Modular Synthesis of Phthalaldehyde Derivatives Enabling Access to Photoacid Generator-Bound Self-Immolative Polymer Resists with Next-Generation Photolithographic Properties

Single-Component High-Resolution Dual-Tone EUV Photoresists Based on Precision Self-Immolative Polymers

Electron beam (EB) and extreme ultraviolet (EUV) lithography are advanced techniques capable of achieving sub-10 nm resolutions, critical for fabricating next-generation nanostructures and semiconductor devices. However, developing EUV photoresists that meet all demands for resolution, line edge roughness (LER), and sensitivity (RLS) remains a significant challenge. Herein, we introduce high-performance photoresists based on single-component self-immolative polymers (SIPs) with inherent signal amplification via cascade degradation. These SIPs function as dual-tone photoresists under both EB and EUV lithography, with performance primarily determined by the exposure dose. Lithographic evaluations show that discrete SIPs provide significant improvements over disperse counterparts, achieving higher resolution and reduced LER. Specifically, a discrete SIP with a DP of 12 produces a line-space pattern with a resolution of approximately 18 nm and an LER of 1.8 nm, compared to 21 nm resolution and 2.5 nm LER for disperse SIPs. Additionally, these SIP-based photoresists, enriched with aromatic structures, exhibit excellent etch resistance. The single-component nature and potential to address the RLS trade-off underscore the promise of discrete SIPs for EUV lithography.

Aqueous Developable and CO2-Sourced Chemical Amplification Photoresist with High Performance

Seeking high-performance photoresists is an important item for semiconductor industry due to the continuous miniaturization and intelligentization of integrated circuits. Polymer resin containing carbonate group has many desirable properties, such as high transmittance, acid sensitivity and chemical formulation, thus serving as promising photoresist material. In this work, a series of aqueous developable CO2-sourced polycarbonates (CO2-PCs) were produced via alternating copolymerization of CO2 and epoxides bearing acid-cleavable cyclic acetal groups in the presence of tetranuclear organoborane catalyst. The produced CO2-PCs were investigated as chemical amplification resists in deep ultraviolet (DUV) lithography. Under the catalysis of photogenerated acid, the acetal (ketal) groups in CO2-PC were hydrolysed into two equivalents of hydroxyl groups, which change the exposed area from hydrophobicity to hydrophilicity, thus enabling the exposed area to be developed with water. Through normalized remaining thickness analysis, the optimal CO2-derived resist achieved a remarkable sensitivity of 1.9 mJ/cm2, a contrast of 7.9, a favorable resolution (750 nm, half pitch), and a good etch resistance (38 % higher than poly(tert-butyl acrylate)). Such performances outperform commercial KrF and ArF chemical amplification resists (i.e., polyhydroxystyrene-derived and polymethacrylate-based resists), which endows broad application prospects in the field of DUV (KrF and ArF) and extreme ultraviolet (EUV) lithography for nanomanufacturing.

Mechanisms of acid generation from ionic photoacid generators for extreme ultraviolet and electron beam lithography

Photoacid generators (PAGs) are important components of chemically amplified resists. The properties of PAGs directly affect the sensitivity of photoresists, line edge roughness, and resolution. Understanding the photoacid generation process in extreme ultraviolet (EUV) and electron beam (EB) lithography is helpful for photoresist design. However, the microscopic mechanisms remain largely unclear and the large variety in the molecular structure of PAGs presents a challenge to overcome. In this work, we investigate the microscopic processes of photoacid production of ionic PAGs for EUV and EB lithography. The PAG dissociation pathway is found to depend on the molecular structure and conformations. The processes of photoacid production and by-product generation are also revealed. The results contribute to a better understanding of the photochemical reactions in EUV and EB lithography, providing insights into the molecular design of novel PAGs and photoresists.

Click to Self-immolation: A "Click" Functionalization Strategy towards Triggerable Self-Immolative Homopolymers and Block Copolymers

Self-immolative polymers (SIPs) are a class of degradable macromolecules that undergo stimuli-triggered head-to-tail depolymerization. However, a general approach to readily end-functionalize SIP precursors for programmed degradation remains elusive, restricting access to complex, functional SIP-based materials. Here we present a "click to self-immolation" strategy based on aroyl azide-capped SIP precursors, enabling the facile construction of diverse SIPs with different trigger units through a Curtius rearrangement and alcohol/thiol-isocyanate "click" reaction. This strategy is also applied to polymer-polymer coupling to access fully depolymerizable block copolymer amphiphiles, even combining different SIP backbones. Our results demonstrate that the depolymerization can be actuated efficiently under physiologically-relevant conditions by the removal of the trigger units and ensuing self-immolation of the p-aminobenzyl carbonate linkage, indicating promise for controlled release applications involving nanoparticles and hydrogels.

Cyclic Polyesters with Closed-Loop Recyclability from A New Chemically Reversible Alternating Copolymerization

Polyesters with both cyclic topology and chemical recyclability are attractive. Here, the alternating copolymerization of cyclic anhydride and o-phthalaldehyde to synthesize a series of cyclic and recyclable polyesters are reported for the first time. Besides readily available monomers, the copolymerization is carried out at 25 °C, uses common Lewis/Brønsted acids as catalysts, and achieves high yields within 1 h. The resulting polyesters possess well-defined alternating sequences, high-purity cyclic topology, and tunable structures using distinct two monomer sets. Of interest, the copolymerization manifests obvious chemical reversibility as revealed by kinetic and thermodynamic studies, making the unprecedented polyesters easy to recycle to their distinct two monomers in a closed loop at high temperatures. This work furnishes a facile and efficient method to synthesize cyclic polyesters with closed-loop recyclability.

Emerging Trends in the Chemistry of End-to-End Depolymerization

Over the past couple of decades, polymers that depolymerize end-to-end upon cleavage of their backbone or activation of a terminal functional group, sometimes referred to as "self-immolative" polymers, have been attracting increasing attention. They are of growing interest in the context of enhancing polymer degradability but also in polymer recycling as they allow monomers to be regenerated in a controlled manner under mild conditions. Furthermore, they are highly promising for applications as smart materials due to their ability to provide an amplified response to a specific signal, as a single sensing event is translated into the generation of many small molecules through a cascade of reactions. From a chemistry perspective, end-to-end depolymerization relies on the principles of self-immolative linkers and polymer ceiling temperature (Tc). In this article, we will introduce the key chemical concepts and foundations of the field and then provide our perspective on recent exciting developments. For example, over the past few years, new depolymerizable backbones, including polyacetals, polydisulfides, polyesters, polythioesters, and polyalkenamers, have been developed, while modern approaches to depolymerize conventional backbones such as polymethacrylates have also been introduced. Progress has also been made on the topological evolution of depolymerizable systems, including the introduction of fully depolymerizable block copolymers, hyperbranched polymers, and polymer networks. Furthermore, precision sequence-defined oligomers have been synthesized and studied for data storage and encryption. Finally, our perspectives on future opportunities and challenges in the field will be discussed.

Chemically Amplified Molecular Glass Photoresist Regulated by 2-Aminoanthracene Additive for Electron Beam Lithography and Extreme Ultraviolet Lithography

2-Aminoanthracene was used as a nucleophilic additive in a molecular glass photoresist, bisphenol A derivative (BPA-6-epoxy), to improve advanced lithography performance. The effect of 2-aminoanthracene on BPA-6-epoxy was studied by electron beam lithography (EBL) and extreme ultraviolet lithography (EUVL). The result indicates that the additive can optimize the pattern outline by regulating epoxy cross-linking reaction, avoiding photoresist footing effectively in EBL. The EUVL result demonstrates that 2-aminoanthracene can significantly reduce line width roughness (LWR) for HP (Half-Pitch) 25 nm (from 4.9 to 3.8 nm) and HP 22 nm (from 6.9 to 3.0 nm). The power spectrum density (PSD) curve further confirms the reduction of roughness at medium and high frequency for HP 25 nm and the whole range of frequency for HP 22 nm, respectively. The study offers useful guidelines to improve the roughness of a chemically amplified molecular glass photoresist with epoxy groups for electron beam lithography and extreme ultraviolet lithography.

Rapid and Selective Photo-degradation of Polymers: Design of an Alternating Copolymer with an o-Nitrobenzyl Ether Pendant

The development of polymers with on-demand degradability is required to alleviate the current global issues on polymer-waste pollution. Therefore, we designed a vinyl ether monomer with an o-nitrobenzyl (oNBn) group as a photo-deprotectable pendant (oNBnVE) and synthesized an alternating copolymer with an oNBn-capped acetal backbone via cationic copolymerization with p-tolualdehyde (pMeBzA). The resultant alternating copolymer could be rapidly degraded into lower-molecular-weight compounds upon simple exposure to UV irradiation without any reactants or catalysts, while it was sufficiently stable toward heat and ambient light. This degradation proceeds via cleavage of the hemiacetal structure generated upon photo-deprotection of the oNBn pendant. The oNBn-peculiar degradability allowed the exclusive photo-degradation of the oNBnVE/pMeBzA segments in a diblock copolymer composed of oNBnVE/pMeBzA and benzyl vinyl ether (BnVE)/pMeBzA segments.