Yokkaichi University

In this study, we present an initial experimental design for Bayesian optimization (BO) applied to the semiconductor process development. For efficient BO, it can be effective to draw initial sampling nodes that cover the search space as uniformly as possible. In particular, in process optimization, it is necessary to appropriately place the sampling nodes within the high-dimensional search space consisting of multiple process parameters. To address this issue, we propose a space-filling Latin hypercube design (LHD) with a small fill distance and a large separation radius based on simulated annealing. Compared with Maximin LHD and Sobol’ design, the proposed design exhibits the smallest fill distance and a large separation radius, which is equivalent to that of Maximin LHD. Through an example focused on optimizing high aspect ratio hole etching, we demonstrate that the proposed design effectively reduces the number of experiments required for the convergence of BO compared to conventional designs. Additionally, it can be applied to various processes such as chemical vapor deposition, atomic layer deposition and wet etching, among others.

Abstract Line width roughness (LWR) in EUV lithography is known to be caused by “Stochastic effects”, such as the chemical composition distribution within the resist thin film and the non-uniformity of chemical reactions. The compositions of chemically amplified resists before coating film on silicon wafer typically include a base polymer, a photoacid generator, a quencher, and a solvent. In this paper, we investigated about solvent effect, which is the main volume of the resist solution. We investigated solvent effect of resist solution by dynamic light scattering (DLS) measurement. The particle size of polymer in several solvents revealed diameters from 4 to 6 nm. The solvent effect in thin film was measured by resonant soft X-ray scattering (RSoXS) method. It was found the distribution of resist compositions differs depending on the type of solvents and the pre-bake temperatures. These results suggested the selection of resist solvent may also contribute to reducing LWR.

The demand for high-density interconnects in semiconductor applications has increased with advancements in generative AI and high-speed communication technologies. This paper presents the development of a novel alkaline-developable photosensitive polyimide (PI) designed for re-distribution layers in next-generation interposers. To address key challenges such as large substrate warpage and sub- <tex>$2 \mu ~\mathrm{m}$</tex> fine-pitch patterning, a Novel PI with a unique pre-imidized design was developed. The Novel PI achieved ultra-high resolution with an aspect ratio of 3.0 or higher and enables low temperature curing at <tex>$170^{\circ} \mathrm{C}$</tex> thereby reducing wafer warpage. Experimental and simulation results indicate that the warpage on 12 -inch wafer using the Novel PI is 40 % less than that of conventional PI. Furthermore, low shrinkage rate of 12 % through cure can decrease the surface topography when coated and cured on Cu traces, which helps stable multi-layer stacking. The double-stack structure using the Novel PI with <tex>$2 \mu ~\mathrm{m}$</tex>-L/S Cu trace was demonstrated successfully and pass reliability tests, including b-HAST and thermal cycling. These results indicate that the Novel PI is a suitable material for re-distribution layers in next-generation interposers.

ABSTRACT Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) is a powerful tool for imaging molecules in biological tissues owing to its high spatial resolution and sensitivity. Effective detection of key molecules in a sample is crucial for detailed evaluation of complex samples such as tissues. In this study, a target is a biomolecule, allantoin (C 4 H 6 N 4 O 3 ), and the allantoin [M + H] + and [M‐H] − are adequately detected using ToF‐SIMS with a Bi cluster ion beam from an allantoin control sample. However, the detection of ions related to allantoin permeated in human skin tissue is not straightforward because there are interfering mass peaks in the ToF‐SISM spectra of control skin samples that make allantoin detection challenging, and the allantoin fragment ions have the same chemical structure as the fragment ion from other biomolecules in the tissue. In order to sufficiently detect the allantoin‐related ions, we focused on ion beams with a higher ionization yield, such as gas cluster ion beams (GCIBs). As a result, a ToF‐SIMS with water GCIB was significantly more effective in detecting the allantoin [M + H] + and [M‐H] − in the skin samples in both positive and negative ion spectra. The results revealed that the water GCIB approach is better suited for studying biological samples, as it effectively distinguishes the mass peaks of allantoin related ions using ToF‐SIMS.

We compared the results of Legionella pneumophila detection in cooling tower water samples using Legiolert and the conventional plate culture method. Both 1 mL and 10 mL volumes of cooling tower water samples were analyzed using Legiolert. The concordance rate of the Legiolert-1 mL test and the plate culture method was 86.7%. The Legiolert-10 mL test and the plate culture method showed 85.0% concordance. Legiolert would be effective for hygiene control in cooling towers because it can easily detect viable L. pneumophila in cooling tower water and produces results comparable to the conventional plate culture method.

Vertical, organic, light‐emitting transistors (VOLETs) combine three of the four essential components of an active matrix lightemitting diode (AMOLED) pixel ‐ the drive transistor, the storage capacitor, and the OLED stack ‐ into a single, highly‐stable, selfemissive structure. VOLETs can be manufactured on amorphous silicon (a‐Si) thin‐film transistor (TFT) backplanes to enable lowcost AMOLED displays with improved brightness and lifetime characteristics. We report on the current status of VOLET development and prospective impact on the active‐matrix display industry.

Homogeneous catalysis using transition metal complexes typically employs a single supporting ligand, which can prove inadequate for diverse requirements at different steps of the catalytic cycle. To navigate this inadequacy, researchers are exploring a mixed-ligand approach, which involves the sequential interaction of two distinct ligands with the metal, fostering various product-forming steps within the same catalytic cycle. Herein, we introduce the successful application of this mixed-ligand approach to the palladium-catalyzed direct arylation of heteroarenes with aryl halides. The key to this success is the use of XPhos and P(2-MeOC6H4)3 (L1) as supporting ligands. This mixed-ligand catalyst facilitates direct arylation with readily available but less reactive aryl chloride, yielding the coupling products in high yield (up to >99%). Moreover, the catalyst enables sequential reactions that leverage the differential reactivity between C–Cl and C–Br bonds, producing π-extended small molecules in a one-pot synthesis. The catalyst also proves effective in direct arylation polymerization (DArP) with dichloroarenes, yielding π-conjugated polymers with well-controlled structures and high molecular weights (Mn up to 191000). Our mechanistic investigations into the mixed-ligand catalyst highlight that XPhos and L1 contribute to activating the C–Cl bond in aryl chlorides and the C–H bonds in heteroarenes, respectively.