Transmission interference spectrometric determination of the thickness and refractive index of barrier films formed anodically on aluminum

Aluminum oxide films were formed anodically under carefully controlled conditions and prepared for transmission by dissolving part of the base metal in a solution containing iodine.A spectrophotometric technique to determine the refractive index of the anodic oxide is presented. This technique, based on the transmission interference spectra of two films with slightly different thicknesses, yielded precise results and enabled problems derived from the relatively low refractive index of alumina to be overcome. The film thickness was also calculated from the data, and the results indicated that the refractive index did not depend on the film thickness, at least for the range under study.The anodic alumina showed normal dispersion over the UV, visible and near- IR regions and its refractive index varied from 1.88 at 200 nm to 1.65 at 1300 nm.     

Complete optical analysis of a non-absorbing thin film on an absorbing substrate by a new method of immersion spectroscopic reflectometry

A new method for determining the thickness and the spectral dependence of the refractive index characterizing a non-absorbing thin film placed on an absorbing substrate is described in this paper. Within this method two spectral dependences of the reflectance corresponding to the system immersed into two different non- absorbing ambients are employed. The main advantage of the method is that the values of the thickness and the refractive index can be determined by means of explicit formulae. The second important advantage is the fact that non-absorbing thin films with relatively small thicknesses can be analysed. The method is applied to amorphous SiO₂ thin films placed on silicon single-crystal wafers.     

Laser reflectometry in situ measurement of lead zirconate titanate film growth

A convenient method is described for optical characterization of thin films during growth. The method has been demonstrated on lead zirconate titanate (PZT) films deposited by pulsed laser ablation for various temperatures. The optical constants of the PZT films as well as the film growth rate were determined in situ by fitting (with three free parameters) the calculated reflectance as a function of film thickness to the experimental reflectance curve as a function of deposition time, as obtained by unpolarized laser reflectometry. The fitted parameters are the uniform complex PZT refractive index and the layer thickness (assumed proportional to time), with the complex refractive index of the platinum substrate being measured previously. These results compare well with the subsequent ellipsometric measurements made to assess the precision of the reflectometry technique.     

Static characterization of magnetic bubble films

A.C. susceptibility and optical interference are combined to determine the material length, saturation magnetization and thickness of garnet bubble films on GGG substrates. These measurements have been automated to provide precisions of better than 1% and throughputs of more than sixty wafers per hour. Derived values of material length and saturation magnetization agree to better than ±3% with those from visual measurements of stripe width and bubble collapse field for a single film composition. Disagreement between results from two film compositions possibly points up a fundamental difference between the measurement techniques.     

Determination of properties of wedged, nonuniformly thick, and absorbing thin films by using a new numerical method

Nonuniformity in the thickness of thin films can severely distort their transmission spectra as compared with those of flat, smooth films. Methods that extract properties such as refractive index, thickness, and extinction coefficient of such films can suffer inaccuracies when they are applied to wedged or nonuniformly thick films. To accurately extract optical properties of nonuniform films, we have developed a novel numerical method and efficient constitutive relations that can determine film properties from just the transmission spectrum for films that are locally smooth with negligible scattering loss. This optimum parameter extraction (OPE) method can accommodate films with two-dimensional thickness variation that would result in significant errors in the values of refractive index and film thickness if not considered. We show that for carefully chosen test cases and for actual pulsed-laser-deposition AlN thin films, properties such as refractive index, extinction coefficient, and film thickness were very accurately determined by using our OPE method. These results are compared with previous techniques to determine the properties of thin films, and the accuracy of and applicable conditions for all these methods are discussed.     

Ellipsometric determination of optical properties of carbazole-containing poly(l-glutamate) thin films prepared from different solvents

In this study, the refractive indices (n) and thicknesses of carbazole-containing hole-transport materials such as poly(γ-carbazolylethyl l-glutamate) (PCELG) and poly(N-vinyl carbazole) (PVCz) films were determined by carrying out ellipsometric measurements. The thicknesses of PCELG and PVCz films determined by ellipsometric analysis were in good agreement with those determined by surface profilometry. The dependence of the refractive indices of the PCELG films on film thickness was classified into two types on the basis of the solvent from which the films were prepared: the refractive indices either increased with increasing film thickness, as in the case of PCELG films prepared from 1,2-dichloroethane (DCE) and monochlorobenzene (?-Cl), or were independent of the film thickness, as in the case of films prepared from 1,1,2,2-tetrachloroethane (TCE). A comparison of these results with the structures of the polymers, as determined by ¹H NMR, reveals that the two types of dependences of the refractive indices of the PCELG thin film on the film thickness can be attributed to the two types of aggregation structures and/or orientational characteristics corresponding to the helical conformation of the polymer. In contrast, the refractive indices of PVCz films are governed mainly by the film thickness. Finally, we would like to emphasize that the combination of ellipsometry and other techniques such as NMR and surface profilometry provide information not only on the film thickness and refractive index but also on the aggregation structure in thin films with thicknesses on the order of 50 nm.     

Determination of film thickness and refractive index in one measurement of phase-modulated ellipsometry

Ellipsometry is often used to determine the refractive index and/or the thickness of a polymer layer on a substrate. However, simultaneous determination of these parameters from a single-wavelength single-angle measurement is not always possible. The present study determines the sensitivity of the method to errors of measurement for the case of phase modulated ellipsometry and identifies conditions for decoupling film thickness and refractive index. For a specific range of film thickness, both the thickness and the refractive index can be determined from a single measurement with high precision. This optimal range of the film thickness is determined for organic thin films, and the analysis is tested on hydrogel-like polymer films in air and in water.     

大口径溶胶-凝胶光学膜层提拉制备工艺控制

大口径溶胶-凝胶化学膜的光学性能指标主要由膜层厚度和折射率决定,提拉法制备工艺的关键技术就是对这两个参数进行精确控制。通过优化胶体制备工艺,并利用椭圆偏振法测量化学膜膜厚及折射率变化情况,获得了提拉速度模型,并进行了实验验证,为大口径化学膜高性能指标提供了技术和工艺保证。     

Calculation of film thickness for dip coated antireflective films

Antireflective films require an accurate film thickness to be able to perform optimally. The ideal thickness on most films is a quarter wavelength optical thickness (QWOT). The physical thickness of the QWOT film depends on the refractive index of the material that is being used. Each layer of the antireflective coating will have different optimal conditions for applying the film. When using the dip coating method, these conditions are withdrawal speed and concentration of solution.When using the currently accepted equations derived by Yang et al. to calculate the film thickness an error of 31.7% was noted when compared with the experimentally measured film thickness. Realising that the refractive index of the film plays a role in determining the thickness of the film, the equations were modified to take refractive index into account. Once this was taken into account, the calculated film thickness deviated from the measured film thickness by 8.7%. This error can be attributed to experimental errors which involve temperature and concentration fluctuations.     

Refractive index of polycrystalline submicrometer polymer thin films: Thickness dependence

Dielectric films used in insulating applications are becoming consistently thinner, hence the thickness of thin and ultathin films is an important design parameter. There exists a need for characterizing and understanding the thickness dependence of properties of films. The refractive index for low dielectric polytetrafluoroethylene crystalline submicrometer thin films is investigated by using an optical spectrometer coupled with a hot stage to monitor their thickness-dependent behavior. It is demonstrated that the refractive index has a strong dependence on film thickness, which can be related to the microstructure and morphology of the film as characterized by Fourier transform infrared spectroscopy and scanning electron microscopy.     

Oxidation of thin titamium films in ambient conditions

The room temperature oxidation of vapor-deposited titanium films was investigated as a function of film thickness by resistivity and ellipsometric measurements. The thickness of the films ranged from 3.0 to 120 nm. The electron mean free path in the films varied from 11.3 to 26.0 nm, and the product of the bulk resistivity and the electron mean free path was 1.5 × 10^-10Ω cm². The values of the surface electron scattering parameter in the films were between 0.2 and 0.6 and decreased to 0.18 at the onset of oxidation. The best value for the complex refractive index of titanium was found to be 3.61-i4.06. The refractive index of the oxide film was 2.75. After a 1 d exposure of the films to room air at atmospheric pressure both the resistance and ellipsometric measurements indicated a residual oxide thickness of 2.6±0.3 nm, regardless of the original metal film thickness. These results disagree with the theoretical and experimental results of Mindel and Pollack, which implied a rapid decrease in oxide thickness with decreasing titanium film thickness.     

Treasure of the Past VII: Measurement of the Thickness and Refractive Index of Very Thin Films and the Optical Properties of Surfaces by Ellipsometry

The use of the ellipsometer for the measurement of the thickness and refractive index of very thin films is reviewed. The Poincaré sphere representation of the state of polarization of light is developed and used to describe the reflection process. Details of the operation of the ellipsometer are examined critically. A computational method is presented by which the thickness of a film of known refractive index on a reflecting substrate of known optical constants may be calculated directly from the ellipsometer readings. A method for computing both the refractive index and thickness of an unknown film is also developed. These methods have been applied to the determination of the thickness of an adsorbed water layer on chromium ferrotype plates and on gold surfaces. In the former case the thickness was 23 to 27 Å, and in the latter was 2 to 5 Å. The measurement of the thickness and refractive index of barium fluoride films evaporated on chromium ferrotype surfaces is used as an illustration of the simultaneous determination of these two quantities.     

Measurement of the Thickness and Refractive Index of Very Thin Films and the Optical Properties of Surfaces by Ellipsometry

The use of the ellipsometer for the measurement of the thickness and refractive index of very thin films is reviewed. The Poincaré sphere representation of the state of polarization of light is developed and used to describe the reflection process. Details of the operation of the ellipsometer are examined critically. A computational method is presented by which the thickness of a film of known refractive index on a reflecting substrate of known optical constants may be calculated directly from the ellipsometer readings. A method for computing both the refractive index and thickness of an unknown film is also developed. These methods have been applied to the determination of the thickness of an adsorbed water layer on chromium ferrotype plates and on gold surfaces. In the former case the thickness was 23 to 27 Å, and in the latter was 2 to 5 Å. The measurement of the thickness and refractive index of barium fluoride films evaporated on chromium ferrotype surfaces is used as an illustration of the simultaneous determination of these two quantities.     

Evolution of optical properties with deposition time of silicon nitride and diamond-like carbon films deposited by radio-frequency plasma-enhanced chemical vapor deposition method

The paper presents investigations of the optical properties of thin high-refractive-index silicon nitride (SiN_x) and diamond-like carbon (DLC) films deposited by the radio-frequency plasma-enhanced chemical vapor deposition method for applications in tuning the functional properties of optical devices working in the infrared spectral range, e.g., optical sensors, filters or resonators. The deposition technique offers the ability to control the film's optical properties and thickness on the nanometer scale. We obtained thin, high-refractive-index films of both types at deposition temperatures below 350 °C, which is acceptable under the thermal budget of most optical devices. In the case of SiN_x films, it was found that for short deposition processes (up to 5 min long) the refractive index of the film increases in parallel with its thickness (up to 50 nm), while for longer processes the refractive index becomes almost constant. For DLC films, the effect of refractive index increase was observed up to 220 nm in film thickness.     

类金刚石薄膜光学特性的椭偏法研究

本文采用脉冲电弧离子镀的方法,在p型硅上沉积类金刚石薄膜,用椭偏法测试薄膜的光学常数.根据沉积方法的特点,建立一个四层结构的膜系,并由每一层的吸收情况合理选择色散关系;结合透过率的测试结果,利用光度法给测出薄膜折射率和厚度的估计值,作为椭偏法拟合的初值,拟合效果良好,得到薄膜的折射率、消光系数和几何厚度.     

Thickness dependence of structural and optical properties of indium tin oxide nanofiber thin films prepared by electron beam evaporation onto quartz substrates

Indium tin oxide (ITO) thin films, produced by electron beam evaporation technique onto quartz substrates maintained at room temperature, are grown as nanofibers. The dependence of structural and optical properties of ITO thin films on the film thickness (99-662 nm) has been reported. The crystal structure and morphology of the films are investigated by X-ray diffraction and scanning electron microscope techniques, respectively. The particle size is found to increase with increasing film thickness without changing the preferred orientation along (2 2 2) direction. The optical properties of the films are investigated in terms of the measurements of the transmittance and reflectance determined at the normal incidence of the light in the wavelength range (250-2500 nm). The absorption coefficient and refractive index are calculated and the related optical parameters are evaluated. The optical band gap is found to decrease with the increase of the film thickness, whereas the refractive index is found to increase. The optical dielectric constant and the ratio of the free carrier concentration to its effective mass are estimated for the films.     

A note on the use of ellipsometry for studying the kinetics of formation of self-assembled monolayers

Ellipsometry is currently one of the most important techniques for characterization of the deposition and growth mode of ultra thin organic films. However, it is well known that for thicknesses normally encountered in organic monolayer films, as would occur for example in self-assembled monolayers, ellipsometry cannot be used to simultaneously determine the thickness and refractive index of the monolayer film. Current practice is to assume a reasonable value for the film refractive index and calculate an effective ‘ellipsometric thickness’. This communication seeks to show that the alternative approach of assuming a thickness for the monolayer (determined by the length of the molecule) and calculating the effective film refractive index lends itself to easier and more meaningful physical interpretation. The Lorentz-Lorenz formula is then used to transform the effective refractive index into a surface coverage and hence to an effective mass coverage. The methodology advanced is applied to the kinetics of formation of a self-assembled monolayer of a well-studied molecule, octadecanethiol on Au.     

Interference Effects in Time-resolved Reflectivity Measurements in Thin Semiconductor Films

The study of non-equilibrium charge carriers in semiconductor films by time-resolved reflectivity measurements is greatly simplified if the change in reflectivity change varies linearly with the photoinduced change in refractive index. In the present work it is shown that interference effects in the transparent layer influence this dependence significantly. The sample reflectivity can either increase or decrease, depending on the film thickness. If the reciprocal absorption coefficient of the semiconductor is smaller than the film thickness, a refractive index profile is created inside the layer. The reflection at this profile diminishes the influence of the beams reflected at the semiconductor-substrate interface. The changes in reflectivity then vary linearly with the changes in refractive index, independently of the film thickness. Numerical calculations were performed to help interpret time-resolved reflectivity measurements on amorphous silicon films.     

Influence of the wettability of silicon substrates on the thickness of sol-gel silica films

The fabrication of thick optical films by spinning from solution on silicon substrates is an important technique for integrated optics applications. In particular, several authors have studied the conditions under which the thickness of sol-gel silica films deposited on silicon wafers from solutions of water, tetraethoxysilane (TEOS) and ethanol can be maximized. The influence of processing parameters, such as composition, ageing period of the solution and spinning rate, have been studied. The effect of the wettability of the silicon substrate on the film thickness was investigated. The wetting characteristics of the silicon surface may be changed by adequate chemical cleaning methods. The hydrophilic wafers obtained by controlled oxidation of the silicon were found to have greater affinity to the film forming solution and to lead to thicker films than hydrophobic wafers obtained by etching the silicon surface with HF solution.     

氧化锌/二氧化硅复合膜的结构色研究

采用静电自组装技术,以氧化锌（ZnO）和二氧化硅（SiO2）溶胶颗粒为前驱体,通过控制双组分膜层的不同厚度,制备出结构色鲜艳的ZnO/SiO2复合膜,并利用分光测色仪、多角度分光光度仪及扫描电子显微镜等研究复合膜的颜色、微观结构和形态特征。研究结果发现,ZnO/SiO2复合膜的亮度和色度均较单一组分薄膜的高,复合薄膜的颜色仍随厚度和观察角度的变化而变化。通过对薄膜的微观结构分析,结合其厚度随周期数的变化规律,发现复合薄膜的厚度随着自组装循环次数的增加而增加,薄膜中的纳米粒子并没有形成明显的高低折射率交替分布的双层结构,可能形成的是高折射率层（H层）、有效折射率层（eff层）和低折射率层（L层）的多层微观结构。这种特殊的多层结构与光作用发生干涉,形成了鲜亮度和饱和度更高的结构色。