Adsorptive Filtration Strategies for Organic Control in IPA

At UltraFacility 2025, George Syu of Entegris Taiwan presented “Advanced Purification Strategy for Organic Impurity Removal in IPA,” outlining ongoing experimental work focused on improving organic contaminant removal from isopropyl alcohol (IPA) using modified PTFE filtration media under varying operating conditions.

As device geometries continue to shrink, the role of ultrapure chemicals – especially IPA - is becoming increasingly critical. Following the conference, UltraFacility spoke with Syu to explore the growing importance of organic contamination control in IPA, and why conventional purification strategies may no longer be adequate at advanced nodes.

Why is contamination control in IPA critical for advanced fabs?

At advanced nodes, overall contamination tolerance becomes much tighter. IPA is used across different parts of the facility, and organic impurities can be present across all manufacturing chains, including bulk chemical manufacture, distribution systems (CDS) and at the tool level. Metal contamination is the most critical, but we still need to consider organics.

What would an effective IPA purification strategy look like in a next-generation fab?

Filtration remains the most practical and direct method to address these contamination challenges. When customers report wafer particle issues, we collect IPA samples from different points in the system, bulk chemical supply, CDS, or the tool.

An effective solution depends on the type of impurity present. If the issue is particles, a standard modified PTFE membrane filter is usually sufficient. This is our most basic solution and is effective for high particle counts. However, if the contamination originates from organic impurities, we need a different approach. We have developed new filtration media with surface modifications that enhance adsorption of organic species.

What makes this new media more effective for organic removal?

The new media incorporates functional surface groups, for example, charged sites that can interact with certain organic molecules.

Conceptually, if the media carries a negative charge, it can attract and retain positively charged or polar organic impurities. The mechanism is based on adsorption rather than simple size exclusion, which is how particle filters work. This allows the filter to remove dissolved or semi-dissolved organic contaminants more efficiently.

From a fab perspective, how does organic contamination differ from metallic contamination?

Metal contamination can usually be detected clearly using methods such as VPD-ICP analysis. It produces a measurable signal. Organic contamination is more difficult to detect. Customers may not directly measure organics in IPA. Instead, they observe wafer particle increases or surface defects and suspect organics as a possible root cause.

For example, linear hydrocarbons may originate from carbon-based system components. These can behave differently from metal contaminants and may contribute indirectly to wafer particle formation. If we remove the organic species from IPA, we believe this can reduce wafer particle-related issues.

Are existing IPA purification solutions sufficient for advanced nodes?

In our testing, we evaluated an existing purifier currently used at customer sites. Its removal efficiency for certain organic contaminants was below 20%. In contrast, our newly developed media demonstrated close to 100% removal efficiency in lab testing. However, this is still under validation with customer samples. We are currently waiting for real-world trial results.

It is also important to note that customers typically care less about the measured organic removal itself, they focus on whether wafer particle counts decrease.

How does filter configuration, single-pass versus recirculation, affect performance?

In some facilities, IPA passes through the filter only once before use. In others, it is installed in a tank recirculation loop. Recirculation generally achieves slightly higher removal efficiency because the fluid passes through the filter multiple times. Single-pass filtration shows slightly lower performance but still above 95% removal efficiency in our testing.

The choice depends on the customer’s system design and contamination control strategy.

Many advanced cleaning processes use heated IPA. How does temperature affect organic impurity removal?

At higher temperatures, removal becomes more challenging. In some processes, IPA is heated to reduce surface tension. However, at elevated temperatures, organic impurities may become more chemically active or more stable in solution, which can reduce adsorption efficiency.

So, compared to room temperature, impurity removal can be more difficult at higher temperatures.

Besides temperature, what other factors influence removal performance?

The baseline purity level of the IPA is also important. In very high quality IPA, there may be less contamination, so it is at a PPT level. These ultra-trace impurities may be more difficult to remove because they are harder to detect and characterize. In contrast, lower-quality IPA with higher contamination levels seem to be easier to treat because the impurities are present at higher concentrations and are easier to target.

As purity requirements increase for advanced chips, contamination control becomes more challenging. This current filter version is not the final solution; further development will likely be needed.

Looking ahead, what are the biggest challenges in organic contamination control?

So far, our research has focused mainly on linear hydrocarbon contamination. But customers may have many different types of organic impurities, possibly ten or more species including alcohols, ketones, and other organic compounds.

We are continuing to test removal performance for different types of organics. It is possible that different classes of organic impurities will require different filtration strategies. A single universal solution may not be sufficient.