Thin Film Deposition Process Research Articles

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.

Overcoming the insulating materials limitation in HiPIMS: Ion-assisted deposition of DLC coatings using bipolar HiPIMS

The present study aims to demonstrate that operating the HiPIMS discharge in bipolar regime (BP-HiPIMS) enables an energy-enhanced deposition process of high-quality hydrogen-free DLC thin films (high hardness, low coefficient of friction, good wear resistance, good adherence to the substrate and very low surface roughness). The structural and mechanical properties of DLC thin films deposited using the BP-HiPIMS technique were compared to those of the films prepared using a conventional HiPIMS process, under various deposition conditions. The BP-HiPIMS technique generates an energetic ion population and a substantial increase in the ion flux as compared to the conventional (monopolar) HiPIMS. This phenomenon overcomes the limitations when working with insulating or high electrical resistivity materials (both substrates and coatings), i.e. the need to accelerate the film-forming species. Energetic enhanced deposition conditions during bipolar HiPIMS facilitate the densification (up to 2.7 g/cm3) of amorphous carbon thin films which results in an increase in the film hardness (23 GPa) when depositing on Si substrates, without using substrate bias voltage, adhesion interfacial layer or substrate pre-treatment. Besides high hardness, the BP-HiPIMS process allows growing DLC coatings with good elastic strain to failure and high resistance to plastic deformation and cracking.

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.

Atomic Layer Deposition of Photoconductive Cu2O Thin Films.

Herein, we report an atomic layer deposition (ALD) process for Cu2O thin films using copper(II) acetate [Cu(OAc)2] and water vapor as precursors. This precursor combination enables the deposition of phase-pure, polycrystalline, and impurity-free Cu2O thin films at temperatures of 180–220 °C. The deposition of Cu(I) oxide films from a Cu(II) precursor without the use of a reducing agent is explained by the thermally induced reduction of Cu(OAc)2 to the volatile copper(I) acetate, CuOAc. In addition to the optimization of ALD process parameters and characterization of film properties, we studied the Cu2O films in the fabrication of photoconductor devices. Our proof-of-concept devices show that approximately 20 nm thick Cu2O films can be used for photodetection in the visible wavelength range and that the thin film photoconductors exhibit improved device characteristics in comparison to bulk Cu2O crystals.

Roughness-Controlled Cu2ZnSn(S,Se)4 Thin-Film Solar Cells with Reduced Charge Recombination.

Copper zinc tin sulfo-selenide (CZTSSe) is a promising light-absorbing material of thin-film solar cells because of its low material cost especially when it is prepared by cost-effective processes like the electrochemical deposition process. The CZTSSe thin-film solar cells, however, suffer from the relatively low efficiency, mostly because of the significant charge recombination. Given that the surface recombination is one of the major recombination paths, controlling the surface roughness, and thus the interfacial area is one of the key factors for improving their device performances. In this study, we demonstrated a simple but effective strategy for reducing the surface roughness during the electrochemical deposition process of the CZTSSe thin films. By adopting an initial nucleation stage with higher deposition currents ahead of the steady-state galvanostatic deposition, the surface of the copper-zinc-tin (CZT) precursor and CZTSSe thin films became significantly smoother and uniform (ΔRrms: -43.8% for CZT, -28.9% for CZTSSe). The effects of the surface roughness on the photovoltaic properties of the CZTSSe thin-film solar cells have been investigated systematically with various characterization techniques like the diode analysis, lifetime measurement, and the temperature dependency of the open-circuit voltage. The device with the smoother surface exhibited higher open-circuit voltage and fill factor, mostly because of the significantly reduced charge recombination, leading to the high conversion efficiency of 8.64% (active).

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.

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.

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).

Prestress-Driven Optical Modulations of Flexible Oxide Thin Films Processed in Stretching Mode

The effects of stress in inorganic thin films have been long studied to minimize the negative influences of thermally-mismatched substrates mainly in terms of crystal growth and mechanical failure. Although it is well known that extra stress in thin films can affect optical properties, like bandgap, via the theoretical calculations of electronic structure, however, experimental verification of the optical modulation has not been available in the flexible systems. Here, we are dealing with a flexible semiconducting inorganic thin film which can be a fairly good representative for any semiconductor-involved flexible devices or components. We intentionally induced extra compressive stress in wide bandgap ZnO thin films by unique in situ stress-driven deposition processing that utilizes a uniaxial stretching mode of polymer substrate. The stretching mode provides homogeneous but biaxial stresses in the hexagonal wurtzite structure, leading to the extension of c-axis and the contraction of a-axis. The asymmetric consequences affect unexpectedly the energy levels of band structure, which is the origin of the in situ stress-driven optical modulations. We verify such changes successfully by using both the experimental and theoretical methods. The in situ deposition process of flexible thin films under a stretching mode provides compressive strain up to ~4.87%, which corresponds to an in-plane stress of less than ~9 GPa. The existence of the compressive stress induces distortion of the hexagonal unit cell as verified by high-resolution TEM images. We experimentally demonstrate the reduction of the optical bandgap by ~150 meV with the maximum compressive strain of ~4.87%. The experimental evidences of optical modulations were supported by the theoretical calculations using density functional theory. The reduced strong interactions between Zn 3d and O 2p orbitals are assumed to be responsible for the bandgap narrowing.

Analysis of Optical Plasma Monitoring in Plasma-Enhanced Atomic Layer Deposition Process of Al₂O₃.

A noninvasive, optical plasma monitoring method in plasma-enhanced atomic layer deposition (PEALD) process for nanoscale water vapor barrier film is presented. Any equipment malfunction, as well as a deviation in the condition of individual components can easily jeopardize the process result. Al₂O₃ deposition process was employed in this research as a test vehicle, and high-speed optical plasma monitoring was demonstrated. It is shown that optical plasma monitoring is useful for not only measuring plasma pulses in real time, but also for the detection of any variation in plasma condition which enables inferring plasma dynamics for advanced process control in nanoscale thin film deposition process.

Strategies for Reducing Particle Defects in Ti and TiN Thin-Film Deposition Processes

Generation of particle defects in semiconductor manufacturing is inevitable, but it has to be minimized to enhance IC yield. There are various causes for the generation of particle defects in different semiconductor manufacturing processes, such as diffusion, thin-film deposition, lithography, etch, and clean. In this paper, primary defect generation mechanisms in thin-film deposition processes, such as atomic layer deposition TiN, radio frequency physical vapor deposition Ti, and physical vapor deposition TiN, are discussed. Various strategies, such as periodic clean optimization, on-load clean, idle pasting, periodic pasting optimization, kit life optimization, target burning optimization, and kit hardware selection that reduce the generation of defects in the thin-film deposition processes are presented. This paper also discusses hardware-induced surface defect and solutions to reduce them.

Analysis of Multi-elemental Thin Films via Calibration-Free Laser-Induced Breakdown Spectroscopy.

Elemental analyses of thin films with complex composition are challenging as the standard analytical techniques based on measurement calibration are difficult to apply. We show that calibration-free laser-induced breakdown spectroscopy (LIBS) presents a powerful solution, enabling quantitative analyses of multielemental thin films with analytical performances better than those obtained with other techniques. The demonstration is given for a nickel-chromium-molybdenum alloy film of 150 nm thickness that was produced by pulsed laser deposition. The LIBS spectra were recorded under experimental conditions that enable simple and accurate modeling of plasma emission. Thus, a calibration-free approach based on the calculation of the spectral radiance of a uniform plasma in local thermodynamic equilibrium was applied to deduce the elemental composition. Supported by analyses via Rutherford backscattering spectrometry and energy-dispersive X-ray spectroscopy, the LIBS measurements evidence nonstoichiometric mass transfer of the alloy during the thin-film deposition process. This technique could be used even for thinner films, provided that the film-composing elements are not present in the substrate.

High growth-rate atomic layer deposition process of cerium oxide thin film for solid oxide fuel cell

Cerium oxide (CeO2) shows superior surface exchange, and therefore is widely used for the cathode interlayer coating material to reduce the activation loss in low temperature solid oxide fuel cell (LT-SOFC). Here, we report on the application of the high growth-rate atomic layer deposition (ALD) process of CeO2 thin films as cathodic interlayers for LT-SOFCs. We demonstrate that the maximum power density of the SOFC with pure CeO2 interlayer increases by 45% compared to the one without interlayer at 450 °C. More importantly, the performance degradation rate of the ALD CeO2 interlayered cell improves by 25 times compared to the cell without interlayer during 24 h operation at 450 °C.

Emerging processes for metallurgical coatings and thin films

Innovation in thin-film deposition processes, thermal spraying and cladding technologies mostly rely on evolutions of their previous iteration. Along with other examples, five case studies of emerging elaboration processes for metallurgical coatings are described coupled with their applications. In the frame of the lifetime extension of components exposed to aggressive media or their functionalization, this article depicts all the developments of the detailed processes. Physical vapor deposition (PVD) of coatings with exceptional properties is possible thanks to sources generating highly ionized metallic vapors. The control of the average energy per incident species and particularly metallic ions strongly influences the characteristics of the deposited layer obtained, for example, with HiPIMS (High Power Impulse Magnetron Sputtering). While PVD techniques are mainly directive regarding the growth of the coating, chemical vapor deposition (CVD) processes manage to homogeneously coat complex 3D shapes. The use of specific precursors in DLI–MOCVD (Direct Liquid Injection – MetalOrganic CVD), carefully selected from the whole metalorganic chemistry, allows one to efficiently treat heat-sensitive substrates and broadens their application range. The third detailed example of emerging technology is suspension plasma spraying (SPS). Projection of various solutions containing nanoparticles leads to the growth of unusual morphologies and microstructures and to the generation of porous coatings with multi-scaled porosity. On the other hand, cold-spray uses metallic powders with higher granulometry and does not modify them during the deposition process. As a result, high-purity and dense materials are deposited with properties similar to those of wrought materials. Whereas cold-spray is suitable only for ductile metals, laser cladding can be applied to ceramics, polymers and of course metals. Laser cladding is a key technology for advanced metallurgical engineering and alloy development due to its capability for functionally graded materials production and combinatorial synthesis.

Process optimization and device variation of Mg-doped ZnO FBARs

Thin film bulk acoustic resonator (FBAR) plays a very important role in radio frequency (RF) filters used in cell phone and other wireless systems. Although FBAR is commercialized, the design/process interactions on the frequency response variation in FBAR device are still lacking. Design and fabrication are two crucial aspects affecting FBAR device performance. In this report, various solidly mounted resonators (SMR) were designed, fabricated and analyzed to study wafer-level site-to-site RF variation on design and fabrication process. As a key process step for SMR FBAR, the optimization process of Mg-doped ZnO piezoelectric thin film deposition was studied by varying thin film sputtering conditions using various sputtering targets and by post annealing treatment after the deposition. The quality of this crucial layer was verified by XRD on its (0 0 2) crystallization and wafer-level FBAR RF characterization. FBAR devices with high quality were fabricated with an excellent resonant behavior near 2 GHz and a maximum return loss of −15 to 25 dB. Quality factor Q ranges from 400 to 800, with a coupling coefficient keff2 of 1.5–3%. Wafer-level and wafer-to-wafer variation of central frequency are within 1.8–2.1 GHz. Computer simulation verified that this frequency variation correlates to the piezoelectric film variation of 1.6–1.9 μm. Process control on this piezoelectric thin film is essential to maintaining the resonator frequency-controlled value when building duplexer RF circuits. The dependency of RF performance on FBAR size, density and orientation is not obvious, compared to that of the wafer-level FBAR device variation on fabrication process. Regarding to the Mg-doping effect in MgxZn1-xO piezoelectric film, the amount of Mg in MgxZn1-xO film during the sputtering process must be properly controlled within 30% to keep the piezoelectric quality. The average acoustic speed of the Mg-doped ZnO film is 6870 m/s with the estimated range of 5760–7980 m/s, which is better than that of pure ZnO film (6330 m/s).

High-performance Full-atomistic Simulation of Optical Thin Films

The experimental study of the dependence of thin film properties on the deposition conditions may be still a great challenge. Today the progress in high performance computing allows one to perform the investigation of these dependencies on the atomistic level using the classical molecular dynamics (MD) simulation. In the present work the computational cost and efficiency of classical full-atomistic simulation of thin film deposition process using the Lonmonosov-2 supercomputer facilities is discussed. It is demonstrated that using 512 computational cores of the Lomonosov-2 supercomputer ensures the simulation of thin film cluster with technologically meaningful thickness of an optical film. Because of a relatively slow growth of the simulation time with the increase of film thickness we guess that simulations clusters with thicknesses that are several times higher than the currently achieved thicknesses about one hundred nanometers is quite realistic if the number of available computational cores will be increased up to several thousands.

Etch Characteristics of Cu Thin Film Using Inductively Coupled Plasma of Non-Greenhouse Gases

This study is to analyze the etch characteristic of line-patterned Cu flims under various etch conditions using non-halogen gases. The etching of Cu films has great difficulty due to very low volitility of Cu compounds formed by the reaction with conventional etch gases. Because of this fact, Cu patterining has been achieved by the damascene process containing thin film deposition and chemical mechanical processing. Although many researches were carried out since 1990s, no remarkable progress has been made. As the dimension of Cu pattern has been shrinked, the etching process of Cu films has become the main issue because the damascene process reveals fatal disadvantages. In this study, inductively coupled plasma reactive ion etching (ICPRIE) of Cu film was performed using non-greenhouse gases. Gas mixtures containing Cl2/Ar, HCl/Ar, HBr/Ar, O2/Ar, and H2/Ar were used to etch Cu thin films. In addition, the influences of the gas concentration, ICP power, gas pressure and dc- bias to substrate on each characteristic were investigated. The etch profiles and etch mechanism of Cu films were examined by field emission scanning electron microscopy, optical emission spectroscopy, and X-ray photoelectron spectroscopy, respectively. Acknowldgments This research was supported by the MOTIE(Ministry of Trade, Industry & Energy (10080450) and KSRC(Korea Semiconductor Research Consortium) support program for the development of the future semiconductor device.

Thin and Thick Film Ceramic-Based Passive Wireless Temperature Sensors for Harsh Environments

The needs for real-time temperature monitoring of energy systems in extreme conditions keeps increasing due to the growth of manufacturing industries. Current technologies utilize thermocouples, infrared laser interferometers, and surface acoustic wave (SAW) sensors. Thermocouples have limited lifespan. The reliability is poor due to continuous redox reaction taking place at the hot junction and any caustic environment will corrode the thermocouple material. Laser interferometers are limited by the spot area of the laser beam and monitoring temperature gradient is difficult, since it is a surface sensitive technique. To overcome the limitations, research has been focused on passive wireless sensor technology where an inductor–capacitor (LC) circuit was used to monitor the temperature and local strain conditions. The primary objective of this work was to study the materials properties of carbide/silicide and oxide composites for the fabrication of ceramic-based LC circuits on a ceramic substrate using thin and thick film deposition methods. This work includes the investigation of the composite precursor, pattern technology and the effect of thermal processing on the final pattern and stability. The relation of volume shrinkage during sintering process and phase development are of interest. The secondary objective of this work was to investigate the electrical properties of the tailored sintered electrodes. One system that will be discussed is the development of a polymer-derived electroceramic electrodes based on two different carbide/silicide compositions. These inks were synthesized by mixing a siloxane/silane compound with an active inorganic filler material. Upon sintering, the organic molecules decomposed and the silicon will react with the inorganic fill at a higher temperature to form a ceramic composite. The reaction kinetics depends on the reaction between terminating functional groups, silicon ``atom, and the filler particle. To understand the reaction kinetics, phase formation, and other mechanical properties (such as volumetric shrinkage), varying ratios of the particle filled polymer matrix was injection molded and sintered at varying temperature rates. The compositions that provided the desired material properties was chosen to direct-write the LC circuit pattern on a ceramic substrate by a 2D printing technology and screen printing technology. The sintered sensor was characterized by XRD, SEM and the electrical characterization of the printed LC circuits were completed on the sensor compositions by a signal analyzer in tandem with an oscilloscope (at temperatures 50-1300oC). Miniaturization of the LC circuit was developed by a thin film deposition process to show the effect of size reduction in various aspects of sensing and adaptability. Miniaturized LC circuit was patterned by depositing by physical vapor deposition onto a ceramic substrate. Additionally, the size reduction will boost the capacitance of the circuit which will assist in the reduction of the signal-to-noise ratio, ease of signal processing and reduces the sophistication of electronics. The fabricated thin films were characterized by grazing incident XRD and SEM to compare the formation of grain boundaries, phases with the thick film composite. The electrical characterization was completed in a similar fashion to compare results with thick film composites.

Probing Ferroic States in Oxide Thin Films Using Optical Second Harmonic Generation

Forthcoming low-energy consumption oxide electronics rely on the deterministic control of ferroelectric and multiferroic domain states at the nanoscale. In this review, we address the recent progress in the field of investigation of ferroic order in thin films and heterostructures, with a focus on non-invasive optical second harmonic generation (SHG). For more than 50 years, SHG has served as an established technique for probing ferroic order in bulk materials. Here, we will survey the specific new aspects introduced to SHG investigation of ferroelectrics and multiferroics by working with thin film structures. We show how SHG can probe complex ferroic domain patterns non-invasively and even if the lateral domain size is below the optical resolution limit or buried beneath an otherwise impenetrable cap layer. We emphasize the potential of SHG to distinguish contributions from individual (multi-) ferroic films or interfaces buried in a device or multilayer architecture. Special attention is given to monitoring switching events in buried ferroic domain- and domain-wall distributions by SHG, thus opening new avenues towards the determination of the domain dynamics. Another aspect studied by SHG is the role of strain. We will finally show that by integrating SHG into the ongoing thin film deposition process, we can monitor the emergence of ferroic order and properties in situ, while they emerge during growth. Our review closes with an outlook, emphasizing the present underrepresentation of ferroic switching dynamics in the study of ferroic oxide heterostructures.

Probing Ferroic States in Oxide Thin Films Using Optical Second Harmonic Generation

Forthcoming low-energy consumption oxide electronics rely on the deterministic control of ferroelectric and multiferroic domain states at the nanoscale. In this review, we address the recent progress in the field of investigation of ferroic order in thin films and heterostructures, with a focus on non-invasive optical second harmonic generation (SHG). For more than 50 years, SHG has served as an established technique for probing ferroic order in bulk materials. Here, we will survey the specific new aspects introduced to SHG investigation of ferroelectrics and multiferroics by working with thin film structures. We show how SHG can probe complex ferroic domain patterns non-invasively and even if the lateral domain size is below the optical resolution limit or buried beneath an otherwise impenetrable cap layer. We emphasize the potential of SHG to distinguish contributions from individual (multi-) ferroic films or interfaces buried in a device or multilayer architecture. Special attention is given to monitoring switching events in buried ferroic domain- and domain-wall distributions by SHG, thus opening new avenues towards the determination of the domain dynamics. Another aspect studied by SHG is the role of strain. We will finally show that by integrating SHG into the ongoing thin film deposition process, we can monitor the emergence of ferroic order and properties in situ, while they emerge during growth. Our review closes with an outlook, emphasizing the present underrepresentation of ferroic switching dynamics in the study of ferroic oxide heterostructures.