Tetramethylammonium Hydroxide Developer Research Articles

Dissolution dynamics of poly(4-hydroxystyrene) partially protected with t-butoxycarbonyl group in alkyltrimethylammonium hydroxide aqueous developers

Novel developers with low biotoxicity have attracted considerable attention with respect to ensuring environmental sustainability. In this study, the dissolution dynamics of poly(4-hydroxylstyrene) (PHS) partially protected with a t-butoxycarbonyl (t-Boc) group in alkyltrimethylammonium hydroxide and tetraethylammonium hydroxide aqueous solutions (0.26 N) were investigated by the quartz crystal microbalance method. One of the methyl groups of tetramethylammonium hydroxide (TMAH) was substituted by ethyl, propyl, and butyl groups. Depending on the developer used, the dissolution dynamics of PHS and t-Boc-protected PHS (t-Boc PHS) films showed different tendencies. The dissolution rate of PHS was higher in the TMAH developer than in the butyltrimethylammonium hydroxide (B-TMAH) developer, whereas that of the t-Boc PHS (30 mol%-protected) film was higher in the B-TMAH developer than in the TMAH developer. The elongation of one of the alkyl chains is beneficial for the penetration of the developer and the separation of nonpolar molecular interactions among t-Boc PHS molecules.

Dissolution dynamics of partially protected poly(4-hydroxystyrene) in tetraalkylammonium hydroxide aqueous solution

A 0.26 M tetramethylammonium hydroxide (TMAH) aqueous solution has been used as a standard developer for manufacturing semiconductor devices. Alternative developers have recently attracted much attention because the 0.26 M TMAH developer may be approaching its performance limit. In this study, we measured the dissolution and swelling behavior of resist polymers in tetraalkylammonium hydroxide (TAAH) aqueous solutions using a quartz crystal microbalance method to clarify the effects of the alkyl chain length of TAAH. The resist polymer was poly(4-hydroxystyrene), whose hydroxyl groups were partially protected with t-butoxycarbonyl groups. When the alkyl chain length of TAAH was increased from two (ethyl) to three (propyl), the dissolution mode markedly changed. The dissolution mode did not depend on the polymer polarity. The change in the dissolution mode is probably caused by the size effect of TAAH, considering the independence of polymer polarity and the discrete change in the dissolution mode.

Analysis of dissolution kinetics of narrow polydispersity poly(4-hydroxystyrene) in alkaline aqueous solution using machine learning

Understanding the dissolution kinetics of resist materials is essential for their efficient development. In this study, we investigated the dissolution kinetics of poly(4-hydroxystyrene) (PHS) with a weight-average molecular weight (M w) of 8000–30 000 and a polydispersity index (M w /M n) of 1.07–1.20. The dissolution kinetics of PHS films was observed in tetramethylammonium hydroxide (TMAH) aqueous developers by a quartz crystal microbalance (QCM) method. The TMAH concentration was changed from 0 to 2.38 wt%. The formation of a thick transient swelling layer at these M w /M n values was suppressed compared with that at M w /M n > 2. QCM data were analyzed using the polynomial regression to clarify the effects of M w and M w /M n on the dissolution kinetics in a narrow polydispersity region. Both dissolving and swelling kinetics largely depended on M w/M n. M w had little effect in 2.38 wt% TMAH developer; however, it had a large effect on the swelling when 2.38 wt% TMAH developer was diluted.

Structural effects on the performance of epoxide-based negative-tone molecular resists

Several 0.26N tetramethylammonium hydroxide (TMAH)-soluble epoxide molecular resists have been synthesized and are reported here. Previously, the patterning performance of 1,1,2,2-tetrakis(p-hydroxyphenyl)ethane-3 epoxide (TPOE-3Ep) was reported and resolved 26 nm lines using extreme ultraviolet lithography. Here, a deeper study is performed to determine the effects of various structural features on the lithographic performance of 0.26N TMAH-soluble molecular resists. Increasing the number of phenols resulted in a notable increase in the glass transition temperature (Tg) of these materials, which required high postexposure bake (PEB) temperatures to achieve normalized remaining thickness (NRT) values of 1 in methyl isobutyl ketone development. Such high PEB temperatures resulted in insoluble material (high NRT values) in unexposed regions in the 248 nm contrast curves. Methyl groups were introduced adjacent to the hydroxyl group of phenol in an attempt to lower the Tg of the resists to allow the use of lower PEB temperatures. The methyl groups only slightly lowered the Tg of the resists, while detrimentally reducing the final NRT. Thus, instead of using the TPOE core or its methylated analog, a smaller core was used, and the resist trihydroxyphenyl ethane (THPE)-2Ep was designed and synthesized to be a low-Tg base-soluble resist. THPE-2Ep has a Tg of 41 °C and showed promising early performance using e-beam lithography and resolves 30 nm lines in 0.26N TMAH developer at a dose of 72 μC/cm2 at a PEB of 50 °C.

Influence of tetramethylammonium hydroxide on niobium nitride thin films

Functionality of superconducting thin-film devices such as superconducting nanowire single photon detectors stems from the geometric effects that take place at the nanoscale. The engineering of these technologies requires high-resolution patterning, often achieved with electron beam lithography. Common lithography processes using hydrogen silsesquioxane (HSQ) as the electron beam resist rely on tetramethylammonium hydroxide (TMAH) as both a developer and a resist adhesion promoter. Despite the strong role played by TMAH in the fabrication of superconducting devices, its potential influence on the superconducting films themselves has not yet been reported. In this work, the authors demonstrate that a 25% TMAH developer damages niobium nitride (NbN) thin films by modifying the surface chemistry and creating an etch contaminant that slows reactive ion etching in CF4. They also show how the identity of the contaminant may be revealed through characterization including measurement of the superconducting film properties and Fourier transform infrared spectroscopy. Although workarounds may be available, the results reveal that processes using 25% TMAH as an adhesion promoter are not preferred for NbN films and that changes to the typical HSQ fabrication procedure will need to be made in order to prevent damage of NbN nanoscale devices.

High-speed atomic force microscopy studies of 193-nm immersion photoresists during tetramethylammonium hydroxide development

This paper reports on our studies of the dynamic process of positive tone photoresist development in real time. Using high-speed atomic force microscopy (HS-AFM) in dilute alkaline developer solution, changes in morphology and nanomechanical properties of patterned resist were monitored. The Bruker Dimension FastScan AFM was used to analyze 193-nm acrylic-based immersion resists in tetramethylammonium hydroxide developer solution. HS-AFM operated in PeakForce Tapping® (Registered Trademark of Bruker, Inc.) mode can allow for concurrent measurements of resist topography, stiffness, adhesion, and deformation during development. These studies focused on HS-AFM topography data as it readily revealed detailed information about initial resist morphology, followed by a resist swelling process, and eventual dissolution of the exposed resist areas. HS-AFM showed potential for tracking and understanding development of patterned resist films and can be useful in evaluating the dissolution properties of different resist designs. Also discussed are the roles of AFM tip shape and resist feature geometry on the measured line edge roughness using a simulation procedure.

Positive-tone crosslinked molecular resist based on acid-catalyzed depolymerization

Presented here is 1,1,1-tris(4-hydroxyphenyl) ethane (THPE)-2VE, a phenol-containing depolymerization resist that demonstrates a 248-nm deep ultraviolet sensitivity (dose-to-clear) of 3 mJ/cm2 as well as a contrast ratio of 7.2 when formulated with 5 mol. % triphenyl sulfonium hexafluoroantimonate as photoacid generator. The 100 keV e-beam contrast curve shows a sensitivity of 24 μC/cm2 for methyl isobutyl ketone (MIBK) development with a contrast ratio of 6.0. A sensitivity of 20 μC/cm2 for 0.26 N tetra methyl ammonium hydroxide (TMAH) development and a contrast ratio of 10.3 was observed for 0.26 N TMAH development. THPE-2VE has been demonstrated to resolve features down to at least 35 nm lines with doses of 48 μC/cm2 in MIBK development with a line edge roughness (LER) (3σ) value of 8.4 nm. In 0.26 N TMAH development, the material required an e-beam dose of 40 μC/cm2 to pattern roughly 35 nm lines with an LER (3σ) value of 8.2 nm. This material shows improved sensitivity and shelf life compared to other depolymerization resist designs previously reported by our group. THPE-2VE has been demonstrated to resolve some of the smallest features reported to date with crosslinked depolymerization resists.

Polymers of norbornenyl‐4‐phenol: Dissolution rate characteristics, positive tone photo‐patterning, and polymer properties

ABSTRACTVinyl addition norbornene polymers with phenol pendent groups are obtained by methanolysis of the 4‐acetoxyphenyl norbornene polymer. Thin films of this polymer blended with additives such as norbornene polymers with hexafluoroalcohol pendent groups and diazonaphthoquinone compounds result in linear dissolution in tetramethylammonium hydroxide developer. Good resolution, positive tone patterns are obtained from image‐wise exposure of thin films of blends of the diazonaphthoquinone additives with both phenol pendent norbornene homopolymer and with norbornene copolymers with both phenol and hexafluoroalcohol pendent groups. Properties such as transparency, dielectric constant, chemical, and thermal resistance were determined for cured copolymer compositions containing an epoxy crosslinker. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44952.

High performance top contact fused thiophene–diketopyrrolopyrrole copolymer transistors using a photolithographic metal lift-off process

High-performance fused thiophene–diketopyrrolopyrrole copolymer (PTDPPTFT4) top-contact transistors have been fabricated using a top contact metal lift-off process. The source–drain (S/D) top metal contacts were directly formed by i-line photolithographic patterning over the organic semiconductor channel through a lift-off method based on a negative tone photoresist. With a fluorinated imaging material (Orthogonal OScR 2312), devices exhibit field effect mobilities up to 2.56cm2V−1s−1 and on/off ratio >107, with channel lengths precisely patterned down to 10μm. Devices prepared from the lift-off process through a commercial negative tone photoresist such as AZ nLOF 2020 instead of the fluorinated photoresist exhibited considerable degradation. De-ionized (DI) water, aqueous tetramethyl ammonium hydroxide (TMAH) developer and organic stripper do not apparently degrade the performance of the PTDPPTFT4 transistors upon dip testing. Indeed the observed degradation originates from the incomplete development of the unexposed photoresist in the TMAH developer. This is detrimental to the PTDPPTFT4 channel due to formation of resist residue over the organic semiconductor surface. This residue eventually leads to a significant increase of the S/D contact resistance upon metal contact deposition.

An In situ Analysis of the Dissolution Characteristics of Half Pitch Line and Space Extreme Ultraviolet Lithography Resist Patterns

The characterization of the resist dissolution is one fundamental area of research that has been continuously investigated. This paper focuses on the preliminary work on the application the high speed atomic force microscope (HS-AFM) for the in situ dissolution analysis half-pitch (hp) lines and spaces (L/S) at standard developer concentration. In earlier works, this has been difficult but through extensive optimization and the use of carbon nano fiber-tipped cantilevers, the dissolution characterization of a 32 nm hp L/S pattern at 0.26 N aqueous tetramethylammonium hydroxide developer (standard developer concentration) was successfully achieved. Based on the results obtained using the EIDEC standard resist (ESR1) it was found that regardless of analysis condition such as resist pattern configuration (isolated or L/S pattern) and developer concentration (diluted or standard), similar dissolution characteristics in the form of resist swelling of exposed areas was observed. Moreover, further investigations using other types of model resist polymer platforms such as poly(hydroxystyrene) (PHS)-based and hybrid (PHS–methacryl)-based model resists have confirmed that dissolution behavior is not affected by the analysis conditions applied.

Alternative developer solutions for extreme ultraviolet resist

The use of the tetrapropylammonium hydroxide (TPAH) and tetrabutylammonium hydroxide (TBAH) aqueous developer solutions is proposed as an alternative to the tetramethylammonium hydroxide (TMAH) aqueous developer solution (semiconductor industry standard). A polyhydroxystyrene-based extreme ultraviolet (EUV) resist was utilized at a film thickness of 60nm. To confirm the effectiveness of these alternative developer solutions in improving linewidth roughness (LWR) performance, patterning exposures were carried out using the small field exposure tool with annular (σouter0.7∕σinner0.3) illumination conditions. Dissolution contrast curves of EUV resist using the TMAH, TPAH, and TBAH developer solutions have shown similar dissolution characteristics which means that the use of these alternative developer solutions might have minimal effect on the resist resolution limit and sensitivity. Imaging performance analysis results have shown negligible effect on the resolution capability and sensitivity. A 20% LWR improvement was observed with the TBAH developer solution [7.2nm at 32nm 1:1 line and space (L/S)] comparing with the TPAH and standard TMAH developer solutions (both at 9.0nm at 32nm 1:1 L/S). This improvement was perceived to be the result of the significant increase in dissolution contrast (higher Rmax and larger slope) with the use of the TBAH developer solution.

Two-step resist-development process of hydrogen silsesquioxane for high-density electron-beam nanopatterning

It is identified that the development of hydrogen-silsesquioxane resist after electron-beam exposure, by using a 25% tetramethylammonium-hydroxide (TMAH) developer, almost stops after 1min of development time and it severely limits the delineation of high-density nanometer-scale patterns. By using x-ray photoelectron spectroscopy, the authors identified that this development-stopping phenomenon is due to the formation of a siloxane-type bond structure which is insoluble to the TMAH developer. Here, the authors propose a two-step development method that involves the removal process of siloxane layer using a dilute hydrofluoric acid between development processes. This method successfully eliminates the insoluble layer, thus generating isolated high-density dot patterns with 25nm pitch.

Depth Profile and Line-Edge Roughness of Low-Molecular-Weight Amorphous Electron Beam Resists

We have investigated the possibility of using amorphous low-molecular-weight polyphenols as chemically amplified positive-tone electron-beam (EB) resists. Low-molecular-weight polyphenol, 4,4'-methylenebis[2-[di(2-methyl-4-hydroxy-5-cyclohexylphenyl)]methyl] phenol (3M6C-MBSA) as a base matrix, was protected by 1-ethoxyethyl (EE) groups to control the dissolution rate in aqueous 0.26 N tetramethylammonium hydroxide developer. The film distribution in the depth direction for resist components determined with time-of-flight secondary ion mass spectometry (TOF-SIMS) and the Fourier amplitude spectra of line-edge roughness (LER) have been investigated to understand the relationship between them for the resists formulated with 3M6C-MBSA and two photo-acid generators (PAG), triphenylsulfonium perfluoro-1-butanesulfonate (TPS-PFBS) and triphenylsulfonium n-octanesulfonate (TPS-nOS). From these results, it was found that the resist film consisting of TPS-nOS showed more homogeneity in the depth direction of the film than did TPS-PFBS, which showed low surface energy and diffused easily to the resist surface through the matrix during a coating and post-applied bake step. The resist with TPS-nOS indicated a lower LER value of 5.1 nm in the wide frequency range, especially in the lower frequency region below 10 µm-1. Therefore, the homogeneity of the film is one of important factors for LER control.

New base-soluble positive-working photosensitive polyimides havingo-nitrobenzyl ester group

A new positive-working polyimide having photosensitive o-nitrobenzyl ester group as side substituent, poly{1,4-phenyleneoxy-1,4-phenylene-3,6-di[4-(o-nitrobenzyloxy)carbonylphenyl]pyromellitimide} (ODA-PI-Nb), was prepared and its aqueous alkali-developability and photosensitivity were investigated. ODA-PI-Nb was synthesized by the esterification reaction of poly[1,4-phenyleneoxy-1.4-phenylene-3,6-di(4-carboxylphenyl)pyromellit imide] (ODA-PI) with o-nitrobenzyl bromide in the presence of triethylamine (Et3N). ODA-PI-Nb obtained was characterized by FT-IR and 1H-NMR spectroscopy. The degree of esterification reaction was found from 1H-NMR absorption of CH2 proton to be over 95 mol%. Upon photo-irradiation ODA-PI-Nb transformed to the freely aqueous alkali-soluble ODA-PI under formation of o-nitrosobenzaldehyde. The thickness loss of thin ODA-PI-Nb films upon post-baking at 400°C was in the 10–15% range. ODA-PI-Nb showed positive-tone behavior in characteristic sensitivity curve and positive patterns were obtained using a typical lithographic process using aqueous tetramethylammonium hydroxide developer. The patterns with excellent resolution were observed and evaluated by optical microscopy and scanning electron microscopy. Copyright © 2005 John Wiley & Sons, Ltd.

Novel positive‐working and aqueous‐base‐developable photosensitive poly(imide benzoxazole) precursor

AbstractA novel positive‐working and aqueous‐base‐developable photosensitive poly(imide benzoxazole) precursor based on a poly(amic acid hydroxyamide) bearing phenolic hydroxyl groups and carboxylic acid groups, a diazonaphthoquinone (DNQ) photosensitive compound, and a solvent was developed. Poly(amic acid hydroxyamide) was prepared through the polymerization of 2,2‐bis(3‐amino‐4‐hydroxyphenyl)hexafluoropropane, trimellitic anhydride chloride, and 4,4′‐oxydibenzoyl chloride. Subsequently, the thermal cyclization of the poly(amic acid hydroxyamide) precursor at 350 °C produced the corresponding poly(imide benzoxazole). The inherent viscosity of the precursor polymer was 0.17 dL/g. The cyclized poly(imide benzoxazole) showed a high glass‐transition temperature of 372 °C and 5% weight loss temperatures of 535 °C in nitrogen and 509 °C in air. The structures of the precursor polymer and the fully cyclized polymer were characterized with Fourier transform infrared and 1H NMR. The photosensitive polyimide precursor containing 25 wt % DNQ photoactive compound showed a sensitivity of 256 mJ/cm2 and a contrast of 1.14 in a 3‐μm film with a 0.6 wt % tetramethylammonium hydroxide developer. A pattern with a resolution of 5 μm was obtained from this composition. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5990–5998, 2004

Novel positive‐working aqueous‐base developable photosensitive polyimide precursors based on diazonaphthoquinone‐capped polyamic esters

AbstractNovel positive‐working aqueous‐base developable photosensitive polyimide (PSPI) precursors based on partially diazonaphthoquinone (DNQ)‐capped polyamic esters bearing phenolic hydroxyl groups and a DNQ photosensitive compound (PIC‐3) were developed. The partially DNQ capped polyamic esters were prepared from an esterification reaction of 1,2‐naphthoquinone diazide‐5‐sulfonyl chloride with the polyamic esters. The partially DNQ capped polyamic esters decreased the dark film loss effectively in the aqueous‐base developer and were able to make thicker film resists compared to the uncapped polyamic esters. The 25 mol % DNQ‐capped BisAPAF–PMDA polyamic ester and BisAPAF–ODPA polyamic ester containing 25 wt % PIC‐3 photosensitive compound showed a sensitivity of 176 and 185 mJ/cm2, and a contrast of 1.68 and 1.02, respectively, in a 3‐μm film with 1.25 wt % tetramethylammonium hydroxide developer. A pattern with a resolution of 5 μm was obtained from both PSPI precursor compositions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2293–2300, 2003

Photosensitive poly(amic acid)/organoclay nanocomposites

A project was carried out aimed at reducing the coefficient of thermal expansion (CTE) of photosensitive polyimide formulations (photoresists) through the incorporation of small amounts of an organoclay. The organoclay was formed by a cation exchange reaction between a NA+-montmorillonite clay and an ammonium salt of dodecylamine. Two polyimide precursors, a poly(amic ester) (PAE) and a poly(amic acid) (PAA), were used in this study. The PAE was prepared by direct polymerization of 2,2′-bis-(3-amino-4-hydroxyphenyl)hexafluoropropane and bis(n-butyl)ester of pyromellitic acid in the presence of phenylphosphonic dichloride as an activator. The polymer had an inherent viscosity of 0.23dL/g. The PAA copolymer was prepared by polymerization of pyromellitic dianhydride, oxydiphthalic anhydride and oxydianiline. The polymer had an inherent viscosity of 1.00dL/g. Two photosensitive resin/clay formulations were prepared from these two PI precursors using 2,3,4-tris(1-oxo-2-diazonaphthoquinone-5-sulfonyloxy)-benzophenone as the photosensitizer and 3wt% organoclay. The films obtained from the PAA formulation were transparent and tough, while the films prepared from the PAE formulation were opaque and brittle. Both X-ray diffraction and transmission electron microscope analyses showed that, although the organoclay was not dispersed well in the PAE matrix, it was dispersed in the PAA matrix on a nanometer scale. The clay particles remained well dispersed after the PAA film was thermally imidized. The CTE of the polyimide film obtained was 23% lower than that of a similar film that did not contain the organoclay. The temperature at which the polyimide underwent a 5% weight loss when subjected to TGA in nitrogen was also increased by 13%. The photosensitive PAA/clay nanocomposite showed a sensitivity of 301mJ/cm2 and a contrast of 1.66 when a 0.2wt% tetramethylammonium hydroxide developer was used. A line/space pattern with a resolution of 10 μm was obtained from this formulation.

Synthesis and characterization of a positive‐working, aqueous‐base‐developable photosensitive polyimide precursor

AbstractA positive‐working, aqueous‐base‐developable photosensitive polyimide precursor based on poly(amic ester)‐bearing phenolic hydroxyl groups and a diazonaphthoquinone photosensitive compound was developed. The poly(amic ester) was prepared from a direct polymerization of 2,2′‐bis‐(3‐amino‐4‐hydroxyphenyl)hexafluoropropane and bis(n‐butyl)ester of pyromellitic acid in the presence of phenylphosphonic dichloride as an activator. Subsequently, the thermal imidization of the poly(amic ester) precursor at 300°C produced the corresponding polyimide. The inherent viscosity of the precursor polymer was 0.23 dL/g. The cyclized polyimide showed a glass‐transition temperature at 356°C and a 5% weight loss at 474°C in nitrogen. The structures of the precursor polymer and the fully cyclized polymer were characterized by Fourier transform infrared spectroscopy and 1H‐NMR. The photosensitive polyimide precursor containing 25 wt % diazonaphthoquinone photoactive compound showed a sensitivity of 150 mJ/cm2 and a contrast of 1.65 in a 3 μm film with 1.25 wt % tetramethylammonium hydroxide developer. A pattern with a resolution of 10 μm was obtained from this composition. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 352–358, 2002

Integration and electrical characterization of photosensitive polyimide

A base line process of photosensitive polyimide was developed to significantly reduce cycle time in backend polyimide processes as compared to the use of conventional nonphotosensitive polyimide. A 6 μm resolution was obtained by the use of a wet etch process of photosensitive polyimide (PSPI) in aqueous tetramethylammonium hydroxide developer. The feasibility of the polyimide as a passivation stress-buffer layer and passivation-etch mask was also demonstrated. Electrical characterization was performed to measure the surface resistance and the intralevel leakage current along the interface between the polyimide and tetraethylorthosilicate. These findings suggested that reduction of the moisture content of the polymer films is critical to ensure electrical isolation during the integration of PSPI into multilevel structures.

Two-component photoresists containing thermally crosslinkable photoacid generators

Bis{4-[2-(vinyloxy)ethoxy]phenyl]-4-methoxyphenylsulfonium triflate (TPS-2VE-Tf) and tris{4-[2'-(vinyloxy)ethoxy]phenyl}sulfonium triflate (TPS-3VE-Tf) were synthesized as thermally crosslinkable photoacid generators (PAGs) and used in a two-component chemically amplified photoresist system. The photoresist films formulated with poly(p-hydroxystyrene) (PHS) as a binder polymer and a thermally crosslinkable PAG are insolubilized in aqueous base by prebaking due to the thermal crosslinking reaction between PHS and the PAG. The insolubilization temperature of the resists and conversion of vinyl ether groups are greatly influenced by the PAG concentration and prebaking temperature, respectively. Upon exposure to deep UV and subsequent postexposure bake, the crosslinks are cleaved by photogenerated acid, leading to effective solubilization of the exposed areas. Photoresists containing TPS-2VE-Tf and TPS-3VE-Tf exhibited sensitivities of 12 and 45 mJ/cm 2 , respectively. Positive-tone images were obtained using a 2.38 wt% aqueous tetramethylammonium hydroxide developer.