Self-assembled Monolayer Films Research Articles

Electron Transfer Capability in Atomic Hydrogen Reactions for Imidazole Groups Bound to the Insulating Alkanethiolate Layer on Au(111).

The charge transfer capability associated with chemical reactions at metal-organic interfaces was studied via the atomic H addition reaction for an imidazole-terminated alkanethiolate self-assembled monolayer (Im-SAM) film on Au(111) at room temperature, using near-edge X-ray absorption fine structure spectroscopy, infrared reflection absorption spectroscopy, work function measurements, and density functional theory calculations. The imidazolium cation is a stable species in liquids; therefore, it is pertinent to determine whether the hydrogenation reactions of the imidazole groups produce imidazolium cations accompanied by electron transfer to the Au substrate, even in the absence of solvate and/or counterions on the insulating alkanethiolate layer. The experiments made it clear that the imidazolium moieties were formed during the irradiation of Im-SAM with atomic H. Theoretical model calculations also revealed that the total energies and molecular orbital levels satisfied the imidazolium cation formation associated with electron transfer. In a detailed analysis of the work function change depending on H irradiation, we confirmed that some of the imidazolium radicals became cations in Im-SAM.

In situ differential atomic force microscopy (AFM) measurement for ultra-thin Thiol SAM patterns by area-selective deposition technique

Developing novel characterization methods is crucial to enhancing the accuracy and precision of measurements in semiconductor ultrathin films. By combining "bottom-up" and "top-down" patterning techniques, we successfully fabricated five uniform alkyl thiol-derived self-assembled monolayer (SAM) patterns. Employing the innovative in situ differential Atomic Force Microscopy (AFM) Measurement, we analyzed the thickness, morphology, and mechanical properties of the thiol films. This method greatly reduced errors caused by uneven substrates, resulting in more precise measurements compared to large-area measurements. It is shown that as the thiol chain length increased, the variation in SAM film thickness aligned consistently with the thickness of a single Atomic Layer Deposition (ALD) cycle, and the surface roughness of the SAM surface mirrored that of ALD. Consequently, the experiment affirms the effectiveness of the SAM film in simulating ALD, providing validation for the precision and feasibility of the in situ differential results. Furthermore, adhesion measurement results revealed a diminishing passivation effect of SAM as the chain length increased. This suggests that an appropriate SAM could be selected as a passivation material through real-time monitoring of the mechanical properties of the mask surface during the Area-Selective Deposition (ASD) process.

Altering Spin Distribution of Tb2Pc3 via Molecular Chirality Manipulation.

Manipulating the chirality of the spin-polarized electronic state is pivotal for understanding many unusual quantum spin phenomena, but it has not been achieved at the single-molecule level. Here, using scanning tunneling microscopy and spectroscopy (STM/STS), we successfully manipulate the chirality of spin distribution in a triple-decker single-molecule magnet tris(phthalocyaninato)bis(terbium(III)) (Tb2Pc3), which is evaporated on a Pb(111) substrate via molecular beam epitaxy. The otherwise achiral Tb2Pc3 becomes chiral after being embedded into the self-assembled monolayer films of bis(phthalocyaninato)terbium(III) (TbPc2). The chirality of the spin distribution in Tb2Pc3 is manifested via the spatial mapping of its Kondo resonance state from its ligand orbital. Our first-principles calculations revealed that the spin and molecular chirality are associated with a small rotation followed by a structural distortion of the top Pc, consistent with the experimental observation. By constructing tailored molecular clusters with the STM tip, a single Tb2Pc3 molecule can be manipulated among achiral and differently handed chiral configurations of spin distributions reversibly. This paves the way for designing chiral spin enantiomers for fundamental studies and developing functional spintronic devices.

Vibrational spectrum perturbations of alkanethiol self-assembled monolayers with noble gases and chlorinated species

This study aims to improve our understanding of some differences in odd and even chain-length alkanethiol self-assembled monolayers (SAMs) using infrared reflection absorption spectroscopy (IRRAS) and density functional theory (DFT). Xe, Kr, CH2Cl2, CD2Cl2, and CDCl3 were used experimentally to perturb the CH2 and CH3 stretches arising from the tail region of the SAM films and changes in position and intensity were monitored in the infrared. Using DFT methods, noble gases and CH2Cl2 were added to models of the SAM monolayers, and energies and vibrational spectra were calculated. It was observed that perturbing species affected the CH3 symmetric and asymmetric stretches on hexadecanethiol SAMs (an “even” SAM with a 16-carbon backbone) while on pentadecanethiol SAMs (an “odd” SAM with a 15-carbon backbone) both CH2 and CH3 symmetric and asymmetric stretches were affected. Films formed with shorter chain-length species, hexanethiol (even) and pentanethiol (odd), had less consistent results, likely due to more disorder in the alkanethiol chains from weaker van der Waals interactions. Adsorption energies for different perturbing species on the monolayers were higher for the hexanethiol than the pentanethiol. The vibrational spectrum of pentanethiol monolayers with adsorbed species mainly showed shifts to higher frequencies for CH2 and CH3 stretches; for hexanethiol, shifts to lower frequencies for CH2 stretches and higher frequencies for CH3 stretches were observed. Thus, the odd and even alkanethiol SAMs were affected differently by the perturbing species as observed both experimentally and computationally.

Bingöl propolis self-assembled monolayer films: Preparation, characterization and application as corrosion inhibitors for copper protection in NaCl environment

Protective thin films prepared from natural products can be used as an economical, efficient and environmentally friendly method to mitigation corrosion. The aim of this study is to prepare self-assembled monolayer (SAM) films of Bingöl propolis (B-PP) sourced from the northern regions of Bingöl province (Adaklı, Kiğı, Yayladere, and Yedisu) under various experimental conditions for the protection of copper against corrosion in a 3.5 % NaCl environment. The B-PP/SAM films were prepared under various conditions including different solvents, film formation times, and B-PP concentrations. The protective performance of the B-PP/SAM films was evaluated using various electrochemical techniques and the films were characterized using various surface characterization techniques. It was found that highly adherent, dense and aesthetically pleasing B-PP/SAM films were homogenously prepared on the copper surface. The assembly conditions significantly influence both the appearance and electrochemical properties of the films. The most effective B-PP/SAM films for copper protection were prepared using ethanol as a solvent containing 1000 ppm B-PP after a 24 h film formation time. According to potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) results, the protection efficiencies were 95.3 %, 95.5 % and 96.8 %, respectively.

Fabrication of Bingöl pollen self-assembled monolayer films on copper as a novel cathode for electrochemical hydrogen production

Preparation of a thin organic film on metallic electrodes can protect substrates against corrosion. These organic underlayers also help electrodeposition of metallic electrocatalysts as well as enhance the quality and performance of electrodes. In this study, a thin self-assembled monolayer film of Bingöl pollen (BP-SAM) was fabricated on a copper substrate (Cu/BP-SAM) in pure water as solvent. The film was prepared by exposing a Cu substrate to a 1000 ppm aqueous pollen solution for 24 h assembly time. Then, a small amount of Ni, known for its good catalytic properties for water splitting process, was electrodeposited over the previously assembled SAM film (Cu/BP-SAM/Ni) to enhance its catalytic effect for hydrogen evolution reaction. The modified surfaces were analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), and contact angle (CA) studies. Water splitting activity of the Cu/BP-SAM and Cu/BP-SAM/Ni electrodes were investigated in 6 M KOH solution at 298 K. The data obtained indicated that the modification of Cu surface with BP-SAM and BP-SAM/Ni reduces polarization resistance (Rp) by 35.3% and 84.4%, respectively at −100 mV cathodic overpotential. The BP-SAM films were adherent to the Cu substracte and have a uniform structure. Ni particles were homogenously deposed over the SAM film and have high quality. The Cu/BP-SAM/Ni electrode has promising electrochemical time-stability during the electrolysis and losses only 6.5% of its activity during the long-time electrolysis.

Functionalizing self-assembled monolayers to reduce interface scattering in ruthenium/dielectric for next-generation microelectronic interconnects

As the number of transistor increases in modern devices, the resistivity of metal lines increases with the downscaling of the vias dimension due to the increased in surface scattering of electrons. Herein, we evaluated the electrical performance and the adhesion strength of the Ru/SiO2 substrate upon functionalizing with benzyliminetriethoxysilane (BITES) and aminoproyltriethoxysilane (APTES) self-assembled monolayers (SAMs)s at the Ru/SiO2 interface. The covalent bonding and retention of the SAM film on the SiO2 surface were characterized via angle-resolved X-ray Photoelectron Spectroscopy (AR-XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (Tof-SIMS), respectively. According to the Fuchs–Sondheimer (FS) model and scratch test, the specularity parameter and the adhesion strength of the Ru/BITES/SiO2 simultaneously improved after thermal annealing compared to the non-functionalized Ru/SiO2 substrate. The effect of different SAM’s terminal groups (amine and benzylimine) on the electron scattering behavior was investigated based on the formation of an interface dipole upon chemisorption of organic molecules on the metal film. Our results indicate that SAM with the benzylimine terminal group formed a larger positive dipole at the SAM layer of the Ru/BITES/SiO2 interface compared to the Ru/APTES/SiO2, leading to an increased in specular electron scattering events and, thus an enhanced electrical performance of the Ru/BITES/SiO2.

Thermal Stability and Orthogonal Functionalization of Organophosphonate Self-Assembled Monolayers as Potential Liners for Cu Interconnect.

In this study, we investigated the thermal stabilities of butylphosphonic acid (BPA) and aminopropyltriethoxysilane (APTES) self-assembled monolayers (SAM) on a Si substrate. The thermal desorption and the thermal cleavage of the BPA and APTES SAM film on the Si substrate were studied by X-ray photoelectron spectroscopy (XPS) upon thermal treatment from 50 to 550 °C. XPS analyses show that the onset of the thermal desorption of the APTES monolayer occurs at 250 °C and the APTES SAM completely decomposed at 400 °C. Conversely, BPA SAM on Si shows that the onset of thermal desorption occurs at 350 °C, and the BPA SAM completely desorbed at approximately 500 °C. Our study revealed that the organophosphonate SAM is a more stable SAM in modifying the dielectric sidewalls of a Cu interconnect when compared to organosilane SAM. To overcome the spontaneous reaction of the organophosphonate film on the metal substrate, a simple orthogonal functionalization method using thiolate SAM as a sacrificial layer was also demonstrated in this study.

Assessment of anti-corrosion behavior of three triazolyl Schiff bases in 3.5 wt% NaCl Solution: Experimental and theoretical approaches

Three triazole Schiff bases [1-(4-Methylphenyl)-N-(1,2,4-triazol-4-yl)methanimine (A1), 4-(1,2,4-triazol-4-yliminomethyl)phenol (A2) and 1-(4-chlorophenyl)-N-(1,2,4-triazol-4-yl)methanimine (A3)] were synthesized in this work. Self-assembled monolayer films (SAMs) were prepared on copper (Cu) surfaces using the compounds mentioned above respectively. The characterization methods such as contact angle (CA), scanning electron microscopy (SEM) and electrochemical measurement were applied to evaluate the inhibition behaviors of the three Schiff bases in 3.5 wt% NaCl solution on coppers. Electrochemical tests proved their prominent corrosion inhibition performances of the three Schiff bases. Adsorption behaviors of the three Schiff bases on the copper surfaces obeyed Langmuir isotherm adsorption model. Quantum chemical calculation and molecular dynamics simulation (MD) further confirmed the relationship between corrosion inhibition performance and molecular structure.

Elaboration and corrosion resistance of self-assembled 2,5-bis(4-pyridyl)− 1,3,4-oxadiazole film on carbon steel: Surface characterisations, electrochemical assessments and surface pre-treatment effect

The self-assembled monolayers (SAMs) of 2,5-bis(4-pyridyl)− 1,3,4-oxadiazole (4-POX) were formed on carbon steel (CS) surface to improve the corrosion resistance of the substrate in 1 M HCl medium. The structural characterisations of 4-POX/SAMs films were performed by using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM), and contact angle measurements. The protection ability of SAM films against CS-substrate corrosion in 1 M HCl was studied using potentiodynamic polarization and AC impedance techniques. FTIR and XPS results showed that the 4-POX molecules adsorbed on the CS surface, and the contact angle values on the modified surface supported the formation of hydrophobic 4-POX/SAMs. The results of electrochemical measurements indicated, when the self-assembling time increased, the corrosion resistance od 4-POX/SAMs film enhaced, reaching a maximum protection efficiency value of 94.6% for 6 h of self-assembly. Different kinds of surface pre-treatments (amorphous phosphatation (Pa), APTES (PAPTES), and N2 plasma (PN2)) of CS-substrate were then applied in order to improve the corrosion resistance of SAM process.

Highly-Directional, Highly-Efficient Solution-Processed Light-Emitting Diodes of All-Face-Down Oriented Colloidal Quantum Well Self-Assembly.

Semiconductor colloidal quantum wells (CQWs) provide anisotropic emission behavior originating from their anisotropic optical transition dipole moments (TDMs). Here, solution-processed colloidal quantum well light-emitting diodes (CQW-LEDs) of a single all-face-down oriented self-assembled monolayer (SAM) film of CQWs that collectively enable a supreme level of IP TDMs at 92% in the ensemble emission are shown. This significantly enhances the outcoupling efficiency from 22% (of standard randomly-oriented emitters) to 34% (of face-down oriented emitters) in the LED. As a result, the external quantum efficiency reaches a record high level of 18.1% for the solution-processed type of CQW-LEDs, putting their efficiency performance on par with the hybrid organic-inorganic evaporation-based CQW-LEDs and all other best solution-processed LEDs. This SAM-CQW-LED architecture allows for a high maximum brightness of 19,800cd m-2 with a long operational lifetime of 247h at 100cd m-2 as well as a stable saturated deep-red emission (651nm) with a low turn-on voltage of 1.7eV at a current density of 1mA cm-2 and a high J90 of 99.58mA cm-2 . These findings indicate the effectiveness of oriented self-assembly of CQWs as an electrically-driven emissive layer in improving outcoupling and external quantum efficiencies in the CQW-LEDs.

Photoswitchable Nanoporous Metal–Organic Framework Monolayer Film for Light-Gated Ion Nanochannel

Two-dimensional metal–organic framework (MOF) monolayer films, which can be considered as large-area, periodically ordered thin films with atom- or single-unit thickness, have attracted extensive attention due to their special properties and wide range of potential applications. However, the preparation of MOF monolayer films is still a great challenge, and the introduction of functional groups into MOF monolayer films is seldom reported. Here, we report the first centimeter-scale, photo-switchable, free-standing MOF monolayer film formed by self-assembly of poly(methyl methacrylate-co-acrylamidoazobenzene)-coated MOF nanoparticles at the water–air interface. This self-assembled MOF monolayer film is extremely thin (∼220 or 50 nm) and has a high MOF loading (85 wt %), while exhibiting remarkable reversible photoswitching properties under alternating exposure to 365 nm UV and white light. Inspired by this, a light-gated ion nanochannel device is fabricated, which enables reversible ″OFF–ON″ changes of the ionic flux and has promising applications in the field of photoelectric conversion. This provides a modular route to design large-area, free-standing functional MOF monolayer films.

Field-induced modification of the electronic structure in BTBT-based organic thin films observed by NEXAFS spectroscopy

We present an in operando near-edge x-ray absorption fine structure (NEXAFS) study on p-type [11-(benzo[b]benzo[4,5]thieno[2,3-d]thiophen-2-yl)dodecyl)] BTBT-based self-assembled monolayer (BTBT-SAM) films. As a 2D-model system, the BTBT-SAM offers direct insight into the active organic semiconductor layer without interfering bulk materials. This allows for the observation of polaronic states caused by charged species at the dielectric/organic interface. Linear NEXAFS dichroism is employed to derive the molecular orientation of the BTBT subunit. Field-induced modifications in the unoccupied molecular orbitals are observed in the NEXAFS spectra. The spectral changes in the on- and off-states are discussed in the context of polaron formation due to charge accumulation induced by the applied electric field.

P‐4.4: Multifunctional Laminated Organic Passivation Layer on InSnZnO Thin‐Film Transistors for Enhanced Reliability

To improve the stability of the ZnO‐based thin‐film transistors (TFTs) in multiple environments, we propose a new multifunctional laminated organic passivation layer (MLO PVL) structure for ITZO TFTs. This MLO PVL structure is composed of a self‐assembled monolayer (SAM) and an ultraviolet (UV) absorber‐modified polydimethylsiloxane (PDMS) layer, which provides the functionality of both passivation layers at the same time. The SAM film could be prepared by vapor‐phase treatment, while the UV‐absorber‐modified PDMS layer could be fabricated using the spin‐coating method. Thus, the MLO PVL could be manufactured through a low‐temperature and low‐cost process. Compared to the unpassivated devices, the MLO‐passivated ITZO TFTs exhibit better properties, such as an on‐off current ratio (Ion/Ioff) of up to 8.99×109, a field‐effect mobility of 19.55 cm2V−1s−1, and a subthreshold swing (SS) down to 100 mV/dec. Furthermore, the MLO‐passivated ITZO TFTs showed an outstanding improvement in the bias stress stability and UV light illumination stress stability with negligible threshold voltage shifts in both positive bias stress (PBS) and positive bias illumination stress (PBIS) tests. This new passivation structure provides a potential strategy for improving the stability of ZnO‐based TFTs.

Potentiometric Biosensors Based on Molecular-Imprinted Self-Assembled Monolayer Films for Rapid Detection of Influenza A Virus and SARS-CoV-2 Spike Protein.

Rapid, yet accurate and sensitive testing has been shown to be critical in the control of spreading pandemic diseases such as COVID-19. Current methods which are highly sensitive and can differentiate different strains are slow and cannot be conveniently applied at the point of care. Rapid tests, meanwhile, require a high titer and are not sufficiently sensitive to discriminate between strains. Here, we report a rapid and facile potentiometric detection method based on nanoscale, three-dimensional molecular imprints of analytes on a self-assembled monolayer (SAM), which can deliver analyte-specific detection of both whole virions and isolated proteins in microliter amounts of bodily fluids within minutes. The detection substrate with nanoscale inverse surface patterns of analytes formed by a SAM identifies a target analyte by recognizing its surface nano- and molecular structures, which can be monitored by temporal measurement of the change in substrate open-circuit potential. The sensor unambiguously detected and differentiated H1N1 and H3N2 influenza A virions as well as the spike proteins of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and Middle-East respiratory syndrome (MERS) coronavirus in human saliva with limits of detection reaching 200 PFU/mL and 100 pg/mL for the viral particles and spike proteins, respectively. The demonstrated speed and specificity of detection, combined with a low required sample volume, high sensitivity, ease of potentiometric measurement, and simple sample collection and preparation, suggest that the technique can be used as a highly effective point-of-care diagnostic platform for a fast, accurate, and specific detection of various viral pathogens and their variants.

Time of Flight – Secondary Ion Mass Spectroscopy Profiling of Self-Assembled Monolayer Patterns Based on Vapor Deposition Technique

It is crucial to develop novel metrology techniques in a semiconductor fabrication process for characterizing a thin film with a thickness of a few nanometers, as well as the material profile of the film accurately. Uniform trichlorosilane (1H,1H,2H,2H-perfluorodecyltrichlorosilane) derived self-assembled monolayer film patterns were fabricated by several conventional semiconductor fabrication techniques incorporated, including photolithography, vapor deposition, and lift-off technique. The patterned trichlorosilane self-assembled monolayer patterns were thoroughly characterized by Time-of-Flight Secondary Ion Mass Spectrometry, and precise two-dimensional self-assembled monolayer patterns were reconstructed through corresponding ions and ion clusters feature peaks. Additionally, three-dimensional self-assembled monolayer patterns were reconstructed layer by layer through gas cluster ion beam etching and two-dimensional mapping analysis in an alternate way, which verifies that vapor-based trichlorosilane self-assembled monolayer patterns were precisely fabricated and Time-of-Flight Secondary Ion Mass Spectrometry is highly surface-sensitive to obtain accurate information about the self-assembled monolayer pattern in a point-by-point manner. Time-of-Flight Secondary Ion Mass Spectrometry technique could be used as a metrology technique in the semiconductor process with high-quality self-assembled monolayer micro and nanostructures.

Dry-Etchable Molecular Layer-Deposited Inhibitor Using Annealed Indicone Film for Nanoscale Area-Selective Deposition.

In semiconductor production, the technology node of a device is becoming extremely small below 5 nm. Area selective deposition (ASD) is a promising technique for creating improved overlay or self-alignment, remedying a conventional top-down method. However, the conventional materials and process (self-assembled monolayer, polymer and carbon film fabricated by chemical vapor deposition, and spin coating) for ASD are not suitable for highly conformal deposition. Thus, we investigated a new strategy to deposit conformal films in ASD by molecular layer deposition (MLD). The MLD processes were conducted for an indicone film deposited by INCA-1 (bis(trimethysily)amidodiethyl indium) and hydroquinone (HQ), as well as an alucone film deposited by TMA (trimethylaluminum) and HQ. After thermal heat treatment of the MLD films, variations in thickness, refractive index, and constituent elements of the annealed MLD films were investigated. The indicone film was used as an inhibiting layer for ASD and was etchable with a dry-etching process. The reactive ion etching process on annealed indicone film was optimized according to plasma power, gas concentration, and working pressure. Ruthenium (Ru) ALD was then performed on the annealed MLD films to investigate nucleation delaying cycles and inhibiting properties. A patterned substrate with an MLD/Si line was created via the RIE process, which was allowed to observe the selectivity of the annealed MLD films. In addition, a patterned substrate of SiO2/annealed indicone/Mo was used to investigate the Ru-selective ALD at the nanoscale. The Ru thin film was selectively deposited on the Mo side-wall surface of a 3D trench structure. The growth of the Ru film was inhibited selectively on an annealed indicone surface of approximately 5 nm.

A Machine-Learning Approach to Correcting Non-Ideal Background Currents in Disordered Self-Assembled Monolayers

In traditional studies of electroactive molecules tethered to metal surfaces through well-ordered self-assembled monolayers (SAMs), cyclic voltammetry is the primary tool used to measure the coverage of the tethered molecules. The charge under the peak in the voltammogram is directly proportional to the coverage of the redox-active molecules. Accurate coverage measurements are possible because well-ordered SAMs exhibit ideal background currents which are easy to subtract from the total current to isolate the SAMs faradaic current. However, for disordered electroactive SAMs with poor surface blocking properties, specific interactions with the metal substrate create non-ideal background currents which are difficult to separate from the SAMs faradaic current. Although analytical approaches exist to account for background currents in other electrochemical systems, they have some fundamental limitations that impede their practical application to electroactive SAMs. In our work, we propose a simple machine-learning approach to empirically correct for background currents in disordered SAMs, and we apply this approach to determine the surface coverage of partially-desorbed ferrocene-terminated monolayers (Fc-SAMs) from gold surfaces. We use LASSO regression and an ensemble of background scans from partially-desorbed unfunctionalized decanethiol SAMs to approximate the Fc-SAM background currents. Using the approximated background, we estimate the coverage of Fc-SAMs after background correction. This technique allows us to explore Fc-SAM coverage as a function of potential when applying potentials near and beyond the onset of the so-called reductive desorption potential of the SAM which induces non-ideal background currents. To verify the accuracy of the coverages determined using our LASSO method, we used two verification methods: 1) backfilling with decanethiol and 2) chemical stripping of the disordered SAM followed by inductively-coupled plasma-mass spectrometry (ICP-MS). The pros and cons of both confirmation methods will be discussed along with a comparison of error rates and limits of detection between traditional background subtraction method and the LASSO method. We propose that this new approach will enable a more quantitative description of disordered SAM films after reductive desorption events.

Synthesis of octadecyltrichlorosilane self-assembled monolayer films by vapor deposition on plasma activated silicon substrates

Molecular films of octadecyltrichlorosilane (OTS) silanized on silicon substrates were obtained by a succession of fabrication steps consisting in plasma hydroxylation of silicon surface, formation of a water layer adsorbed on hydroxylated surface by substrate exposure to water vapor and OTS vapor deposition. All fabrication steps were realized in the same vacuum chamber to avoid surface contamination and to control the amount of water adsorbed on the hydroxylated surface. It is proved that the amount of water on the substrate surface plays a key role in fabrication of smooth OTS molecular films, large amounts of water on substrates resulting in formation of 3D OTS aggregates. The atomic force microscopy (AFM) investigations of the film surface revealed formation of liquid-expanded and liquid-condensed domains in OTS molecular films. Annealing of the OTS films promotes film dehydration, increases the film hydrophobicity and reduces nanoscopic adhesion and friction forces between silicon AFM tips and film surface.

Chemical and structural characterization of EUV photoresists as a function of depth by standing-wave x-ray photoelectron spectroscopy

The success in the miniaturization of the electronic device constituents depends mostly on the photolithographic techniques. Recently, to achieve patterning at the sub-10-nm node, extreme ultraviolet (EUV) lithography has been introduced into high volume production. Continued scaling of EUV via increased numerical aperture to achieve nodes at 3-nm and below requires the development of fundamentally new patterning materials and new characterization methods. Current EUV-resist film thicknesses are in the 20- to 40-nm range, and further thickness reduction is required for the next generation. Therefore, interfaces become exceedingly important, and the properties of the resist film would be dominated by top and bottom interfacial effects. X-ray photoelectron spectroscopy (XPS) combined with standing-wave excitation (SW-XPS), a fairly new method in the EUV lithography field, previously had been largely applied in multilayers and superlattices for characterizing the composition and electronic structure of buried layers and interfaces as a function of depth. We applied the SW-XPS method to organic/inorganic photoresists to provide depth-selective information on their structural and chemical conditions of as a function of temperature, EUV exposure, different underlayers, and other fundamental parameters. As a first attempt, we perform an SW-XPS feasibility study on self-assembled monolayer (SAM) films after exposure to an electron beam. By SW-XPS, we determined that the interface between the Al2O3 underlayer and the SAMs is smooth, with a mean roughness of about 0.2 nm. Moreover, we determined that the SAM chains are, on average, tilted by ∼30 deg off the sample normal. The SW-XPS results also suggest that the SAM is not a perfectly aligned and uniform monolayer, with some areas having thickness higher than a single monolayer. We demonstrated that SW-XPS can provide useful information on ultrathin materials with high potential for being used as a characterization method of organic/inorganic photoresists.