Empowering Semiconductor and Device Performance with Improved Point-of-Use Filtration

Advancements in photolithography enable semiconductor manufacturers to make improvements in process efficiency, wafer yield, and ultimately the devices purchased by end-users. Last year, Entegris focused in part on extreme ultraviolet (EUV) applications, the evolution of chemically amplified resists (CARs), and their limitations in sensitivity, resolution, and line edge roughness (LER) when exposed to EUV radiation as influencers to wafer defects.

In a joint study with Inpria, imec, and Entegris, various point-of-use filters were studied in a normalized test to measure the correlation between key filter factors and bridge defects. This research was presented in a poster at SPIE Advanced Lithography + Patterning 2024 and served as a jumping-off point for much of the research we’ll present at this year’s conference. Here are some of the learnings we’re most excited about.

Tailoring Membrane Characteristics to Improve Photoresist Performance

In our research with Inpria and imec, we discovered two new UPE membranes which showed the greatest improvements based on unique membrane design characteristics. These included continued shrinkage of physical pore size, pore size uniformity, the overall morphology of the membrane, and membrane thickness.

Each of these elements are levers that membrane and device designers use to find optimized combinations to improve material purity. The right combination of elements can solve contamination challenges with each resist and within the specific application conditions each tool presents.

Membrane Concept #1: Enhancing Tortuosity

The first successful concept involved enhancing membrane tortuosity while keeping membrane film thickness constant. In other words, this membrane still relies on sieving to remove potential contaminants. Its effectiveness is increased by creating more convoluted paths within the membrane. The longer pathway is associated with a greater likelihood that a contaminant particle will become trapped.

In addition to this advantage, the first successful filter design exhibits smaller pore sizes. This means that the filter has a greater chance of screening out larger particles. Additionally, the reduced pore size ensures that different samples of the same membrane will perform more consistently. In our study, this membrane concept beat two other membranes in terms of reducing bridge defects.

Membrane Concept #2: Targeting Contamination from Metal Oxide Resists (MORs)

In a related study, Entegris tested UPE filter designs against Inpria MORs. This chemistry improves on traditional CARs in terms of sensitivity, resolution, and LER when exposed to EUV. We tested a group of filters, including Concept #1 above and a standard 3 nm UPE filter as the control. Our other new design introduced the concept of depth, which allowed us to explore more mechanisms for filtration. These included impaction, interception, and size exclusion.

After testing, we found that Concept #1 achieved a 20% improvement in defectivity over traditional 3 nm UPE, while our second design achieved an improvement of 10%. While we weren’t able to achieve a definitive answer as to why these designs performed better, we’re developing a theory that the ability to retain soft particles like gel aggregates plays a critical role in membrane effectiveness.

With their own nuances, Concept #1 and #2 can be applied to match the conditions that meet the needs of each fab application and resist formulation. To learn more, watch the short summary from Entegris’ Photo Applications Manager, Tetsu Kohyama.

Anticipating Further Progress in Filtration Research

As we all look forward to the SPIE Lithography + Patterning 2025 conference, we’re excited to bring our latest work about EUV, CARs, MORs, membrane design, device optimization, and more. By optimizing an advanced lithography process, we can realize chipmakers’ goals for increased yields and reduced defectivity. We can’t wait to see what’s possible.

To learn more about Entegris’ photolithography solutions, visit us at SPIE or contact our customer service representatives today