Film Thickness Measurements Research Articles

High-Precision Thickness Measurement of Cu Film on Si-Based Wafer Using Erasable Printed Eddy Current Coil and High-Sensitivity Associated Circuit Techniques

The eddy current coil is widely adopted to measure the thickness of copper (Cu) film on the silicon (Si) based wafer. However, the lift-off distance (LOD) variation between the coil and Cu film has a strong negative effect on the accuracy and repetitiveness of the thickness measurement. Therefore, it is necessary to eliminate the impact of LOD variation. In this article, a high-precision thickness measurement method is proposed to determine the thickness of Cu film on the Si-based wafer by using the techniques of the erasable printed eddy current coil (EPECC) and the high-sensitivity associated circuit. The theoretical feasibility and sensitivity improvement of the conceptual design are analyzed in detail. As a proof of concept, a prototype of the proposed method is fabricated. The EPECC is prepared on the back surface of the wafer, and the LOD is unvaried during the measurement. Experimental results show that comparing with the traditional eddy current coil, the measurement stability, precision, and accuracy of the Cu film thickness by the proposed method are significantly improved even under severe vibration conditions. The relative error is 2% in repeated measurements.

Film thickness, interfacial waviness and heat transfer during downflow condensation of R134a

• Condensation tests are performed with R134a in a 3.38 mm tube. • Simultaneous film thickness and heat transfer measurements are carried out. • The experimental results of R134a are compared to those of R245fa. • The interfacial waves inception is delayed for R134a due to the high vapor density. • Models for condensation heat transfer, film thickness and void fraction are assessed. Coupled measurements of liquid film thickness and heat transfer during condensation inside minichannels are rare in the literature due to the technical difficulties in performing accurate and non-intrusive measures. The availability of such experimental data is fundamental for better understanding the occurring physical mechanisms and for the proper design of heat exchangers. To cover this gap, in the present work liquid film thickness and heat transfer coefficients have been simultaneously measured during vertical downflow condensation inside a 3.38 mm inner diameter channel. Condensation tests have been run with refrigerant R134a at mass flux between 30 and 150 kg m −2 s −1 and 30 °C saturation temperature. The instantaneous liquid film thickness and interfacial waves are detected by combining two complementary optical methods: shadowgraph technique (applied to a sequence of flow pattern images recorded by a high speed camera) and chromatic confocal imaging. In the data analysis, the experimental results of R134a have been discussed in comparison to R245fa condensation data taken during a previous experimental campaign at much lower pressure. On average, R134a displays higher liquid film thickness than R245fa and the appearance of high-amplitude disturbance waves, which promote the thinning of the liquid film and enhance the heat transfer, is detected at higher mass flux for R134a as compared to R245fa. The liquid film thickness is found to decrease with the increasing mass flux for both fluids, except from 30 to 50 kg m −2 s −1 due to the transition between shear stress-driven and gravity-driven downflow condensation. The accuracy of several well-known models for the prediction of heat transfer coefficient, film thickness and void fraction has been assessed with comparison to the experimental data of both R134a and R245fa.

Experimental Measurement of Film Thicknesses on a Static Film Former and a Film Centrifugal Sprayer

Experimental Measurement of Film Thicknesses on a Static Film Former and a Film Centrifugal Sprayer

Evaluation of Moisture Sensitivity Performance of Stone Mastic Asphalt Mixes with Additional Filler: A Laboratory Comparison of Dry and Wet Mixing Methods

Gap-graded mixtures are one of the areas of improving the permanent deformation strength of hot-mixed asphalt mixtures. Additional filler materials can be needed due to the high bitumen amount and the less fine aggregate amount in the mixture. In this study, the effects of filler additives on moisture susceptibility of the gap-graded hot-mixed asphalt mixtures and mixing methods are investigated. Filler additives such as class C and class F fly ashes and hydrated lime are used 0.5 %, 1.0 %, 2.0 %, and 4 % of the total weight of mixture instead of mineral filler. Design mixtures are prepared according to the Turkish Highway Technical Specifications (THTS). To determine the effect of mixing methods, dry and wet (slurry) methods are used to mix the filler materials. Modified Lottman method (AASHTO T283) are used to determine the moisture susceptibility. An indirect tensile strength test is the measurement of bitumen film thickness which is also conducted. Test results showed that class C fly ash is significantly improved the moisture susceptibility of mixtures. While the slurry method does not give the expected improvement on class C fly ash added mixtures, it shows a positive effect on class F fly ash and hydrated lime added mixtures.

Non-Destructive Characterization of Selected Types of Films and Other Layers via White Light Reflectance Spectroscopy (WLRS)

In this work, we consider White Light Reflectance Spectroscopy (WLRS) as an optical methodology for the accurate, fast and non-destructive measurement of film thickness in the 1 nm to the 1 mm range and for applications that include microelectronics, photonics, bioanalysis and packaging. Films to which WLRS is applicable can be either homogeneous or layered-composite ones, while thickness and composition might be fixed or varying with time; in the latter case, real-time monitoring of the kinetics of processes such as certain transitions, film dissolution and bioreactions is possible. We present the basic principles of WLRS and a selection of characteristic application examples of current interest, and we also briefly compare WLRS with alternative methods for film measurement.

Measuring Film Thickness in Starved Grease-Lubricated Ball Bearings: An Improved Electrical Capacitance Method

Presented in this article is a new method to measure the film thickness in a rolling bearing running under starved conditions, such as in grease-lubricated bearings, using the electrical capacitance method. The method was used to study the impact of speed on film thickness. Results show that fully flooded conditions prevail at lower speeds where the film thickness increases with increasing speed. At higher speeds, where grease-lubricated bearings run under starved lubrication conditions, this increase is less pronounced. At even higher speeds, the film thickness becomes almost independent of the speed.

Measurement of thin liquid film thickness in pipes based on optical interferometry

Measurement of thin liquid film thickness in pipes based on optical interferometry

Electrochemical-driven green recovery of lithium, graphite and cathode from lithium-ion batteries using water

The expected exponential increase in consumption of lithium-ion batteries (LIBs) would pose a unique challenge to the availability of near-critical resources like lithium and graphite in the upcoming decade. We present a lithium recovery process that utilizes a degradation mechanism, i.e., lithium plating, as a tool to concentrate metallic lithium at the anode/separator interface for convenient extraction at room temperature – using only water. Electrochemical characterization of fast charged (1–6 C) LIBs yielded a maximum capacity fade of 50% over ten cycles. The lithium plating was confirmed via voltage plateau analysis, coulombic efficiency, and DC resistance measurements. A maximum lithium plating condition was observed to exist between 4C and 5C, thereby limiting the energy consumption in the extraction process. Post-mortem film thickness measurement showed an incrementing film deposition with a maximum of 35 µm thickness. SEM and XPS analysis confirmed increasing concentration of a dense dendritic metallic lithium deposition on the anode/separator interface with C-rate. A green recovery process was adopted to extract the concentrated metallic lithium using distilled water. The lithium from the plated film, solid/electrolyte interface (SEI), electrolyte, anode, and cathode, was extracted as salts. A 37% improvement in lithium recoverability was achieved with fast charging under ambient conditions. XPS analysis showed ∼92% of lithium yield with no residual lithium in the graphite. In addition, the battery-grade graphite was recovered with 97% purity after heat treatment of the washed anode film, and concentrated transition metals oxides in the cathode to 93% purity for convenient extraction.

Effect of asymmetric material entrance on lubrication in cold rolling

An Integrated Digital Image Correlation (IDIC) method has been applied to the cold rolling process, the images clearly visualise the geometry of the roll bite and the inlet zone. A key, novel finding is that despite using coils and applying entry tension, the strip can enter asymmetrically in the rolling mill. Moreover, it is shown that asymmetric strip feeding results in an uneven lubricant film thickness between top and bottom strip surface. A method is detailed to feed the strip truly symmetrically in the mill, a procedure that is necessary for a meaningful experimental validation of lubricant film thickness models. For symmetric rolling processes the measured film thickness corresponds significantly better with the theory than for asymmetric processes.

µPIV Measurements Of The Phase-Averaged Velocity Distribution Within Wavy Films

Thin-film flows are frequently used in process engineering and are still of great interest in research. In most cases, waves occur which are believed to have a positive effect on the material and heat transport and significantly influence the film properties. A combination of μ-particle image velocimetry and confocal chromatic distance measurement is used to measure phase-averaged flow velocities in film waves. A trigger signal is sent to the PIV system and a recording starts when a wave reaches the wave crest threshold. This makes it possible to trigger the μPIV system depending on the temporal film thickness. The functionality and quality of the measurements depend on the correct positioning of the confocal chromatic sensor. Simultaneously to the velocity measurement, the minimum, average, and maximum film thickness, as well as the wave amplitude and wave frequency, are recorded. Film flow is investigated on a glass plate at various angles (5˚-15˚) of inclination, Reynolds numbers (30-200), and measurement positions. The results are compared with the theoretical solutions according to Nusselt. In addition, the influence of the tilt angle and the measuring position is explained. The measuring position, in particular, has a non-negligible influence since the film properties are largely dependent on the distance to the inlet. Compared to the theoretical solutions according to Nusselt, the velocities and film thicknesses may be significantly greater due to the presence of the waves. With increasing inclination angle and distance to the inlet, the measured mean and maximum velocities of the film flow increase. They almost double when the inclination angle increases from 5˚ to 15˚. When comparing the velocities depending on the measuring position (300-500mm), it is noticeable that the velocities increase between 5-15%, depending on the angle, due to wave development and gravity.

A Novel Set-Up for In Situ Measurement and Mapping of Lubricant Film Thickness in a Model Rolling Bearing Using Interferometry and Ratiometric Fluorescence Imaging

This paper describes a unique experimental set-up constructed for studies of lubricant behaviour in an operating rolling element bearing including in situ quantitative measurements of film thickness in and around the element-raceway contact. The set-up is based on a deep groove ball bearing in which the outer race is made of sapphire to allow full optical access to the zone in which the rolling elements are loaded against it. This allows direct imaging of lubricant films under both steady-state and transient conditions and at contact pressures and rotational speeds representative of those present in real rolling element bearings. Optical interferometry is used to measure thin EHL films inside the ball–raceway contacts while a specific laser induced fluorescence approach, referred to as ratiometric fluorescence, is implemented to observe the lubricant distribution and quantify its thickness ahead of the ball–raceway contact. Results are presented to validate the accuracy of the method and to investigate the influence of bulk lubricant viscosity and bearing speed on contact film thickness, inlet starvation and lubricant distribution around the ball–raceway contact. To the best of our knowledge, the work described here is the first to directly measure lubricant distribution and EHL film thickness in a ball–raceway contact in an operating radial rolling bearing.Graphical

Real-time coating thickness measurement and defect recognition of film coated tablets with machine vision and deep learning

This paper presents a system, where images acquired with a digital camera are coupled with image analysis and deep learning to identify and categorize film coating defects and to measure the film coating thickness of tablets. There were 5 different classes of defective tablets, and the YOLOv5 algorithm was utilized to recognize defects, the accuracy of the classification was 98.2%. In order to characterize coating thickness, the diameter of the tablets in pixels was measured, which was used to measure the coating thickness of the tablets. The proposed system can be easily scaled up to match the production capability of continuous film coaters. With the developed technique, the complete screening of the produced tablets can be achieved in real-time resulting in the improvement of quality control.

Spectroscopic imaging ellipsometry for two-dimensional thin film thickness measurement using a digital light processing projector

An improved version of spectroscopic imaging ellipsometry is described for accurate reconstruction of two-dimensional thin film thickness. A digital light processing projector enables a selected area of the back focal plane of the objective lens to be illuminated so that the angle of incidence and the polarization state of the light source vary depending on the area of the back focal plane being illuminated. By combining multiple images of the object plane obtained at different polarization states, every pixel in the field of view has its own ellipsometric parameters; therefore a reconstruction of two-dimensional thin film thickness is possible. Because the proposed ellipsometry system has a co-axial optical structure in which the objective lens is arranged in the normal direction to the measurement target, the spatial resolution is improved due to the application of a high-magnitude objective lens. In addition, spectroscopic analysis can be conducted using a number of band-pass filters which each have a central wavelength. The effect of the proposed method on thin film thickness measurement was evaluated by comparing the experimental results with a topographic profile obtained using a commercial atomic force microscope.

Impact of physico-chemical properties on falling liquid films flow over flat and corrugated surfaces

In this paper, an optical technique based on fluorescence intensity is applied and calibrated to simultaneously measure film thickness (up to 8 mm) and interfacial velocity of the liquid film flow. Thus, thin-film flows at intermediate and low Reynolds number (13 < Re < 290) are experimentally studied with special attention given to the spatial variation, the frequency of the waves, and interfacial liquid velocity associated with global visual observation. Two fluids (water-ethanol mixture) characterized by low surface tension (σ = 35 and 50 mN/m) and three fluids (water-glycerin mixture) with high viscosity (µ = 5, 10, and 15 mPa.s) are used to investigate the influence of physico-chemical properties on thin-film flow on flat and corrugated plate topologies. First, the effect of physico-chemical properties on the global variation of waves shape and instability evolution has been investigated. Different work fluids were used in the same experimental conditions on a flat plate. Results showed that decreasing surface tension has a stabilizing effect on the flow, dampening the capillary waves that should otherwise arise. At high viscosity, solitary waves with high thickness followed by an undisturbed thin-film with a constant thickness appear. The impact of liquid flow rate and inclination (θ = 10° and 20°) was also studied. It shows that at higher inclination the film thickness decreases and then increases as the liquid flow rate increases. Next, the impact of counter-current gas was studied and we demonstrated that the amplitude of the main waves significantly increases even at low gas velocity while the effect on the velocity of the wave starts to be significant at a counter-current gas velocity of 3 – 4 m/s. Finally, the effect of the corrugation of the solid plate at a high inclination angle (θ = 60°) shows the onset of the breaking waves phenomenon, especially for fluids with low surface tension.

High-accuracy ultrasonic method for in-situ monitoring of oil film thickness in a thrust bearing

The ultrasonic method has been widely applied to measure the oil film thickness – a critical variable that reflects lubrication conditions. However, due to the thermal dependence of ultrasonic signals, significant deviations in film thickness measurements are introduced, hindering the in-situ application of the ultrasonic technique. To address this issue, a real-time temperature compensation method that can accurately obtain the frequency domain information of the reference signal is proposed. Specifically, the reflection from the substrate-coating interface compensates for the thermal effect on the phase increment and amplitude attenuation – this is noted as “self-calibration”. An extra experimental test with a substrate-coating-air structure is performed to calibrate the thermal effect on the coating-induced phase shift – this part is denoted as “pre-calibration”. The combination of “self-calibration” and “pre-calibration” enables the overall temperature compensation strategy. After the effectiveness validation with a temperature-controlled experiment, the proposed method is implemented in a thrust bearing in a heavy-duty hydropower generator with full running conditions, including loading and unloading, normal speed and shut-down. The largely ranged oil film thickness (3–330 μm) is ultrasonically measured and compared with the theoretical value, showing a higher measurement accuracy than the eddy current method.

Characteristics of Gas-Liquid Slug Flow in Microchannel by Instantaneous Liquid Film Thickness Measurement

Characteristics of Gas-Liquid Slug Flow in Microchannel by Instantaneous Liquid Film Thickness Measurement

Three-dimensional analysis of aligner gaps and thickness distributions, using hard x-ray tomography with micrometer resolution.

The morphology of a polymer aligner, designed according to an orthodontic treatment plan, determines clinical outcomes. A fundamental element of orthodontic tooth movement with aligner treatment is the fit of the aligner's surface to the individual teeth. Gaps between the aligner and teeth do occur because current aligner fabrication is not capable of completely reproducing the complex anatomy of the individual denture. Our study aims at a quantitative three-dimensional assessment of the fit between optically transparent aligners placed on a polymeric model of the upper dental arch for two thermofoil thicknesses at preselected thermoforming temperatures. Using an intraoral scan of a subject's upper dental arch, eight models were printed using a stereolithographic system. A series of eight NaturAligners® was manufactured with a pressure molding process, using thermofoils with thicknesses of 550 and and preselected process temperatures between 110°C and 210°C. These aligners placed on the corresponding models were imaged by an advanced micro computed tomography system. The aligners and the models were segmented to extract the gaps and aligners' local thicknesses as a function of the processing temperature for the two foil thicknesses. The results indicate that the aligners show a better fit when the foils are processed at higher temperatures. Nevertheless, processing temperatures can be kept below 150°C, as the gain becomes negligible. Thermal processing reduces the average thickness of the aligners to 60% with respect to the planar starting foil. These thickness distributions demonstrate that the aligners are generally thicker on the occlusal surfaces of molars and premolars but thinner around the incisors and buccal as well as on oral surfaces. Hard x-ray tomography with micrometer resolution is a powerful technique employed to localize the gaps between aligners and teeth, and it also enables film thickness measurements after thermoforming. The thicker film on the occlusal surfaces is most welcome because of aligner abrasion during wear. The NaturAligner® surfaces consist of a -thin cellulose layer, and thus the microplastics released via abrasion of less than this thickness are expected to be substantially less critical than for other commercially available, optically transparent aligners.

Ultrasonic measurement of oil film thickness in a four-layer structure for applications including sliding bearings with a thin coating

Owing to the non-destructive feature, ultrasonic techniques have been developed to measure the oil film thickness in sliding bearings. If a bearing has a thick coating, then the ultrasonic reflection from a four-layer structure consisting of pad-coating-oil-steel is equivalent to that of coating-oil-steel, where classical three-layered ultrasonic models can be applicable to estimate the thickness of oil film. However, in the case of thinly coated bearings, the measurement accuracy of existing models deteriorates due to signal overlapping. Despite two signal processing methods that have been attempted to isolate the desirable oil film echoes, the challenge remains when dealing with widely ranged oil film thickness. In contrast, this paper presents a unified ultrasonic model that enables accurate measurements of oil film thickness that is widely ranged in a thinly coated bearing. This model is mathematically derived from multi-layer continuum models with the oil thickness and the complex reflection coefficients correlated. It also takes into account two typical locations of the embedded transducer in the bearing. The viability of the proposed method is experimentally validated using a high-precision calibration rig, showing that the oil film that ranges from 6 μm to 97 μm can be accurately measured in the application to thinly coated (around 400 μm) bearings, where the measurement errors are not greater than 7.4%.

Optical measurements on a budget: A 3D-printed ellipsometer

Ellipsometry is an optical analysis technique that is useful for characterizing the physical properties of a thin-film system. Light reflected from a sample surface undergoes a change in polarization due to phase delay and anisotropic reflection. This enables one to perform non-destructive measurements of film thickness, surface roughness, refractive index, and other optical constants. Ellipsometric techniques are particularly convenient for characterizing coatings or films in the semiconductor and optics industries. However, these techniques may be inaccessible to undergraduate students and educators due to the prohibitive cost of ellipsometers and similar instrumentation. In response to this roadblock, we describe the construction of a simple, inexpensive, manually operated, rotating analyzer ellipsometer (RAE). Required materials include a laser pointer, polarizing film, photometric detector, and a 3D-printed opto-mechanical framework, which are all readily accessible at most institutions. The instrument's performance was evaluated by comparing thickness measurements of tetraethyl orthosilicate films to those determined by a commercially available reflectometer. An average film thickness difference of 0.77% was measured using the two instruments.

Flow-Through Atmospheric Pressure-Atomic Layer Deposition Reactor for Thin-Film Deposition in Capillary Columns.

We demonstrate the development of a new atmospheric pressure-atomic layer deposition(AP-ALD) system to coat the inner walls of capillary columns for gas chromatography (GC). Unlike traditional ALD, this reactor operates at near-atmospheric pressure and addresses the challenges of depositing thin films inside capillaries, which include long pump down times, deposition in high-aspect-ratio materials, and temperature control. We show ALD of alumina in 5 and 12 m capillaries (0.53 mm ID) via sequential half reactions of trimethylaluminum and water. Our system yields pinhole-free, uniform thin films. It includes small witness chambers for witness silicon shards before and after the capillary. An engineering flow/transport analysis of the device is provided. Our ALD alumina thin films are characterized by spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy, transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy. Alumina film growth achieved is 1.4-1.5 Å/cycle, which is consistent with previously reported results. Film thickness measurements by SE on witness shards of silicon and by TEM at both ends of the capillary are in good agreement. A capillary column coated with alumina is used to separate different gases by GC, although the retention times of gases are essentially the same as with an untreated fused silica capillary. This successful deposition of ALD alumina in long capillaries opens the door for other possible ALD coatings, including hybrid organic-inorganic coatings, using the 450+ ALD precursors available today.