Acceleration of 3D nanofabrication using highly sensitive cationic photoresists

Two-photon laser direct write lithography (TPL) is a state-of-the-art technique used to create nanoscale structures. It works by utilizing a specific material known as a photoresist, which changes its chemical properties when exposed to light. These materials absorb laser light in a unique way, allowing precise control during exposure to laser light.

Unlike traditional ultraviolet (UV) photolithography, which uses light to create images, TPL can create complex three-dimensional images, including features such as overhangs and hanging elements, at a resolution smaller than the width of a human hair. (3D) shapes can be constructed directly. However, the production speed of TPL cannot match that of UV lithography. Highly sensitive photoresists are essential to speed up the TPL process.

To this day, the classic SU-8 epoxy photoresist series remains a popular choice due to its many advantages, including high depth-to-width ratio, minimal shrinkage, and no problems with oxygen interference during processing. I am. However, cationic photoresists such as SU-8 generally take longer to manufacture and have less detailed structures than free radical-based photoresists, which can limit their use in creating complex microdevices. There is a gender.

Recently, a research team led by Professor Cuifan Kuang from the Zhejiang Laboratory of Zhejiang University has made great progress by developing a new type of cationic epoxy photoresist. This innovative material showed approximately 600 times higher sensitivity than conventional SU-8 photoresist to two-photon laser exposure, thanks to a unique bimolecular sensitization system.

The research results are published in the journal Advanced Functional Materials.

Professor Quan explains: “We use nanogratings to demonstrate 3D fabricated structures with features smaller than 200 nanometers (nm) and fast writing speeds of 100 millimeters per second (mm/s), achieving microscopic We demonstrated the potential for application in high-throughput nanofabrication of 3D devices. ”

The bimolecular photosensitized initiation system developed in this study effectively separates the processes of light absorption and energy transfer and enhances the light absorption ability of the material. The researchers introduced 5-nitroacenaphthene, a photosensitizer that broadens the absorption spectrum, allowing it 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 multifunctional epoxy as a building block, the researchers created a new cationic photoresist called TP-EO. has been created. This innovative material is capable of achieving impressive lithography speeds of 100 mm/s and can produce fine features with a minimum width of approximately 170 nm. The performance of TP-EO is superior to other existing cationic photoresists in terms of speed and resolution.

To demonstrate the potential applications of TP-EO resin, researchers successfully fabricated topological liquid diodes with nanoscale features.

Professor Quan said, “Such high-performance TP-EO photoresists are suitable for scalable fabrication of complex architectures for a variety of applications, including optical gratings, diffractive elements, microelectromechanical systems, microfluidic devices, and tissue engineering scaffolds. ”.