found that molecular contamination was not included in the detection scope. Adjustment method: Supplement molecular pollution detection to confirm target pollutant concentration. After adjustment, the control direction is clarified.

In another project, after adding a chemical filter to the equipment, the system resistance increased and the air volume decreased. Adjustment method: Check the combined resistance of the chemical filter and particle filter, and adjust the fan working point. After adjustment, the air volume and filtration effect are both satisfied.

These two situations illustrate that the pollution control of lithography equipment needs to consider both particle and molecular pollution, and the two types of controls should be designed and verified separately.

Key points for selection and acceptance inspection

Aili industrial equipment supporting support

Pollution control of lithography equipment involves two types of targets: particle and molecular contamination. Aili Industrial has collaborative capabilities in fans, motors, filters, control systems and complete machine assembly links. It can check the combined configuration of particle filtration and chemical filtration, air supply direction and fan working point based on the sensitive objects of the equipment, target pollutants and system resistance, helping to implement the two types of controls into the equipment plan respectively, rather than selecting based solely on particle levels. Device side supporting can be viewed 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。