Targeting Defect Sources in NTD CARs: Filtration Strategies for Single-Print EUV Lithography

Achieving single-print capability with high-NA EUV scanners is a critical milestone for advanced logic device manufacturing. Chemically amplified resists (CARs), especially in negative-tone development (NTD) processes, are prone to scum and bridge defects caused by polymer aggregation and incomplete resist clearance. These defects threaten pattern fidelity and yield, and are exacerbated by both stochastic and traditional contamination sources.

Experiment:
To address these challenges, Entegris evaluated two surface-modified UPE filter membranes, Functionalized UPE A and Functionalized UPE B, designed to target specific polymer components in NTD CARs. The study assessed their impact on polymer retention, dispersity index (PDI), and defectivity.

Using a Fujifilm NTD CAR co-polymer, both filters were tested under identical conditions. Analytical methods included UV-Vis spectroscopy, GPC, and H-NMR to measure polymer adsorption, molecular weight, and unit composition. Defectivity was evaluated using AEI inspections on wafers exposed with a 44 nm pitch on an ASML NXE3400 EUV scanner.

Results:

Functionalized UPE B: Higher adsorption of high-molecular-weight polymers. Improved PDI, promoting better polymer homogeneity. Resulted in higher bridge defect counts.
Functionalized UPE A: More selective adsorption of phenol-rich polymers (Unit A). Lower defect density despite less PDI improvement.

What’s Next:
This study reveals that while stochastic defect mitigation via PDI improvement is important, traditional defect sources—particularly phenol-rich polymers—remain dominant in NTD CAR defectivity. Filtration strategies must therefore target both high-molecular-weight and chemically active polymer components to optimize EUV resist performance.

Future work will focus on refining membrane functionality to balance stochastic suppression with targeted contaminant removal, supporting the industry's push toward reliable single-print EUV patterning at sub-3 nm nodes.

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