3D Sub‐Diffraction Printing by Multicolor Photoinhibition Lithography: From Optics to Chemistry

Abstract

Photoinhibition lithography (PIL) is a nanoscale fabrication technique that uses multicolor visible light to enable the printing of arbitrary 3D structures beyond the diffraction limit. Photoinhibition allows the control and confinement of the exposed region for photoinitiation during the photolithographic process, thus improving the resolution of existing lithographic techniques, such as direct laser writing. Because PIL enables super-resolution 3D printing, it has a multitude of applications. In this review, practical applications of PIL in the areas of photonics, data storage, and biotechnology are highlighted; in addition, its unique features are revealed. The theory and recent advances in PIL for sub-diffraction printing and high-throughput fabrication are also discussed. Besides, challenges and tentative solutions are discussed with the hope of providing a preliminary roadmap for technological breakthroughs in PIL to enable developments of resolution and throughput.

Dip-In Photoresist for Photoinhibited Two-Photon Lithography to Realize High-Precision Direct Laser Writing on Wafer

“…Because of this challenge, the concept of photoinhibited two-photon lithography (PI-TPL) was introduced. As one kind of PI-TPP, stimulated emission depletion inspired TPL (STED-TPL) comes from the field of super-resolution STED microscopy. , The basic concepts behind STED-TPL are to selectively activate the polymerization of the photoresist. Generally, the near-infrared femtosecond laser (used as the excitation) for TPL is overlaid with a shaped continuous laser (which acts as inhibition light) that has a light intensity distribution where the maximum is at its periphery and the minimum is in the center. , Using this approach means that only the photoresist located at the center of a superimposed spot undergoes polymerization, while polymerization of the photoresist at the periphery of the focal spot is inhibited due to the shaped inhibition light. , Therefore, diffraction-unlimited optical lithography can be obtained via STED-TPL by increasing the light intensity of the shaped inhibition light .…”

“…It is noteworthy that the initiator used in this photoresist is highly significant; that is, the wavelength of the excitation beam and inhibition beam should be equal to a half of the energy gap between S 0 –S 1– n (corresponding to UV–vis absorption) and S 1 –S Vibration–Rotation (corresponding to fluorescence emission), respectively. Over the past decades, tremendous efforts have been pursued to find the ultimate critical dimensions of STED-TPL, and remarkable features sizes as low as 50 nm have been reported. ,, …”

“…As one kind of PI-TPP, stimulated emission depletion inspired TPL (STED-TPL) comes from the field of super-resolution STED microscopy. 13,14 The basic concepts behind STED-TPL are to selectively activate the polymerization of the photoresist. Generally, the near-infrared femtosecond laser (used as the excitation) for TPL is overlaid with a shaped continuous laser (which acts as inhibition light) that has a light intensity distribution where the maximum is at its periphery and the minimum is in the center.…”

“…Over the past decades, tremendous efforts have been pursued to find the ultimate critical dimensions of STED-TPL, and remarkable features sizes as low as 50 nm have been reported. 13,15,20 Unfortunately, because of the lack of the refractive-indexmatched photoresist (i.e., Rim-P), early works on STED-TPL had to use a transparent substrate, in which the objective lens must be immersed into a refractive-index-matched oil 1.518 for an oil mode) rather than a photoresist. This enabled the elimination of optical aberrations alongside an improved numerical aperture.…”

Nanomicelles Array for Ultrahigh‐Density Data Storage

“…[ 20 ] These techniques produce nanomemory cells with adjustable dimensions and high stabilities, which can be extended to integrated architectures to produce high‐density arrays. However, device fabrication often requires complex and challenging lithography techniques (e.g., photolithography, [ 21 ] ultraviolet nanoimprint lithography, [ 22 ] and electron‐beam lithography [ 23 ] ), which are limited by their characteristic resolutions, and can lead to mechanical delamination of the cell layers and contamination by solvents or resins. In contrast, the bottom‐up approach involves the pre‐preparation of nanomemory cells and their subsequent assembly into nano devices, thereby avoiding the issues related to the complex top‐down approach.…”