Accurate Film Thickness Measurements Research Articles

Imaging and investigation with PLIF40 for improved film thickness measurements in annular flow

Gas–liquid annular flow occurs frequently in industrial production processes, and the accurate measurement of film thickness is essential for applying its mass and heat transfer properties. The non-invasive planar laser-induced fluorescence (PLIF) method is widely employed in annular flow investigation. However, both methods of PLIF90 and PLIF70 (the measurement angles between laser and camera are set to 90°and 70°) suffer from total reflection. In this paper, the effect of measurement angle on total reflection, measurement accuracy, and robustness are quantitatively investigated. Accordingly, a PLIF40 method is proposed, which minimizes the influence of total reflection by reducing the measurement angle to 40°. Sub-pixel-based edge detection and liquid film smoothing algorithms are developed to accurately identify liquid films with missing edge details, resulting in a measurement error of 0.09 mm. The flow structure is qualitatively diagnosed by waveform reconstruction and wave height extraction combined with the film thickness distribution. Furthermore, the prediction models for average film thickness are established and compared with the classical prediction models to demonstrate the accuracy and reliability of PLIF40.

A model for interpreting depth profiles of confocal Raman measurements in reflective and transmitting materials

AbstractWe present a model and experimental evaluation of the depth profiles of total intensity in confocal Raman microscopy. The model assumes a Gaussian‐like beam for excitation and Raman emission to obtain a general description of the depth profile from an arbitrary sample. For samples that emit from the surface (i.e., that do not transmit light at the excitation wavelength), this model simplifies to a Lorenzian depth profile from which Rayleigh range can be extracted by the half‐width at half maxima. We extend the model to the case of transparent samples that offer significant refractive index mismatch across the surface. We show that in these cases, the axial increase of depth of focus can be approximated by two Gaussian foci, one at the paraxial focus and one at an oblique focus. This model accurately describes experimentally observed depth profiles of reflective samples and transparent samples. We further extend the analysis to the case of thin transparent films to demonstrate that the model can be used in conjunction with physical measurements to produce accurate measurements of film thickness.

Study of vapor film dynamics and heat transfer through an image processing technique

Understanding of two-phase heat transfer mechanisms on downward-facing hemispherical vessels is crucial during external reactor vessel cooling (ERVC) under severe accident conditions. Film boiling is the predominant heat transfer regime in the initial stages of quenching under these circumstances. In this work, the process of downward-facing film boiling on the outer surface of a hemispherical vessel is studied using high-speed video. High-speed video is a valuable measurement technique because it does not require any invasive sensors that may alter the natural liquid-vapor interface in film boiling. With high-speed video and a few image processing techniques, accurate measurements of film thickness have been made at four different degrees of subcooling (0, 3, 5, and 10 °C) and angular locations (0, 14, 28, and 42°) on a hemispherical vessel. With increasing subcooling and decreasing angular location, the vapor film thickness has been found to decrease. Average film thickness at 0 °C (respectively, 10 °C) subcooling and one second after immersion is found to be approximately 2 mm (respectively, 0.5 mm). High-speed videos taken at 650 frames per second (fps) have shown significant oscillations at the liquid-vapor interface during film boiling. Additionally, oscillations in the film thickness and its wave characteristics have been analyzed at the prescribed angular locations and degrees of subcooling. From the visual data, insights regarding the heat transfer behavior of film boiling are obtained. Additionally, the characteristics of the interfacial oscillations have been related to the heat flux distribution. The mechanism for the interfacial oscillations can be attributed to disturbances in the balance between the wall and interfacial heat fluxes, along with the hydrodynamic instability.

Monte Carlo simulation of Auger electron emission from thin film on substrate

A Monte Carlo simulation of production and emission of Auger electron signals in Auger electron spectroscopy (AES) has been performed to calculate the dependence of Auger electron intensity on film thickness for a film/substrate specimen. The electron spectrum is simulated, covering the energy range from the elastic peak down to Auger electron peak, by including bulk loss peak of electronic excitation. This simulation is based on the use of Mott’s cross section for electron elastic scattering and Penn’s dielectric function approach to electron inelastic scattering. Bulk plasmon excitation peaks contributed from both film and substrate are found in the low loss region near the elastic peak and the AES signal peak. The background subtraction was then performed for the simulated Auger electron spectrum, leading to obtain the approximate exponential decay behavior of Auger signal intensity varied with the film thickness. It is found that single value of effective attenuation length (EAL) is not enough for an accurate measurement of film thickness. We define two attenuation parameters to characterize the decay functional shape used as the calibration curve for accurate film thickness determination if the universal expression on experimental condition will be found.

Characterisation of Thin Films Using a Coherence Scanning Interferometry

Accurate measurement of film thickness and its uniformity are very important to the performance of many coated surfaces and for many applications are critical. Effective inspection of the film thickness and uniformity is the key to high performance. Conventionally, film thickness is meas- ured using a spectrophotometer/reflectometer, ellipsometer or a physical step measurement; however, these techniques all have limitations. Coherence Scanning Interferometry (CSI) is an established method to measure surface topography as this technique offers many advantages such as speed, ease of use and accuracy. The measurement of “thick” films (exceeding ~1.5 μm) which gives rise to clearly separate fringe bunches is a well-established CSI capability. However, a methodology known as the ‘helical complex field’ (HCF) [1] [2] function allows film thickness to be measured down to ~25 nm. This new method, combined with Coherence Correlation Interferometry (CCI) [3] offers film thickness measurements with sub-nanometre vertical resolution and ~1 μm lateral resolution. It is ideally suited for detailed analysis of coated optical surfaces. In this paper, the fundamentals of the techniques are described and some case studies are presented.

Study on Measurement of Thin Film Thickness with Lateral Shearing Interferometry

The film thickness is an important technical indicator of film devices, and its accuracy directly affects various performances of optical components. In fabrication process of film device, fast and accurate measurement of film thickness has positive significance on product quality control. In this paper, measure film thickness with lateral shearing interferometry. Collect interferograms through structured lateral shearing interference platform, process interferogram with Fast Fourier Transform method to extract phase, unwrap the wrapped phase to achieve phase value. Finally, calculate film thickness based on lateral shearing interference principle. The thickness of sample is 119.6800nm measured by this method, basically the same with the result 120.6036nm that measured by ZYGO interferometer. This experiment shows that lateral shearing interferometry not only suit to measurement of film thickness, but also abundant high-precision method of measuring film thickness, and has high practical value.

Study on the Accurate Measurement of Film Thickness

The thin-film technology is the hotspot of todays material science research.The thickness is an important physical parameter of the film thickness, so measurement naturally becomes the important work of research into material properties. With the wide application of thin film technology and optoelectronic devices, optical films have been widely used in the weaponary basic research and development and production of special devices. Facing the continuous update and development of weapons and equipment, higher requirements are put forward in precision measuring various parameters of the optical film. The thickness of the film is one of the key parameters in film design and manufacturing process, especially the rapid development of nanoscale thin-film technology, making the accurate measurement of the thickness of the film become a hot issue in the field of thin technology research, and has caused concern of technicians.

The determination of the pressure–viscosity coefficient of a lubricant through an accurate film thickness formula and accurate film thickness measurements. Part 2: high L values

The pressure–viscosity coefficient of a traction fluid is determined by fitting calculation results on accurate film thickness measurements, obtained at different speeds, loads, and temperatures. Through experiments, covering a range of 5.6 < M < 12 000, 2.1 < L < 17.5, film thickness values are calculated using a numerical method and approximation formulas from 12 models. It is concluded that, to assess the pressure–viscosity coefficient of the fluid, the Chittenden et al. approximation formula applied to circular contacts is the best choice, having an inaccuracy in between (−15%, +11%). This expression has been used far outside the regime of the numerical data where it was based upon.

The determination of the pressure—viscosity coefficient of a lubricant through an accurate film thickness formula and accurate film thickness measurements

The pressure—viscosity coefficient is an indispensable property in the elastohydrodynamic (EHD) lubrication of hard contacts, but often not known. A guess will easily lead to enormous errors in the film thickness. This article describes a method to deduct this coefficient by adapting the value of the pressure—viscosity coefficient until the differences between accurate film thickness approxi-mation values and accurate film thickness measurements over a wide range of values are at a minimum. Eleven film thickness approximation formulas are compared in describing the film thickness of a test fluid with known value of the pressure—viscosity coefficient. The measurement method is based on spacer layer interferometry. It is concluded that for circular contacts the newer more versatile expressions are not better than some older approximations, which are limited to a smaller region of conditions, and that the older fits are as least as appropriate to find the pressure—viscosity coefficient of fluids, in spite of the limited data where they have been based on.

Mechanical properties of ultrananocrystalline diamond thin films relevant to MEMS/NEMS devices

The mechanical properties of ultrananocrystalline diamond (UNCD) thin films were measured using microcantilever deflection and membrane deflection techniques. Bending tests on several free-standing UNCD cantilevers, 0.5 μm thick, 20 μm wide and 80 μm long, yielded elastic modulus values of 916–959 GPa. The tests showed good reproducibility by repeated testing on the same cantilever and by testing several cantilevers of different lengths. The largest source of error in the method was accurate measurement of film thickness. Elastic modulus measurements performed with the novel membrane deflection experiment (MDE), developed by Espinosa and co-workers, gave results similar to those from the microcantilever-based tests. Tests were performed on UNCD specimens grown by both micro and nano wafer-seeding techniques. The elastic modulus was measured to be between 930–970 GPa for the microseeding and between 945–963 GPa for the nanoseeding technique. The MDE test also provided the fracture strength, which for UNCD was found to vary from 0.89 to 2.42 GPa for the microseeded samples and from 3.95 to 5.03 for the nanoseeded samples. The narrowing of the elastic modulus variation and major increase in fracture strength is believed to result from a reduction in surface roughness, less stress concentration, when employing the nanoseeding technique. Although both methods yielded reliable values of elastic modulus, the MDE was found to be more versatile since it yielded additional information about the structure and material properties, such as strength and initial stress state.

Measuring interfacial waves on film flowing down tube inner wall using laser focus displacement meter

To elucidate details of the fascinating nonlinear phenomena of waves on a film, spatial temporal knowledge of the interfacial waves is essential. This paper presents a new method for measuring waves on a film flowing down the inner wall of a vertical tube, using a laser focus displacement meter. The purpose of the study was to clarify the effectiveness of the new method for obtaining detailed information of film thickness or wave characteristics, and to investigate the effect of film entry length on the phenomena. With this method, accurate measurements of film thickness in real time, with sensitivity of 0.2 μm and 1 kHz, were achieved. The error caused by refraction of the laser beam passing through an acrylic tube, whose outer wall surface was flat, and water was estimated. As the entry length increased, the ripple on the flowing film grew to a solitary wave of about 0.5 mm in height, then the wave became a two-wave system. In the entry region, the wave amplitude decreased as the flow rate increased, in the same manner as that in a film flowing down a plate wall.

Measuring interfacial waves on film flowing down a vertical plate wall in the entry region using laser focus displacement meters

Waves on a film flowing down a vertical wall appear in many processes. The resulting interfacial waves show fascinating nonlinear phenomena, including solitary waves and complex disordered patterns. Measurements have often been made of these phenomena using electrical resistance or electrical capacitance methods, optical methods, and laser beam methods. This paper presents a new way of measuring the interfacial waves on a film flowing down a vertical plate wall in an entry region, using two laser focus displacement meters. The purpose of the study was to clarify the effectiveness of the new method for obtaining detailed information on the waves, and to investigate the effect of the entry length on the phenomena. With this method, accurate measurements of film thickness were achieved in real time with a sensitivity of 2 μm and 1 kHz. The error caused by refraction of the laser beam passing through a transparent wall was clarified. The present results for wave velocity and maximum film thickness agreed well with past experimental and theoretical studies. In short entry length conditions, the average measured film thickness and wave velocity agreed with those calculated using Nusselt’s Law, indicating that the flow is laminar even at a high flow rate. As a result of this study, an empirical equation expressing wave frequency in the entry region was formulated.

Determination of Grain-Boundary Film Thickness by the Fresnel Fringe Imaging Technique

The defocus Fresnel fringe imaging (FFI) technique is applied to the determination of nanoscale amorphous grain-boundary film thickness in a silicon nitride ceramic. By using only the transmitted beam and imaging out of focus, an amorphous grain-boundary film can be detected. The thickness of the amorphous film is determined by extrapolating the fringe spacing data obtained from a series of defocus images to zero defocus. High-resolution electron microscopy (HREM) has been suggested as the method capable of providing the most accurate measurements of film thickness (±0·1 nm). Thus, the thickness of a grain-boundary film obtained by FFI is compared with that measured by HREM. It is found that FFI can provide a reliable value for grain-boundary film thickness, with an accuracy of ±0·15 nm. Additionally, FFI is easier to use, and is applicable to any grain boundary of interest whereas the HREM method has some limitations. This make it more amenable to gathering statistical information on grain boundary thickness. It is suggested that FFI is a valid and useful method for determining the thin intergranular film thickness.

Measuring a Film Flowing Down a Vertical Wall Using Laser Focus Displacement Meters. 1st Report. Measuring Principle and Film Thickness.

A film flowing down a vertical wall exhibit as many distinct wave features. The produced interfacial waves show fascinating non-linear phenomena, including solitary waves and complex disordered patterns. Abundant measurements have been made of these phenomena using electrical resistance, electrical capacitance, optical, and laser beam methods. In this paper, we present a new way of measuring the thickness of a film flowing down a vertical wall in an entry region using two laser focus displacement meters. With this method, we achieved accurate measurements of film thickness in real time with a sensitivity of 0.2 micron and 1 kilohertz. We also clarified errors caused by the refraction of laser beam passing through the wall and liquid. In the entry region, the wave amplitude decreased as the flow rate increased, which was contrary to results obtained in the past in a fully development region. The average measured film thickness agreed with that calculated using Nusselt's Law, indicating the flow to be laminar in the entry region even at a high flow rate.

混相流先端技術 第９回 レーザーフォーカス変位計による液膜界面波の測定

A film flowing on a wall exhibits as many distinct wave features. The produced interfacial waves show fascinating non-linear phenomena, including solitary waves and complex disordered patterns. Abundant measurements have been made of these phenomena using electrical resistance or electrical-capacity methods, optical methods, and laser beam methods. In this paper, a new way of measurement of the interfacial waves is presented using laser focus displacement meters which allow accurate measurements of film thickness in real time with a sensitivity of 2 microns and 1 kilohertz. With this method, detailed information on the waves was obtained on a film flowing down a vertical wall in an entry region. The measured average film thickness and wave velocity agreed with that calculated using Nusselt's law, indicating the flow to be laminar in the entry region even at a high flow rate. Research on multifluid with progress and improvement in microscopic measuring is expected to be conducted increasingly in the future.

Measurements of the primary instabilities of film flows

We present novel measurements of the primary instabilities of thin liquid films flowing down an incline. A fluorescence imaging method allows accurate measurements of film thickness h(x, y, t) in real time with a sensitivity of several microns, and laser beam deflection yields local measurements with a sensitivity of less than one micron. We locate the instability with good accuracy despite the fact that it occurs (asymptotically) at zero wavenumber, and determine the critical Reynolds number Rc for the onset of waves as a function of angle β. The measurements of Rc(β) are found to be in good agreement with calculations, as are the growth rates and wave velocities. We show experimentally that the initial instability is convective and that the waves are noisesustained. This means that the waveform and its amplitude are strongly affected by external noise at the source. We investigate the role of noise by varying the level of periodic external forcing. The nonlinear evolution of the waves depends strongly on the initial wavenumber (or the frequency f). A new phase boundary f*s(R) is measured, which separates the regimes of saturated finite amplitude waves (at high f) from multipeaked solitary waves (at low f). This boundary probably corresponds approximately to the sign reversal of the third Landau coefficient in weakly nonlinear theory. Finally, we show that periodic waves are unstable over a wide frequency band with respect to a convective subharmonic instability. This instability leads to disordered two-dimensional waves.

Refractive Index Dispersion of Dielectric Films Used in the Semiconductor Industry

In order to obtain accurate film thickness measurements using various spectroscopic reflection techniques, it is necessary to have accurate refractive index measurements over the spectral range. A simplified representation of the dispersion of many of the films and materials used in the manufacture of semiconductor devices is compared with more conventional dispersion relations, especially with the Cauchy series. In the visible range, the simplified dispersion relation gives accurate refractive indexes by use of only one material‐dependent parameter and the refractive index of the material at 546 nm. When the dispersion of the material is large, then two parameters are required in addition to the 546 nm refractive index. Under such conditions, the Cauchy relation requires three terms to give an accurate representation of the dispersion. The various parameters and Cauchy coefficients for oxides, nitrides, photoresists, polyimides, and glasses were determined.

Refractive-index dispersion of garnet films derived from accurate measurement of film thickness

Refractive-index dispersion of magnetic garnet films of composition (YSmLuCa)3(GeFe)5O12 is reported in a wavelength range of 0.55–1.5 μ. The dispersion was calculated from the film’s optical interference data and thickness value which was accurately determined by the technique of thin-film optical waveguide measurement. The calculated index values at the interference fringe locations were fitted to a two-term Sellmeier formulation. The accuracy was estimated to be better than 0.3%.

Separation of the Linear and Parabolic Terms in the Steam Oxidation of Silicon

Using accurate film thickness measurements, it was found possible to separate linear and parabolic terms in the steam oxidation of silicon, and thus obtain much more precise expressions for the thermal oxidation under different conditions. The combined linear-parabolic relation was found to be applicable to various crystallographic orientations. The pure parabolic “constant” obtained from this relation was the same for different crystal orientations, but the linear term in the relation was found to be very surface sensitive. By these techniques, more accurate parabolic rate “constants” can be obtained and the linearity of the log k vs 1/T plot can be extended to much lower temperatures. The activation energy of the parabolic term for steam oxidation was found to be only 16 kcal/mole. The effect of neglecting the linear term in various methods of computing the parabolic rate is discussed.

Evaluation of Vapor-Plated Oxide Films for Capacitor Dielectrics

The development of vapor-plating techniques has made possible the preparation of a variety of oxide dielectric films. The work described in this paper is a preliminary evaluation of the physical and chemical properties of some of these films and their suitability for use as capacitor dielectrics. The physical structure of the films has been investigated by X-ray diffraction techniques. Physical and chemical stability of the films was evaluated by thermal shock tests, resistance to scratch and nature of scratch fractures produced, and a variety of chemical treatments. Optical interferomatic techniques were developed for the accurate measurement of film thickness for determination of dielectric constant, dielectric strength and resistivity. Electrical properties of the films were evaluated by capacitor measurements. Results indicate that vapor plated oxide dielectrics have good potential for capacitor applications. This technique has allowed fabrication of capacitors which show a dissipation factor of less than 1 per cent in the frequency range of 100 cps to 300 kc, a capacitance of more than 100 uuf/mm2, and a time constant of open circuit voltage decay in excess of 1000 seconds. Environmental and accelerated aging tests were carried out on the capacitors and a good correlation with the physical and chemical stability of the films was shown. Other applications for these films are under study.