Sequential infiltration synthesis and pattern transfer using 6 nm half-pitch carbohydrate-based fingerprint block copolymer

Directed self-assembly of block copolymers is considered one of the candidates to fulfill the requirements of the next technological nodes [1,2]. Polymer domains are aligned by using a chemical and/or a topographical pre-pattern in which preferential surfaces to one of the two blocks or neutral wetting areas are created. In particular, polystyrene-block-polymetylmethacrylate (PS-b-PMMA) has been extensively studied during the last years showing strong capabilities to define periodic nanostructures. However, the relatively low Flory-Huggins parameter and, the resulting low segregation strength of PS-b-PMMA systems, limit their achievable resolution to around 11 nm [3]. The application of block copolymer on sub-10 nm technologies requires the development of the new block copolymer generation known as high- block copolymers. Additionally, an important requirement for their integration on the lithography roadmap is the capability of selectively remove one of the two blocks. The etch contrast between the two domains is typically low due to their organic chemistry. In this sense, selective sequential infiltration synthesis by ALD into one of the blocks can be used in order to incorporate an inorganic material. The formed organic/inorganic blend sustains better the plasma etching to remove the non-infiltrated organic block. In this contribution, we show the use of high- polystyrene-b-polylactide acid (PS-b-PLA) lamellar block copolymer for line/space applications. PS-b-PLA has a larger Flory-Huggins parameter (=0.218 at room temperature[4]) compared with PS-b-PMMA, allowing the size reduction of the self-assembled domains. The method to control the orientation of the polymer domains is similar to the one typically used for PS-b-PMMA. Chemical contrast and the subsequent alignment of the polymer domains are achieved by the definition of a chemical pre-pattern on a random copolymer PS-r-PMMA (48% of PS) (figure 1). The polymer brush is grafted on the substrate and then locally modified by the combination of e-beam lithography and soft oxygen plasma. Afterwards, the PS-b-PLA block copolymer is spin-coated and thermally annealed on the chemically pre-patterned substrate. A chemical contrast is observed between the modified and unmodified stripes. While, the lamellar domains are oriented perpendicular to the substrate on unmodified areas, PLA domains are strongly attracted to the O2 modified surfaces inducing a parallel orientation to the substrate. Additionally, the wetting behavior of the polymer domains is also studied through the difference of surface free energy between the substrate and each polymer block. The energy estimated by the Young´s equation [Δγ =γSA -γSB= γAB·cos(ØAB)], where γSA and γSB are the interface tensions between homo-polymers A and B with the substrate, and ØAB is the contact angle between A and B homo-polymers which is obtained in de-wetting experiments. Finally, sequential infiltration synthesis is used to selectively infiltrate alumina (Al3O2) on PLA domains (figure 2). A selective infiltration is achieved because the precursor molecules react with the carbonyl (C=O) groups that are only present in the PLA block. After five cycles of SIS, the SIS modified PLA domains become more resistant to O2 plasma etching than PS enabling the PS etching without using other kind of hard-masks. The research leading to these results received funding from the European Union's Seventh Framework Program FP7/2007-2013, under the project CoLiSA and the European Nanoelectronics Initiative Advisory Council under the project PLACYD (ENIAC-2013-2). L. Evangelio acknowledges MECD for the PhD contract FPU13/03746 [1] R. Ruiz, H. Kang, F. A. Detcheverry, E. Dobisz, D. S. Kercher, T. R. Albrecht, J. J. de Pablo, P. F. Nealey, Science 321 (2008) 936-939. [2] M. Fernández-Regúlez, L, Evangelio, M. Lorenzoni, J. Fraxedas, F. Perez-Murano, ACS Appl. Mater. Interfaces 6 (2014) 21596-21602. [3] L. Wan, R. Ruiz, H. Gao, K. C. Patel, T. R. Albrecht, J. Yin, J. Kim, Y. Cao, G. Lin, ACS Nano 9 (2015) 7506-7514 [4] A. S. Zalusky, R. Olayo-Valles , J. H. Wolf , M. A. Hillmyer, J. Am. Chem. Soc. 124 (2002) 12761-12773

Vapor phase infiltration into a self-assembled block copolymer (BCP) to create a hybrid material in one of the constituent blocks can enhance the etch selectivity for pattern transfer. Multiple pulse infiltration into carbohydrate-based high-χ BCP has previously been shown to enable sub-10 nm feature pattern transfer. By optimizing the amount of infiltrated material, the etch selectivity should be further improved. Here, an investigation of semi-static sequential infiltration synthesis of trimethyl aluminum (TMA) and water into maltoheptaose (MH) films, and into hydroxyl-terminated poly(styrene) (PS-OH) films, was performed, by varying the process parameters temperature, precursor pulse duration, and precursor exposure length. It was found that, by decreasing the exposure time from 100 to 20 s, the volumetric percentage on included pure Al2O3 in MH could be increased from 2 to 40 vol% at the expense of a decreased infiltration depth. Furthermore, the degree of infiltration was minimally affected by temperature between 64 and 100 °C. Shorter precursor pulse durations of 10 ms TMA and 5 ms water, as well as longer precursor pulses of 75 ms TMA and 45 ms water, were both shown to promote a higher degree, 40 vol%, of infiltrated alumina in MH. As proof of concept, 12 nm pitch pattern transfer into silicon was demonstrated using the method and can be concluded to be one of few studies showing pattern transfer at such small pitch. These results are expected to be of use for further understanding of the mechanisms involved in sequential infiltration synthesis of TMA/water into MH, and for further optimization of carbohydrate-based etch masks for sub-10 nm pattern transfer. Enabling techniques for high aspect ratio pattern transfer at the single nanometer scale could be of high interest, e.g., in the high-end transistor industry.

Selective deposition of amorphous hydrogenated carbon films used as masks for reactive ion etching of Si using CF 4

Enhanced EUV lithography (EUVL) resist performance, combined with optimized post processing techniques, are vital to ensure continued scaling and meet the requirements for the industry N5 node and beyond. Sequential infiltration synthesis (SIS) is a post lithography technique that has the potential to significantly improve the EUVL patterning process for stochastic nano-failures and line roughness, both major topics in EUV lithography research. SIS is an ALD-like technique that infiltrates polymeric photoresists, forming a metal framework using the lithography pattern as a template. Hardening of the photoresist improves the pattern quality and gives more flexibility to subsequent pattern transfer steps. We have evaluated the performance of SIS for an EUV Chemically Amplified Resist (CAR) platform printing 32 nm pitch line/space patterns and ultimately structures that are representative of standard semiconductor manufacturing. A combined lithography-SIS-etch process and a standard lithography-etch process were optimized for an industry relevant stack with pattern transfer into a TiN layer. This allows for the first time a justified comparison between a EUVL-SIS and a standard EUVL patterning process, showing the benefits of SIS regarding roughness, exposure latitude and nano-failure mitigation. Power Spectral Density (PSD) analysis accurately demonstrates and explains the type of roughness improvement. Nano-failure analysis is done by measuring large areas at different exposure doses and shows the improvement of the nano-failure free window when applying a EUVL-SIS patterning process. We conclude by examining to which extent combining the best lithography process with an optimized SIS step will lead to a better roughness and nano-failure performance, essential to meeting industry requirements.

Today’s nanofabrication techniques require multistep and costly processes in order to fabricate complex, multi-materials nanostructures. Performing atomic layer deposition (ALD) within polymeric templates can offer a simple solution for nanostructure fabrication. In this process, named sequential infiltration synthesis (SIS), high partial pressures and long exposures times lead to inorganic materials growth within polymers. Sequential polymer removal results in polymer-templated inorganic nanostructure. While SIS shows great potential in fabricating large variety of structures, it is currently limited to a single material growth process.In our research, we utilized SIS properties to achieve two different objectives: selective spatial growth and homogenous growth for doped materials. We demonstrated, for the first time, multi-material SIS process with control over the spatial location of each material and fabricate heterostructure nanorods and nanowires. Doping materials were fabricated using simultaneously growth of two precursors.We studied SIS within self-assembled block copolymer (BCP) films and electrospun polymer fibers and developed multi-material SIS, where two metal oxides are grown together in a single process, with precise control over their location within the polymer template. We used cylinder forming poly (styrene-block-methyl methacrylate) (PS-b-PMMA) films and electrospun PMMA as the polymeric template and DEZ (diethyl zinc), TMA (trimethyl aluminum) as the organometallic precursors. We achieved control over the growth location of each metal oxide by tuning the organometallic precursors diffusion time, forming heterostructures after polymer removal. A short exposure of the first precursor resulted in a limited growth only at the outer part of the polymer, while a long exposure of the second precursor enabled it to reach the full depth of the polymer besides the section which was already occupied by the first precursor. An exposure to water completed the cycle. We demonstrated this process on BCP films to achieve AlOx-ZnO nanorods arrays (Figure 1A-B) and on polymer fibers to achieve AlOx-ZnO fibers (Figure 1C-D). We performed structural characterization using scanning and transmission electron microscopy (SEM and TEM, respectively) to characterize the nanowires and nanorods as well as three-dimensional characterization scanning TEM (STEM) tomography and energy-dispersive X-ray spectroscopy (EDS) STEM tomography in order to probe the structure and the chemical composition in 3D. To fabricate doped materials, we applied SIS process with TMA and DEZ in the same exposure within homopolymer film. We preformed SEM-EDS to quantify each element and evaluate the doping percentage. This research opens new pathways for multi-materials nano scale structure fabrication through ALD-based growth within polymers.Figure 1 caption: AlOx-ZnO nanorods array: cross-sectional views using A) EsB detector and B) secondary electron in-lens detector. AlOx-ZnO fibers C) EDS map D) HAADF image [1] R. Azoulay et al., Small, 15, 1904657 (2019).[2] R. Azoulay et al., ACS Appl. Nano Mater., 5, 7228 (2022). Figure 1

Photocatalytic self-cleaning coatings with a high surface area are important for a wide range of applications, including optical coatings, solar panels, mirrors, etc. Here, we designed a highly porous TiO2 coating with photoinduced self-cleaning characteristics and very high hydrophilicity. This was achieved using the swelling-assisted sequential infiltration synthesis (SIS) of a block copolymer (BCP) template, which was followed by polymer removal via oxidative thermal annealing. The quartz crystal microbalance (QCM) was employed to optimize the infiltration process by estimating the mass of material infiltrated into the polymer template as a function of the number of SIS cycles. This adopted swelling-assisted SIS approach resulted in a smooth uniform TiO2 film with an interconnected network of pores. The synthesized film exhibited good crystallinity in the anatase phase. The resulting nanoporous TiO2 coatings were tested for their functional characteristics. Exposure to UV irradiation for 1 h induced an improvement in the hydrophilicity of coatings with wetting angle reducing to unmeasurable values upon contact with water droplets. Furthermore, their self-cleaning characteristics were tested by measuring the photocatalytic degradation of methylene blue (MB). The synthesized porous TiO2 nanostructures displayed promising photocatalytic activity, demonstrating the degradation of approximately 92% of MB after 180 min under ultraviolet (UV) light irradiation. Thus, the level of performance was comparable to the photoactivity of commercial anatase TiO2 nanoparticles of the same quantity. Our results highlight a new robust approach for designing hydrophilic self-cleaning coatings with controlled porosity and composition.

Nanoscale patterning of inorganics is crucial for the fabrication of advanced electronic, photonic, and energy devices. The emerging sequential infiltration synthesis (SIS) method fabricates nanofeatures by block-selective vapor-phase growth in block copolymer templates with tunable patterns. Yet, SIS has been demonstrated mainly for Al2O3 and a few other metal oxides, while deriving metal nanostructures from a single SIS process is a challenge. Here, we present SIS of the Ru metal in polystyrene-block-polymethyl methacrylate (PS-b-PMMA) templates without any pretreatment, using alternating infiltration of RuO4 and H2. RuO4 interacts selectively and strongly with the aromatic C═C and C–H groups in PS, leaving the PMMA domains inert. Density functional theory calculations corroborate that the PS–RuO4 interaction is energetically favorable, with a calculated interaction energy of −1.65 eV, whereas for PMMA–RuO4, the calculated energy of −0.05 eV indicates an unfavorable interaction. Morphological analysis on the di-BCP after the RuO4-H2 process indicates an increase in contrast as a function of SIS cycles and templated Ru incorporation. The crystalline nature of the Ru deposits is confirmed using grazing incidence wide-angle X-ray scattering. Plasma-aided removal of the organic components yields Ru nanolines with lateral dimensions of ca 20 nm. We further highlight the broad potential of RuO4 as a reactant for SIS by generating RuO2 nanopatterns via alternating RuO4 and methanol infiltration.

Sequential infiltration synthesis (SIS) is derivative of atomic layer deposition (ALD) that expands the morphological palate of materials to enable an even greater variety of applications. During SIS, a vapor phase precursor reversibly and selectively adducts with a polymer matrix. By controlling the polymer moieties, precursor chemistry, and reaction parameters such as time, temperature, and pressure, the process can yield precise deposition and high growth rates (equivalent to > 30 nm/cycle) in complex matrices that are 100s of nanometers thick. In our work, we leverage those parameters to deposit nano-porous In2O3 electrodes for water remediation. Electrified water treatment has the potential to greatly improve energy and cost efficiency over current methods. SIS has been used previously to create well-defined nano-porous structures, yet there has not been a report of an electrode developed via SIS. Our work describes how amorphous InOHx clusters deposited by SIS combine to form an interconnected and electrically conductive network of crystalline In2O3. Changes in optical parameters, probed by spectroscopic ellipsometry, reveal that the oxygen annealing burns off the polymer and leads to partial densification of the film. XRD and TEM further demonstrate the development of a crystalline network of In2O3 with grain sizes of approximately 20 nm. Additional annealing in forming gas yields resistivity values on the order of 10-3 Ω*m. Aside from the annealing conditions, the microstructure of the In2O3 network also influences electrical properties. Using SIS to control the volume fraction of In2O3 in PMMA, annealed samples were prepared with porosity ranging from 30-80% In2O3. As the amount of In2O3 increases, Hall measurements reveal that the resistivity decreases and the mobility increases, which suggests that the prevalence of charge conduction pathways within the In2O3 film can be controlled. We demonstrate nano-porous In2O3 films with tunable electrical properties and further highlight the opportunity to precisely control properties of In2O3 for applications such as water remediation.

Sequential infiltration synthesis (SIS) is a route to the precision deposition of inorganic solids in analogy to atomic layer deposition but occurs within (vs upon) a soft material template. SIS has enabled exquisite nanoscale morphological complexity in various oxides through selective nucleation in block copolymers templates. However, the earliest stages of SIS growth remain unresolved, including the atomic structure of nuclei and the evolution of local coordination environments, before and after polymer template removal. We employed In K-edge extended X-ray absorption fine structure and atomic pair distribution function analysis of high-energy X-ray scattering to unravel (1) the structural evolution of InOxHy clusters inside a poly(methyl methacrylate) (PMMA) host matrix and (2) the formation of porous In2O3 solids (obtained after annealing) as a function of SIS cycle number. Early SIS cycles result in InOxHy cluster growth with high aspect ratio, followed by the formation of a three-dimensional network with additional SIS cycles. That the atomic structures of the InOxHy clusters can be modeled as multinuclear clusters with bonding patterns related to those in In2O3 and In(OH)3 crystal structures suggests that SIS may be an efficient route to 3D arrays of discrete-atom-number clusters. Annealing the mixed inorganic/polymer films in air removes the PMMA template and consolidates the as-grown clusters into cubic In2O3 nanocrystals with structural details that also depend on SIS cycle number.

Directed self-assembly (DSA) of block copolymers (BCPs) is one of the most promising techniques to tackle the everincreasing demand for sub-lithographic features in semiconductor industries. BCPs with high Flory Huggins parameter (χ) are of particular interest due to their ability to self-assemble at the length scale in sub-10 nm regime. However, such high-χ BCPs typically have imbalanced surface energies between respective blocks, making it a challenge to achieve desired perpendicular orientation. To address this challenge, we mixed a polymeric additive with poly(2-vinylpyridine)- block-polystyrene-block-poly(2-vinylpyridine) (P2VP-b-PS-b-P2VP) and successfully achieved perpendicular orientation control of the triblock copolymer. The polymeric additive has lower surface energy than both PS and P2VP blocks, and it selectively interacts with high surface energy P2VP blocks via hydrogen bonding. As a result, the surface energies of PS and P2VP blocks are balanced and perpendicular orientation forms upon thermal annealing. Using this approach, we demonstrate 5X density multiplication DSA with a half pitch of 8.5 nm via chemo-epitaxy. This material system is also amenable to sequential infiltration synthesis (SIS) without the need to remove the additive, revealing its pattern transfer potential. We believe that this integration-friendly DSA approach using simple thermal annealing holds the promise of bringing high-χ BCPs to advanced nanopatterning applications.

Physical and chemical surface modifications are commonly used in many applications such as energy generation and storage, microelectronics, water purification, gas separation, and medical/plant biology. In recent several years, sequential infiltration synthesis (SIS), a variant of atomic layer deposition (ALD), has emerged as a promising technology that uses self-limiting reactions to create hybrid organic/inorganic materials within the polymer-free volume. Herein, we employed ALD/SIS of Al2O3, SnO2, Ga2O3, TiO2, and In2O3 to precisely tune the pore size and surface characteristics of track-etched polycarbonate membranes. We used in situ Fourier transform infrared spectroscopy to elucidate the chemistry for Al2O3 SIS in polycarbonate and in situ quartz crystal microbalance measurements to probe the extent of Al2O3 infiltration during SIS in polycarbonate thin films. Next, we used scanning electron microscopy, thermogravimetric analysis, and water permeance measurements to probe the pore size reduction and conformality of SIS Al2O3 in the track-etched polycarbonate membranes. We then used water permeance measurements to compare the water flux for a series of membranes with similar pore size but different pore wall chemistry and compared these results with water contact angle measurements. Interestingly, the hydrophilic metal oxide coatings yielded higher water flux values compared to hydrophobic coatings. Finally, we examined ion-selective transport in the modified track-etched polycarbonate membranes and rationalized the results using zeta potential measurements of the ALD metal oxides. Keywords: atomic layer deposition; sequential infiltration synthesis; metal oxides; hydrophilicity/hydrophobicity; permeability; surface charge; ion conductivity/selectivity.

In this work, an alternative dry etching approach for parylene AF4 is presented based on a photoresist soft mask, which results in a relatively simpler, faster, cheaper and environmentally friendly process in comparison to the typical dry etching process with a hard mask. 2.5 µm thick parylene AF4 was deposited on a silicon (Si) substrate by vapor deposition polymerization (VDP). A 5 µm thick photoresist was used as a soft mask, while parylene AF4 patterning was done using an oxygen (O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> )-argon (Ar) inductively coupled plasma reactive ion etching (ICP-RIE) process. The AF4:photoresist selectivity was around 1 while the AF 4 etching rate was roughly 275 nm/min for an Ar/02 ratio of 0.1 at 20mTorr and ICP:CCP powers of 1000W:50W respectively. The influence of the ICP plasma parameters on the AF 4 etching rate was investigated and the results suggested a predominant oxygen radicals-based reactive chemical etching mechanism.

Sequential infiltration synthesis (SIS) is a powerfulapproachfor templated growth of solid materials, such as oxides or metals,that exploits the difference in interaction of a precursor moleculewith a polymer or block copolymer. While there have been studies showingthat infiltration of trimethyl-aluminum (TMA) in polymers can be usedto grow Al2O3, there are still many atomic leveldetails of the SIS process that require more investigation, includingthe origin of the differences in infiltration of TMA into differentpolymers. In this paper, we investigated in detail the infiltrationof Al2O3 into poly­(methyl methacrylate) (PMMA)and poly­(lactic acid) (PLA) experimentally and theoretically. SISwas performed in a standard ALD reactor, operating at 70 °C inquasi-static mode, using TMA and water as the metal and oxygen precursors,respectively. Operando spectroscopic ellipsometry and ex-situ X-rayphotoelectron spectroscopy (XPS) evidenced that Al2O3 incorporation in PLA is significantly higher than in PMMAeven if, in both cases, TMA incorporation occurs through the formationof an Al–O covalent bond at the C–O–C group.The extent of swelling of the polymers upon TMA infiltration is assessedand is clearly larger for TMA in PLA than in PMMA. First-principlesdensity functional theory (DFT) calculations highlighted that bothpolymers display swelling upon TMA infiltration, saturating with increasingTMA, consistent with operando ellipsometry observations. The DFT resultsalso show the origin of the larger swelling in PLA compared to TMA.Changes in vibrational modes of carbonyl backbone groups in the polymersare used to demonstrate TMA-polymer interactions from both experimentand simulation. The differences in TMA infiltration and swelling arisefrom differences in the TMA-polymer C–O–C group interaction,which is more exothermic in PLA than in PMMA, in agreement with experimentalresults. The combination of experimental and theoretical studies hereinreported provides a toolkit to disclose the complexities of SIS atthe molecular level.

Self-assembly block copolymers have drawn a lot of attention for its great potential on critical dimension (CD) control and line-edge roughness (LER) reduction, which become more and more crucial as the CD of transistors is only tens of nanometers nowadays. In this study, lamellar-forming poly(styrene-b-methyl methacrylate) copolymer which fabricates line patterns was chosen for its ability to provide higher aspect ratio and vertical sidewall profile in template stage, thus more suitable for the following etching process to substrate. A dry plasma etching process using pure oxygen and pure argon plasma as example chemical etching gas and physical etching gas, respectively, was studied. Etching selectivity and lateral etch rate, which are responsible for the final template height and CD loss, had been characterized on a capacitive reactive ion etching tool. The templates formed by the proposed process had high aspect ratios, excellent pattern fidelity, and low LER values. The PS lateral etch rate was small enough to provide a wide process window for retaining the CD of the pattern during the template forming process. Subsequent silicon etching using the PS template made by dry etching process yielded a steep and smooth sidewall profile.

Capacitively coupled plasma reactive ion etching of silicon by injecting nitrogen trifluoride (NF3) gas was conducted, and the etching process was studied with a residual gas analyzer and an optical emission spectroscopy. During the etching of silicon by the NF3 plasma, the currents of F+ and SiF+3 ions were obtained from the residual gas analyzer. At the same time, the line intensity of fluorine was measured using optical emission spectroscopy. The ion currents of F+ and SiF+3 and the line intensity of fluorine were highest for etching at high pressure. With the results of this study, the general characteristics of reactive ion etching of silicon by using NF3 plasma were confirmed. In addition, by simply changing the flow rate of NF3, a high NF3 flow rate was found to result in a high etch rate because of the reduced residence time.