Polyarylenesulfonium Salt as a Novel and Versatile Nonchemically Amplified Negative Tone Photoresist for High-Resolution Extreme Ultraviolet Lithography Applications

Unexpected MoO3/Al Interfacial Reaction Lowering the Performance of Organic Solar Cells upon Thermal Annealing and Methods for Suppression

Understanding the degradation mechanism and improving the thermal stability of organic solar cells are essential for this new photovoltaic technology. In this work, we found that the high-performance polymer solar cells suffer from significant performance decay upon thermal annealing at 150 °C owing to the fast decay of VOC and FF. We demonstrated that the thermal annealing process leads to a severe chemical reaction of MoO3 with Al, forming an Al2O3 barrier layer at the MoO3/Al interface, which lowers the built-in potential (Vbi) of the cells and consequently reduces charge collection efficiency. Inserting a thin C60 interlayer between MoO3/Al slows the chemical reaction of MoO3 with Al, which ensures a high Vbi and charge collection efficiency for the annealed MoO3/C60/Al cells. Such a protection effect of the C60 layer in improving device performance against thermal annealing was also confirmed for cells with different polymer photoactive layers and metal electrodes, demonstrating the generality of the interfacial degradation of the cells and the protection effect of the C60 layer. Finally, we demonstrated that the inverted polymer solar cells with the C60-modified anode showed almost no performance decay upon high-temperature hot-press encapsulation, demonstrating excellent heat tolerance of this new device structure.

Enhanced Lithography Performance with Imino/Imido Benzenesulfonate Photoacid Generator-Bound Polymer Resists

The inherent acid diffusion during post-exposure baking poses significant challenges in balancing resolution, line-edge roughness, and sensitivity (RLS), thereby constraining the performance of chemically amplified photoresists (CARs) in advanced lithography. This study introduces a novel series of alkene-functionalized imino/imido benzenesulfonate photoacid generators (PAGs), characterized by their solubility, thermal stability, and polymerization attributes. These derivatives can copolymerize with acrylates and methacrylates to form PAG-bound copolymers, integrating non-ionic PAG units and acid-cleavable bulky alicyclic substituents, facilitating their use as "single-component" resists devoid of additives. Upon exposure to electron beams or ultraviolet radiation, the sulfonamide esters undergo N─O bond scission, producing photoacids that catalyze the deprotection of acidolytic groups. Compared to PAG-blended systems, these PAG-bound systems curtail acid diffusion by generating long-chain sulfonic acids, while preserving high sensitivity. The formulated single-component CARs demonstrate superior resolution and roughness, achieving a minimum linewidth of 42 nm at an electron beam dose of 73 µC cm- 2. This research provides a rational design for polymerizable imino/imido benzenesulfonate PAGs and single-component CARs, offering a viable solution to the RLS problem.

A novel non-chemically amplified resist based on polystyrene-iodonium derivatives for electron beam lithography

To break the resolution limitation of traditional resists, more work is needed on non-chemically amplified resists (non-CARs). Non-CARs based on iodonium salt modified polystyrene (PS-I) were prepared with controllable molecular weight and structure. The properties of the resist can be adjusted by the uploading of iodonium salts on the polymer chain, the materials with a higher proportion of iodonium salts show better lithography performance. By comparing contrast curves and quality of the lithographic patterns, the optimum developing condition of 4-methyl-2-pentanone and ethyl alcohol (v:v = 1:7) was selected. The high-resolution stripes of 15 nm half-pitch (HP) can be achieved by PS-I0.58in e-beam lithography (EBL). PS-I0.58shows the advanced lithography performance in the patterns of 16 nm HP and 18 nm HP stripes with low line edge roughness (3.0 nm and 2.4 nm). The resist shows excellent potential for further pattern transfer, the etch selectivity of resist PS-I0.58to the silicon was close to 12:1. The lithographic mechanism of PS-I was investigated by experimental and theoretical calculation, which indicates the polarity of materials changes results in the solubility switch. This work provides a new option and useful guidelines for the development of high-resolution resist.

Sulfonium-Functionalized Polystyrene-Based Nonchemically Amplified Resists Enabling Sub-13 nm Nanolithography

Nonchemically amplified resists based on triphenyl sulfonium triflate-modified polystyrene (PSTS) were prepared by a facile method of modification of polystyrene with sulfonium groups. The uploading of the sulfonium group can be well-controlled by changing the feed ratio of raw materials, resulting in PSTS_0.5 and PSTS_0.7 resists with sulfonium ratios of 50 and 70%, respectively. The optimum developer (methyl isobutyl ketone/ethanol = 1:7) is obtained by analyzing contrast curves of electron beam lithography (EBL). PSTS_0.7 exhibits a better resolution (18 nm half-pitch (HP)) than the PSTS_0.5 resist (20 nm HP) at the same developing conditions for EBL. This novel resist platform was further evaluated by extreme ultraviolet lithography, and patterning performance down to 13 nm HP at a dose of 186 mJ cm^-2 with a line edge roughness of 2.8 nm was achieved. Our detailed study of the reaction and patterning mechanism suggests that the decomposition of the polar triflate and triphenyl sulfonium groups into nonpolar sulfide or polystyrene plays an important role in the solubility switch.

Regioselective C-H Sulfanylation of Aryl Sulfoxides by Means of Pummerer-Type Activation

A regioselective C-H sulfanylation of aryl sulfoxides with alkyl aryl sulfides in the presence of acid anhydride was developed, which resulted in the formation of 1,4-disulfanylarenes after dealkylation of initially formed sulfonium salts. The reaction began with Pummerer-type activation of aryl sulfoxides followed by nucleophilic attack of alkyl aryl sulfides. The nucleophilic attack occurred exclusively at the para positions, or at specific positions in case the para position was not available, under perfect control by the dominating sulfoxide directors regardless of any other substituents. The initially formed aryl sulfonium salts were isolable and usefully served as aryl halide surrogates for palladium-catalyzed arylation with sodium tetraarylborates.