Accelerating 3D Nanofabrication with Sensitive

Two-photon direct-writing laser lithography, or TPL, is an advanced technology used to create tiny nanoscale structures. It works by using special materials known as photoresists, which change their chemical properties when exposed to light. These materials uniquely absorb laser light, providing precise control while exposed to laser beams. Unlike conventional ultraviolet (UV) photolithography, which uses light to create images, TPL can directly create complex three-dimensional (3D) shapes, including features such as protrusions and pendants, with a resolution smaller than the width of a human hair. However, the production speed of TPL cannot match that of UV lithography. To speed up the TPL process, highly sensitive photoresists are needed. Today, the classic SU-8 series of epoxy photoresists remains a popular choice due to its many advantages, such as high depth-to-width ratio, minimal shrinkage and no problems with oxygen interference during processing. However, the fabrication of cationic photoresists such as SU-8 typically takes longer and results in less detailed structures compared to free radical-based photoresists, which may limit their application in complex microdevices.

Recently, a research team led by Professor Cuifang Kuang from the Zhejiang Laboratory of Zhejiang University made a significant breakthrough by developing a new type of cationic epoxy photoresist. This innovative material demonstrated approximately 600 times greater sensitivity to two-photon laser irradiation than traditional SU-8 photoresist due to a unique bimolecular sensitization system. Professor Kuang explains: “We demonstrated fabricated 3D structures with fine features of less than 200 nanometers (nm) and high writing speeds of 100 millimeters per second (mm/s) using nanogratings to demonstrate the potential application for high-throughput nanofabrication of microscopic 3D images. devices.” Their findings were published in Advanced functional materials September 6, 2024

The bimolecular photosensitized initiation system developed in the study effectively separates the processes of light absorption and energy transfer, increasing the material’s ability to absorb light. The researchers introduced 5-nitroacenaphthene, a photosensitizer that broadens the absorption spectrum to capture light wavelengths up to 430 nm. By combining this photosensitizer with a pyrazoline-based sulfonium salt as a photoacid generator (PAG) and a polyfunctional epoxy resin as a building block, the team created a new cationic photoresist called TP-EO. This innovative material can achieve an impressive lithography speed of 100 mm/s and produce fine parts with a minimum width of about 170 nm. TP-EO’s performance in speed and resolution is better than other existing cationic photoresists. To demonstrate the potential application of TP-EO resin, the researchers successfully fabricated a topological liquid diode with nanoscale characteristics. Professor Kuang expresses optimism about the future, stating: “Such a high-performance TP-EO photoresist is suitable for the scalable fabrication of complex architectures for various applications such as optical gratings, diffraction elements, microelectromechanical systems, microfluidic devices, and tissue engineering scaffolds.”

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Link

DOI: https://doi.org/10.1002/adfm.202409859.