Numerical algorithm for spectroscopic ellipsometry of thick transparent films

We present a numerical method for spectroscopic ellipsometry of thick transparent films. When an analytical expression for the dispersion of the refractive index (which contains several unknown coefficients) is assumed, the procedure is based on fitting the coefficients at a fixed thickness. Then the thickness is varied within a range (according to its approximate value). The final result given by our method is as follows: The sample thickness is considered to be the one that gives the best fitting. The refractive index is defined by the coefficients obtained for this thickness.     

纳米尺度HfO_2薄膜的光谱椭偏模型建立

为了建立厚度为1 nm左右HfO_2超薄膜的光谱椭偏测量方法,采用掠入射X射线反射技术进行国家/地区实验室间比对认证,其膜厚准确量值作为参比值,建立了HfO_2超薄膜的光谱椭偏结构拟合模型。研究了HfO_2超薄膜的光谱椭偏色散模型和拟合参数,最后确定了拟合色散模型为Tauc-Lorentz 3,拟合光谱范围为3.45~4.35 eV,表面污染层孔隙比例为60:40。     

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.     

Determination of refractive index and thickness of thick transparent films by variable-angle spectroscopic ellipsometry: application to benzocyclobutene films

An analysis procedure for evaluating the refractive index and the thickness of 5-10-μm-thick transparent films has been developed based on variable-angle spectroscopic ellipsometry. As an example of application, results from an analysis of benzocyclobutene films are presented. The sensitivities in ψ and Δ with respect to the refractive index and the thickness of the films are also discussed.     

亚波长分辨光刻介质特性研究

利用365nm波段光源、扫描电镜、台阶仪、原子力显微镜和椭偏仪,研究了亚波长分辨光刻介质X AR-N 7700/30型光刻胶的显影速度、对比度、薄膜厚度和折射率等化学、物理特性参数。光刻胶未曝光部分显影速度为23.15nm/s,曝光部分为1.85nm/s,光刻胶的对比度高达2.5,稀释至30%的质量浓度时,光刻胶可旋涂成45nm厚的薄膜。     

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。     

Determination of the refractive index of single crystal bulk samples and micro-structures

We present comparative studies for the exact determination of the refractive index of single crystals using spectroscopic ellipsometry and photonic-mode-structure investigations by means of spatially resolved photoluminescence spectroscopy, especially in the near band-gap spectral range. By applying such complementary methods we can overcome the uncertainties in the determination of the bulk refractive index introduced by surface properties. The physical effects used are the electromagnetic field reflection used by spectroscopic ellipsometry at large scale planar single crystals and the whispering-gallery-mode formation by total internal reflection in confined micro-structures. We demonstrate the applicability of such studies using the example of uniaxial ZnO bulk samples and micro-wires. By assuming a surface near region with electronic properties different from the bulk material, the method presented here gives the refractive index dispersion for both types of samples in an energy range from 1 to 3.4 eV.     

Simultaneous determination of refractive index, extinction coefficient, and void distribution of titanium dioxide thin film by optical methods

The refractive index n(λ) and the extinction coefficient k(λ) of a TiO(2) film prepared by electron-beam evaporation are determined in the spectral region 1.5-5.5 eV. The transmission spectrum of the TiO(2) film on a vitreous silica specimen is inverted to get the k(λ) of TiO(2) in its interband transition region. Above 3.5 eV, k(λ) is used to get the coefficients of the quantum mechanically derived dispersion relation of an amorphous TiO(2). These coefficients and n(∞) are used to determine n(λ). The modeling procedure is applied to spectroscopic ellipsometry data of a TiO(2) film on a c-Si specimen, and the void distribution of the film is revealed. With spectroscopic ellipsometry data above the fundamental band gap, valuable information about surface roughness is obtained. The effective thickness of this rough surface layer is confirmed by an atomic force microscopy measurement.     

Extraction of complex refractive index of absorbing films from ellipsometry measurement

Numerical extraction of complex refractive index of an unknown absorbing layer inside a multilayer sample from ellipsometry measurement is discussed. The approach of point by point extraction considering all points of spectroscopic data as independent data points is investigated. This problem has typically multiple solutions and the standard method consisting in fitting calculated to experimental point is likely to converge to a wrong solution if a precise guess value is not given. An alternate method is proposed, based on the determination of contours of the ellipsometric function, to provide all solutions in an as extended as wanted range of complex refractive index values. The method is tested through different kinds of sample examples. Errors relative to any of the parameters used in the sample model are calculated and discussed. This method should be helpful in many practical cases of ellipsometry data interpretation.     

Monitoring the layer-by-layer self-assembly of graphene and graphene oxide by spectroscopic ellipsometry

Thin films of graphene oxide, graphene and copper (II) phthalocyanine dye have been successfully fabricated by electrostatic layer-by-layer (LbL) assembly approach. We present the first variable angle spectroscopic ellipsometry (VASE) investigation on these graphene-dye hybrid thin films. The thickness evaluation suggested that our LbL assembly process produces highly uniform and reproducible thin films. We demonstrate that the refractive indices of the graphene-dye thin films undergo dramatic variation in the range close to the absorption of the dyes. This investigation provides new insight to the optical properties of graphene containing thin films and shall help to establish an appropriate optical model for graphene-based hybrid materials.     

Ellipsometry study of poly(o-methoxyaniline) thin films

Spin-coated poly(o-methoxyaniline) (POMA) thin films on various substrates were investigated using spectroscopic ellipsometry (SE) in the 1.5–4.5 eV photon energy range. Spin-coating process parameters are reported (spin speed and concentration). Substrates with higher surface energy were found to increase polymer film thickness and decrease roughness. An optical model was developed using SE data along with complementary data from atomic force microscopy and UV–vis spectroscopy to obtain optical properties—refractive index n and extinction coefficient k for POMA. The model includes Lorentz oscillators for the POMA film and a Bruggeman effective medium approximation for roughness. In-plane film optical anisotropy was not observed, but a small out of plane anisotropy was detected for the polymer.     

Application of ellipsometry techniques to biological materials

Ellipsometry is well-suited for bioadsorption studies and numerous reports, mainly using null ellipsometry, are found on this subject whereas investigations addressing structural properties of thin biolayers are few. Here two examples based on the use of spectroscopic ellipsometry (SE) on the latter are briefly discussed. In the first example, time evolution of thickness, spectral refractive index and surface mass density of a fibrinogen matrix forming on a silicon substrate are investigated with SE and a structural model of the protein matrix is discussed. In the second example a model dielectric function concept for protein monolayers is presented. The model allows parameterization of the optical properties which facilitates monitoring of temperature induced degradation of a protein layer. More recently, photonic structures in beetles have been studied with SE. It is shown here that full Mueller-matrix SE can resolve very complex nanostructures in scarab beetles, more specifically chiral structures causing reflected light to become circularly polarized.     

Real time <Emphasis Type="Italic">in situ</Emphasis> spectroscopic ellipsometry of the growth and plasmonic properties of au nanoparticles on SiO<Subscript>2</Subscript>

The evolution of the film thickness and plasmonic properties for sputtered deposited Au nanoparticles on SiO₂ layers have been monitored in real time using in situ spectroscopic ellipsometry in the photon energy range 0.75–4.1 eV. The spectroscopic ellipsometry data were analyzed with an optical model in which the optical constants for the Au nanoparticles were parameterized by B-splines which simultaneously provide an accurate determination of an effective thickness and an effective dielectric function. The effective thickness is interpreted with support of transmission and scanning electron microscopy and Rutherford backscattering measurements. Further parameterization of the optical constants by physical oscillators in the isolated spherical particle region allows the microstructural parameters such as size and Au fraction to be extracted. Real time in situ monitoring allows the growth of nanoparticles from the nucleation phase to near percolation to be followed, and there is a red-shift of the plasmon resonance absorption peak as the nanoparticles increase in size and their interaction becomes stronger.      

浮法玻璃表面光学常数分析

本文通过光谱椭偏仪测量浮法玻璃空气面和锡面的偏振信息,利用Cauchy光学模型分析得到浮法玻璃两表面的布鲁斯特角和光学常数,分析结果表明浮法玻璃空气面、锡面、理想玻璃界面的布鲁斯特角分别为56.7°、57°和56.8°,空气面形成疏松的表面层,厚度为2.75nm,折射率小于玻璃本底,锡面形成锡扩散表面层,厚度为81.29nm,折射率大于玻璃本底折射率,并且随厚度呈现出非线性梯度变化,结合透光率数据分析得到玻璃消光系数在10-6量级。由于浮法玻璃空气面和锡面的折射率明显不同,需要在后续玻璃镀膜光学设计时区别对待。     

Development of an optical model for steady state porous anodic films on aluminium formed in phosphoric acid

Porous anodic oxide films on aluminium formed in phosphoric acid (PAA) have been characterized nondestructively by spectroscopic ellipsometry. Compared to previous studies on porous films formed in sulfuric acid, the optical behaviour of PAA films reveals new features which have been attributed to film-substrate interface roughness and optical anisotropy effects. On one hand relatively large interface roughness has been simulated by a graded index model. On the other hand, the implementation of uniaxial anisotropy in the optical model of the PAA film enables to interpret spectroscopic ellipsometry data acquired at multiple angles of incidence in terms of the morphology of the films. More specifically, accurate and physically realistic values are found for the porosity and porous film thickness. Although more difficult to interpret from the optical findings, the thickness of the barrier part of the porous film can also be estimated. The ellipsometry characterizations are confirmed by complementary TEM analysis of various films. Finally, the anisotropy exhibited by the PAA films is in line with recent theoretical predictions of the optical behaviour of arrays of parallel cylindrical capillaries in an isotropic medium proposed by other authors.     

Study of the formation of chromate conversion coatings on Alclad 2024 aluminum alloy using spectroscopic ellipsometry

The influence of pH of a chromate bath on the morphological and chemical properties of a chromate conversion coating, formed on Alclad 2024-T3 aluminum alloy, has been investigated by variable angle spectroscopic ellipsometry in the visible and infra-red regions. Other techniques such as glow discharge optical emission spectroscopy, transmission and scanning electron microscopy, atomic force microscopy and Auger electron spectroscopy have been used in order to confirm and sustain the results obtained with this technique. The combination of different analytical methods showed a decrease in thickness together with changes in the morphology and chemical composition of the chromate film when the pH is increased from 1.2 to 2.4. Although the complexity of the chromate system and the pronounced roughness of commercial rolled aluminum limit the accuracy of spectroscopic ellipsometry, it is demonstrated that this technique can be usefully applied to the study of thin chromate films formed on industrially relevant aluminum products.     

Spectrographic ellipsometry study of a liquid crystal display substrate consisting of thin films of SiO2, polyimide and indium tin oxide on glass

Variable angle spectrometric ellipsometry at room temperature is used to determine thin film parameters of substrates used in liquid crystal displays. These substrates consist of sequential thin films of polyimide (PI), on indium tin oxide (ITO),on SiO₂ deposited on a glass backing approximately 1.1 mm thick. These films were studied by sequentially examining more complex systems of films (SiO₂, SiO₂-ITO, SiO₂-ITO-PI). The SiO₂ layer appears to be optically uniform and flat. The ITO film is difficult to characterize. When this surface film's lower surface is SiO₂ and upper surface is an air-ITO-interface it is found that including surface roughness and variation of the optical properties with ITO thickness in the model improved the fit; suggesting that both phenomena exist in the ITO films. However, the surface roughness and graded nature of optical properties could be not determinable by ellipsometry when the ITO is coated with a polyimide film. The PI films are ellipsometrically flat and over the wavelength range from 500 to 1400 nm the real refractive index of polyimide films varying in thickness between 25 and 80 nm is well modeled by a two-term Cauchy model with no absorption. The ellipsometric thickness of the ITO layer is the same as the profilometric thickness; however, the ellipsometric thickness of the polyimide layers is roughly 10 nm larger than that obtained from the profilometer. These final observations are consistent with the literature.     

Non-destructive thickness determination of thin cobalt and cobalt disilicide layers on silicon substrates

The thickness of thin cobalt and cobalt disilicide layers has been measured by spectroscopic ellipsometry (SE). The results obtained by this non-destructive technique are compared with measurements done by two well-established but destructive techniques, namely Rutherford backscattering spectrometry (RBS) and high resolution transmission electron microscopy (HREM). The thickness values obtained by SE are in good agreement with the values measured by RBS and HREM. Spectroscopic ellipsometry allows one to determine the thickness of the metal and silicide layers on device wafers, thereby avoiding the need to use destructive techniques on test wafers or fully processed device wafers.     

Optical characterization of hybrid antireflective coatings using spectrophotometric and ellipsometric measurements

A hybrid antireflective coating combining homogeneous layers and linear gradient refractive index layers has been deposited using different techniques. The samples were analyzed optically based on spectrophotometric and spectroscopic ellipsometry measurements under different angles of incidence in order to precisely characterize the coatings. The Lorentz-Lorenz model has been used to calculate the refractive index of material mixtures in gradient and constant index layers of the coating. The obtained refractive index profiles have been compared with the targeted ones to detect errors in processes of deposition.     

Wavefront control of SiO2-based ultraviolet narrow-bandpass filters prepared by plasma ion-assisted deposition

Metal oxide layers produced by plasma ion-assisted deposition are extensively used for complex optical coatings due to the availability of materials, the high packing density of films, and the smooth surfaces. Stringent optical surface figure specifications necessary for both laser optics and precision optics require film stress to be well-controlled and surface deformation to be corrected or compensated. SiO(2)- based single-cavity UV narrow-bandpass filters were prepared by plasma ion-assisted deposition. The correlation between film stress, refractive index, deposition parameters, and postdeposition annealing was established. The film stress was calculated based on interferometric surface deformation. The refractive index and film thickness were determined by means of variable angle spectroscopic ellipsometry. The center wavelength of the filters was obtained through spectral transmission measurement. The results suggest that the wavefront distortion of the multilayer coatings is dominated by the compressive stress of the SiO(2) layers and can be controlled and corrected by the amount of plasma ion momentum transfer, substrate temperature, postdeposition annealing, and stress compensation via backside SiO(2) coating. Based on the understanding of the mechanical and optical properties, the wavefront correction technique enables us to satisfy stringent surface figure specifications.