Film Deposition Process Research Articles

Determining the local pressure during aerosol deposition using glass memory

AbstractAerosol deposition (AD) is a dynamic loading process that can be envisioned as a shock wave loading, necessitating the consideration of the elastic/plastic response of solid materials. Due to the dynamic nature of this process, however, experimental determination of the local pressures during the deposition process is difficult. This work addresses this by investigating the compression and subsequent structure modification of a silicate glass after room‐temperature AD on a silicate glass substrate with Raman spectroscopy. Clear structural changes in the short‐ and middle‐range order of the silicate glass were observed, both as intertetrahedral angle distribution and as ring statistic. Therefore, the AD induced permanent densification of the glass, equivalent, in a hydrostatic approximation, to a minimal pressure of 10.5 ± 1.5 GPa during the film deposition process. Furthermore, the analysis of the Nd3+ photoluminescence of the 4F3/2 − 4I9/2 transition provided complementary information on the glass network modifications occurring during film formation. More than a pure hydrostatic densification, the AD seems to present a very intense shear deformation. This work opens up the perspective of evaluating the mechanical response of film‐substrate and of the particles themselves, and provides critical information on the mechanisms responsible for the AD film formation.

Influence of Annealing Temperature on the Properties of ZnGa2O4 Thin Films by Magnetron Sputtering

Zinc gallate (ZnGa2O4) thin films were grown on sapphire (0001) substrate using radio frequency (RF) magnetron sputtering. After the thin film deposition process, the grown ZnGa2O4 was annealed at a temperature ranging from 500 to 900 °C at atmospheric conditions. The average crystallite size of the grown ZnGa2O4 thin films increased from 11.94 to 27.05 nm as the annealing temperature rose from 500 to 900 °C. Excess Ga released from ZnGa2O4 during thermal annealing treatment resulted in the appearance of a Ga2O3 phase. High-resolution transmission electron microscope image analysis revealed that the preferential crystallographic orientation of the well-arranged, quasi-single-crystalline ZnGa2O4 (111) plane lattice fringes were formed after the thermal annealing process. The effect of crystallite sizes and lattice strain on the width of the X-ray diffraction peak of the annealed ZnGa2O4 thin films were investigated using Williamson-Hall analysis. The results indicate that the crystalline quality of the deposited ZnGa2O4 thin film improved at higher annealing temperatures.

Stability studies on a sensitive EUV photoresist based on zinc metal oxoclusters

Background: Hybrid inorganic-organic materials have emerged as promising candidates for EUV resists. However, knowledge on their stability when deposited as thin films is essential for their performance in EUV lithography. Aim: We investigate whether the molecular structure of Zn-based metal oxoclusters is preserved upon thin film deposition and study aging processes of the thin film under different atmospheres, since these chemical changes affect the solubility properties of the material. Approach: A hybrid cluster that combines the high EUV photon absorption cross-sections of zinc and fluorine with the reactivity of methacrylate organic ligands was synthesized. The structural modifications upon thin film formation and after aging in air, nitrogen, and vacuum were studied using a combination of spectroscopic techniques. Preliminary studies on the lithographic performance of this material were performed by EUV interference lithography. Results: The Zn-based compound undergoes structural rearrangements upon thin film deposition as compared to the bulk material. The thin films degrade in air over 24 h, yet they are found to be stable for the duration and conditions of the lithography process and show high sensitivity. Conclusions: The easy dissociation of the ligands might facilitate hydrolysis and rearrangements after spin-coating, which could affect the reproducibility of EUV lithography.

Effects of gas pressure and discharge current on beam composition in a magnetron discharge ion source.

The magnetron discharge plasma is commonly used in thin film deposition processes, but it can also be utilized for ion beam production. We have developed and investigated an ion source based on planar magnetron discharge. We show that under certain conditions, the discharge, running in a high current pulsed mode, effectively produces plasmas with a high fraction of ions formed from the magnetron target material. The ion beam extracted from the discharge plasma and its composition were studied using a time-of-flight method. The plasma electron temperature was measured by using a double Langmuir probe. We find that the increased working gas pressure and discharge current lower the electron temperature, leading to an increased fraction of target material ions in the plasma and therefore also in the extracted ion beam due to their lower ionization potential compared to that of the working gas.

Effect of substrate surface on DR-19 films deposition process with using EFA-PVD method

The Disperse Red 19 (DR-19) with its conjugated chain structure is known to offer great potential for photonic device applications, such as optical switching and optical data storage. This researches aim to study surfactant effect of silane substrate and the effect of external electric field applied during the deposition process on properties of the resulted DR-19 film. This researches using Electric Field Assisted Physical Vapor Deposition (EFA-PVD) method. The characterization of the film structure was performed by means of XRD. The deposited molecular orientation was characterized with UV-Vis spectroscopic measurement. Based on these spectroscopic data, it is shown that anchoring mechanism with hydrogen bonding does occurred between DR-19 molecule and silane substrate responsible of the stability of the fabricated film. Result of this research show that DR-19 films have been obtained which exhibit crystalline structure with the molecules deposited in parallel polar orientation perpendicular to the silane substrate surface and regular head to tail stacking when increasing external electric field. This is understood to be result of the formation of strong hydrogen bonding acting as the anchoring mechanism.

Fabrication of arrayed microwells with wrinkle microstructure by ink-jet and diamond-like carbon thin film deposition process

Fabrication of microwells is an important technology to create and enhance the functions needed for the biological applications of microfluidic devices. In this paper, how to fabricate arrayed microwells on poly(dimethylsiloxane) (PDMS) substrates handily using an ink-jet processing was presented. More, the microwells having wrinkle microstructures with several μm size on the surfaces were fabricated by a combination procedure of the ink-jet and diamond-like carbon (DLC) thin film deposition. The shapes of the microwells were hexagon and circle, and the sizes were in the ranges of 100–170 μm in diagonal or diameter and 3–30 μm in depth. To investigate the effect of the microwells on cellular behaviors, mouse myoblast cells were cultured on the PDMS substrates. The results demonstrated that the microwells with wrinkle microstructures had the ability to form spherically shaped cell aggregates of around 100 μm size, which were considered to be multicellular spheroids.

Method of the coating thickness and transmittance control during the film deposition process

A method of the coating thickness and transmittance control during the film deposition is proposed. The photometric setup on the basis of vacuum resistive evaporation installation is presented. The stages of the spectral data processing algorithm are described. The substrate holder carousel is shown as part of the installation.

Characterization of Tin Phosphide Films for All-Solid-State Battery Anode Fabricated By Aerosol Deposition

Aerosol deposition (AD) method has many advantages compared to the conventional film deposition process [1]. This method uses impact consolidation at room temperature between raw ceramic particles and substrate during aerosolized powders crash onto the substrate. The film formed by AD has relatively dense structure made of nanocrystalline particles and its structural and physical properties is similar to base powder material. This feature is attractive for the fabrication of oxide-based solid state batteries, because various electrode layers can be formed on solid electrolyte without any thermal treatment [2-4]. In order to achieve higher energy density of the all-solid-state battery, the use of both cathode and anode materials with high capacity are required. Tin phosphide Sn4P3 is one of the high capacity anode materials for lithium ion batteries, with the thoretical lithium storage capacity of 1256 mAh g-1 [5]. In lithium insertion process, Sn4P3 forms Sn and Li3P and Li3P would act as a matrix suppressing the volume change during alloying reaction and keep the electrode particles mechanically connected together. Moreover, Li3P has good ionic conductivity so that self-formation of a good ionic conduction matrix is formed in the electrode in lithium insertion process. Therefore, Sn4P3 is considered to be attractive candidate for anode with high capacity of all-solid-state lithium-ion batteries. In this study, we fabricated Sn4P3 film electrode by AD on both SUS316L plate and garnet-type Ta-doped Li7La3Zr2O12 (LLZTO) solid electrolyte and electrical and electrochemical properties of the films were investigated. Ball-milled Sn4P3 powder with the size of 0.5-1 µm was used as raw material for Sn4P3 film fabrication. The powders were aerosolized with N2 carrier gas at flow rate of 10-20 L/min and splayed through the nozzle onto SUS316L plate or LLZTO sintered pellet fixed on X-Y stage in vacuumed deposition chamber to form Sn4P3 film. From XRD measurement, the diffraction peaks for Sn4P3 were clearly confirmed in as-deposited films by AD and other impurity phases were not observed. Sn4P3 films have relatively dense structure composed of deformed and fractured particles via impact consolidation. Electronic conductivity of Sn4P3 film by AD is in the range of 10-3-10-2 S cm-1 at room temperature, which is slightly lower than pressed Sn4P3 powders. Li metal foil was attached on the other end face of LLZTO pellet with AD Sn4P3 film to consist all-solid-state cell sample. Galvanostatic testing for Sn4P3/LLZTO/Li was carried out at 0-2.5 V, 0.07 mA cm-2 (corresponding to 200 mA g-1) and 100ºC. As a result, reversible charge and discharge reaction in Sn4P3/LLZTO/Li solid-state cell was demonstrated, with an initial reversible capacity of 800 mAh g-1. Influence of controlling the cell voltage range on the cycling stability for Sn4P3/LLZTO/Li solid-state cell will be discussed.This work was partly supported by JSPS KAKENHI Grant numbers 16K06218 and 16KK0127.

Review Article: Atomic layer deposition of doped ZnO films

This article reviews the process-structure-property relationship in doped ZnO thin films via atomic layer deposition (ALD). ALD is an important manufacturing-scalable, layer-by-layer, thin film deposition process that precisely controls dopant type and concentration at the nanoscale. ZnO is an important technological material, which can be doped to modulate structure and composition to tailor a wide variety of optical and electronic properties. ALD doped ZnO is viewed as a transparent conducting oxide for application in solar cells, flexible transparent electronics, and light-emitting diodes. To date, there are 22 elements that have been reported as dopants in ZnO via ALD. This article studies the underlying trends across dopants and establishes generalized relationships for (1) the role of ALD process parameters, (2) the impact of these parameters on the structure of the ZnO matrix, and (3) the impact of dopants on the optical and electrical properties. The article ends with a brief discussion on the limitations of the ALD-based doping scheme, knowledge gaps in the compositional maps, and a perspective on the future of ALD doped ZnO films.

Synthesis and dielectric properties of printable strontium titanate/polyvinylpyrrolidone nanocomposites

In this work, printable strontium titanate based dielectric nanocomposites have been synthesised and their dielectric properties were studied. Herein, a cost effective, environment friendly polymer, polyvinylpyrrolidone was chosen as the matrix. Two different thin film deposition processes, including spin coating and slot-die have been demonstrated and dielectric properties have been systematically investigated. In particular, 70% weight ratio of strontium titanate loaded nanocomposite showed a remarkable dielectric constant of 70 and dielectric loss of 0.12 at 1 MHz. The results indicate that strontium titanate/polyvinylpyrrolidone nanocomposite may have potential applications in future printable electronics.

Impact of Pit Defects on the Initial Electrical Characteristics of Planar-MOSFET Devices

In this paper, the effects of various defects on the initial electrical characteristics of planar-MOSFET devices were investigated. The measurement results revealed that some pit defects that resulted from the fabrication process were as harmful as traditional killer defects in Schottky barrier diode devices. These pit defects could be observed and distinguished by photoluminescence imaging technology. It is necessary to inspect wafers during fabrication—especially before the film deposition process, when the pit defects are easily overlaid and hidden.

Nonlinear model predictive control of a multiscale thin film deposition process using artificial neural networks

The purpose of this study was to employ Artificial Neural Networks (ANNs) to develop data-driven models that would enable the shrinking horizon nonlinear model predictive control of a computationally intensive stochastic multiscale system. The system of choice was a simulation of thin film formation by chemical vapour deposition. Two ANNs were trained to estimate the system’s observables. The ANNs were subsequently employed in a shrinking horizon optimization scheme to obtain the optimal time-varying profiles of the manipulated variables that would meet the desired thin film properties at the end of the batch. The resulting profiles were validated using the stochastic multiscale system and a good agreement with the predictions of the ANNs was observed. Due to their observed computational efficiency, accuracy, and the ability to reject disturbances, the ANNs seem to be a promising approach for online optimization and control of computationally demanding multiscale process systems.

3D-Printed Low-Cost Spectroelectrochemical Cell for In Situ Raman Measurements.

Raman spectroelectrochemistry is a powerful technique for characterizing structural changes of materials during electrochemical reactions and investigating the mechanism of film deposition and adsorption processes on the surfaces of electrodes. Moreover, in situ measurements enable identification of catalytic sites and reaction intermediates, which facilitates the comprehension of reaction mechanisms. The limitations of this technique include the high-cost and the complexity of the experimental arrangement required by commercial spectroelectrochemical cells (SEC). Thus, 3D-printing technology emerges as an excellent alternative for the production of SEC, with desirable shape, low-cost, and robustness in a short period of time. In this work, an SEC and a 3D-printed working electrode were fabricated from acrylonitrile-butadiene-styrene (ABS) and conductive graphene polylactic acid (PLA) filaments, respectively. The proposed SEC and the 3D-printed electrode were printed within 3.5 h with an estimated cost of materials of less than US $2. Then, the 3D-printed SEC and the electrode were used in a study of structural changes of Prussian blue according to different voltage bias.

Thin-film growth behavior of non-planar vanadium oxide phthalocyanine**Project supported by the National Natural Science Foundation of China (Grant No. 51673214) and the National Key Research and Development Program of China (Grant No. 2017YFA0206600).

The thin film properties of organic semiconductors are very important to the device performance. Herein, non-planar vanadyl phthalocyanine (VOPc) thin films grown on rigid substrates of indium tin oxide, silicon dioxide, and flexible substrate of kapton by organic molecular beam deposition under vacuum conditions are systematically studied via atomic force microscopy and x-ray diffraction. The results clearly reveal that the morphology and grain size are strongly dependent on the substrate temperature during the process of film deposition. Meanwhile, the VOPc films with the structure of phase I or phase II can be modulated via in situ annealing and post-annealing temperature. Furthermore, the crystalline structure and molecular orientation of vapor-deposited VOPc can be controlled using molecular template layer 3, 4, 9, 10-perylene-tetracarboxylic dianhydride (PTCDA), the VOPc film of which exhibits the phase I structure. The deep understanding of growth mechanism of non-planar VOPc film provides valuable information for controlling structure-property relationship and accelerates the application in electronic and optoelectronic devices.

In-operando imaging of polysulfide catholytes for Li–S batteries and implications for kinetics and mechanical stability

Enhancing the electrochemical performance of lithium-sulfur batteries requires improved fundamental understanding of the reduction and oxidation of the soluble lithium polysulfide species. To this end, we have designed a ‘donut-shaped’ cell to enable direct optical observation of phase transformations of a liquid polysulfide catholyte to solid lithium sulfide during electrochemical cycling. We use this technique to image the spatio-temporal distribution of the solid lithium sulfide as it deposits on a carbon matrix at different charging rates. These experiments indicate that the reduction and oxidation of polysulfide catholyte occurs as a thin film deposition and growth process during both lithiation and delithiation. We then investigate the ramifications of these morpological changes in terms of mechanical stability by measuring the evolution of stress during discharge of the polysulfide catholyte. The stress measurements indicate that the average stress during discharging decreases with increasing the charging rate, which we attribute to less dense deposition of lithium sulfide at high discharge rates.

Effect of discharge power and silicon content on optical and mechanical properties of carbon-rich amorphous silicon carbide films obtained by PECVD

We studied optical and mechanical properties of a-SixC1-x:H films prepared by the PECVD technique from the mixture of CH4, SiH4, H2 and Ar. RF discharge power and silane flow rate were chosen as parameters of the film deposition process that allowed to vary film properties. It was shown that variations of silane flow rate (10, 20 sccm) and discharge power in the 100–300 W range allow to obtain films with the following characteristics: optical bandgap 2.5–4.1 eV; refractive index of 1.8–2.1; hardness (H) 8.6–14.8 GPa; Young modulus (E) 64–143 GPa. The film deposition rate varied from 10 to 35 nm/min. By selecting deposition regimes, we deposited films with high ratio between film hardness and Young modulus (H/E = 0.13). The variations of optical and mechanical properties of the films by changing discharge power and silane flow are interpreted within a model accounting film composition and phase-structural transformations. Good combination of optical and mechanical properties of the developed films makes them promising for application as protective, passivation and anti-reflection coatings.

Atmospheric-Pressure Microwave Plasma Torch for CVD Technology of Diamond Synthesis

An electrodeless microwave jet plasma source is considered, and its various applications in the technology of chemical vapor deposition of diamond films and dimension increasing of small diamond single crystals synthesized at high pressures and temperatures are discussed. The plasma jet is ignited in an atmospheric-pressure gas (argon) flow with hydrogen and methane additives. The operation of the microwave jet reactor is described, and the plasma characteristics measured using emission spectroscopy are presented. The brightly glowing atmospheric-pressure plasma jet is ignited and stably burns at a microwave power of ≤1 kW supplied from a microwave oven magnetron. The specific microwave power density absorbed by the compact plasma jet (≤104 W/cm3) is comparable with that absorbed by a dc arc. The growth rate of the polycrystalline diamond layer amounts to 40 µm/h. The process of film deposition on the substrate can be controlled by scanning the substrate surface with the jet.

Modeling reactive magnetron sputtering: Opportunities and challenges

The complexity of the reactive magnetron sputtering process is demonstrated by four simulation examples. The examples, commonly encountered during the application of this process for thin film deposition, are described by a numerical model for reactive sputter deposition. A short description of the current model precedes these case studies. In the first example, redeposition of sputtered atoms on the target is studied by its effect on the hysteresis behavior often observed during reactive sputtering. Secondly, the complexity of current-voltage characteristics during reactive magnetron sputtering is treated. The influence of substrate rotation and the pulsing of the discharge current illustrate the time dependence of the reactive sputtering process. As a conclusion, the two main challenges for a further improvement of the model are discussed.

Imaging of π-conjugated polymer/fullerene blends used in organic photovoltaics by nonlinear photoluminescence emission

A number of image microscopies have been applied to films of π-conjugated polymers and their fullerene blends used in photovoltaic applications; however, they seldom are able to map the polymer/fullerene grain interfaces and detect microscopic defects in the blend films. We have conducted multiphoton microscopy using a 65-fs mode-locked laser at 1.56 μm for spectroscopy and mapping of films of two prototype π-conjugated polymers, namely MEH-PPV and P3HT combined with their blends of PCBM fullerene molecules. The pristine polymer films have shown third harmonic generation and three-photon photoluminescence emission bands that are used for mapping the film topography with micrometer spatial resolution. Since the nonlinear photoluminescence band of the photogenerated charge transfer excitons (CTE) at the polymer/fullerene interfaces in films of polymer/fullerene blends is substantially redshifted compared to that of the excitons in pristine polymers, we could readily map the polymer/fullerene grain interfaces using the nonlinear CTE photoluminescence emission. From the multiphoton imaging of the polymer/fullerene films, we show that the polymer super-grains in MEH-PPV/PCBM are substantially larger than those in P3HT/PCBM, which may be detrimental to charge transport and, in turn, to photovoltaic applications, in agreement with smaller power conversion efficiencies obtained for solar cells based on the former blend. In addition, we also found second harmonic generation emission bands in the MEH-PPV/PCBM blend that result from micron-size embedded defects that do not possess inversion symmetry that forms during the film deposition process at ambient conditions. Multiphoton microscopy and spectroscopy are valuable additions to the tools of organic semiconductor films and devices for investigating the properties and growth of polymer/fullerene blends used for photovoltaic applications with micron spatial resolution.

Study on Interface Engineering of TiN/SiO2 Layers to Reduce the Parasitic Capacitance in CMOS Circuits

Recent developments in CMOS (Complementary Metal-Oxide-Semiconductor) technology have heightened the need for high-quality interface between mold and metal line, in order to decrease the RC delay in CMOS circuit. This technical trend indicates that the understanding of the interface reaction between the silicon dioxide (SiO2) and the titanium nitride (TiN) is emerging as an important issue in the thin film deposition process. However, only few researchers have focused on the interface researches to investigate the formation of parasitic capacitance and its material properties of TiN/SiO2 layer. In this work, we report the formation mechanism of Titanium dioxide (TiO2) on SiO2 surface during the TiN deposition process based on a Plasma Enhanced Chemical Vapor Deposition (PECVD) and Titanium tetrachloride (TiCl4) gas reactions. This research has explored the effects of the partial pressure of TiCl4 gas in the initial step of TiN deposition on the formation of the intermetallic compound of TiN/SiO2 interface layer. The results of atomic composition and the position of valance band of the composite material analyzed by X-ray photoelectron spectroscopy (XPS) reveals that the parasitic capacitance material is the TiO2. The high partial pressure of TiCl4 leads to an increased oxygen-titanium ratio (O/Ti ratio) and a decreased maximum position of valance band at the interface between TiN and SiO2, which is attributed to TiO2 formation. Furthermore, we investigated the effect of the thickness of TiO2 and its Oxygen intensity induced by TiCl4 gas treatment on the change of the parasitic capacitance using X-ray fluorescence (XRF) analysis and Secondary Ion mass spectrometry (SIMS).