Deposition Process Research Articles

In situ mass spectrometric investigation to probe GeSn growth dynamics and mechanisms in the chemical vapor deposition processes

GeSn has attracted increasing attention due to its tunable bandgap from indirect to direct resulting in unique electronic and optoelectronic capabilities. Chemical vapor deposition (CVD) is well acknowledged as an advanced growth method for GeSn, demonstrating its capability with grown materials for infrared lasers and detector development. As an in situ diagnostics of the CVD process, a residual gas analyzer (RGA) could enable the detection of all gaseous species during growth, thus probing the growth dynamics and mechanism. Therefore, it is highly desirable but is lacking in the (Si)GeSn research community. This work utilized an RGA equipped with a specialized differential vacuum pumping system to analyze the mass spectra of the GeSn CVD precursors of SnCl4, GeH4, and their combination. The spectra of SnCl4 collected from gas samples at a standard base pressure of 0.3 Torr display consistent fragments with central mass-to-charge ratios (m/z) of 78, 120, 155, 225, and 260, corresponding to Sn+, SnCl2+, SnCl+, SnCl2+, SnCl3+, and SnCl4+, respectively. These profiles closely resemble those observed in the National Institute of Standards and Technology and Wiley and Matsumoto et al. The simultaneous introduction of SnCl4 and GeH4 at a combined pressure of several tens of Torr yields spectra, indicating a chemical reaction that produces GeCl4 at room temperature in the vacuum chamber and tubing. Utilizing Gaussian16 and ORCA codes, the ab initio and density functional thermochemistry computations were employed to predict potential essential reactions and validate the experimental findings.

Metal Painting by Plasma Jet

AbstractConducting metal interconnections are essential to link electronic components or multiple circuits for electronic device fabrication. Scalable, rapid, and sustainable methods for printing adherent metal interconnections on dielectric materials are lacking, which stifles the development of new electronic consumer devices. Here a breakthrough single‐step and rapid process to deposit highly conducting metal tracks is introduced, using an atmospheric pressure plasma jet. The deposition process used a rudimentary aqueous solution of metal salts as ink, that was introduced as a mist into a helium plasma gas. The metal salt was reduced and deposited with spatiotemporal control using a plasma jet generated at radio frequency with 15 W power at room temperature and pressure. The conductive metal layers were highly adhesive on glass, ceramics, polymeric materials, even biological surfaces such as plant leaves and animal skin, depostedwith little damage to the substrate. The conductivity of deposited tracks on glass shows 50.8 ± 8.6% and 5.2 ± 1.6% of bulk silver and copper metal conductivity respectively.

Microstructure-Assisted Wafer-Scale Fabrication of Perovskite Microlaser Arrays.

All inorganic lead halide perovskites exhibit fascinating optical and optoelectronic characteristics for on-chip lasing, but the lack of precise control of wafer-scale fabrication for perovskite microstructure arrays restricts their potential applications in on-chip-integrated devices. In this work, a microstructure-template assisted crystallization method is demonstrated via a designed chemical vapor deposition process, achieving the controllable fabrication of homogeneous perovskite micro-hemispheroid (PeMH) arrays spanning the entire surface area of a 4-inch wafer. Benefiting from the low-loss whispering gallery resonance and plasmon-enhanced light-matter interactions in well-confined hybrid cavities, this CsPbX3/Ag (X = Cl, Br) plasmonic microlasers exhibit quite low thresholds below 10µJcm-2. Interestingly, these thresholds can be efficiently modulated through the manipulation of plasmonic resonance and electromagnetic field mode in PeMHs owning various diameters. This strategy not only provides a valuable methodology for the large-scale fabrication of perovskite microstructures but also endorses the potential of all-inorganic perovskite nanostructures as promising candidates for on-chip-integrated light sources.

Remarkable Bias‐Stress Stability of Ultrathin Atomic‐Layer‐Deposited Indium Oxide Thin‐Film Transistors Enabled by Plasma Fluorination

AbstractA low‐thermal‐budget fabrication approach is developed to realize high‐performance fluorine‐doped indium oxide (In2O3:F) thin‐film transistors (TFTs) with remarkable bias‐stress stability. The ultrathin transistor channel layer is prepared by a re‐developed atomic layer deposition (ALD) process of using cyclopentadienyl indium(I) (InCp) and O2 plasma to deposit a crystalline In2O3 film, followed by a new fluorine doping strategy to use CF4 plasma to afford the In2O3:F layer. As revealed by the density functional theory (DFT) analysis, the fluorine doping can stabilize the lattice oxygen and electrically passivate the problematic VO defects in In2O3 by forming the FOFi spectator defects. Therefore, the fabricated In2O3:F TFTs show simultaneously excellent electrical performance and remarkable bias‐stress stability, with high µFE of 35.9 cm2 V−1 s−1, positive Vth of 0.36 V, steep SS of 94.3 mV dec−1, small hysteresis of 33 mV, and small ΔVth of −111 and 49 mV under NBS and PBS, respectively. This work demonstrates the high promise of the fluorinated ALD In2O3:F TFTs for the CMOS back‐end‐of‐line (BEOL) compatible technologies toward advanced monolithic 3D integration.

Fabrication of humidity monitoring sensor using porous silicon nitride structures for alkaline conditions

Porous silicon nitride structures were fabricated for a humidity sensor. The porous silicon structures were fabricated by the metal-assisted chemical etching process, and the conformal silicon nitride thin film was deposited by the atomic layer deposition process. The optimized porous sensor with the 10 nm-thick silicon nitride thin film had a hydrophilic surface and compared to other sensors, had an excellent humidity sensing response. Especially, it showed a superior humidity sensing response at 1 kHz with fast response and recovery times of 13.3 s and 12.4 s, respectively, were observed. Based on the electrochemical impedance spectroscopy results, the equivalent circuits and humidity sensing mechanism were discussed. The chemical stability of the silicon nitride was characterized using Tafel analysis in alkaline electrolytes. Additionally, the sensor's humidity sensing capabilities were tested under cement-embedded conditions.

Crystalline as-deposited TiO 2 anatase thin films grown from TDMAT and water using thermal atomic layer deposition with in situ layer-by-layer air annealing

We report a new thermal atomic layer deposition (thermal-ALD) process including an air exposure as a third precursor to deposit crystalline TiO2 anatase thin films from tetrakis(dimethylamido)titanium(IV) (TDMAT) and water at deposition temperatures as low as 180 °C and film thicknesses as low as 10 nm. This ALD process enables TiO2-antase crystal growth during the deposition at low temperatures (< 220 °C). This additional oxidant pulse is used to fully oxidize the Ti to a 4+ state in the amorphous film, lowering the barrier to crystalline anatase formation. This new approach is informed by preliminary studies of post-deposition annealing (PDA) of thermal ALD films in both nitrogen and air atmospheres, which demonstrate the importance of having an oxidizing atmosphere to achieve the nucleation of the crystalline anatase phase. This oxidizing atmosphere is subsequently introduced into the ALD cycle as a third precursor and is shown to be more effective and efficient in promoting the crystalline transformation than even by post-deposition annealing. The crystalline anatase phase is verified by Raman spectroscopy and grazing incidence X-ray diffraction (GIXRD). The mechanism for crystallization during the TDMAT/H2O/air ALD cycle is probed by chemical state analysis via X-ray photoelectron spectroscopy (XPS). We propose that sub-oxidation in TiO2 thin films deposited by the thermal-ALD process inhibits crystallization during ALD from TDMAT/H2O chemistry. Scanning electron microscopy (SEM) is used to investigate the microstructure of these TiO2 thin films as a function of thickness (5 nm to 50 nm) and deposition temperature (180 °C to 220 °C). The reported layer-by-layer air anneal process is found to crystallize entire films in shorter total process times than thermal-ALD with ex situ post deposition annealing at identical temperatures, presumably due to the improved surface diffusion kinetics accessed during the deposition process.

Hydrophobization of Cold Plasma Activated Glass Surfaces by Hexamethyldisilazane Treatment.

The objective of this study was to investigate the modification of glass surfaces by the synergistic combination of cold plasma and chemical surface modification techniques. Glass surface hydrophobicity was obtained as a result of various plasma and deposition operational conditions. The mechanisms governing the hydrophobization process were also studied. Glass plates were activated with plasma using different gases (oxygen and argon) at different treatment times, ranging from 30 to 1800 s. Then, the plasma-treated surfaces were exposed to hexamethyldisilazane vapors at different temperatures, i.e., 25, 60, and 100 °C. Complete characterization, including contact angle measurements, surface free energy calculations, 3D profilometry, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and scanning electron microscopy, was accomplished. It was found that the extent of the hydrophobicity effect depends on both the plasma pre-treatment and the specific conditions of the hexamethyldisilazane deposition process. Plasma activation led to the formation of active sites on the glass surface, which promoted the adsorption and reaction of hexamethyldisilazane species, thereby inducing surface chemical modification. Longer plasma pre-treatment resulted in stronger modification on the glass surface, resulting in changes in the surface roughness. The largest water contact angle of ≈100° was obtained for the surface activated by argon plasma for 1800 s and exposed to hexamethyldisilazane vapors at 25 °C. The changes in the surface properties were caused by the introduction of the hydrophobic trimethylsilyl groups onto the glass surface as well as roughness development.

Adsorption of dimethylaluminum isopropoxide (DMAI) on the Al2O3 surface: A machine-learning potential study

Dimethylaluminum isopropoxide (DMAI) is attracting attention as an alternative precursor for atomic layer deposition (ALD) of aluminum oxide (Al2O3). However, the surface chemical reaction mechanisms of DMAI during ALD regarding its dimeric structure under vacuum deposition process conditions has yet to be clear. In this work, the adsorption mechanism of dimeric and monomeric DMAI on a fully hydroxylated Al2O3 surface is studied using machine-learning potential (MLP) calculations. The initial adsorption of DMAI appears facile and would result in the coexistence of both methyl and isopropoxy ligands on the surface. The reactivity of DMAI is smaller than that of TMA, owing to the propensity of DMAI to adopt a dimeric form. Especially when the substrate is partially covered by other adsorbate species, the large molecular size and low reactivity of dimeric DMAI considerably hinder its reactivity toward surface adsorption. Current results are in good correspondence with the previous experimental results, where lower growth per cycle (GPC) and higher selectivity in area-selective ALD (AS-ALD) could be observed by using DMAI than compared to those of TMA processes.

Process development and validation of next generation 3D calibration standards for application in optical microscopy

Abstract A scalable wafer-based fabrication process for a new generation of 3D standards enabling the 3D calibration of optical microscopes is presented and validated. The 3D standards are based on step pyramids with several layers in the µm range and a system of cylindrical knops distributed across the layers as marks for coordinate based calibration. This enables calibration for the three coordinate axes and the orthogonality error between them in a single measurement step. The requirements necessary for such a calibration, as optical non-transparency, reproducible flatness of the pyramid step heights and the lowest possible deviations of the lateral marks coordinates, are met by optimizing the manufacturing process: The deviation of the height steps distributed over the wafer is ±3.6 nm and is primarily caused by the layer deposition processes. The lateral manufacturing accuracy was determined using calibrated scanning electron microscope (SEM) and show a mean deviation of 20 or 60 nm, depending on the lateral size of the structures. The electron beam lithography process and the level of inaccuracy of the SEM standard have an influence on the lateral scaling accuracy. Based on the tactilely generated height values and the coordinates of the mark determined by a calibrated SEM, an example calibration of a confocal laser scanning microscope was successfully performed and showed good conformity to conventional calibration techniques.

Use of plasma process diagnostic sensors for the monitoring of in situ dry cleaning of plasma enhanced chemical vapor deposition chamber

A potential source of particle contamination due to poorly maintained PECVD chamber condition forces to perform in situ dry cleaning also actively employed before the wet-cleaning chamber maintenance period. In this paper, we demonstrate the use of plasma process diagnostic sensors, optical emission spectroscope, and quadrupole mass spectrometer for in situ plasma monitoring of the dry-cleaning step. It is worthwhile to know the thin film residue on the chamber’s inner wall, but it is difficult to collect the deposited thin film sample from the wall since the preparation of the sample from the equipment is impossible. To alleviate the concern, we prepared silicon wafer samples mounted on the chamber sidewall over the prolonged exposure of the SiO2 deposition process, and the collected sensory data were investigated under the dry-cleaning condition. The residue film obtained through the experiment was characterized by Fourier transform infrared, x-ray photoelectron spectroscopy, atomic force microscopy, and scanning electron microscopy. We found a useful insight into the chamber dry-cleaning end point detection application through residual gas analysis, and the results contribute to process engineers setting up the in situ dry-cleaning recipe to make sure that subsequent deposition can be consistently maintained.

Review and perspective of dry etching and deposition process modeling of Si and Si dielectric films for advanced CMOS device applications

Abstract Dry etching and deposition of Si and Si dielectric films are critical processes for achieving of high performance in advanced complementary metal-oxide-semiconductor (CMOS) devices. To accurately predict and control fluctuations in these process properties during mass production, it is essential that dry process simulation technology considers various factors. These include fluctuations in plasma-chamber wall interaction, effects of by-products on critical dimensions, Si recess dependence on wafer open area ratios and local pattern structures, the time-dependent distribution of plasma-induced damage associated with feature-scale profiles, and film properties such as density, permeability, and adhesion. Addressing these considerations can overcome issues with conventional simulations that lack the accuracy required for mass production. This paper reviews these advanced simulation technologies and discusses the perspective of fusion physical models with machine learning, incorporating real-time monitoring in manufacturing equipment, known as process informatics. This approach is anticipated to usher in the era of full digital twins.

Enhancing microscale additive manufacturing: Electrolyte-column localized electrochemical deposition for microwire and microdevice substrate connection

Electrochemical deposition is a microscale additive manufacturing technology. Due to the excellent performance of electrodeposited coating layers which exhibit no thermal stress, low porosity, and minimal microcracks, electrodeposition has been used in the connections of microdevices to solve the problems of shrinkage and deformation of microparts caused by thermal stress generated by conventional connections. Due to the low efficiency of Meniscus-Confined electrodeposition, a novel connection process for microwires and microdevice substrate using electrolyte-column localized electrochemical deposition (ECL-ECD) is proposed. The connecting mechanism is determined through simulation and experimentation. Simulation results indicated that the current density in the connection area exhibited a Gaussian distribution and the deposition layer preferentially grew at the interface between the microwire and the substrate. A high-speed camera was used to observe the liquid beam throughout the experiment, the results indicated that the microwires didn’t affect the stability of the liquid beam, and the ECL-ECD had excellent domain fixation. Smooth and dense surfaces on the connection area of the microwire and substrate were obtained at a current density of 50–60 A/dm2. Performance testing results showed that the connection point has excellent corrosion resistance and electrical properties. When the deposition time was short, the microwire was detached from the deposition area due to relatively thin deposition layer thickness and the tensile strength was only 133.82 MPa during the tensile testing. When the appropriate deposition process parameters were chosen, the fracture occurred on the microwire under tensile load and the fracture strength was 198.84 MPa, which equals the tensile strength of the microwire and indicated that the connection point can provide sufficient strength. The experimental results demonstrated that ECL-ECD can provide an effective and reliable connection process for the microwires interconnection.

Air-sea exchange of PAHs in the Taiwan Strait: Seasonal dynamics and regulation mechanisms revealed by machine learning approach

In this study, to understand the seasonal dynamics of air-sea exchange and its regulation mechanisms, we investigated polycyclic aromatic hydrocarbons (PAHs) at the air-sea interface in the western Taiwan Strait in combination with measurements and machine learning (ML) predictions. For 3-ring PAHs and most of 4- to 6-ring, volatilization and deposition fluxes were observed, respectively. Seasonal variations in air-sea exchange flux suggest the influence of monsoon transitions. Results of interpretable ML approach (XGBoost) indicated that volatilization of 3-ring PAHs was significantly controlled by dissolved PAH concentrations (contributed 24.0 %), and the gaseous deposition of 4- to 6-ring PAHs was related to more contaminated air masses originating from North China during the northeast monsoon. Henry’s law constant emerged as a secondary factor, influencing the intensity of air-sea exchange, particularly for low molecular weight PAHs. Among environmental parameters, notably high wind speed emerges as the primary factor and biological pump’s depletion of PAHs in surface seawater amplifies the gaseous deposition process. The distinct dynamics of exchanges at the air-water interface for PAHs in the western TWS can be attributed to variations in primary emission intensities, biological activity, and the inconsistent pathways of long-range atmospheric transport, particularly within the context of the monsoon transition.

Study on structural, optical, and electrical properties of yttrium doped molybdenum oxide thin film and its MIS diode performance

In this study, Orthorhombic pure MoO3 and various weight percentages of Y-doped MoO3 nanostructure arrays were successfully deposited using the simple jet nebulizer spray pyrolysis process at an ideal substrate temperature of 500 °C. In order to create metal-insulator-semiconductor-based Schottky barrier diodes, Y-doped MoO3 nanostructure arrays were employed as an insulating layer. The influence of Y-doped MoO3 concentration during the deposition process was carefully analyzed in relation to the structural, morphological, optical, and electrical characteristics of Y-doped MoO3 nanostructure array films. The produced films' crystalline nature with an orthorhombic phase was shown by the XRD pattern. An FE-SEM was used to analyse the solidly linked plate-like structure of Y-doped MoO3 at higher concentrations of 6 wt%. The EDAX spectrum was used to confirm the stoichiometric relationship between the elements O, Mo, and Y. The band gap values of the Y-doped MoO3 were determined using UV–Vis spectroscopy to range from 3.3 to 3.18 eV with doped concentrations. The film made with 6 wt% Y doped MoO3 showed a sharp improvement in electrical conductivity according to a DC electrical analysis. Notably, MIS diode made with 6 wt% Y-doped MoO3 in particular showed a low ideality factor (n = 2.63), strong photosensitivity (PS = 17,509.62%), responsivity of 738 mA/W, and a maximum QE of 97.49% under illumination (130 mW/cm2). Additionally, a 6 wt percent Y-based diode obtained a greater detectivity of D* = 7.16 1009 jones in a dark environment condition.

Exploring the Friction and Wear Mechanisms of Nickel Titanium Alloy Fabricated by Laser Powder and Wire-Based Directed Energy Deposition

The NiTi alloy has attracted significant interest owing to its notable wear and corrosion resistance, suggesting the significant promise of utilizing additively manufactured NiTi alloys in tribological applications. In this study, dry sliding wear tests with sliding velocity of 0.1 m/s for total distance of 250 m at room temperature, 50 °C, 100 °C, and 200 °C were carried out on samples of NiTi alloy samples fabricated using laser powder and laser wire directed energy deposition (LP-DED and LW-DED) processes. Enhanced friction and wear behavior of LP-DED samples were captured at lower temperatures due to higher hardness and the stable dominating NiTi B2 austenite phase in the sample microstructure as confirmed from x-ray diffraction (XRD) analysis. Accumulated transferred material at lower temperatures played a crucial role in modifying the wear mechanisms. However, at higher temperatures both LP-DED and LW-DED samples presented similar wear mechanisms.

Contrastive learning based on hierarchical graph of microstructures through directed energy deposition process to establish process-structure–property relationship via autoencoder

n this study, an innovative algorithm is developed to transform microstructures to hierarchical graphs without manual feature engineering. The hierarchical graph comprises two layers. Initially, pixel data, which includes Euler angles, phase, and position, forms the pixel-wise graphs within individual grains. Following this foundation, the grains serve as nodes, constituting the second layer. Importantly, the hierarchical graph preserves essential measurement data and structural details for training machine learning models. After that, a contrastive learning model based on hierarchical graph is designed to capture representations of microstructures obtained by the electron backscatter diffraction (EBSD) technique. This model can be directly extended for other microscopy techniques, such as Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray spectroscopy (EDX), and Transmission Electron Microscopy (TEM). Using the learned microstructure representations, an autoencoder model for the directed energy deposition (DED) is developed to establish the relationship among process parameters, microstructures, and material properties, completing the process-structure–property cycle quantitatively. The performance of the present model is naturally benchmarked against two other models: a contrastive learning model based on pixel-wise graph (without manual feature engineering) and a contrastive learning model based on grain-wise graph (employing manual feature engineering). The results of the present model highlight the potential in decoding the process-structure–property relationships in the DED process.

The development of low-cost spin coater with wireless IoT control for thin film deposition

A low-cost spin coater with a wireless remote system that can deposit thin films of uniform thickness and quality at a significantly lower cost than traditional methods. The system consists of three main parts, a motorized spindle, a spin-coating head, and a control system connected to the network. The mechanical design on the mechanical part, spin coater system design with ESP32, and implementation of wireless control through visual basic. The network-enabled control system allows for real-time monitoring and adjustment of the deposition process, which can improve efficiency and reproducibility. This low-cost spin coating system represents a promising solution for organizations seeking to access thin film deposition technology at a fraction of the cost of traditional systems. By integrating wireless IoT control into low-cost spin coaters, the impact of this technology on coating uniformity will provide valuable insights for future advancements in this field.

Prediction of solidification structure in the laser metal deposition of IN625 superalloy using the numerical and experimental techniques

Extensive research has been conducted in the field of direct laser deposition (DLD) process simulation. In this study, the finite volume method was used to predict the solidification microstructure and melt pool status in the IN625 cladding process. By fitting the data and matching the Hunt-Fleming relationship, the values of a=29.1827 and n=0.354 were obtained. A columnar structure was observed near the G/R=1.4e6 line, a combination of columnar and equiaxed structures between the G/R=1.4e6 and G/R=0.3e6 lines, and a fully equiaxed structure at points below the G/R=0.3e6 line. Finally, using the RSM method, a suitable area for achieving directional solidification (columnar dendrite with minimum orientation), with a power of more than 225 W and a powder/scan speed ratio (F/S) of less than 40 mg/mm, was determined.

Wear-Resistant Coatings Produced from TiN–TiB2 and TiN–Si3N4 Composites by Electrospark Deposition and Laser Processing

Wear-Resistant Coatings Produced from TiN–TiB2 and TiN–Si3N4 Composites by Electrospark Deposition and Laser Processing

Molten glass-mediated conditional CVD growth of MoS2 monolayers and effect of surface treatment on their optical properties

In the rapidly developing field of optoelectronics, the utilization of transition-metal dichalcogenides with adjustable band gaps holds great promise. MoS2, in particular, has garnered considerable attention owing to its versatility. However, a persistent challenge is to establish a simple, reliable and scalable method for large-scale synthesis of continuous monolayer films. In this study, we report the growth of continuous large-area monolayer MoS2 films using a glass-assisted chemical vapor deposition (CVD) process. High-quality monolayer films were achieved by precisely controlling carrier gas flow and sulfur vaporization with a customized CVD system. Additionally, we explored the impact of chemical treatment using lithium bistrifluoromethylsulfonylamine (Li-TFSI) salt on the optical properties of monolayer MoS2 crystals. To investigate the evolution of excitonic characteristics, we conditionally grew monolayer MoS2 flakes by controlling sulfur evaporation. We reported two scenarios on MoS2 films and flakes based on substrate-related strain and defect density. Our findings revealed that high-quality monolayer MoS2 films exhibited lower treatment efficiency due to substrate-induced surface strain. whereas defective monolayer MoS2 flakes demonstrated a higher treatment sensitivity due to the p-doping effect. The Li-TFSI-induced changes in exciton density were elucidated through photoluminescence, Raman, and x-ray photoelectron spectroscopy results. Furthermore, we demonstrated treatment-related healing in flakes under variable laser excitation power. The advancements highlighted in our study carry significant implications for the scalable fabrication of diverse optoelectronic devices, potentially paving the way for widespread real-world applications.