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Optical analysis of room temperature magnetron sputtered ITO films by reflectometry and spectroscopic ellipsometry
Abstract
Indium-tin-oxide (ITO) thin films were prepared by reactive magnetron sputtering; their optical constants and thickness were determined by spectral reflectometry (SR) in the wavelength range from 400 nm to 800 nm and spectroscopic ellipsometry (SE) in the wavelength range from 191 nm to 1690 nm. A comparative evaluation of the measured data from SR and SE has been made using the same single layer optical model based on the Cauchy dispersion relation. The introduction of a surface roughness layer into the optical model considerably improved the fit quality during evaluation of SE data. Vertical inhomogeneity of the ITO thin films was assessed using a multilayer optical model describing porosity gradient and the three-layer optical model suggested by Jung [Y.S. Jung, Thin Solid Films
467, 36 (2004)] from the SE data.
... Other methods are based on processing ellipsometric data [5][6][7]. The most efficient methods for the optical characterization of homogeneous thin films utilize the simultaneous processing of photometric and ellipsometric data [8,9]. The optical characterization of inhomogeneous thin films is more complicated compared to that of homogeneous thin films because these films exhibited two defects consisting of uniaxial anisotropy with the optical axis perpendicular to the boundaries and the slight random roughness of the upper boundaries. ...
The optical characterization of non-absorbing, homogeneous, isotropic polymer-like thin films with correlated, differently rough boundaries is essential in optimizing their performance in various applications. A central aim of this study is to derive the general formulae necessary for the characterization of such films. The applicability of this theory is illustrated through the characterization of a polymer-like thin film deposited by plasma-enhanced chemical vapor deposition onto a silicon substrate with a randomly rough surface, focusing on the analysis of its rough boundaries over a wide range of spatial frequencies. The method is based on processing experimental data obtained using variable-angle spectroscopic ellipsometry and spectroscopic reflectometry. The transition layer is considered at the lower boundary of the polymer-like thin film. The spectral dependencies of the optical constants of the polymer-like thin film and the transition layer are determined using the Campi–Coriasso dispersion model. The reflectance data are processed using a combination of Rayleigh–Rice theory and scalar diffraction theory in the near-infrared and visible spectral ranges, while scalar diffraction theory is used for the processing of reflectance data within the ultraviolet range. Rayleigh–Rice theory alone is sufficient for the processing of the ellipsometric data across the entire spectral range. We accurately determine the thicknesses of the polymer-like thin film and the transition layer, as well as the roughness parameters of both boundaries, with the root mean square (rms) values cross-validated using atomic force microscopy. Notably, the rms values derived from optical measurements and atomic force microscopy show excellent agreement. These findings confirm the reliability of the optical method for the detailed characterization of thin films with differently rough boundaries, supporting the applicability of the proposed method in high-precision film analysis.
... Photovoltaic technology is found to potentially be one of the most encouraging renewable energy sources [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Thin-film solar cells, in particular, have substantiated the highest commitment, are economically viable, and are reliable integrating photovoltaic panels onto a roof and constructing arrays of panels to be used in a power plant [22][23][24][25][26]. While Shockley-Queisser (SQ) model [27] predicts that the highest power conversion efficiency (PCE) for a single-junction solar cell is 32.23% at a bandgap of the absorber layer is around 1.14 eV , the PCE of over 20% achieved in thin film solar-cells (TFSCs) based on silicon, CIGS, and CdTe absorber [28,29]. ...
Antimony (Sb) chalcogenides, particularly antimony selenide (Sb2Se3), have gained attention as promising semiconductor materials in order to create and advance competitive solar cells. These materials exhibit a range of desirable qualities, such as excellent absorption rate, ability to modify band gap, and plentiful in the crust of the earth. This article describes an antimony selenide (Sb2Se3) absorber-based high-efficient thin film solar cell (TFSC) with copper oxide (Cu2O) as a back surface field (BSF) by dint of Al/ITO/TiO2/Sb2Se3/Cu2O/Ni heterostructure using SCAPS-1D Simulator. This research entails an in-depth assessment of various physical and electrical characteristics of every solar active semiconductor TiO2, Sb2Se3, and Cu2O covering the thickness of each layer, concentration of carrier doping, defect density in the bulk and at the interface, carrier generation rate together with recombination. Initially, the variation in photovoltaic parameters of open circuit voltage (Voc), short-circuit current density (Jsc), fill factor (FF), power conversion efficiency (PCE), and quantum efficiency (QE) investigated without the BSF layer, followed by a comprehensive analysis on the role of Cu2O BSF layer for enhancing cell’s performance explored systematically. The proposed heterostructure shows improved PCE of over 32% (which was 21% without BSF) with JSC of 37.492 mA/cm2, VOC of 1.024 V, and FF of 83.595%. Thus, the utilization of a heterostructure comprising an Sb2Se3 absorber and copper oxide Cu2O BSF layer demonstrates significant promise in the development and production of high-efficiency greenery thin-film solar cells (TFSCs).
... While significant attention has been dedicated to developing suitable methods for the optical characterization of homogeneous thin films, as evidenced by the abundance of publications on the subject represented here by a small selection [1][2][3][4][5][6][7][8][9], much less attention has been paid to the optical characterization of inhomogeneous thin films with refractive index profiles along the axis perpendicular to the film boundaries. Nevertheless, several papers have addressed this issue [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. ...
In this study, a novel approach for characterizing the optical properties of inhomogeneous thin films is presented, with a particular focus on samples exhibiting absorption in some part of the measured spectral range. Conventional methods of measuring the samples only from the film side can be limited by incomplete information at the lower boundary of the film, leading to potentially unreliable results. To address this issue, depositing the thin films onto non-absorbing substrates to enable measurements from both sides of the sample is proposed. To demonstrate the efficacy of this approach, a combination of variable-angle spectroscopic ellipsometry and spectrophotometry at near-normal incidence was employed to optically characterize three inhomogeneous polymer-like thin films. The spectral dependencies of the optical constants were modeled using the Kramers–Kronig consistent model. It was found that it is necessary to consider thin, weakly absorbing transition layers between the films and the substrates. The obtained results show excellent agreement between the fits and the measured data, providing validation of the structural and dispersion models, as well as the overall characterization procedure. The proposed approach offers a method for optically characterizing a diverse range of inhomogeneous thin films, providing more reliable results when compared to traditional one-sided measurements.
... Initial parameter guesses were provided by the ellipsometer software library. We assumed the ITO could be treated as a single bulk layer with a surface roughness layer modeled as an EMA mixture with vacuum, as suggested by Lohner et al [34]. After reduction, we assumed the film could be approximated by an upper layer with optical constants changed by reduction on top of a lower layer that was unchanged. ...
Absorption of light in superconducting electronics is a major limitation on the quality of circuit architectures that integrate optical components with superconducting components. A 10 nm thick film of a typical superconducting material like niobium can absorb over half of any incident optical radiation. We propose instead using superconductors which are transparent to the wavelengths used elsewhere in the system. In this paper we investigated reduced indium tin oxide (ITO) as a potential transparent superconductor for electronics. We fabricated and characterized superconducting wires of reduced indium tin oxide. We also showed that a \SI{10}{nm} thick film of the material would only absorb about 1 - 20\% of light between 500 - 1700 nm.
... There are many papers dealing with methods of the optical characterization of homogeneous thin films published in the literature (see e.g. [1][2][3][4][5][6][7][8][9][10][11][12]). Nevertheless, several papers devoted to the optical characterization of inhomogeneous thin films have been published too (see e.g. ...
Results concerning the optical characterization of two inhomogeneous polymer-like thin films deposited by the plasma enhanced chemical vapor deposition onto silicon single crystal substrates are presented. One of these films is deposited onto a smooth silicon surface while the latter film is deposited on a randomly rough silicon surface with a wide interval of spatial frequencies. A combination of variable-angle spectroscopic ellipsometry and spectroscopic reflectometry applied at near-normal incidence are utilized for characterizing both the films. An inhomogeneity of the films is described by the method based on multiple-beam interference of light and method replacing inhomogeneous thin films by multilayer systems. Homogeneous transition layers between the films and substrates are considered. The Campi–Coriasso dispersion model is used to express spectral dependencies of the optical constants of the polymer-like films and transition layers. A combination of the scalar diffraction theory and Rayleigh–Rice theory is used to include boundary roughness into formulae for the optical quantities of the rough polymer-like film. Within the optical characterization, the spectral dependencies of the optical constants at the upper and lower boundaries of both the polymer-like films are determined together with their thickness values and profiles of the optical constants. Roughness parameters are determined for the rough film. The values of the roughness parameters are confirmed by atomic force microscopy. Moreover, the optical constants and thicknesses of both the transition layers are determined. A discussion of the achieved results for both the polymer-like films and transition layers is performed.
... These studies are realized using the optical characterization of the films mentioned. An enormous attention has been devoted to developing methods of the optical characterization of homogeneous thin films (see e.g., [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]). Less attention has been devoted to the optical characterization of inhomogeneous thin films [20][21][22][23][24][25]. ...
This review paper is devoted to optics of inhomogeneous thin films exhibiting defects consisting in transition layers, overlayers, thickness nonuniformity, boundary roughness and uniaxial anisotropy. The theoretical approaches enabling the inclusion of these defects into formulae expressing the optical quantities of these inhomogeneous thin films are summarized. These approaches are based on the recursive and matrix formalisms for the transition layers and overlayers, averaging of the elements of the Mueller matrix using local thickness distribution or polynomial formulation for the thickness nonuniformity, scalar diffraction theory and Rayleigh-Rice theory or their combination for boundary roughness and Yeh matrix formalism for uniaxial anisotropy. The theoretical results are illustrated using selected examples of the optical characterization of the inhomogeneous polymer-like thin films exhibiting the combination of the transition layers and thickness nonuniformity and inhomogeneous thin films of nonstoichiometric silicon nitride with the combination of boundary roughness and uniaxial anisotropy. This characterization is realized by variable angle spectroscopic ellipsometry and spectroscopic reflectometry. It is shown that using these optical techniques, the complete optical characterization of the mentioned thin films can be performed. Thus, it is presented that the values of all the parameters characterizing these films can be determined.
... An enormous number of papers concerning the characterization of the homogeneous thin films has been published (see e.g. [1][2][3][4][5][6][7][8][9][10][11][12]). A less attention has been devoted to the optical characterization of the inhomogeneous thin films. ...
The method of variable angle spectroscopic ellipsometry usable for the complete optical characterization of inhomogeneous thin films exhibiting complicated thickness non-uniformity together with transition layers at their lower boundaries is presented in this paper. The inhomogeneity of these films is described by means of the multiple-beam interference model. The thickness non-uniformity is taken into account by averaging the elements of the Mueller matrix along the area of the light spot of the ellipsometer on the films. The local thicknesses are expressed using polynomials in the coordinates along the surfaces of the films. The efficiency of the method is illustrated by means of the optical characterization of a selected sample of the polymer-like thin film of SiO x C y H z prepared by plasma enhanced chemical vapor deposition onto the silicon single crystal substrate. The Campi–Coriasso dispersion model is used to determine the spectral dependencies of the optical constants at the upper and lower boundaries of this film. The profiles of these optical constants are determined too. The thickness non-uniformity is described using a model with local thicknesses given by the polynomial with at most quadratic terms. In this way it is possible to determine the geometry of the upper boundary. The thickness and spectral dependencies of the optical constants of the transition layer are determined as well. Imaging spectroscopic reflectometry is utilized for confirming the results concerning the thickness non-uniformity obtained using ellipsometry.
... An enormous attention has been devoted to the optical characterization of homogeneous thin films (see e.g. [1][2][3][4][5][6][7][8][9][10]). In the three last decades the number of the articles concerning the optical characterization of inhomogeneous thin films increased because of applications of these films in optics industry (see e.g. ...
In this paper the complete optical characterization of an inhomogeneous polymer-like thin film of SiO x C y H z exhibiting a thickness non-uniformity and transition layer at the boundary between the silicon substrate and this film is performed using variable angle spectroscopic ellipsometry. The Campi-Coriasso dispersion model was utilized for describing the spectral dependencies of the optical constants of the SiO x C y H z thin film and transition layer. The multiple-beam interference model was used for expressing inhomogeneity of the SiO x C y H z thin film. The thickness non-uniformity of this film was taken into account by means of the averaging of the elements of the Mueller matrix performed using the thickness distribution for the wedge-shaped non-uniformity. The spectral dependencies of the optical constants of the SiO x C y H z thin film at the upper and lower boundaries together with the spectral dependencies of the optical constants of the transition layer were determined. Furthermore, the thickness values of the SiO x C y H z film and transition layer, profiles of the optical constants of the SiO x C y H z thin film and the rms value of local thicknesses corresponding to its thickness non-uniformity were determined. Thus, all the parameters characterizing this complicated film were determined without any auxiliary methods.
... This reality is demonstrated by enormous number of scientific articles and many monographs dealing with optics of thin films. Enormous attention has been devoted to optics of homogeneous thin films in particular (see eg [1][2][3][4][5][6][7][8][9][10][11][12][13]). A less attention has been devoted to optics of inhomogeneous thin films since from the optical point of view these films are more complicated than homogeneous thin films. ...
In this paper the overview of the most important approximate methods for the optical characterization of inhomogeneous thin films is presented. The following approximate methods are introduced: Wentzel–Kramers–Brillouin–Jeffreys approximation, method based on substituting inhomogeneous thin films by multilayer systems, method based on modifying recursive approach and method utilizing multiple-beam interference model. Principles and mathematical formulations of these methods are described. A comparison of these methods is carried out from the practical point of view, ie advantages and disadvantages of individual methods are discussed. Examples of the optical characterization of three inhomogeneous thin films consisting of non-stoichiometric silicon nitride are introduced in order to illustrate efficiency and practical meaning of the presented approximate methods.
Absorption of light in superconducting electronics is a major limitation on the quality of circuit architectures that integrate optical components with superconducting components. A 10 nm thick film of a typical superconducting material like niobium can absorb over half of any incident optical radiation. We propose instead using superconductors which are transparent to the wavelengths used elsewhere in the system. In this paper we investigated reduced indium tin oxide (ITO) as a potential transparent superconductor for electronics. We fabricated and characterized superconducting wires of reduced indium tin oxide. We also showed that a 10 nm thick film of the material would only absorb about 1 - 20% of light between 500 - 1700 nm.
Indium tin oxide (ITO) films with various thicknesses are deposited on glass substrates using a DC magnetron sputtering technique. The microstructure and chemical composition of the sputtered samples are examined by scanning electron microscopy (SEM), X-Ray Diffraction (XRD) and Energy Dispersive X-Ray Spectroscopy (EDS). Two-layer and three-layer optical models of the sputtered ITO films are constructed for fitting the experimental results of the spectroscopic ellipsometry. The results obtained from the two models for the resistivity, carrier density and carrier mobility are compared with those obtained via Hall effect measurements. Finally, the three-layer optical model is used to evaluate the refractive index and extinction coefficient spectra of the various samples. In general, the present results show that the three-layer model, in which the transition layer between the ITO film and the glass substrate is included, provides a better approximation of the SE results than the two-layer model. However, both models yield a reasonable estimate of the Hall resistivity. The results obtained using the three-layer model show that the carrier density and carrier mobility in the bulk layer are lower and higher, respectively, than those in the transition layer. In addition, it is shown that the refractive index of the bulk layer is lower than that of the transition layer in the UV and visible spectrum. Moreover, the extinction coefficient of the transition layer is significantly higher than that of the bulk layer in the near IR-region.
Indium-tin-oxide (ITO) films deposited by sputtering and e-gun evaporation on both transparent (Corning glass) and opaque (c-Si, c-Si/SiO2) substrates and in c-Si/a-Si:H/ITO heterostructures have been analyzed by spectroscopic ellipsometry (SE) in the range 1.5-5.0 eV. Taking the SE advantage of being applicable to absorbent substrate, ellipsometry is used to determine the spectra of the refractive index and extinction coefficient of the ITO films. The effect of the substrate surface on the ITO optical properties is focused and discussed. To this aim, a parametrized equation combining the Drude model, which considers the free-carrier response at the infrared end, and a double Lorentzian oscillator, which takes into account the interband transition contribution at the UV end, is used to model the ITO optical properties in the useful UV-visible range, whatever the substrate and deposition technique. Ellipsometric analysis is corroborated by sheet resistance measurements.
Indium tin oxide (ITO) thin films were prepared on glass substrates by an electron beam evaporation technique from a mixture of In2O3 and SnO2. The films were annealed in air for 30 min at 350°C. The electrical and optical properties of these films were investigated as a function of the substrate temperature. The films were deposited at substrate temperatures ranging from 50 to 350°C at an oxygen partial pressure of 5×10−5 mbar. The dopant concentration, resistivity, electrical conductivity, activation energy, optical transmission and band gap energy were investigated. It was found that the activation energy decreased with an increase in the film thickness. A transmittance value of 92% in the visible region of the spectrum and a resistivity of 3×10−6 Ωm was obtained at a substrate temperature of 350°C. Structural studies showed that the films were polycrystalline.
Tin-doped Indium oxide thin films in different compositions (Sn = 0,5,10,15,20 at.wt%) were prepared on glass substrates at the substrate temperature of 250 °C in an oxygen atmosphere by electron beam evaporation. The structural and morphological studies were carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The grain size of the ITO films decreased when increasing the dopant concentration of Sn in the In2O3 lattice. Optical properties of the films were studied in the UV-Visible-NIR region (300–1000 nm). The optical energy band gap (Eg), as determined by the dependence of the absorption coefficient on the photon energy at short wavelengths was found to increase from 3.61 to 3.89 eV revealing the ascending loading profile of dopant concentration. Optical Parameters, such as absorption depth, refractive index (n), extinction coefficient (k), packing density, porosity, dispersion energy and single effective oscillator energy were also studied to show the composition dependence of tin-doped indium oxide films.
Thin films of ITO (Sn-doped In2O3) were coated on Corning #1737 glass substrates (50×50 mm2) heated at 600 °C, after introducing an aerosol with air to a furnace heated at 620 °C. The aerosol was produced by ultrasonic vibration of 0.2 M In(III)-acetylacetonate together with 5 mol% Sn(IV)-bis-acetylacetonate-dibromide dissolved in acetylacetone. Film structure and electrical resistivity at room temperature depend on air flow rate: (1) at 10 l/min ITO films grew with (100)-preferred orientation because (400) and (800) peaks were clearly observed and the electrical resistivity was approximately (1–2)×10−4 Ωcm; (2) when the air flow rate was reduced to 7.5 and 5 l/min, the (400) and (800) peak intensities became small and their resistivity was (2–4)×10−4 Ωcm. The optical energy band gap (3.90 eV), which is estimated from the relationship between the square of the optical absorption coefficient times the frequency of the electromagnetic wave and the frequency near the absorption edge, is independent of film thickness and air flow rate. Some comments on the (100)-preferred orientation thin-film growth and on the resistivity change due to the flow rate are provided.
Variable angle of incidence spectroscopic ellipsometry (VASE®)∗ is a rapid and powerful non-destructive optical technique often used to characterize thin films and multilayered structures. A monochromatic, linearly polarized beam of light is reflected from a sample surface at a known angle of incidence, and the resulting polarization state of the reflected beam is measured as a function of wavelength and angle of incidence. Acquired data are then used to determine the optical constants, film thicknesses, and other parameters in the assumed model for the sample. The VASE® experiment is particularly useful for the characterization of materials for flat panel displays. In the present work, we demonstrate the use of VASE® on several specific materials for display applications: conducting indium tin oxide (ITO), hydrogenated amorphous silicon, and silicon dioxide, all deposited onto glass substrates.
The electrical and optical properties of room temperature laser deposited indium tin oxide films were studied. It was found that the resistivity of the film was quite sensitive to the deposition conditions. At the optimized conditions, film with a bulk resistivity value of 2.8 × 10−4Ω cm and optical transmission of greater than 90% could be obtained. By using an in situ resistance measurement, it was shown that the initial growth mode was via island formation. Additionally, a classic transition from two- to three-dimensional behavior for the resistance was observed. The mean free path obtained was 550 Å.
ITO-film NO2 gas sensors (thickness=15 nm) were prepared by DC magnetron sputtering. The highest sensitivity was obtained at the sensor temperature of 523 K. When the NO2 gas flow in a measurement tube was terminated, the as-prepared ITO-film sensor showed a gradual decrease of NO2 concentration without NO2 gas leak. We attribute this phenomenon to the desorption of decomposed NO2 from the sensor surface. By annealing the sensor in NO2 gas at 573 K, the sensor showed no decrease of the concentration and could be used for detecting the photodecomposition of NO2. XPS revealed that annealing in NO2 gas for 0.5 h caused a CO-like bond to be formed on the sensor surface. This may become a stable adsorption site for NO2, thus inhibiting decomposition.