Step Coverage Research Articles

Optimization of physical vapor deposition process for low background nanoimprinted SERS substrate in quantitative melamine analysis

Uniformity, sensitivity, reproducibility, and cost are the critical parameters of practical surface-enhanced-Raman-spectroscopy (SERS) substrates. Herein, we proposed a High-Aspect-Ratio-Nano-Pillar-Array (HARNPA) substrate deposited silver by physical vapor deposition (PVD) methods (e.g. E-beam evaporation, sputtering, and a two-stage intermittent sputtering) to fabricate high-performance SERS substrates. The substrate by the E-beam evaporation has a significant SERS effect, but the Raman background induced by the exposure of the polymer HARNPA limits the analyte choice. The substrate by the sputtering method has better step coverage of silver but a lower enhancement factor. Therefore, we proposed a process of two-stage intermittent sputtering to solve these limitations. In addition, we define a factor called the signal-to-background peak ratio (S/B peak ratio) to evaluate the influence of the Raman background from the SERS substrate. Finally, we accomplished a SERS substrate with an S/B peak ratio of 3.48 by intermittent sputtering, which has the best linearity (R2 = 0.97) of the melamine concentration curve and the lowest detection limit (LoD = 5.6 × 10-7 M) that meets the regulatory requirements for melamine detection (3.96 × 10-6 M). The benefits of our SERS substrates are easy fabrication, high sensitivity (EF = 1.44 × 107), high reproducibility (CV = 8.4 %), and excellent uniformity (CV = 7 % in 4″ area), which are beneficial for mass production in the future.

Synthesis of highly conformal titanium nitride films via tert-butyl chloride-assisted atomic layer deposition

Integrating the desired properties of dynamic random-access memory (DRAM) capacitors is challenging owing to the continuous downscaling of semiconductor devices. In this paper, we propose inhibitor (tert-butyl chloride, t-BCl)-assisted atomic layer deposition (IA ALD) as a technique for obtaining a highly conformal titanium nitride (TiN) film for DRAM capacitor electrodes. IA ALD relies on an ABC-type ALD cycle, where a t-BCl precursor and reactants are sequentially applied in numerous cycles during the film growth process. The t-BCl molecules function as a medium to prevent excess TiN film deposition at the capacitor hole entrance by controlling the surface reactivity of the precursors and the modulation of the growth per cycle (GPC). The results indicated that the step coverage (>99%) of the TiN film deposited on a substrate with an aspect ratio (ratio of height to width) of 20:1 was significantly increased, while the electrical and intrinsic properties of the TiN film remained unaffected. As the t-BCl feeding rate increased from 25 to 100 sccm, the GPC decreased from 0.352 to 0.146 Å, while the film resistivity remained unaffected. X-ray photoelectron spectroscopy confirmed that there was no change in the composition of the TiN film. In addition, secondary ion mass spectroscopy analysis confirmed that t-BCl did not contain C components and that the amount of Cl impurities decreased. Furthermore, density functional theory simulations, which were performed to study the IA ALD process mechanism, suggested that the film growth rate was reduced because the physisorption of t-BCl molecules partially blocked the reactive adsorption sites for the TiCl4 precursor.

High-Performance Hydroxide Exchange Membrane Fuel Cell Comprising an Atomic Layer-Deposited Silver Cathode.

Atomic layer deposition (ALD) is emerging as an efficient tool for the precise manufacture of catalysts, owing to its sophisticated surface tailoring capabilities. To overcome the techno-economic limitations of fuel cell electric vehicles (FCEVs), which are considered suitable alternatives to battery electric vehicles (BEVs), the development of cost-efficient high-performance catalysts is essential. In this study, we successfully fabricated a Pt-free cathode for a hydroxide exchange membrane fuel cell (HEMFC) with excellent oxygen reduction activity under extremely low loading of Ag electrocatalysts using ALD. Microstructural analysis confirmed that the surface modification by ALD-Ag nanoparticles exhibited excellent step coverage characteristics on porous carbon nanotubes (CNTs). An HEMFC comprising a CNT cathode surface-decorated with ALD-Ag nanoparticles delivered a high peak power density of 2154 mW mgAg-1 in an alkaline environment at 65 °C. This study demonstrates the applicability of ALD for the manufacture of highly active low-cost electrocatalysts for high-performance HEMFCs.

Heteroleptic Titanium Complexes Bearing Amidoxime Ligands As Precursors for TiN Thin Films ALD

This presentation reports the synthesis of three novel titanium complexes containing amidoxime ligands as potential precursors for titanium nitride (TiN) thin films fabricated using atomic layer deposition (ALD). A series of ligands, viz., N'-methoxy-N-methylacetimidamide (mnnoH), N'-ethoxy-N-methylacetimidamide (ennoH), and N'-methoxy-N-methylbenzimidamide (pnnoH), were successfully synthesized and used to produce Ti(mnno)(NMe2)3 (4), Ti(enno)(NMe2)3 (5), and Ti(pnno)(NMe2)3 (6). Thermogravimetric analysis curves of complexes 4–6 revealed a single-step weight loss up to 200 °C. Pyrolysis occurred beyond 200 °C. Among the three new complexes, 5 was liquid at room temperature. Therefore, an ALD process for the growth of TiN was developed using Ti(enno)(NMe2)3 (5) as a novel precursor. A TiN thin film was deposited from the Ti(enno)(NMe2)3 (5) precursor and NH3 plasma, and self-limiting growth was achieved by varying the injection/purge duration. TiN thin film growths were observed with a growth per cycle (GPC) of 0.03–0.075 nm∙cy-1 at deposition temperatures between 150 and 300 °C, while the measured resistivity was as low as 250 μΩ·cm. The high reactivity of the precursor promotes nucleation, resulting in TiN thin films with smooth, good step coverage, and preferentially orientated microstructure.

Multiscale CFD modelling for conformal atomic layer deposition in high aspect ratio nanostructures

The high-quality and conformal thin film is of great importance to performances of functional materials and devices with high aspect ratio nanostructures. Atomic layer deposition (ALD) is known for outstanding step coverage, yet the ideal coatings in high aspect ratio nanostructures requires the process optimization. In this work, we report a computationally efficient multiscale computational fluid dynamics (CFD) model for an accurate study of ALD process in high aspect ratio nanostructures. The continuum model of precursor mass transfer and surface micro-kinetics in the high aspect ratio nanostructure is coupled to the reactor scale CFD model. The dynamic distribution of the precursor in the high aspect ratio nanostructure is captured and the competition of the surface deposition with the precursor transfer has been analyzed. The complete ALD process parameters including pulse, pressure-holding and purging are studied. Increasing the gas flow rate correspondingly reduces the gas phase reaction, ensures the conformability, and shortens the process time. Pressure-holding leads to a better film conformality for the diffusion-limited ALD process, especially for precursors of low reactivity. The experiment of ALD coating in nanopores with an aspect ratio up to 100:1 agrees well with our simulation results, indicating the validity of the multiscale model. Multiscale modelling provides a manner to quantitatively study the comprehensive effects of full-scale parameters for better conformity and process efficiency.

Atomic Layer Deposition Route to Scalable, Electronic-Grade van der Waals Te Thin Films.

Scalable production and integration techniques for van der Waals (vdW) layered materials are vital for their implementation in next-generation nanoelectronics. Among available approaches, perhaps the most well-received is atomic layer deposition (ALD) due to its self-limiting layer-by-layer growth mode. However, ALD-grown vdW materials generally require high processing temperatures and/or additional postdeposition annealing steps for crystallization. Also, the collection of ALD-producible vdW materials is rather limited by the lack of a material-specific tailored process design. Here, we report the annealing-free wafer-scale growth of monoelemental vdW tellurium (Te) thin films using a rationally designed ALD process at temperatures as low as 50 °C. They exhibit exceptional homogeneity/crystallinity, precise layer controllability, and 100% step coverage, all of which are enabled by introducing a dual-function co-reactant and adopting a so-called repeating dosing technique. Electronically, vdW-coupled and mixed-dimensional vertical p-n heterojunctions with MoS2 and n-Si, respectively, are demonstrated with well-defined current rectification as well as spatial uniformity. Additionally, we showcase an ALD-Te-based threshold switching selector with fast switching time (∼40 ns), selectivity (∼104), and low Vth (∼1.3 V). This synthetic strategy allows the low-thermal-budget production of vdW semiconducting materials in a scalable fashion, thereby providing a promising approach for monolithic integration into arbitrary 3D device architectures.

Study on the Deposition Characteristics of Molybdenum Thin Films Deposited by the Thermal Atomic Layer Deposition Method Using MoO2Cl2 as a Precursor

In this study, we conducted research on manufacturing molybdenum (Mo) thin films by a thermal atomic layer deposition method using solid MoO2Cl2 as a precursor. Mo thin films are widely used as gate electrodes and electrodes in metal-oxide semiconductor field-effect transistors. Tungsten (W) has primarily been used as a conventional gate electrode, but it suffers from reduced resistivity due to the residual fluorine component generated from the deposition process. Thus, herein, we developed a Mo thin film with low resistivity that can substitute W. The MoO2Cl2 precursor used to deposit the Mo thin film exists in a solid state. For solid precursors, the vapor pressure does not remain constant compared to that of liquid precursors, thereby making it difficult to set process conditions. Furthermore, the use of solid precursors at temperatures 600 °C and above has many limitations. Herein, H2 was used as the reactive gas for the deposition of Mo thin films, and the deposition temperature was increased to 650 °C, which was the maximum processing temperature of the aluminum nitride heater. Additionally, deposition rate, resistivity change, and surface morphology characteristics were compared. While resistivity decreased to 12.9 μΩ∙cm with the increase of deposition temperature from 600 °C to 650 °C, surface roughness (Rq) was increased to 0.560 nm with step coverage of 97%. X-ray diffraction analysis confirmed the crystallization change in the Mo thin film with increasing process temperature, and a certain thickness of the seed layer was required for nucleation on the initial wafer of the Mo thin film. Thus, the molybdenum nitride thin film was deposited after the 4 nm deposition of Mo thin film. This study confirmed that crystallinity of Mo thin films must be increased to reduce their resistivity and that a seed layer for initial nucleation is required.

Plasma Enhanced Atomic Layer Deposition of Silicon Nitride for Two Different Aminosilane Precursors Using Very High Frequency (162 MHz) Plasma Source.

Plasma enhanced atomic layer deposition (PEALD) of silicon nitride (SiNx) using very high frequency (VHF, 162 MHz) plasma source was investigated at the process temperatures of 100, 200, and 300 °C. Two aminosilane precursors having different numbers of amino ligands, bis(tert-butylamino)silane (BTBAS) and di(sec-butylamino)silane (DSBAS), were used as Si precursors. A comparative study was also conducted to verify the effect of the number of amino ligands on the properties of SiNx film. At all process temperatures, DSBAS, having one amino ligand, performed better than BTBAS in various aspects. SiNx films deposited using DSBAS had lower surface roughness, higher film density, lower wet etch rate, improved electrical characteristics, and higher growth rate than those deposited using BTBAS. With the combination of a VHF plasma source and DSBAS with one amino ligand, the SiNx films grown at 300 °C exhibited low wet etch rates (≤2 nm/min) in a dilute HF solution (100:1 of deionized water:HF) as well as low C content below the XPS detection limit. Also, excellent step coverage close to 100% on high aspect ratio (30:1) trench structures was obtained by using VHF plasma, which could provide sufficient flux of plasma species inside the trenches in conjunction with DSBAS having fewer amino ligands than BTBAS.

Conformal Growth of Hexagonal Boron Nitride on High-Aspect-Ratio Silicon-Based Nanotrenches

We successfully accomplished the conformal growth of sp2-hybridized few-layer h-BN over an array of Si-based nanotrenches with a 45 nm pitch and an aspect ratio of ∼7:1 by using the pulsed-mode metal–organic chemical vapor deposition (MOCVD) method. Surface-sensitive X-ray absorption fine structure spectroscopy and density functional theory calculations revealed that the B–O bonds formed on the noncatalytic SiO2 surface act as nucleation sites for the subsequential formation of mixed sp2- and sp3-hybridized BON2 and BN3 at the very initial stage of the pulsed-mode injection of MOCVD precursors, enabling the conformal growth of few-layer sp2-hybridized h-BN with an excellent step coverage. We believe that these results can provide a broad avenue for the implementation of fascinating two-dimensional layered materials for current state-of-the-art three-dimensional Si-based nanoscale architectures, overcoming the downscaling limits.

Telemonitoring of the Continuum of Care of Hepatitis C During the COVID-19 Pandemic in Brazil.

Introduction: To accomplish elimination of hepatitis C virus (HCV) by 2030, as proposed by the World Health Organization, the Brazilian Ministry of Health outlined the Hepatitis C Elimination Plan, which provides coverage of all critical steps in the continuum of care (CoC) of hepatitis C. As expected, the advent of COVID-19 pandemic has disrupted the CoC of hepatitis C worldwide. The Brazilian Liver Institute launched a remote patient monitoring (RPM) program to assist the general population at risk in HCV testing and to provide linkage and retention to care for HCV-positive subjects. The RPM program was also designed to relink HCV-positive patients lost to follow-up during the COVID-19 pandemic due to their limited access to the health care system. Methods: The HCV telemonitoring number was highly advertised in Brazilian media. The RPM program was conducted by dedicated health care personnel trained to follow a predefined script designed to provide awareness, ensure consistent information for educational purposes, and recruit eligible participants to be tested for HCV. Results: From August 2020 to December 2021, 3,738 subjects entered in contact with RPM. There were 26,884 interactions (mean 7.2 interactions per participant), mostly by WhatsApp (78%). Twenty out of those 221 subjects (9%) who tested were HCV positive. Those subjects altogether with 128 other patients with HCV, tested elsewhere, were followed in the HCV CoC. Up to now, 94% of them were linked to care, 24% are undergoing treatment and 8% achieved sustained virological response (SVR). Conclusions: Our preliminary results showed that HCV CoC telemonitoring was a feasible and useful strategy to follow HCV at-risk subjects through all cascade of care until SVR during the COVID-19 health care disruption. It could be used beyond the defervescence of SARS-CoV-2 pandemic to ensure linkage to care of those HCV-positive patients.

Amidoxime-Containing Ti Precursors for Atomic Layer Deposition of TiN Thin Films with Suppressed Columnar Microstructure.

This paper reports the synthesis of three novel titanium complexes containing amidoxime ligands as potential precursors for titanium nitride (TiN) thin films fabricated using atomic layer deposition (ALD). A series of ligands, viz., N'-methoxy-N-methylacetimidamide (mnnoH), N'-ethoxy-N-methylacetimidamide (ennoH), and N'-methoxy-N-methylbenzimidamide (pnnoH), were successfully synthesized and used to produce Ti(mnno)(NMe2)3 (4), Ti(enno)(NMe2)3 (5), and Ti(pnno)(NMe2)3 (6). Thermogravimetric analysis curves of complexes 4-6 revealed a single-step weight loss up to 200 °C. Pyrolysis occurred beyond 200 °C. Among the three new complexes, 5 was liquid at room temperature. Therefore, TiN was synthesized by ALD using Ti(enno)(NMe2)3 (5) as a novel precursor. A TiN thin film was deposited from the Ti(enno)(NMe2)3 (5) precursor and NH3 plasma, and self-limiting growth was achieved by varying the injection/purge duration. TiN thin film growths were observed with a growth per cycle (GPC) of 0.05-0.13 nm·cy-1 at deposition temperatures between 150 and 300 °C, while the measured resistivity was as low as 420 μΩ·cm. The high reactivity of the precursor promotes nucleation, resulting in TiN thin films with smooth, good step coverage and preferentially orientated microstructure.

Amorphous Ge-Se-S chalcogenide alloys via post plasma sulfurization of atomic layer deposition GeSe for ovonic threshold switch applications

For the future scaling of 3D cross-point (X-point) memory, it is necessary to implement atomic layer deposition (ALD) of chalcogenides for ovonic threshold switch (OTS) applications. We investigated ternary Ge-Se-S amorphous chalcogenide alloys based on ALD process, motivated by the expectation of low off-current and stable OTS behavior by partially replacing S in binary Ge-Se. Ge-Se-S alloys were synthesized by post-deposition sulfurization of ALD GeSe2 thin films. Especially, we investigated the growth characteristics and film properties of ALD GeSe2 using HGeCl3 precursors with Se(SiMe3)2 together with density-functional theory (DFT) calculations. By changing the temperature and the low-temperature plasma sulfurization time, the compositions of 10-nm-thick Ge-Se-S thin films were controlled along the GeSe2-Ge2S pseudo-binary line in ternary phase diagram. It was confirmed that the Ge5Se3S2 alloys maintained an amorphous phase and excellent step coverage, similar to ALD GeSe2. Finally, we compared the OTS electrical characteristics of 10-nm-thick ALD GeSe2 with Ge5Se3S2 amorphous chalcogenide thin films in a mushroom-type device with a 50-nm bottom electrode. The novel Ge5Se3S2 had a slightly larger threshold voltage (Vth) drift than GeSe2 but exhibited the advantages of a higher threshold field, lower off-current, and smaller Vth fluctuation up to 106 cycles. Data availabilityThe data that has been used is confidential.

Super-conformal TiN thin film deposition by carrier pulse purge atomic layer deposition system: Chamber design optimization with computational fluid dynamics

Owing to the increase in demand for the shrinkage of semiconductor design rules and the advent of the three-dimensional structure of semiconductor devices, atomic layer deposition (ALD) has emerged as an attractive alternative to conventional chemical vapor deposition techniques. Although the development of precursors and characterization of ALD films have been widely studied, few studies have been conducted on the modification of ALD parameters and optimization of the ALD process. In this study, an advanced ALD titanium nitride (TiN) system was designed using a pumping and purging simulationBased on the simulation results, we adopted a carrier pulse purge method, where TiCl4 fed, purge N2, pulse purge N2, purge N2, NH3 fed, purge N2, pulse purge N2, and purge N2 were alternatively injected into the chamber in the ALD cycle. Compared to the conventional purge method, the carrier pulse purge method can reduce the ALD cycle time by 18.27% and yields a high-quality (high step coverage, 98 %) TiN film with lower electrical resistivity and chlorine impurity. This carrier pulse purge method can ultimately lead to improved throughput and productivity in the semiconductor industry by reducing the ALD cycle time.

Preparation of wafer-scale highly conformalamorphous hafnium dioxide thin films by atomic layer deposition using a thermally stable boratabenzene ligand-containing hafnium precursor

In the present study, HfO2 thin films were fabricated via atomic layer deposition (ALD) using a novel heteroleptic metal organic precursor [tris (dimethylamino) dimethylaminoboratabenzene hafnium] [η6:η1-(C5H5BNMe2)Hf(NMe2)3; (BBHf)] along with O2 as the oxygen source at a range of growth temperatures (i.e., 150–350 °C). This novel precursor is a heteroleptic complex synthesized by the introduction of a boratabenzene ligand (BB) into the parent Hf metal sphere to achieve an enhanced thermal stability. In this system, O2 is used as a mild oxygen-containing reactant to replace the typically employed ozone (O3). Distinctive self-limiting deposition was established with a comparatively high growth per cycle value of 0.068 nm, and linear growth was observed as a function of the ALD cycle number. Thermal decomposition was not detected at or below 350 °C, thereby indicating the improved thermal stability compared to when frequently used Cp (cyclopentadienyl)-amide precursors are employed. Under the ALD deposition conditions employed herein (275 °C), a complete step coverage was achieved with a good conformality on high aspect ratio dual trenches [top and bottom widths = 40 and 15 nm, respectively, aspect ratio (AR) ≈ 6.3], and uniformity was obtained on the large planar substrate (15 cm diameter). Upon annealing at 700 °C, the as-grown film formed an amorphous structure with a slightly enhanced crystallinity, while annealing at 850 °C led to the generation of nanocrystalline HfO2 films with amorphous structures, as indicated by X-ray diffraction measurements. The as-grown films were determined to be slightly rich in oxygen compared to the stoichiometry of HfO2, although they also contained significant amounts of residual impurities, such as H, B, and C (∼6, 6, and 7 at.%, respectively), as confirmed by Rutherford backscattering spectrometry and elastic recoil detection analyses. The impurity levels were further reduced by increasing the growth temperature and by subsequent post-annealing, as evidenced by X-ray photoelectron spectroscopy and secondary-ion mass spectrometry analyses. Finally, ellipsometry analysis was performed to measure the optical properties of the prepared ALD-HfO2 thin films. It is expected that the described process may be of significance in the preparation of high-k films wherein thermally stable amorphous films with extremely conformal and uniform coatings are required to fabricate next-generation electronic devices.

Microkinetic modeling with machine learning predicted binding energies of reaction intermediates of ethanol steam reforming: The limitations

Machine learning based methods have shown great potential in binding energy predictions for surface species, and root mean squared error (RMSE) has been considered as an important indicator to assess the accuracy of the model. In this work, error propagation from energetic prediction to kinetic properties evaluation, e.g. dominant reaction pathways and reaction activities, was assessed and quantified for ethanol steam reforming reaction. The results show that the identification of the dominant pathway is independent of the RMSE of the energetic prediction model but closely related to the predicted energetics of competing steps. The reaction rate is influenced by two factors, namely energetics of the rate-determining step and free site coverage at steady state. Interestingly, the rate-determining step alone can dominate the reaction activity within high temperature range, whereas a global error indicator regarding all surface intermediates must be taken into account in the low temperature range. This work put a straightforward example of error propagation, showing that the RMSE of the energy prediction model cannot guarantee the accuracy of evaluations of kinetic properties.

The Effect of Deposition Temperature of TiN Thin Film Deposition Using Thermal Atomic Layer Deposition

In this study, the effect of deposition temperature of TiN thin films deposited using the thermal atomic layer deposition (ALD) method was investigated. TiCl4 precursor and NH3 reactive gas were used, and the deposition rate, resistivity change, and surface morphology characteristics were compared in the deposition temperature range of 400 °C–600 °C. While resistivity decreased to 177 µΩcm as the deposition temperature increased to 600 °C, an increase in surface roughness (Rq) to 0.69 nm and a deterioration in the step coverage were identified. In order to obtain a high-quality TiN thin film with excellent resistivity and step coverage characteristics even at low deposition temperatures, the TiN thin film was post-treated with plasma in a combination of N2/He gas ratio of 3:2 to confirm the change in resistivity. X-ray diffraction analysis confirmed crystallization change in the TiN thin film caused by plasma energy. As a result, the resistivity of the TiN thin film deposited at 400 °C was confirmed to be lowered by about 25%.

Uniformity of HfO2 Thin Films Prepared on Trench Structures via Plasma-Enhanced Atomic Layer Deposition.

In this study, we assessed the physical and chemical properties of HfO2 thin films deposited by plasma-enhanced atomic layer deposition (PEALD). We confirmed the self-limiting nature of the surface reactions involved in the HfO2 thin film's growth by tracing the changes in the growth rate and refractive index with respect to the different dose times of the Hf precursor and O2 plasma. The PEALD conditions were optimized with consideration of the lowest surface roughness of the films, which was measured by atomic force microscopy (AFM). High-resolution X-ray photoelectron spectroscopy (XPS) was utilized to characterize the chemical compositions, and the local chemical environments of the HfO2 thin films were characterized based on their surface roughness and chemical compositions. The surface roughness and chemical bonding states were significantly influenced by the flow rate and plasma power of the O2 plasma. We also examined the uniformity of the films on an 8″ Si wafer and analyzed the step coverage on a trench structure of 1:13 aspect ratio. In addition, the crystallinity and crystalline phases of the thin films prepared under different annealing conditions and underlying layers were analyzed.

Conformal chemical vapor deposition of boron-rich boron carbide thin films from triethylboron

We report conformal chemical vapor deposition (CVD) of boron carbide (BxC) thin films on silicon substrates with 8:1 aspect-ratio morphologies, using triethylboron [B(C2H5)3] as a single source CVD precursor. Step coverage (SC) calculated from the cross-sectional scanning electron microscopy measurements shows that films deposited at ≤450 °C were highly conformal (SC = 1). We attribute this to the low reaction probability at low substrate temperatures enabling more gas phase diffusion into the features. The chemical state of the material, determined by x-ray photoelectron spectroscopy, shows as a carbide with B–B, B–C, C–B, and C–C chemical bonds. Quantitative analysis by time-of-flight elastic recoil detection analysis reveals that films deposited at 450 °C are boron-rich with around 82.5 at. % B, 15.6 at. % C, 1.3 at. % O, and 0.6 at. % H, i.e., about B5C. The film density as measured by x-ray reflectometry varies from 1.9 to 2.28 g/cm3 depending on deposition temperature.

Molecular layer deposition of alucone in high aspect ratio trenches: The effect of TMA outgassing on step-coverage

Infiltration of trimethylaluminum (TMA) in molecular layer deposition-enabled alucone thin films on planar substrates is a common observation reported in the literature. An insufficient TMA purge time in such cases is often found to lead to a CVD component in the overall film growth due to the reactions between the outgassing TMA and the co-reactant. In this work, the effect of the CVD component on the step coverage of alucone films when grown in high-aspect ratio trenches is studied. The thickness was initially found to increase with increasing distance from the trench aperture before starting to decrease up to the film’s maximum penetration depth. With the support of modeling, the reason behind the observed thickness profile was investigated and attributed to the combination of an increasing outgassing rate of TMA and a decreasing ethylene glycol (EG) concentration along the trench depth. Furthermore, the maximum thickness and the position where it is obtained in the trench are found to depend on TMA and EG doses, TMA purge time, the trench height, and the trench depth. Finally, the possibility of adopting the additional CVD component in film growth for void-less gap fill of 3D trenches is discussed, as well as the suppression of the same CVD component, without compromising the growth rate, by using dimethylaluminum isopropoxide as a substitute for TMA is evaluated.

High-efficiency (over 33 %) indoor organic photovoltaics with band-aligned and defect-suppressed interlayers

In recent years, the emergence of the Internet of Things (IoT) has led to growing interest in the use of organic-based artificial light cells (OALCs; indoor organic photovoltaics) to harvest ambient light energy. This study employs atomic layer deposition (ALD)-processed vanadium oxide (V2O5) hole-transport-layers (HTLs) in non-fullerene acceptor-based OALCs to achieve record power conversion efficiency (PCE) exceeding 33 % under a light-emitting diode lamp (19500 lx; light intensity IL = 4.5 mW/cm2). The material most widely used for HTLs is poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). OALCs with ALD-processed V2O5 HTLs substantially outperform those with PEDOT:PSS HTLs because they have superior hole selectivity, excellent electron-blocking, a smaller interfacial area, and substantially enhanced step coverage which significantly suppresses charge recombination. Moreover, the proposed V2O5-based OALCs have diffusion-free characteristics into the photoactive region and demonstrate excellent performance stability, maintaining a PCE of 92 % after 1000 h under ambient conditions. The results provide insights that enable simultaneous improvements in the efficiency and ambient stability of OALCs for low-powered IoT applications.