Spectral Ellipsometry Research Articles

Peculiarities of deformation of round thin-film membranes and experimental determination of their effective characteristics

The features of thin-film membranes, which are formed above round holes in silicon substrates using the Bosch-process are considered. The membrane has a complex shape due to the presence of the stress state of the initial films. The analysis of the dependence of the membrane deflection w on the supplied overpressure P is used to calculate the mechanical characteristics of the membranes. In this case, it is necessary to determine directly on the membrane its diameter, the thickness of the constituent layers, the change in the topography of the membrane surface over its entire area as the overpressure increases. Determination of the membrane diameter and the thicknesses of the constituent layers is shown by the example of p-Si*/SiNx/SiO2 and SiNx/SiO2/SiNx/SiO2 membranes. We used spectral ellipsometry, energy-dispersive X-ray spectroscopy, optical profilometry, optical microscopy. The influence of the peculiarities of the fixing conditions on the stress-strain state of membranes is shown, and the assessment is carried out by means of numerical modeling. A technique has been developed for measuring and calculating the mechanical characteristics of membranes that have an initial deflection. The calculation result is shown on the example of a membrane with an initial deflection of 2 μm --- SiNx/SiO2/SiNx/SiO2 and a membrane with an initial deflection of 30 μm --- Al/SiO2/Al. Keywords: stress, bulging method, films, thin-layer coating, film thickness, membrane, pressure blister test, residual stress, microelectromechanical systems, MEMS, silicon substrate, large deformations, strain, deflections, circular membrane, bulge testing.

Optical properties of ferroelectric films Hf-=SUB=-x-=/SUB=-Zr-=SUB=-y-=/SUB=-O-=SUB=-2-=/SUB=- and La : Hf-=SUB=-x-=/SUB=-Zr-=SUB=-y-=/SUB=-O-=SUB=-2-=/SUB=- according to ellipsometry data

Recently ferroelectric properties have been found in hafnia-based nanosized films. Such films are of the utmost interest for development of a universal memory, which combines the advantages of random access memory and flash memory. The paper studies optical properties of hafnia-zirconium oxide films HfxZryO2 and lanthanum-alloyed hafnia-zirconium oxide films La : HfxZryO2. Fluctuations of thickness in HfxZryO2 do not exceed 3.5%, fluctuations of thickness in La : HfxZryO2 films --- 3.2%. Optical properties are analyzed based on effective-medium theory. According to effective-medium theory data, HfxZryO2 films contain 46% HfO2, 54% ZrO2, La : HfxZryO2 films contain 47.5% HfO2, 52.4% ZrO2, 2.5% La2O3. Keywords: ferroelectric, refraction index, spectral ellipsometry, effective-medium theory.

Исследование плазмонного резонанса в Bi-=SUB=-2-=/SUB=-Se-=SUB=-3-=/SUB=- и Sb-=SUB=-2-=/SUB=-Te-=SUB=-3-=/SUB=- методом инфракрасной спектральной эллипсометрии

In the infrared region of the spectrum (IR), the optical properties of single-crystal samples of narrow-gap degenerate semiconductors Bi2Se3 and Sb2Te3 are investigated by infrared spectral ellipsometry (SE). The transport properties of the Drude fitting of dielectric functions obtained by spectroscopic ellipsometry are studied. The behavior of the bulk and surface plasmon polaritons is investigated in detail. The dispersion and mean free path of the plasmon, the depth of the skin layer for the conducting and dielectric surfaces are calculated. The contribution of the plasmon to the optical properties is estimated from the spectral density for the Bi2Se3 and Sb2Te3 samples.

Study of plasmon resonance in Bi-=SUB=-2-=/SUB=-Se-=SUB=-3-=/SUB=- and Sb-=SUB=-2-=/SUB=-Te-=SUB=-3-=/SUB=- by infrared spectral ellipsometry

In the infrared region of the spectrum (IR), the optical properties of single-crystal samples of narrow-gap degenerate semiconductors Bi2Se3 and Sb2Te3 are investigated by infrared spectral ellipsometry (SE). The transport properties of the Drude fitting of dielectric functions obtained by spectroscopic ellipsometry are studied. The behavior of the bulk and surface plasmon polaritons is investigated in detail. The dispersion and mean free path of the plasmon, the depth of the skin layer for the conducting and dielectric surfaces are calculated. The contribution of the plasmon to the optical properties is estimated from the spectral density for the Bi2Se3 and Sb2Te3 samples. Keywords: ellipsometry, plasmon, plasmonics, plasmon dispersion, plasmon mean free path, plasmon penetration depth.

Study of plasmon resonance in Bi-=SUB=-2-=/SUB=-Se-=SUB=-3-=/SUB=- and Sb-=SUB=-2-=/SUB=-Te-=SUB=-3-=/SUB=- by infrared spectral ellipsometry

In the infrared region of the spectrum (IR), the optical properties of single-crystal samples of narrow-gap degenerate semiconductors Bi2Se3 and Sb2Te3 are investigated by infrared spectral ellipsometry (SE). The transport properties of the Drude fitting of dielectric functions obtained by spectroscopic ellipsometry are studied. The behavior of the bulk and surface plasmon polaritons is investigated in detail. The dispersion and mean free path of the plasmon, the depth of the skin layer for the conducting and dielectric surfaces are calculated. The contribution of the plasmon to the optical properties is estimated from the spectral density for the Bi2Se3 and Sb2Te3 samples. Keywords: ellipsometry, plasmon, plasmonics, plasmon dispersion, plasmon mean free path, plasmon penetration depth.

Refractive Index of Heavily Germanium-Doped Gallium Nitride Measured by Spectral Reflectometry and Ellipsometry.

Gallium nitride (GaN) doped with germanium at a level of 1020 cm−3 is proposed as a viable material for cladding layers in blue- and green-emitting laser diodes. Spectral reflectometry and ellipsometry are used to provide evidence of a reduced index of refraction in such layers. The refractive-index contrast to undoped GaN is about 0.990, which is comparable to undoped aluminium gallium nitride (AlGaN) with an aluminium composition of 6%. Germanium-doped GaN layers are lattice-matched to native GaN substrates; therefore, they introduce no strain, cracks, and wafer bowing. Their use, in place of strained AlGaN layers, will enable significant improvements to the production process yield.

Surface Topography of Si/TiO2 Stacked Layers on Silicon Substrate Deposited by KrF Excimer Laser Ablation

This study investigates the surface topography of the deposited thin films versus the distance between target and substrate (dTS) inside a laser ablation equipment. The profile of the rough surface was obtained by atomic force microscopy data analysis based on power spectral density and the roughness-length scale (RLS) functions. The roughing on the top film is analyzed considering the previous topography of the underneath surface for each consecutive TiO2 and Si deposition onto Si (100) wafer. The buried oxide layer inside of Si/TiO2/c-Si structure, obtained by KrF excimer laser ablation was characterized by complementary techniques as spectral ellipsometry, X-ray reflectometry, and X-ray diffraction.

Optical Parameters of As-Deposited and Annealed (Ga0.3In0.7)2Se3 Thin Films

The (Ga0.3In0.7)2Se3 films deposited by the thermal evaporation technique are annealed in the inert atmosphere (argon) for 1 h at temperatures of 50, 100, and 150 ∘C. The spectral ellipsometry is applied for measuring the spectral dependences of the refractive and extinction coefficients of as-deposited and annealed (Ga0.3In0.7)2Se3 films. The optical transmission spectra, as well as the optical absorption spectra of (Ga0.3In0.7)2Se3 films, are studied depending on the annealing temperature. The optical absorption edge for annealed (Ga0.3In0.7)2Se3 films is shifted to the short-wavelength region and broadens, as the annealing temperature increases. Parameters of the Urbach absorption edge are determined for as-deposited and annealed (Ga0.3In0.7)2Se3 films. The spectral dependences of the refractive index are analyzed in the framework of the Wemple–DiDomenico model. The nonlinear increase of the energy pseudogap, Urbach energy, and refractive index with the annealing temperature are revealed.

Order of magnitude enhancement of inherently selective atomic layer deposition of zirconia on silicon without deposition on copper: The role of precursor

Zirconia atomic layer deposition (ALD) using zirconium 2-methyl 2-butoxide (ZMB) and ethanol is reported for the first time. The process selectively deposits a uniform ZrO2 film on silicon with a high deposition rate (∼2 Å/cycle), without any deposition on copper at a relatively low temperature (200 °C) and up to at least 200 cycles. This is the largest thickness of inherently surface selective ZrO2 ALD ever reported (∼400 Å) and is at least 10 times more selective than that achieved using a similar deposition process but with a different precursor, tris(dimethylamino)cyclopentadienyl Zirconium (ZyALD™). The selectively deposited ZrO2 films were characterized using spectral ellipsometry, X-ray photoelectron spectroscopy, extended X-ray absorption fine structure spectroscopy (EXAFS), atomic force microscopy and energy dispersive spectroscopy obtained during scanning electron microscopy and scanning transmission electron microscopy. Surface characterization techniques employed here confirmed the chemical nature and topography of the deposited ZrO2, whereas EXAFS showed the ZrO2 to be amorphous on silicon having local bonding structure similar to that of ZrO2 deposited with ZyALD™ precursor.

Pulsed laser deposition of high-transparency molybdenum oxide thin films

Molybdenum oxide is an intensively studied material, thanks to its high bandgap, high work function, and potentially also photochromism, plasmonic properties, and layered structure. In this contribution, we employ Pulsed Laser Deposition (PLD) from stoichiometric MoO3 and metal Mo target at temperature range of 25 °C–500 °C and oxygen pressure variation of 0.1 mbar–0.4 mbar to deposit high transparency MoO3 layers. The combination of Photothermal Deflection Spectroscopy (PDS) and Spectral Ellipsometry is applied to accurately track all the optical properties. The X-ray diffraction and Scanning Electron Microscopy (SEM) are used to monitor crystallinity and surface morphology. We have observed that with increasing temperature, initially amorphous layer becomes smoother and denser, bandgap narrows and sub-gap absorption increases. This trend can be reversed by increasing oxygen pressure. Above 400 °C, the material starts crystallizing, first in monoclinic β-MoO3 phase and then in orthorhombic α-MoO3 phase. The high pressure promotes crystallinity, however increases surface roughness. Depositions form metal Mo target follow the same trends as in the case of stoichiometric MoO3 target, however the deposition from stoichiometric target produces lower sub-gap absorptance. Sub-gap absorptance centred around 1000 nm depends strongly on deposition temperature and weakly on oxygen pressure.

Precision of Silicon Oxynitride Refractive-Index Profile Retrieval Using Optical Characterization

Layers with gradient refractive-index profile are an attractive alternative to conventional homogeneous stack coatings. However, the optical characterization and monitoring of the graded refractive-index profile is a complex issue, which has been typically solved by using a simplified model of mixed materials. Although this approach provides a solution to the problem, the precision, which can be expected from optical characterization of the refractive index gradient, remains unclear. In this work, we study optical characterization of SiO_xN_y layers deposited via reactive dual ion beam sputtering. To characterize the deposited layers, we use several methods including reflectance, and transmittance spectra at a broad range of incident angles, together with spectral ellipsometry. All the data were simultaneously fitted with a general profile of refractive index. The expected profile used in our fit was based on characterization of SiO_xN_y layers with a varying stoichiometry. By altering of the profile, we discussed sensitivity of such alternation on fit quality and we studied ambiguity of merit-function minimization. We demonstrate that while the scanning of particular parameters of the profile can be seemingly very precise, we obtain a very good agreement between the experimental data and model for a broad range of gradient shapes, where the refractive-index value on major part of the profile can differ as much as 0.02 from the mean value.

Activation of film growth on indium phosphide by pulsed photon treatment

Photon activation of various physicochemical processes by the radiation of powerful pulsed xenon lamps (radiation range of 0.2-1.2 µm) is one of the promising areas of material science. The aim of this study was to determine the effect of preoxidative pulsed photon treatment on the process of thermal oxidation of indium phosphide with a nanosized layer of V2O5 on the surface, as well as its effect on the composition and morphology of the formed films. We determined the optimal mode of pre-oxidative pulsed photon treatment of magnetron-formed V2O5/InP heterostructures with a radiation density of 15 J/cm2. By laser and spectral ellipsometry methods, photon activation of V2O5/InP before thermal oxidation was found to increase the thickness of the formed films practically twofold. X-ray diffraction analysis confirms the intensification of the phosphate formation process. The morphological characteristics of the films were determined by atomic force microscopy.Pre-oxidative pulsed photon treatment with an optimal radiation density of 15 J/cm2 activates the thermal oxidation of V2O5/InP heterostructures. It is associated with the formation of new active centres and accelerated rearrangement of chemical bonds in the intermediate complexes of the V2O5 catalyst with semiconductor components

Depth of glass poling - via optical transmission spectra

We demonstrate a simple non-destructive technique to deduce the thickness and average index of a modified layer formed beneath a glass surface by thermal poling. It is based on using periodic oscillations in optical transmission of poled glasses, which are due to the reflection of light at the interface of the poled glass region differing in composition and, respectively, in refractive index. The approach is verified by spectral ellipsometry, chemical etching and secondary ion mass spectrometry of poled soda-lime glass slides.

Application of the Spectral Ellipsometry Method to Study the Processes of Atomic Layer Deposition

Application of the Spectral Ellipsometry Method to Study the Processes of Atomic Layer Deposition

Permittivity features of multilayer nanoisland systems [FeNi–Al2O3

We study the permittivity (ε) of multilayer nanoisland systems [FeNi–Al2O3]N with different layer thicknesses using spectral ellipsometry. A “metallic” behavior of the permittivity (Re(ε)<0) is found in structures with island FeNi layers, when there is a strong exchange interaction between the layers (dielectric layer thickness d<2 nm). When the exchange interaction in structures is strongly suppressed (Al2O3 layer's thickness d>4 nm), Re(ε)>0, which corresponds to the dielectric behavior of the permittivity. We conclude that the exchange interaction has a significant effect on the permittivity of structures. We also show that the Re(ε) dependences on the FeNi layer thickness for multilayer and single-layer structures are very close when the dielectric layer thickness d>4 nm.

TEOS thin films obtained by plasma polymerization on Ti6Al4V alloys: Influence of the deposition pressure on surface properties and cellular response

The modification of surfaces by the application of thin films has been used in the regenerative medicine area to increase the biocompatibility of metal implants. Titanium alloy has been recently used as substrate in polymerization for biomedical application. In this context, silane films were obtained by plasma polymerization in favor of the sol-gel method and the influence of different pressures in obtaining these films by argon plasma polymerization was evaluated from the alkoxysilane precursor tetraethoxysilane (TEOS) on the Ti6Al4V alloy. The morphological characterization of the films was performed by AFM, Profilometry and Spectral Ellipsometry and the chemical composition was analyzed by XPS. The biological behavior was evaluated by analyzing the mitochondrial activity and cellular viability of mesenchymal stem cells. The plasma polymerization process resulted in the deposition of a nanometric Si-based film formed, predominantly, by Si-O and organosilane bonds. The films that were applied on a sanded surface, with lower pressures in the plasma polymerization process, presented a lower layer thickness and wettability than the films obtained on nanotextured surfaces. Considering absorbance values, the Ti6Al4V samples mechanically sanded and deposited by plasma polymerization at 230 µatm presented better cell viability than samples with nanotextured surfaces coated with plasma polymerized film, indicating this material has potential to biomedical application.

Nanoindentation of AlN, GaN, and AlGaN films grown by HVPE on SiC/Si hybrid substrates

This paper presents an experimental study of structural and mechanical characteristics of thin films of AlN, GaN, and AlGaN grown on hybrid SiC/Si substrates by the method of HVPE. The surface roughness of the films and substrates has been measured. The thickness and molecular composition of the films have been determined by spectral ellipsometry. An analysis of elastic deformation occurring in the films as a result of indentation has been made. The values of hardness and Young’s modulus of the films have been calculated.

Structure, Optical and Electrical Properties of the High Doped ZnO Thin Films Deposited By RF Magnetron Sputtering of Powder Target in Methane Ambient

The ZnO thin films were deposited by RF-magnetron sputtering of ZnO powder target using pure argon, argon with hydrogen and argon with methane as reactive gas. Surface morphology and crystalline structure of the films were studied by SEM, XRD and XRR techniques. Chemical composition and optical properties were investigated by SIMS, Raman scattering spectroscopy (RSS), PL spectroscopy and spectral ellipsometry. Electrical measurements were performed on the ZnO films deposited on SiO2-Si and silicon wafers n- and p-type with Ni contacts by TLM, IV, CV characteristics, admittance spectroscopy, Van der Pauw and Hall methods. It was found that growth morphology, crystalline structure, optical and electrical properties of the films are strongly affected by adding methane to argon during the deposition process. Adding of methane resulted in a destruction of hexagonal phase texture and considerable increase a size of ZnO nanocrystallites (from 50 nm for argon to 200 nm for argon/methane working gas). SIMS measurements demonstrated that methane promoted hydrogen incorporation into the ZnO film that was more than an order of magnitude larger in comparison with adding molecular hydrogen in the gas mixture at the same concentration. Adding of methane resulted in a high energy shift of near band edge ultraviolet photoluminescence band, quenching of deep level emission in the visible spectral range and increase of optical band gap from 3.24 to 3.45 eV. The strongest effect of methane has been found for electrical resistivity that reduced by 3 orders of magnitude in comparison with films deposited in pure argon. Additionally, electrical conductance of the ZnO film deposited at high methane concentration does not depend on measurement temperature. Hall method with combination with Van der Pauw resistivity measurements shows: strong n-type doping of the film; donor concentration more than 1020 cm-3 slightly depending on methane concentration; maximum electron mobility about 7 cm2/V s. The direct comparison of resistivity and donor concentration of the films deposited using methane and molecular hydrogen as doping precursors has demonstrated that doping efficiency of methane is about an order of magnitude larger than that of molecular hydrogen under similar deposition conditions. On the other hand, methane addition in working gas resulted in an intensity decrease of the E2L (100 cm-1) and E2H (438 cm-1) lines in the RSS that can be associated with some disturbance of the ZnO structure. Additionally a peak at 71 cm-1 was observed in some films that can be related to the metallic Zn. The possible mechanisms of the ZnO film formation, nature of the doping and electron transport mechanisms will be discussed.

Processes of electroluminescence degradation of light-emitting structures based on thin silicon oxide and nitride films

SiO2 /Si, SiN1.2/SiO2 /Si and SiO2 /SiN0.9/SiO2 /Si structures have been fabricated by chemical vapor deposition and thermal oxidation of silicon. The elemental composition and thicknesses of dielectric layers have been studied using Rutherford backscattering spectroscopy, scanning electron microscopy, and spectral ellipsometry. The electroluminescence (EL) of the samples has been investigated in the “electrolyte–dielectric–semiconductor” system at a positive bias voltage applied to the silicon substrate. An intense band with maxima at 1.9 eV appears on the EL spectra of the SiO2 /Si sample, while the EL spectra of the SiN1.2/SiO2 /Si and SiO2 /SiN0.9/SiO2 /Si samples are characterized by the presence of bands with the maximum values of 1.9, 2.3 and 2.7 eV. The nature of these bands is discussed. Passing a charge in the range of 100–500 mC/ cm2 through the SiO2 /SiN0.9/SiO2 /Si sample, an increase in the EL intensity was recorded in the entire visible range. Passing a charge of 1 C/cm2 through a sample with a three-layer dielectric film resulted in the EL intensity decrease. It can be explained by the upper oxide layer degradation. It has been shown that silicon nitride deposited on top of the SiO2 layer protects the oxide layer from field degradation and premature breakdown. The most stable electroluminescence when exposed to a strong electric field is observed for the structure SiN1.2/SiO2 /Si.

Structural, electrical, and optical properties of ITO thin films and their influence on performance of CdS/CdTe thin-film solar cells

ITO was prepared by mixing gradient In2O3 and SnO2 powders using solid-phase reaction manner. Using electron beam gun tool, ITO films with varied thicknesses were fabricated. The structures and electrical and optical parameters of the prepared films were studied. XRD patterns were used to establish the micro-structural parameters (lattice strain and crystallite size). The SEM shows improvement of grain size with the increase of the film thickness. The electrical parameters of ITO films were measured by means of the standard four-point probe method. It was found that when the film thickness increases from 75 to 375 nm, the resistivity decreases to lower value of 1.65 × 10–4 Ω cm and slightly increases to 1.93 × 10–4 Ω cm at thickness of 375 nm. The ITO films with lower electrical properties are appropriate for high-efficiency CdTe solar cells. In terms of spectral ellipsometry, three optical layer models (adhesive layer of the substrate/B-spline layer of ITO film/surface roughness layer) were applied to estimate the film thickness with high accuracy. The absorption coefficient and energy gap were calculated from the transmission and reflection spectra in the strong absorption region. As the film thickness increases, the optical energy gap was found to increase from 3.56 to 3.69 eV. In terms of Hall effect measurements, both carrier concentration and hall mobility were determined. In addition, influences of ITO layers with various thicknesses on the performance of CdS/CdTe solar cells were checked. When the ITO window layer thickness is 325 nm, Jsc = 17 mA/cm2, Voc = 0.82 V, and FF = 57.4%, the calculated highest power conversion efficiency (PCE) is 8.6%.