Tetramethylammonium Hydroxide Solution Research Articles

Effect of Wet Etching on AlGaN‐Based Ultraviolet‐B Laser Diodes Grown on Wet‐Etched Periodic AlN Nanopillars

The effect of wet etching on the characteristics of ultraviolet‐B (UV‐B) lasers fabricated on AlGaN templates grown as crystals or wet‐etched AlN nanopillars is compared in detail. Specifically, a tetramethylammonium hydroxide (TMAH) solution is used to form templates with AlN nanopillars of different diameters, followed by determining the dependence of the dislocation density in AlGaN crystals grown on the templates, the threshold power density (Pth) of an optically pumped UV‐B laser, and the threshold current density (Jth) of a UV‐B laser diode (LD) on the extent of etching. It is observed that the pillar diameter decreases almost linearly as the etching time with the TMAH solution increases. The dislocation density of AlGaN crystals grown on AlGaN templates is almost independent of the etching time. Meanwhile, Pth of the optically pumped UV‐B laser is almost halved upon etching with TMAH. Finally, the Jth of the UV‐B LD tends to decrease by 10%–20% upon etching. The optical gain is estimated by optical excitation; wet etching of AlN nanopillars with TMAH solution results in a larger optical gain at the same excitation intensity, indicating that nonradiative recombination centers, such as point defects, are reduced.

Piezoelectric Micromachined Ultrasonic Transducers with Micro-Hole Inter-Etch and Sealing Process on (111) Silicon Wafer

Piezoelectric micromachined ultrasound transducers (PMUTs) have gained significant popularity in the field of ultrasound ranging and medical imaging owing to their small size, low power consumption, and affordability. The scar-free “MIS” (micro-hole inter-etch and sealing) process, a novel bulk-silicon manufacturing technique, has been successfully developed for the fabrication of pressure sensors, flow sensors, and accelerometers. In this study, we utilize the MIS process to fabricate cavity diaphragm structures for PMUTs, resulting in the formation of a flat cavity diaphragm structure through anisotropic etching of (111) wafers in a 70 °C tetramethylammonium hydroxide (TMAH) solution. This study investigates the corrosion characteristics of the MIS technology on (111) silicon wafers, arranges micro-pores etched on bulk silicon around the desired cavity structure in a regular pattern, and takes into consideration the distance compensation for lateral corrosion, resulting in a fully connected cavity structure closely approximating an ortho-hexagonal shape. By utilizing a sputtering process to deposit metallic molybdenum as upper and lower electrodes, as well as piezoelectric materials above the cavity structure, we have successfully fabricated aluminum nitride (AlN) piezoelectric ultrasonic transducer arrays of various sizes and structures. The final hexagonal PMUT cells of various sizes that were fabricated achieved a maximum quality factor (Q) of 251 and a displacement sensitivity of 18.49 nm/V across a range of resonant frequencies from 6.28 MHz to 11.99 MHz. This fabrication design facilitates the achievement of IC-compatible and cost-effective mass production of PMUT array devices with high resonance frequencies.

Quantitative analysis of iodine and bromine in soil using an energy-dispersive X-ray fluorescence spectrometer with three-dimensional polarized optics.

A nondestructive and simple method for the determination of bromine and iodine in soil was investigated using an energy-dispersive X-ray fluorescence spectrometer equipped with three-dimensional polarized optics. Using a gadolinium X-ray tube and Mo and Al2O3 as optimal secondary target materials, K-lines were detected for bromine and iodine. The minimum detection limits for bromine and iodine were calculated using JSAC0411, a certified reference material of soil for metal composition analysis, and were 0.77mg/kg for bromine and 2.3mg/kg for iodine at a measurement time of 600s. The results of the determination of bromine and iodine in soil samples by the standard addition method were 256 ± 8mg/kg for iodine and 67.9 ± 1.3mg/kg for bromine with JSAC0411, which were in close agreement with the results measured by inductively coupled plasma mass spectrometry (ICP-MS) after alkaline extraction with tetramethylammonium hydroxide (TMAH) solution. The method developed in this study is an excellent technique for direct analysis of soil by X-ray fluorescence analysis without any pretreatment such as alkaline extraction. It is expected to be a practical analytical method for elucidating the dynamics of bromine and iodine in agricultural land and soil.

A SP-ICP-MS protocol for the detection of metal nanoparticles composition and size in tattooed ex vivo human skin explants

We developed and validated a protocol based on Single Particle Inductively Coupled Plasma Mass Spectrometry (SP ICP-MS) to detect composition and size of metal nanoparticles (MNPs) in tattoo inks end ex vivo tattooed human skin explants. The explants were tattooed with different inks using an ordinary tattoo machine. Then, 72 hours after tattooing, skin explants were subjected to alkaline extraction by tetramethylammonium hydroxide solution and MNPs of Ag, Al2O3, Au, Cr2O3, CuO, Fe2O3, TiO2 and ZnO were analysed for particle composition and size by SP ICP-MS. The method was validated by assessing the limit of detection, accuracy, precision, and size stability over 72 hours. Particles of Al2O3, Cr2O3, CuO, Fe2O3, TiO2 and ZnO were observed in human skin in the range from 27 nm to 153 nm, and from 26 nm to 228 nm in tattoo inks. Ag and Au NPs were not found neither in inks nor in the skin. Advantages of the protocol were the ability to simultaneously detect the composition of particles and their size, the straightforward sample preparation, the high sensitivity and precision, and the speed of execution of the analysis. The developed methodology can be applied to skin exposed to other consumer products topically applied, such as sunscreens, cosmetics, personal care products and medical devices, which can be all sources of MNPs, in order to improve knowledge and support the human exposure assessment process.

Preparation and properties of lightweight, conformal, and load‐bearing TiC/Si3N4 absorbing composites by gel casting

AbstractIn view of the lack of conformal, load‐bearing, light‐weight, and high temperature‐resistant integrated wave‐absorbing composites suitable for extremely complex conditions, the gel‐casting process was successfully applied to porous Si3N4 wave‐absorbing composites in this work. A universal low‐slurry for gel casting was prepared by using two dispersants acting together (tetramethylammonium hydroxide solution and sodium lauryl sulfate), which ensured the smooth completion of the gel casting process. Combining the thermogravimetric and differential thermal gravity curves of the composite green body, reasonable parameters of the rubber discharge process are given to avoid the problem of the green body swelling and cracking. The porous TiC/Si3N4 composites were successfully prepared by holding them at 1650°C for 3 h. The bending strength, density, minimum reflection loss, absorption bandwidth, and matched thickness in the P‐band of the composites with 30 wt.% TiC addition were 54.08 ± 3.02 MPa, 1.906 g/cm3, ‐37.75 dB, 1.9 GHz, and 4.1 mm, respectively. The electromagnetic wave loss mechanisms of the composites are a combination of conductivity loss, multiple reflections and scattering, interfacial polarization, and defect polarization.

An Efficient Design of the Piezoresistive Pressure Sensor Applied for Micro Aerial Vehicle

In this research, the developing process of a piezoresistive pressure sensor working in the atmosphere environment applied in micro aerial vehicle using the MEMS fabrication method is introduced. The sensor consists of four Au/Cr piezoresistors in a Wheatstone bridge configuration on a wet oxidized silicon diaphragm. To fabricate the sensor, three lithographic steps were conducted: the first one is to define the resistors and Au/Cr lines/pads, the second and the third ones are to determine the width and the thickness of the square SiO2/Si diaphragm, respectively. The sensor diaphragm shape and thickness were defined by the anisotropic etching of Si in tetramethylammonium hydroxide (TMAH) solution, and the resistors array are formed by sputtering and wet etching method. The sensor size is 6000 μm by 6000 μm. The sensor output voltage was measured for various applied pressure levels from -0.9to 1.2 bar with 5V voltage supply. The fabricated pressure sensor also exhibits a sensitivity of 50.1 mV/bar

Effective pretreatment for thermally-assisted hydrolysis and methylation GC-MS of intractably cross-linked acrylate copolymers

Thermally-assisted hydrolysis and methylation-gas chromatography-mass spectrometry (THM-GC-MS) using tetramethylammonium hydroxide (TMAH) is an effective approach for the characterization of condensation polymers with ester linkages such as ultraviolet (UV)-cured acrylate resins. However, for intractably cured acrylic resins, reliable structural characterization is often difficult by conventional THM-GC-MS owing to insufficient THM reactions. In this study, a pretreatment to effectively improve THM efficiency was proposed, in which the resin sample was preliminarily soaked and dissolved in a TMAH-methanol solution in a microtube. An aliquot of the TMAH solution was then introduced into the pyrolyzer at 400 °C to produce THM-GC-MS. The effectiveness of the proposed pretreatment was demonstrated using a UV-cured acrylate copolymer consisting of bulky and high-molecular weight bifunctional acrylate (9,9-Bis[4-(2-acryloyloxy ethoxy) phenyl]fluorene) and monofunctional acylate (2-(9 H-Carbazol-9-yl)ethyl acrylate) monomers, for which THM reactions did not proceed efficiently in conventional THM-GC-MS. Conversely, by the modified THM-GC-MS process with a pretreatment involving immersion at room temperature for 24 h or at 60 °C for 30 min, the characteristic decomposition products for each monomer unit were clearly observed in the chromatograms, and the copolymer composition could be precisely estimated from the relative yields of the observed decomposition products. In addition, a methyl acrylate peak, formed from unreacted acrylate moieties in the photocured copolymer, appeared in the chromatogram. Its relative yields were correlated to the double bond conversion in the cured sample. The observed results were successfully interpreted to clarify the curing process of the photocured acrylate copolymer samples.

Fluorine-free MXene activate peroxymonosulfate to remove tetracyclic antibiotics

The most typical synthesis method for MXene is to etch the Al layer from its MAX phase using an acidic solution containing fluorine. However, etching with fluorine-containing reagents can lead to environmental contamination and experimental safety issues. Herein, fluorine-free Ti3C2Tx (Ff-Ti3C2Tx) was successfully prepared by using a safer and more environmentally friendly tetramethylammonium hydroxide solution (TMAOH) at a controlled temperature of 40 °C and reacting continuously for one week. Based on the characterization results, we demonstrated that the prepared Ff-Ti3C2Tx exhibits outstanding hydrophilicity and exposes more active sites on the surface, which is beneficial towards activating peroxymonosulfate (PMS). The catalyst exhibited superior degradation of tetracycline hydrochloride (TC) than Fluorine-Ti3C2Tx (F-Ti3C2Tx). The effects of catalyst dosage, optimum concentration of PMS, initial pH, common coexisting ions (Cl−, SO42−, HCO3− and humic acid) and different real water environments on TC degradation were systematically investigated in the Ff-Ti3C2Tx/PMS system. Meanwhile, the degradation effects of both Doxycycline (DC) and Oxytetracycline (OTC) reached more than 89.7%. In addition, Ff-Ti3C2Tx exhibited excellent reusability with a mineralization efficiency of 49.7%. Based on the electron paramagnetic resonance (EPR) test, quenching experience, radical probe experiments, electrochemical measurements and XPS characterization, a possible activation mechanism was proposed. The contribution of reactive oxygen species (ROS) was calculated, 1O2 (45.3%) and ·O2− (30.2%) play a major role in the degradation of TC. Furthermore, a possible degradation pathway was proposed by liquid chromatography-mass spectrometry (LC-MS) with a decreasing trend in the toxicity of TC intermediates. This work not only demonstrates a novel strategy for preparing fluorine-free MXene via simple TMAOH etching, but it also provides new insight into the use of MXene as a catalyst directly in the activation of PMS.

Synthesis and characterization of aqueous base developable negative-tone poly(imide-amic acid) copolymers by the effect of the imidization ratio

Negative-tone photosensitive poly(imide-amic acid) (PIA) copolymers were synthesized from a chemical imidization process using poly(amic acid) that was prepared from a polycondensation reaction of 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 4,4′-oxydianiline (ODA), and di[2-(methacryloyloxy)ethyl]-5-aminoisophthalate (Di-HEMA-AP) with photoreactive acrylate groups. The imidization ratio was controlled by the reaction time, and the synthesized PIA copolymers were investigated using spectroscopic methods. The photolithographic behaviors of the formulations composed of PAA and PIA copolymers, Michler’s Ketone (MK), and crosslinker were evaluated using a 2.38 wt. % tetramethylammonium hydroxide (TMAH) solution. The solubility decreased with increasing imidization ratio in an alkaline base solution because of the reducing content of carboxylic acid groups in the polymer main chain. The formulations from PIA copolymers gave clear patterns without distortion by UV light i-line irradiation and followed 2.38 wt. % TMAH solution development.

Synthesis and lithographic properties of positive-tone poly(benzoxazole)s by the effect of amine end-cappers

Positive-tone photosensitive poly(o-hydroxyamide) (PHA) precursors were synthesized from the polycondensation reaction of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (Bis-AP-AF), 4,4’-oxybisbenzoyl chloride (OBC) and three mono-functional amines as end-cappers. The synthesized PHA precursors were characterized and converted to polybenzoxazoles (PBOs) by thermal cyclization reaction. The photoresist formulations composed of the prepared PHA precursor and diazonaphthoquinone (DNQ) photoactive compound were prepared, and the photolithographic properties of the photoresist formulations were investigated by UV light irradiation, followed by a 2.38 wt.% tetramethylammonium hydroxide (TMAH) solution treatment in terms of the chemical structure of end-cappers. The dissolution rate at 2.38 wt.% TMAH solution by various UV light exposure doses and the shrinkage ratio by thermal cyclization of micro-patterns by UV light irradiation and developing process from the photoresist formulations are affected by the chemical structure of end-cappers.

Recessed-gate AlGaN/GaN MIS-FETs with dual 2DEG channels

In this study, a normally-on AlGaN/GaN metal–insulator-semiconductor high electron mobility transistor (MIS-HEMT) and a normally-off AlGaN/GaN metal–insulator-semiconductor field-effect transistor (MIS-FET) with recessed MIS gate are fabricated by dual-channel epitaxy structure. The recessed region is cleaned by dipping it into diluted buffered oxide etch (BOE), HCl, and tetramethylammonium hydroxide (TMAH) solutions. After cleaning, a 20 nm Al2O3 is deposited by atomic layer deposition (ALD). Then, the post-deposition annealing is executed. Non-recessed MIS-HEMT demonstrates a threshold voltage of −9.81 V, a high drain current of 660.76 mA mm−1, and a small on-resistance of 6.47 Ω mm. Recessed gate MIS-FET shows a positive threshold voltage of 1.46 V with a drain current of 144.81 mA mm−1. In addition, the devices present a high gate breakdown voltage of 26.5 V by non-recessed MIS-HEMT and 18.5 V by recessed MIS-FET. Both devices show a low I–V hysteresis under double sweep I D–V GS measurement.

Pinhole‐Free Ultrathin Silicon Oxide Layer by Ozone‐Dissolved Deionized Water

The pinhole‐free silicon oxide (SiO x ) layer grown using dissolved ozone in deionized water (DI‐O3) is demonstrated. An ultrathin SiO x layer of thickness 1.53 nm ± 1.5% is grown on silicon wafer using 7 ppm DI‐O3. A four‐step methodology, including 25 wt% aq. tetramethylammonium hydroxide (TMAH) solution at 80 °C, is employed to magnify the pinhole signatures in the underlying silicon and visualized with dark‐field optical microscopy (DFOM) and scanning electron microscopy (SEM). The DFOM images show spots on the surface of wafer that originate from airborne particles, contamination, etc. SEM images reveal the absence of etch pits in silicon even after etching of SiO x /silicon in TMAH for 300 s. The minority carrier lifetime and interface states density in AlO x ‐capped SiO x /Si structure are ≥2 ms at carrier density of 1 × 1015 cm−3 and less than 2 × 1011 cm−2 eV−1, respectively.

Synthesis and Chemoresistive Properties of Single-Layer MXene Ti2CTx

As part of the study, we have developed a method for obtaining a single-layer Ti2CTx MXene by the interaction of Ti2AlC with a mixture of hydrochloric acid and sodium fluoride followed by delamination using a tetramethylammonium hydroxide solution and ultrasonic exposure. The obtained stable aqueous dispersion of Ti2CTx has been applied by microplotter printing onto a specialized sensor chip, which has been dried at a temperature of 150°C under reduced pressure. The coating has been studied using modern physicochemical methods of analysis. According to the data of X-ray spectral elemental microanalysis, the ratio n(Ti) : n(F + Cl) = 2 : (0.82–0.85), n(F) : n(Cl) ≈ 6 : 4; aluminum impurity does not exceed 1.5–2.0%. Data have been obtained on the local electrophysical properties of the Ti2CTx coating: on the value of the electron work function from the surface of the material, the distribution of charge carriers, and the capacitance gradient of the “probe tip–sample microregion” capacitor. For the first time, at an operating temperature of 30°C, extremely high chemoresistive responses of the Ti2CTx receptor layer to the content of 1 and 5% oxygen in nitrogen have been determined, which amounted to 8.6 and >276, respectively.

Selective Etching of Si versus Si1-xGex in Tetramethyl Ammonium Hydroxide Solutions with Surfactant.

We investigated the selective etching of Si versus Si1−xGex with various Ge concentrations (x = 0.13, 0.21, 0.30, 0.44) in tetramethyl ammonium hydroxide (TMAH) solution. Our results show that the Si1−xGex with a higher Ge concentration was etched slower due to the reduction in the Si(Ge)–OH bond. Owing to the difference in the etching rate, Si was selectively etched in the Si0.7Ge0.3/Si/Si0.7Ge0.3 multi-layer. The etching rate of Si depends on the Si surface orientation, as TMAH is an anisotropic etchant. The (111) and (010) facets were formed in TMAH, when Si was laterally etched in the <110> and <100> directions in the multi-layer, respectively. We also investigated the effect of the addition of Triton X-100 in TMAH on the wet etching process. Our results confirmed that the presence of 0.1 vol% Triton reduced the roughness of the etched Si and Si1−xGex surfaces. Moreover, the addition of Triton to TMAH could change the facet formation from (010) to (011) during Si etching in the <100>-direction. The facet change could reduce the lateral etching rate of Si and consequently reduce selectivity. The decrease in the layer thickness also reduced the lateral Si etching rate in the multi-layer.

Stability Indicating RP-HPLC and Spectrophotometric Methods for Simultaneous Estimation of Sodium Benzoate and Cefdinir in the Presence of its Degradation Products-Application to Blank Subtraction Method.

Empower 3 software is important in modeling, optimization, and reducing the time of manual calculation of related substance by subtracting the baseline of a blank chromatogram from the unknown sample automatically; so, the major objective of the developed method is to introduce a new, selective, and economical high performance liquid chromatography (HPLC) and spectrophotometric method for simultaneous estimation of sodium benzoate (SDB) and cefdinir (CFR) in the presence of its degradation products. Chromatographic separation is optimized and adjusted using two methods; method (I) is characterized for separation of active pharmaceutical ingredient (CFR) in pure and dosage forms using Atlantis dC18 column [4.6 mm x 250 mm (5 μm particle size or equivalent)] with a mobile phase consisting of methanol: 0.02 M phosphate buffer solution pH 3.0 (40:60 v/v) at a flow rate of 1.0 mL/minute, injection volume 10 μL and wavelength 254 nm. Method (II) is identified for related substances in a Hichrom C18 column (15 x 0.46 cm), 5 μm particle size or equivalent, using a binary gradient consisting of solution A [0.1% tetramethylammonium hydroxide solution (pH: 5.5) with 0.1 M EDTA (1000:0.4 v/v)] and solution B (0.1% tetramethylammonium hydroxide solution (pH 5.5): acetonitrile: methanol : 0.1 M EDTA (500:300:200:0.4 v/v) using injection volume 10 μL for reversed-phase HPLC with a wavelength equals to 254 nm and flow rate 1.0 mL/min. Two ecofriendly spectrophotometric methods were successfully used to resolve the spectral overlap of drugs. Method A, the first derivative of ratio spectra spectrophotometric method (1stDD) where CFR was determined at two wavelengths 283.5 nm, 313.4 nm and SDB was determined at 216.7 nm, 235.5 nm. Method B, ratio subtraction method is performed to overcome the interference between CFR and the preservative SDB. The ultraviolet spectrum of the laboratory mixture is divided by that of CFR (20 μg/mL) as a divisor then subtracting the amplitudes in the plateau region at 250-315 nm (the constant) from that of the ratio spectrum. The zero-order spectra of SDB were obtained at 225 nm by multiplying the resulting ratio spectra by the divisor (CFR), zero order of CFR was been estimated at a wavelength value of 283 nm after multiplication of the divisor by the obtained constant. The optimized method was adjusted and validated as per International Conference on Harmonization guidelines and could be easily utilized by quality control laboratories and for laboratory-prepared mixtures.

Extraction and quantification of polystyrene nanoplastics from biological samples

Accurate quantification of nanoplastics (NPs) in complex matrices remains a challenge, especially for biological samples containing high content of organic matters. Herein, a new method extracting and quantifying polystyrene (PS) NPs from biological samples was developed. The extraction included alkaline digestion, centrifugation, and cloud point extraction (CPE), and the quantification included gold nanoparticles formation and labeling on surfaces of the extracted NPs and thereafter measurement with single particle inductively coupled plasma mass spectrometry (SP-ICP-MS). Results show that 25% tetramethylammonium hydroxide solution was an effective alkaline digestion solution for biological matrices, and CPE after centrifugation (3000 rpm, 10 min) was applicable to purify and enrich PS NPs with different sizes (100 and 500 nm) and surface functionalities (-COOH and –NH2 modifications) from the digestion solution. The efficiency of Au labeling on PS NPs surface was improved by about 70% in the presence of 100 μM cetyltrimethylammonium bromide. The performance of the quantification method was examined by extraction and measurement of PS NPs spiked in four representative organism samples including bacteria, algae, nematode, and earthworm, and was further validated by analyzing the accumulated PS NPs in exposed nematodes. Good recovery rates (65 ± 10%–122 ± 22%) were achieved for spiking levels of 5–50 μg g−1; the limit of detection was 3.7 × 107 particles g−1, corresponding to the mass concentration of about 0.02 and 2.5 μg g−1 for the 100 nm and 500 nm PS NPs, respectively. The established extraction and quantification methods are efficient and sensitive, providing a useful approach for further exploring the environmental behavior and toxicity of NPs.

Deposition-last lithographically defined epitaxial complex oxide devices on Si(100)

The epitaxial growth of SrTiO3 on Si(100) substrates that have been lithographically patterned to realize deposition-last, lithographically defined oxide devices on Si is explored. In contrast to traditional deposition-last techniques which create a physical hard mask on top of the substrate prior to epitaxial growth, a pseudomask is instead created by texturing the Si substrate surface itself. The Si is textured through a combination of reactive ion etching and wet-etching using a tetramethylammonium hydroxide solution. Desorbing the native SiOx at high temperatures prior to epitaxial growth in ultrahigh vacuum presents no complications as the patterned substrate is comprised entirely of Si. The inverted profile in which the epitaxial oxide device layer is above the textured pseudomask circumvents shadowing during deposition associated with conventional hard masks, thereby opening a pathway for highly scaled devices to be created.

Toward Controllable Wet Etching of Monocrystalline Silicon: Roles of Mechanically Driven Defects.

Wet chemical etching is essential not only for processing silicon (Si) wafers but also for forming diverse structures, significantly promoting the development of the semiconductor industry. However, tight control of etched topography at the nanoscale and even atom-scale in a controllable and reproducible fashion can be hardly achieved in either laboratory research or industrial production, seriously hindering further enhancement of high-performance Si-based electronic devices. Herein, the roles of mechanically driven defects in wet etching were systematically investigated toward promoting controllable wet etching of monocrystalline Si. The role of antietching of mechanically driven amorphous Si (a-Si) and the role of promoting etching of distorted Si (including dislocations and stacking faults) were revealed in anisotropic or isotropic etchants. It was also found that the nucleation of nanocrystals in the a-Si area with increasing contact pressure can lead to deactivation of the antietching mask, and the required contact pressure for deactivation in KOH and tetramethyl ammonium hydroxide solutions was much higher than that in HF/HNO3 mixtures. The selective etching mechanisms for every defect including a-Si, distorted Si, and nanocrystals were further addressed down to the atom-scale based on the proposed dissolution model. This study provides insights into deeply understanding the role of defects in wet etching and pushes forward the idea of controllable wet chemical etching in the Si-based semiconductor industry.

Swelling and dissolution kinetics of poly(4-hydroxystyrene) in tetrabutylammonium hydroxide (TBAH) aqueous solutions studied by quartz crystal microbalance (QCM) method—in comparison with tetramethylammonium hydroxide (TMAH) aqueous solutions

The dissolution (including the formation of a transient swelling layer) of a resist polymer is key to realizing ultrafine patterning. However, the details of the dissolution of resist polymers remain unclarified. In this study, the swelling and dissolution kinetics of poly(4-hydroxystyrene) (PHS) films in tetramethylammonium hydroxide (TMAH) and tetrabutylammonium hydroxide (TBAH) aqueous solutions were investigated by a quartz crystal microbalance method. PHS is a typical backbone polymer (a dissolution agent) of chemically amplified resists. The swelling and dissolution kinetics of PHS were observed by changing the protection ratio of the hydroxyl groups of PHS and the alkaline concentration in developers. Not only the dissolution rate but also the mode of dissolution depended on the molecular structure of tetraalkylammonium cations. For polymer matrices with strong hydrogen bond networks such as PHS, the penetration of tetrabutylammonium cations is considered to be strongly suppressed by their long alkyl chains.

Dependence of photoresist dissolution dynamics in alkaline developers on alkyl chain length of tetraalkylammonium hydroxide

Extreme ultraviolet (EUV) lithography is already being applied to the high-volume manufacturing of semiconductor devices. Although EUV lithography has enabled fine pitch scaling, such sub-20 nm order fabrication has also imposed the issue of stochastic defects (in the form of randomly generated line bridges and breaks). To resolve such an issue, understanding the development process is essential. In this study, the dissolution dynamics of three types of EUV photoresist were investigated for four types of alkaline developer using a quartz crystal microbalance method to clarify the swelling and dissolution kinetics during photoresist development. In experiments, tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), and tetrabutylammonium hydroxide (TBAH) aqueous solutions were used as developers. Poly(4-hydroxystyrene) (PHS)-type, acryl-type, and hybrid-type photoresists were examined. The effect of the alkyl chain length of tetraalkylammonium cations depended on the type of photoresist. The dissolution dynamics depended on the combination of types of photoresist and developer.