Can ULPA remove AMC and gaseous pollutants?

This question is asked a lot in semiconductor and precision manufacturing projects, but the answer itself is clear: No, this is not what ULPA is for.

ULPA controls particulate matter. AMC (Airborne Molecular Contamination, gaseous molecular contamination) is a gaseous pollution, the molecular weight is much smaller than the particles, and the filtration mechanism is completely different. Expecting to improve the ULPA rating to solve the AMC problem is wrong from the beginning.

But this does not mean that ULPA has no place in AMC control. The relationship between the two is division of labor, not substitution.

What is AMC and why it needs to be controlled separately

AMC refers to pollutants that exist in gaseous form in the air and can be roughly divided into several categories according to their properties:

Acid gases : such as hydrogen fluoride, hydrogen chloride, and sulfur oxides, are corrosive to certain processes and materials.

Alkaline gas : such as ammonia, which may affect the exposure effect during the photolithography process.

Organic contaminants : volatile organic compounds, plasticizers, etc., may form thin films on the wafer surface.

Dopants : compounds such as boron and phosphorus, the presence of trace amounts may affect the electrical properties of semiconductor devices.

What these substances have in common is that they are not particles and cannot be stopped by ULPA. Controlling them requires chemical filtration, which relies on adsorption, neutralization, or other chemical reactions to remove the target species from the air stream. The specific configuration should be selected according to the type and concentration of the target species. One material does not fit all.

Why efficiency ratings cannot replace AMC metrics

The grades of ULPA are U15, U16, and U17, which describe the penetration rate of particles under specified conditions.

Chemical filtration focuses on different indicators: removal efficiency of specific pollutants, adsorption capacity, penetration time, and applicable temperature and humidity range.

These two sets of indicators are not on the same dimension. A U16 rating indicates the product's ability to filter particles, but does not indicate its effectiveness in treating ammonia, acidic gases or organic matter. If the procurement document only says 'ULPA required', it will not solve the AMC problem; conversely, the specifications of the chemical filter cannot indicate the level of particle control.

What to check for combined systems

In actual projects, particle filtration and chemical filtration often need to be used together. There are a few places to check in particular at this time:

Resistance stacks up. The chemical filtration section increases the total system resistance. When configuring, the resistance of each section should be accumulated to check whether the fan operating point can still meet the design air volume. Supporting For the FFU fan filter unit system, the performance of the unit after adding a filter section must also be confirmed.

Installation sequence. Which particulate filtration or chemical filtration comes first will affect their respective loads and maintenance cycles. Pre-particle filtration can reduce the possibility of dust contamination of the chemical filter section. In turn, the location of the chemical filter section may also affect the replacement space of the particle filter.

The medium loses dust. Some chemical filter materials may generate small amounts of dust during operation. If installed downstream of ULPA, this part of dust will directly enter the clean side, and it needs to be evaluated whether a protection section needs to be installed behind it.

Maintenance cycles are out of sync. The chemical filter is replaced based on adsorption capacity and penetration, and the particle filter is based on pressure difference and leak detection. The maintenance rhythms of the two are different. The ledgers must be recorded separately and cannot be processed in a unified cycle.

Upstream load and temperature and humidity conditions. The efficiency of chemical filtration is affected by temperature and humidity. When the air inlet conditions exceed the applicable range, the treatment effect may decrease. These conditions should be stated together when selecting.

Procurement information should be written separately

The most problematic aspect of the AMC project is that the two requirements are mixed together in the technical document.

A reasonable approach is to separate them into categories: particle control requirements include ULPA levels, testing standards, and air volume; AMC control requirements include target pollutant types, air intake concentrations, allowable penetration concentrations, temperature and humidity conditions, and determination methods.

These two sets of requirements correspond to different products, different tests, and different acceptance methods. Mixed together, it is difficult for the supplier to quote accurately, and it is difficult to tell which indicator is not up to standard during acceptance.

involving The selection of HEPA/ULPA air filters should be judged in the particle control column; the treatment plan for gaseous pollutants needs to be discussed separately.

Project judgment example

A certain photolithography area is concerned with both particles and acidic gases.

The reasonable configuration idea is: use ULPA at the end to control particles, and set up a chemical filtration section at a suitable location to process acid gas. The specifications, resistance and maintenance cycles of the two sections are confirmed separately, and the total system resistance and fan operating point are uniformly checked.

If only ULPA is installed, the particle index may meet the standard, but the acid gas problem still exists; if only chemical filtration is installed, particle control cannot be guaranteed. The two are in a cooperative relationship and one cannot exist without the other. Device-side applications such as The EFU equipment-end fan filter unit has a compact internal space. How to arrange the two-stage filtration and how to maintain maintenance channels need to be taken into consideration during the equipment structure design stage.

Selection and Acceptance Checklist

About Aili Industrial’s combination configuration support

The difficulty in the configuration of AMC projects is often not in a single product, but in how to coordinate the particle filtration section and the chemical filtration section, how to balance the resistance, and how to arrange maintenance.

Aili Industrial's manufacturing system covers filters, motors, fans, control systems and complete machine assembly, and can provide ULPA ultra-high efficiency filter and supporting air supply equipment. For projects involving both particulate and gaseous pollution control, the location, resistance, and interfaces of each treatment section can be checked together during the planning stage, rather than separately purchased and then coordinated on site.

A list of particle control targets and AMC targets are provided during the inquiry to help confirm the appropriate configuration combination. The specific plan shall be subject to the technical documents and test results confirmed by the project.