Resistless EUV lithography: Photon-induced oxide patterning on silicon

Lithography-Free Chalcogenide Canvas for Photonic Integrated Circuits

Chalcogenide integrated photonic devices have garnered widespread attention due to their excellent wideband transparency. However, current fabrication methods primarily rely on mature silicon-based CMOS processes, which are not readily adaptable to chalcogenides, significantly hindering their development. Here, we present a flexible fabrication approach that judiciously leverages the intrinsic oxidation susceptibility of chalcogenide materials, transforming chalcogenide thin films into a lithography-free canvas for versatile integrated photonic devices. Using antimony sulfide (Sb2S3) as an example, we demonstrate low-threshold laser-induced local oxidation using a continuous laser, achieving a refractive index modulation exceeding 0.7 and a spatial resolution of 0.6 μm in the near-infrared region. This technique enables flexible fabrication of various chalcogenide photonic devices. Based on this technique, we further fabricate a dynamic planar Fresnel zone plate, demonstrating dynamic beam focusing by exploiting the phase-change property of Sb2S3, as well as high-precision spatial-spectral reconstruction at near-infrared using a millimeter-scale chalcogenide metasurface array. Our findings reveal the potential of chalcogenide thin films as a promising canvas for advanced photonic applications, providing a simplified and versatile fabrication pathway that significantly advances the field of chalcogenide integrated photonic devices.

Etchant-Free Dry-Developable Extreme Ultraviolet Photoresist Materials Utilizing N-Heterocyclic Carbene-Metal Complexes

Extreme ultraviolet (EUV) lithography has enabled significant reductions in device dimensions but is often limited by capillary force-driven pattern collapse in conventional wet processes. Recent dry-development approaches, while promising, frequently require toxic etchants or specialized equipment, limiting their broader applicability and highlighting the need for more sustainable, cost-effective alternatives. In this study, highly reactive, etchant-free dry-developable EUV photoresists using N-heterocyclic carbene (NHC)-based metal-ligand complexes, achieving half-saturation at EUV doses of 8.5 or 27 mJ cm-2, are synthesized. A simple thermal dry development process is employed, utilizing a standard furnace to remove unexposed areas of the photoresist, leading to 80 nm resolution with line-edge roughness (LER) comparable to wet-developed patterns. Moreover, EUV-induced chemical reactions of the NHC metal-ligand complexes are investigated via EUV-photoelectron spectroscopy, near-edge X-ray absorption fine structures, X-ray photoelectron spectroscopy, and density functional theory. It is suggested that the high EUV sensitivity of the NHC metal-ligand complexes is attributed to branching polymerization reactions initiated by secondary electron and photoelectron generation. These EUV-sensitive, dry-developable NHC metal-organic photoresists offer a sustainable and economical alternative to conventional techniques, eliminating the need for toxic and corrosive etchants while achieving high-resolution nanopatterns through simple thermal treatment, thus advancing future nanofabrication technologies.

Sequentially photocatalytic degradation of mussel-inspired polydopamine: From nanoscale disassembly to effective mineralization

Mussel-inspired polydopamine (PDA) coating has been utilized extensively as versatile deposition strategies that can functionalize surfaces of virtually all substrates. However, the strong adhesion, stability and intermolecular interaction of PDA make it inefficient in certain applications. Herein, a green and efficient photocatalytic method was reported to remove adhesion and degrade PDA by using TiO2-H2O2 as photocatalyst. The photodegradation process of the PDA spheres was first undergone nanoscale disassembly to form soluble PDA oligomers or well-dispersed nanoparticles. Most of the disassembled PDA can be photodegraded and finally mineralized to CO2 and H2O. Various PDA coated templates and PDA hollow structures can be photodegraded by this strategy. Such process provides a practical strategy for constructing the patterned and gradient surfaces by the "top-down" method under the control of light scope and intensity. This sequential degradation strategy is beneficial to achieve the decomposition of highly crosslinked polymers.

Photon Momentum Enabled Light Absorption in Silicon

Photons do not carry sufficient momentum to induce indirect optical transitions in semiconducting materials, such as silicon, necessitating the assistance of lattice phonons to conserve momentum. Compared to direct bandgap semiconductors, this renders silicon a less attractive material for a wide variety of optoelectronic applications. In this work, we introduce an alternative strategy to fulfill the momentum-matching requirement in indirect optical transitions. We demonstrate that when confined to scales below ∼3 nm, photons acquire sufficient momentum to allow electronic transitions at the band edge of Si without the assistance of a phonon. Confined photons allow simultaneous energy and momentum conservation in two-body photon-electron scattering; in effect, converting silicon into a direct bandgap semiconductor. We show that this less-explored concept of light-matter interaction leads to a marked increase in the absorptivity of Si from the UV to the near-IR. The strategy provides opportunities for more efficient use of indirect semiconductors in photovoltaics, energy conversion, light detection, and emission.

Recent Advances in Metal-Oxide-Based Photoresists for EUV Lithography

Extreme ultraviolet lithography (EUVL) is a leading technology in semiconductor manufacturing, enabling the creation of high-resolution patterns essential for advanced microelectronics. This review highlights recent progress in inorganic metal-oxide-based photoresists, with a focus on their applications in EUVL. The unique properties of zinc-based, tin-oxygen, and IVB group inorganic photoresists are examined, showcasing their enhanced chemical reactivity and precise patterning capabilities. Key advancements include the development of zinc oxide and tin oxide nanoparticles, which demonstrate significant improvements in photon absorption and solubility under extreme ultraviolet exposure. Additionally, the review delves into the photochemical reactions of tin-oxygen clusters and the influence of various ligands on film density and cross-linking. The findings suggest that these inorganic photoresists not only improve photolithographic performance but also hold potential for broader applications, such as pyroelectric infrared sensors and 3D printing. Future research directions are outlined, including the optimization of process parameters, the exploration of new ligand and metal combinations, and the evaluation of the environmental benefits of inorganic photoresists over traditional organic ones. These advancements are poised to further enhance the resolution and patterning capabilities required for next-generation semiconductor devices.

Si-Containing Reverse-Gradient Block Copolymer for Inorganic Pattern Amplification in EUV Lithography

Although extreme ultraviolet lithography (EUVL) has emerged as a leading technology for achieving high quality sub-10 nm patterns, the insufficient pattern height of photoresist patterns remains a challenge. Directed self-assembly (DSA) of block copolymers (BCPs) is expected to be a complementary technology for EUVL due to its ability to form periodic nanostructures. However, for a combination with EUV patterns, it is essential to develop advanced BCP systems that are suited to inorganic-containing EUV photoresists and offer improved resolution limits, pattern quality, and etch resistance. Here, we report a reverse-gradient BCP system, poly[(styrene-gradient-pentafluorostyrene)-b-4-tert-butyldimetilsiloxystyrene] [P(S-g-PFS)-b-P4BDSS] BCP, which enables universally vertically oriented lamellae even in the absence of a neutral layer, while also containing a Si-containing block with high etch resistance. The gradient block, characterized by a gradual compositional transition from the block junction to the tail, plays a crucial role in creating an adequate surface energy contrast that energetically drives the formation of perpendicular lamellae without neutral layer. When used as a pattern height enhancement layer in EUVL, a high aspect ratio (3.29) of patterns was achieved, thereby offering a supplementary solution for next-generation EUVL.

EUV-induced hydrogen desorption as a step towards large-scale silicon quantum device patterning

Atomically precise hydrogen desorption lithography using scanning tunnelling microscopy (STM) has enabled the development of single-atom, quantum-electronic devices on a laboratory scale. Scaling up this technology to mass-produce these devices requires bridging the gap between the precision of STM and the processes used in next-generation semiconductor manufacturing. Here, we demonstrate the ability to remove hydrogen from a monohydride Si(001):H surface using extreme ultraviolet (EUV) light. We quantify the desorption characteristics using various techniques, including STM, X-ray photoelectron spectroscopy (XPS), and photoemission electron microscopy (XPEEM). Our results show that desorption is induced by secondary electrons from valence band excitations, consistent with an exactly solvable non-linear differential equation and compatible with the current 13.5 nm (~92 eV) EUV standard for photolithography; the data imply useful exposure times of order minutes for the 300 W sources characteristic of EUV infrastructure. This is an important step towards the EUV patterning of silicon surfaces without traditional resists, by offering the possibility for parallel processing in the fabrication of classical and quantum devices through deterministic doping.