Spectroscopic Ellipsometry Analysis Research Articles

Effects of ultraviolet sterilization exposure on the structural and surface properties of graphite-/polymer-like carbon films

Existing research on the biological responses of amorphous carbon films has not adequately explored the influences of exposure to ultraviolet (UV) sterilization at 253.7 nm before cell culture. Thus, in this study, two types of amorphous carbon films, namely hydrogen-rich graphite-like carbon (GLC) and hydrogen-free polymer-like carbon (PLC) films, were deposited on Si substrates. The influences of different doses of UV sterilization exposure (at 253.7 nm) on the structures and surface properties of the amorphous carbon films were investigated. Spectroscopic ellipsometry and Raman analysis showed that there is no significant change in the optical constants and Raman spectra of GLC and PLC films. The surface properties of the amorphous carbon films, characterized by water contact angle measurements and X-ray photoelectron spectroscopy analysis, indicated that both types of films exhibited hydrophilicity and surface oxidation in response to UV sterilization. However, the effects of UV sterilization on PLC were more notable than those on GLC. Our findings highlight the need for standardization and optimization of UV sterilization conditions for specific films to promote the application of amorphous carbon film coatings in the medical domain.

Optical Properties of Europium-Doped Silicon-Based Thin Films

The integration of a silicon-based light emitter into existing CMOS technology has long been intriguing due to its optoelectronic compatibility with microelectronics [1]. However, the indirect band gap nature of bulk silicon has hindered its effectiveness as a light emitter. In addressing this limitation, rare earth ions have emerged as significantly interesting candidates owing to their unique optical and electronic properties. Rare earth-doped silicon structures have earned special attention as they exhibit sharp light emission in different spectral regions [2] . This notable feature is attributed to the effective excitation of rare earth ions within the host matrix. Efficiently excited rare earth ions can produce visible emissions ranging from infrared to ultraviolet, presenting possibilities in diverse applications such as solid-state lighting, displays, lasers, photovoltaics, and optical communication. The incorporation of rare earth-doped silicon structures presents a promising solution to overcome the challenges posed by silicon's intrinsic properties, thereby paving the way for improved performance across a diverse range of optoelectronic applications. Europium is a attractive rare earth material with two optically active states, Eu2+ and Eu3+, enabling it to generate a diverse range of color emissions extending from blue to red depending on the surrounding matrix [3].In this study, we investigated the optical properties and compositions of europium (Eu)-doped thin films including silicon oxide, silicon oxynitride, and silicon carbonitride. For this purpose, thin films were fabricated by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) with in-situ magnetron sputtering on p-type 3" Si (100) substrates. In-situ Eu doping was performed by a radio frequency (RF) magnetron sputtering gun, using a 0.25 in. thick, 2 in. (diameter) 99.9% pure Eu sputtering target. Precursor gases, including silane (diluted in 90% argon), oxygen (diluted in 90% argon), nitrogen (diluted in 90% argon), and ethane were utilized. Annealing was performed on the as-deposited films over a broad temperature range, from 600° to 1100°C, in a nitrogen (N2) environment. Rutherford backscattering spectrometry (RBS) was performed to determine the atomic concentration of the film constituents. Variable angle spectroscopic ellipsometry (VASE) analysis was conducted to investigate the optical properties of the films. Room temperature photoluminescence (PL) experiments were performed using a laser diode excitation source operating at a wavelength of 375nm. Notably, bright visible emission was observed in some of the thin films. Finally, we discuss the influence of the atomic concentration of Eu and the annealing temperature on the emission properties observed in the photoluminescence experiments.[1] F. Azmi, Y. Gao, Z. Khatami, and P. Mascher, “ Tunable emission from Eu:SiOxNy thin films prepared by integrated magnetron sputtering and plasma enhanced chemical vapor deposition ,” J. Vac. Sci. Technol. A, vol. 40, no. 4, p. 043402, 2022, doi: 10.1116/6.0001761.[2] A. Brik et al., “Annealing Effects on Structural Characteristics of Europium Doped Silicon-Rich Silicon Nitride,” Silicon, vol. 14, no. 14, pp. 8417–8425, 2022, doi: 10.1007/s12633-021-01636-w.[3] D. Li, X. Zhang, L. Jin, and D. Yang, “Structure and luminescence evolution of annealed Europium-doped silicon oxides films,” Opt. Express, vol. 18, no. 26, p. 27191, 2010, doi: 10.1364/oe.18.027191.

Sequential Infiltration Synthesis of Al2O3 in PMMA Thin Films: Temperature Investigation by Operando Spectroscopic Ellipsometry.

Sequential infiltration synthesis (SIS) is a scalable and valuable technique for the synthesis of organic-inorganic materials with several potential applications at the industrial level. Despite the increasing interest for this technique, a clear picture of the fundamental physicochemical phenomena governing the SIS process is still missing. In this work, infiltration of Al2O3 into thin poly(methyl methacrylate) (PMMA) films using trimethyl aluminum (TMA) and H2O as precursors is investigated by operando dynamic spectroscopic ellipsometry (SE) analysis. The TMA diffusion coefficient values at temperatures ranging from 70 to 100 °C are determined, and the activation energy for the TMA diffusion process in PMMA is found to be Ea = 2.51 ± 0.03 eV. Additionally, systematic data about reactivity of TMA molecules with the PMMA matrix as a function of temperature are obtained. These results provide important information, paving the way to the development of a comprehensive theory for the modeling of the SIS process.

(First Best Student Paper Award) Polymer to Silicon Direct Bonding for Microelectronics

Direct bonding consists in spontaneously bringing into contact two solid surfaces without any intermediate liquid. A liquid is defined here as a being thick enough to have fluid characteristics. Silicon direct bonding is widely used in microelectronics, for instance for the production of silicon-on-insulator substrates (for transistor manufacturing). Direct bonding can be performed between identical surfaces, for example, two silicon substrates. However, direct bonding is also feasible with two different surfaces such as silicon and metal.Direct bonding of two solid materials requires very strict surface conditions such as planarity, particle cleanliness and low surface roughness. The surface Root Mean Square (RMS) roughness should be lower than 0.5 nm for hydrophilic silicon bonding and 0.3 nm for hydrophobic silicon bonding [1].We will focus here on direct bonding with polymer films. It is a quite innovative bonding as polymers are materials with very different properties compared to silicon. They are indeed not crystalline, much less rigid and most of the time hydrophobic.Five different polymers thin films are used to evaluate direct bonding with polymers: LOR2A, BARC AR26N, SOC HM8102, TOK TDMR and LTC9310. Thicknesses are between 32 nm and 6 µm. Those polymers are deposited on 200 or 300 mm diameter Si substrates.First of all, polymers are characterized by Fourier-Transform Infrared Spectroscopy (FTIR), spectroscopic ellipsometry and Thermogravimetric Analysis (TGA). Contact angles of the different polymers are in the 58° to 77° range, a feature which is a characteristic of hydrophobic surfaces. For comparison, the contact angle is lower than 5° for hydrophilic silicon (SiO2) and 78° for hydrophobic H-passivated silicon (Si). The surface roughness of the five different polymers is evaluated by Atomic Force Microscopy (AFM), with RMS roughness ranging from 0.29 to 0.40 nm found. Such values are in-between the 0.3 nm and 0.5 nm thresholds for hydrophobic and hydrophilic surface bonding, respectively. However, direct bonding is feasible between polymers and hydrophilic or hydrophobic silicon surfaces in all cases. Bonding waves are observed and characterized by infrared imaging. Adhesion energies for bonding with the five different polymers are between 40 and 70 mJ/m². Meanwhile, the bonding wave velocity is in the 10-19 mm/s range. Data for polymer to hydrophilic silicon bonding are provided in Table 1. They can be compared to Table 2 data for hydrophilic and hydrophobic silicon bonding (i.e. ceramic bonding) as they have equivalent water contact angles. Polymer to Si direct bonding has higher adhesion energy and bonding wave velocity than SiO2 to Si ceramic direct bonding. The bonding interface, characterized by Scanning Acoustic Microscopy (SAM), does not reveal any bonding defects. Bonded stacks can be annealed at different temperatures. Acoustic images of bonding with BARC are shown in Figure 1 for different annealing temperatures. It is possible to measure their adherence energy after annealing using the DCB (Double Cantilever Beam) technique [2]. BARC adherence energies are given in Figure 2. As with ceramic bonding, bonding strengthens as the temperature increases. The covalent bonds density should increase during the annealing. The bonding degradation at 250°C and especially 300°C evidenced by Scanning Acoustic Microscopy (SAM) is in line with TGA findings on polymer degradation, with a threshold at 280°C. X-ray Photoelectron Spectroscopy is being used to identify interactions between the silicon surface and the polymer. A mechanism will be proposed for these innovative bondings.[1] H. Moriceau et al., « Overview of recent direct wafer bonding advances and applications », Adv. Nat. Sci. Nanosci. Nanotechnol., vol. 1, no 4, p. 043004, févr. 2011, doi: 10.1088/2043-6262/1/4/043004.[2] W. P. Maszara, G. Goetz, A. Caviglia, et J. B. McKitterick, « Bonding of silicon wafers for silicon‐on‐insulator », J. Appl. Phys., vol. 64, no 10, p. 4943-4950, nov. 1988, doi: 10.1063/1.342443. Figure 1

Plasticizer-Induced Enhancement of Mesoscale Dissymmetry in Thin Films of Chiral Polymers with Variable Chain Length.

Conjugated polymers with chiral side chains are of interest in areas including chiral photonics, optoelectronics, and chemical and biological sensing. However, the low dissymmetry factors of most neat polymer thin films have limited their practical application. Here, a robust method to increase the absorption dissymmetry factor in a poly-fluorene-thiophene (PF8TS series) system is demonstrated by varying molecular weight and introducing an achiral plasticizer, polyethylene mono alcohol (PEM-OH). Extending chain length within the optimal range and adding this long-chain alcohol significantly enhance the chiroptical properties of spin-coated and annealed thin films. Mueller matrix spectroscopic ellipsometry (MMSE) analysis shows good agreement with the steady-state transmission measurements confirming a strong chiral response (circular dichroism (CD)and circular birefringence (CB)), ruling out linear dichroism, birefringence, and specific reflection effects. Solid-state NMR studies of annealed hybrid chiral polymer systems show enhancement of signals associated with aromatic π-stacked backbone and the ordered side-chain conformations. Further studies using Raman spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC), atomic force microscopy (AFM), and polarized optical microscopy (POM) indicate that PEM-OH facilitates mesoscopic crystal domain ordering upon annealing. This provides new insights into routes for tuning optical activity in conjugated polymers.

A Lightweight Neural Network for Spectroscopic Ellipsometry Analysis

AbstractEllipsometry is a widely used technique in thin film characterizations. To extract the optical properties of the films from the measured data, regression data fitting techniques have been developed that iteratively find a set of optical parameters that best fit the observations. However, this iterative process often faces challenges in converging to the correct solution, and it can be time‐consuming. To address these issues, an 8‐bit quantized lightweight method of neural network analysis for spectroscopic ellipsometry are proposed. This method features compact neural network modules to enhance speed and efficiency. The effectiveness of the approach through experimental verification is validated on a diverse range of material films, including metals, semiconductors, and dielectrics. The approach is fully automatic and lightweight, which offers a new perspective on balancing predictive accuracy with limited computational resources. This method holds the potential to achieve automatic, rapid, and high‐throughput optical characterization of films, facilitating real‐time quality monitoring for repeatable high‐precision film manufacturing.

Deposition of Thin Electroconductive Layers of Tin (II) Sulfide on the Copper Surface Using the Hydrometallurgical Method: Electrical and Optical Studies.

Thin films of tin (II) sulfide (SnS) were deposited onto a 500 µm thick copper substrate by a chemical bath method. The effect of sodium (Na) doping in these films was studied. The synthesis of the films was performed at temperatures of 60, 70, and 80 °C for 5 min. The microstructure of the SnS films analyzed by scanning electron microscopy (SEM) showed a compact morphology of the films deposited at 80 °C. The edges of the SnS grains were rounded off with the addition of a commercial surfactant. The thickness of different SnS layers deposited on the copper substrate was found to be 230 nm from spectroscopic ellipsometry and cross-section analysis using SEM. The deposition parameters such as temperature, surfactant addition, and sodium doping time did not affect the thickness of the layers. From the X-ray diffraction (XRD) analysis, the size of the SnS crystallites was found to be around 44 nm. Depending on the process conditions, Na doping affects the size of the crystallites in different ways. A study of the conductivity of SnS films provides a specific conductivity value of 0.3 S. The energy dispersive analysis of X-rays (EDAX) equipped with the SEM revealed the Sn:S stoichiometry of the film to be 1:1, which was confirmed by the X-ray photoelectron spectroscopy (XPS) analysis. The determined band-gap of SnS is equal to 1.27 eV and is in good agreement with the literature data.

Zinc Oxide Nanoparticles-Solution-Based Synthesis and Characterizations.

Zinc oxide (ZnO) nanoparticles have shown great potential because of their versatile and promising applications in different fields, including solar cells. Various methods of synthesizing ZnO materials have been reported. In this work, controlled synthesis of ZnO nanoparticles was achieved via a simple, cost-effective, and facile synthetic method. Using transmittance spectra and film thickness of ZnO, the optical band gap energies were calculated. For as-synthesized and annealed ZnO films, the bandgap energies were found to be 3.40 eV and 3.30 eV, respectively. The nature of the optical transition indicates that the material is a direct bandgap semiconductor. Spectroscopic ellipsometry (SE) analysis was used to extract dielectric functions where the onset of optical absorption of ZnO was observed at lower photon energy due to annealing of the nanoparticle film. Similarly, X-ray diffraction (XRD) and scanning electron microscopy (SEM) data revealed that the material is pure and crystalline in nature, with the average crystallite size of ~9 nm.

Optical properties and thermal degradation of NbB2/Nb(BNO)/Al2O3 spectrally selective tandem absorber

The development of any new ceramic absorber demands the evaluation of different performance-limiting properties. In a recently published paper from our research group, we reported the development of NbB2-based new tandem absorber. In our efforts to investigate further potentiality for concentrated solar power applications, this study reports the optical and angular dependent reflectance properties of the NbB2/Nb(BNO)/Al2O3 spectrally selective absorber. The optical properties (extinction coefficient and refractive index) and the dielectric constants of the coatings were determined using spectroscopic ellipsometry analysis. Such analysis together with SCOUT simulation of the reflectance spectrum, confirms the refractive index gradient from the substrate to the top layer. The angular-dependent reflectance measurement demonstrates good solar absorptance (from 8 to 48°). More importantly, the coatings exhibited good thermal stability up to 200 h in vacuum at 500 °C. Extensive transmission electron microscopy analysis reveals the traces of oxygen in the layers. The moderate decrease in absorptance can be rationalised due to the compaction and formation of an oxide layer. Based on the obtained results and earlier published studies, the potential of the NbB2-based coatings as solar selective absorber for concentrated solar power applications is established.

Optimization of the dielectric-function modeling by B-splines in spectroscopic ellipsometry analysis: A hybrid approach

Currently, a Kramers–Kronig consistent B(asis)-spline representation of the dielectric function is an efficient and widely used method for accurate modeling of the material optical functions in ellipsometric data analysis. However, the B-spline approach to the dielectric function modeling should include an appropriate and user-independent way of a knot vector generation, i.e., the proper selection of the number and locations of knots. In this paper, we advocate for a systematic approach which combines a specific knot allocation method, based on so-called “Integral Span”, a slope-weighting factor, with a selection of optimal number of knots using the Akaike and Bayesian Information Criteria, two statistical estimators, thereby replacing an intuitive and time-consuming “trial-and-error” strategy. The proposed hybrid approach is used to optimize the B-spline models for an epitaxial cobalt disilicide (CoSi2) thin film and a crystalline silicon substrate (c-Si).

(Student Award, 2nd Place) Optical and Mechanical Properties of Europium-Doped Sicn Thin Films Prepared By Integrated Ecr-PECVD and Magnetron Sputtering

Silicon carbonitride (SiCN) is a wide bandgap semiconductor material that has drawn significant interest over the past few decades due to its excellent optical, electrical, and mechanical properties[1]. Rare earth doping in wide bandgap semiconductors has several prospective applications in the field of photoelectric devices, solid-state lasers, flat panel displays, and high-energy radiation detectors [2]. Among the various rare earth materials, europium (Eu) is particularly interesting due to its optically active divalent and trivalent states capable of emitting in different visible spectral ranges [3].In this work, Eu-doped SiCN thin films were prepared by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) with integrated magnetron sputtering [4] on p-type 3” Si (100) substrates. Silane (diluted in 90% argon), nitrogen (diluted in 90% argon) and ethane (C2H6) were used as precursor gases, and a 99.9% pure Eu sputtering target was used as a sputtering source. To understand the effect of C incorporation in the Eu-doped SiCN matrix, we have prepared a set of samples without C. The as-deposited samples were annealed over a wide range of temperatures from 600 to 1100° C in an internet N2 environment. Rutherford backscattering spectrometry (RBS) was performed to determine the atomic concentration of the constituents. Variable angle spectroscopic ellipsometry (VASE) analysis was performed to investigate the optical properties of the films. The room temperature photoluminescence (PL) experiments were carried out with a laser diode excitation source, operating at a wavelength of 375nm. Finally, we performed nanoindentation measurements to understand the deformation behavior of SiCN films as a function of the incorporation of C. The indentation hardness and Young’s modulus of the films were investigated for different Eu and C concentrations.

Band-gap engineering of rutile-structured SnO2−GeO2−SiO2 alloy system

Rutile-structured germanium oxide $(\mathrm{r}\text{\ensuremath{-}}{\mathrm{GeO}}_{2})$, an ultrawide band-gap (UWBG) semiconductor, is a promising candidate for future high-power electronics because of its excellent properties, including ambipolar dopability, high carrier mobilities, and a higher thermal conductivity than $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$. In this paper, focusing on a wide variety of its applications, we propose an UWBG alloy system based on $\mathrm{r}\text{\ensuremath{-}}{\mathrm{GeO}}_{2}$ and other rutile-structured oxides $({\mathrm{SnO}}_{2}\text{\ensuremath{-}}{\mathrm{GeO}}_{2}\text{\ensuremath{-}}{\mathrm{SiO}}_{2})$ and clarify the electronic structure and electrical properties based on experiments and the first-principles calculations. Experimentally, (001)-oriented $\mathrm{r}\text{\ensuremath{-}}{\mathrm{Ge}}_{x}{\mathrm{Sn}}_{1\ensuremath{-}x}{\mathrm{O}}_{2}$ alloy thin films with an entire range of Ge compositions $(x)$ were grown by a mist chemical vapor deposition technique. Structural characterizations show that the fabricated $\mathrm{r}\text{\ensuremath{-}}{\mathrm{Ge}}_{x}{\mathrm{Sn}}_{1\ensuremath{-}x}{\mathrm{O}}_{2}$ alloy films with $x\ensuremath{\le}0.96$ and the well-crystallized part of the film with $x=1.00$ have uniform chemical compositions and the same epitaxial relations with $\mathrm{r}\text{\ensuremath{-}}{\mathrm{TiO}}_{2}$ (001) substrates. Transmission electron microscopy observations reveal that there are few dislocations in $\mathrm{r}\text{\ensuremath{-}}{\mathrm{Ge}}_{0.66}{\mathrm{Sn}}_{0.34}{\mathrm{O}}_{2}$ because of relatively small in-plane lattice mismatch. In contrast, many dislocations are observed near the film/substrate interface in $\mathrm{r}\text{\ensuremath{-}}{\mathrm{Ge}}_{0.96}{\mathrm{Sn}}_{0.04}{\mathrm{O}}_{2}$. Lattice constants of the alloys both along the $a$ and $c$ axes decrease with increase in Ge compositions. Their band gaps were determined by spectroscopic ellipsometry analysis, indicating that the band gaps increase as Ge compositions increase $(3.81\ensuremath{-}4.44\phantom{\rule{0.16em}{0ex}}\mathrm{eV})$ with a bowing parameter of 1.2 eV. The values of lattice constants and the trend of band-gap transitions obtained by calculations are in good agreement with those of experimentally obtained each other. Then we presented the calculated natural band alignments of $\mathrm{r}\text{\ensuremath{-}}{\mathrm{Ge}}_{x}{\mathrm{Sn}}_{1\ensuremath{-}x}{\mathrm{O}}_{2}$ and $\mathrm{r}\text{\ensuremath{-}}{\mathrm{Ge}}_{x}{\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{O}}_{2}$ alloys, suggesting the possibility of $p$-type doping in $\mathrm{r}\text{\ensuremath{-}}{\mathrm{GeO}}_{2}$ and Ge-rich $\mathrm{r}\text{\ensuremath{-}}{\mathrm{Ge}}_{x}{\mathrm{Sn}}_{1\ensuremath{-}x}{\mathrm{O}}_{2}$ and availability of $\mathrm{r}\text{\ensuremath{-}}{\mathrm{SiO}}_{2}$ and Si-rich $\mathrm{r}\text{\ensuremath{-}}{\mathrm{Ge}}_{x}{\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{O}}_{2}$ as a blocking layer of other rutile-structured devices. Finally, electrical measurements demonstrated $n$-type conductivities in $\mathrm{r}\text{\ensuremath{-}}{\mathrm{Ge}}_{x}{\mathrm{Sn}}_{1\ensuremath{-}x}{\mathrm{O}}_{2}$ $(x\ensuremath{\le}0.57)$.

A model for spectroscopic ellipsometry analysis of plasma-activated Si surfaces for direct wafer bonding

In this work, the impact of plasma treatment on Si wafers with native oxide on top was systematically investigated using spectroscopic ellipsometry. A general applicable three-layer optical model structure for ellipsometry data fitting was developed and employed on samples treated with the N2, O2, and N2/O2 mixture plasma. Oxide-growth, amorphization of crystalline Si, and the formation of a transition layer between the SiO2 and the amorphous Si were detected. The estimated thicknesses of produced layers were confirmed by complementary methods, which allow precise ultra-thin layers thicknesses detection, namely, angle-resolved x-ray photoelectron spectroscopy and transmission electron microscopy. The depth-resolved chemical composition and the direct thickness measurements of the produced amorphous structure revealed pronounced elemental gradients and the absence of sharp interfaces. Nitrogen gas used in the plasma process was found to be implanted mainly at the interface of the SiO2/transition layer in the form of Si3N4. However, it was verified that it is feasible to employ one general ellipsometry model consisting of SiO2/transition layer/amorphous Si on crystalline Si for all plasma species due to comparably low Si3N4 concentrations as well as its refractive index n and absorption k similarity to SiO2. Spectroscopic ellipsometry is nondestructive and can be efficiently applied to analyze whole wafers without any sample preparation. It can be concluded that the present approach to ellipsometry model development and verification is well suited for plasma-activated direct wafer bonding processes.

Spectroscopic ellipsometry study of Cu2Zn(GexSi1-x)Se4 bulk poly-crystals

The present study addresses to the synthesis and determination of the dielectric function of Cu2Zn(GexSi1-x)Se4 solid solutions with x = 0.4 and 0.8 over the range 1–4.5 eV by spectroscopic ellipsometry analysis, with the aim to achieve a suitable band gap tuning. The dielectric function of the samples is determined using the Adachi model. From the analysis the lowest E0 transition and high energy E1A and E1B transitions are identified. It is found that the band gap varies nonlinearly on composition in the Cu2Zn(GexSi1-x)Se4 alloys and band gap values as large as 1.87 eV are obtained. These results are essential for the design of efficient tailored photovoltaic solar cells and show the high potential of the kesterite compounds for the development of low-cost sustainable future solar cells.

Optical and Mechanical Properties of Europium-Doped Silicon Oxynitride Thin Films

Light emission from silicon-based systems has gained significant interest over the past few decades with the vision of developing an optoelectronic platform that can be integrated with the existing metal-oxide-semiconductor (MOS) technology [1]. Rare earth doping of silicon-based materials is a promising approach to fabricating efficient light emitting devices because of their excellent luminescence properties and their chemical stability [2]. Europium (Eu) ions are attractive dopants for silicon photonic applications due to their intense emission in the visible spectral region. The efficiency of such photonic devices can be influenced by the mechanical properties of the Eu-doped films. Thus, the integration of these films in photonic devices requires an understanding of their mechanical properties as well. In this work, we discuss the relationship between the photoluminescence (PL) behavior and the elasticity and hardness of Eu doped silicon oxynitride (SiON) thin films.We have fabricated thin films using an electron cyclotron resonance plasma-enhanced chemical vapor deposition system with integrated magnetron sputtering system [3] on p-type 3” Si (100) substrates. Silane (diluted in 90% argon) and nitrogen (diluted in 90% argon) were used as precursor gases, while a 99.9% pure Eu sputtering target was used as a sputtering source. Different sets of samples were fabricated by changing the sputtering power and argon flow rate to understand the effect of deposition parameters on the dopant concentration and the optical and mechanical properties. Post-deposition annealing in nitrogen and a mixture of nitrogen with hydrogen (5%) were performed over a wide range of temperatures from 600° to 1100° C. The effect of hydrogen passivation was studied as well. The atomic concentration of the constituents was identified by Rutherford backscattering spectrometry. Optical properties were investigated by variable angle spectroscopic ellipsometry (VASE) analysis. The PL spectra were obtained at room temperature with a laser diode excitation source, operating at a wavelength of 375nm. Finally, we performed nanoindentation measurements to understand the deformation behavior of SiON films with the incorporation of Eu. The indentation hardness and Young’s modulus of the films were investigated, respectively, for different Eu concentrations and different deposition parameters.Reference[1] A. Moadhen, H. Elhouichet, M. Oueslati, and M. Férid, “Photoluminescence properties of europium-doped porous silicon nanocomposites,” J. Lumin., vol. 99, no. 1, pp. 13–17, 2002, doi: 10.1016/S0022-2313(02)00322-8.[2] Z. Lin R. Huang, H. Wang, Y. Wang, Y. Zhang, Y. Gao, J. Song, C. Song, H. Li, “Dense nanosized europium silicate clusters induced light emission enhancement in Eu-doped silicon oxycarbide films,” J. Alloys Compd., vol. 694, pp. 946–951, 2017, doi: 10.1016/j.jallcom.2016.10.132.[3] J. W. Miller, Z. Khatami, J. Wojcik, J. D. B. Bradley, and P. Mascher, “Integrated ECR-PECVD and magnetron sputtering system for rare-earth-doped Si-based materials,” Surf. Coatings Technol., vol. 336, pp. 99–105, 2018, doi: 10.1016/j.surfcoat.2017.08.051.

Roles of Oxygen Interstitial Defects in Atomic-Layer Deposited InGaZnO Thin Films with Controlling the Cationic Compositions and Gate-Stack Processes for the Devices with Subμm Channel Lengths.

Roles of oxygen interstitial defects located in the In-Ga-Zn-O (IGZO) thin films prepared by atomic layer deposition were investigated with controlling the cationic compositions and gate-stack process conditions. It was found from the spectroscopic ellipsometry analysis that the excess oxygens increased with increasing the In contents within the IGZO channels. While the device using the IGZO channel with an In/Ga ratio of 0.2 did not show marked differences with the variations in the oxidant types during the gate-stack formation, the device characteristics were severely deteriorated with increasing the In/Ga ratio to 1.4, when the Al2O3 gate insulator (GI) was prepared with the H2O oxidants (H2O-Al2O3) due to a higher amount of excess oxygen in the channel. Additionally, during the deposition process of the Al-doped ZnO (AZO) gate electrode (GE) replacing from the indium-tin oxide (ITO) GE, the thermal annealing effect at 180 °C facilitated the passivation of oxygen vacancy and the strengthening of metal-oxygen bonding, which could stabilize the TFT operations. From these results, the gate-stack structure employing O3-processed Al2O3 GI (O3-Al2O3) and AZO GE (OA) was suggested to be most suitable for the device using IGZO channel with a higher In content. On the other hand, the device employing H2O-Al2O3 GI and AZO GE exhibited larger negative shifts of threshold voltage (VTH) under positive-bias-temperature stress (PBTS) condition than the device employing O3- Al2O3 GI and ITO GE due to larger hydrogen contents within the gate stacks. Anomalous negative shifts of VTH were accelerated with increasing the In contents of the IGZO channel. When the channel length of the fabricated device were scaled down to submicrometer regime, the OA gate stacks successfully alleviated the short-channel effects.

Interpretation of hydrogen incorporation into radio frequency sputtered amorphous silicon based on Berg modelling

Incorporated hydrogen and its bonding configuration have an effect on the electrical and structural properties of hydrogenated amorphous silicon (a-Si) thin films. On one hand hydrogenization is known to be very efficient in reducing the density of dangling bonds responsible for deep levels in the bandgap; the technological process that carries out the incorporation of hydrogen improves the device parameters. On the other hand, the H–Si–H bonding configuration may negatively affect the microstructure of the amorphous lattice and promote the creation of voids.In this work the incorporation of hydrogen into radio frequency sputtered amorphous silicon thin films is interpreted by means of Berg-model handling the hydrogen incorporation as a reactive sputtering process involving ionization of molecular hydrogen followed by reactions between elemental target atoms to compound molecules. This approach is suitable for the interpretation of hydrogen incorporation into a-Si films based on the fact that the amount of incorporated hydrogen is proportional to the current. The imaginary and the real part of the dielectric function deduced from spectroscopic ellipsometry are investigated as a function of hydrogen flow. Using the results of spectroscopic ellipsometry and elastic recoil detection analysis presented earlier, as well as the equations of Berg model, the metal and compound sputtering rate and the sticking coefficient between silicon and hydrogen atoms are calculated.

In situ studies on atomic layer etching of aluminum oxide using sequential reactions with trimethylaluminum and hydrogen fluoride

Controlled thin film etching is essential for future semiconductor devices, especially with complex high aspect ratio structures. Therefore, self-limiting atomic layer etching processes are of great interest to the semiconductor industry. In this work, a process for atomic layer etching of aluminum oxide (Al2O3) films using sequential and self-limiting thermal reactions with trimethylaluminum and hydrogen fluoride as reactants was demonstrated. The Al2O3 films were grown by atomic layer deposition using trimethylaluminum and water. The cycle-by-cycle etching was monitored throughout the entire atomic layer etching process time using in situ and in real-time spectroscopic ellipsometry. The studies revealed that the sequential surface reactions were self-limiting versus reactant exposure. Spectroscopic ellipsometry analysis also confirmed the linear removal of Al2O3. Various process pressures ranging from 50 to 200 Pa were employed for Al2O3 etching. The Al2O3 etch rates increased with process pressures: Al2O3 etch rates of 0.92, 1.14, 1.22, and 1.31 Å/cycle were obtained at 300 °C for process pressures of 50, 100, 150, and 200 Pa, respectively. The Al2O3 etch rates increased with the temperature from 0.55 Å/cycle at 250 °C to 1.38 Å/cycle at 350 °C. Furthermore, this paper examined the temperature dependence of the rivalry between the removal (Al2O3 etching) and growth (AlF3 deposition) processes using the reactants trimethylaluminum and hydrogen fluoride. The authors determined that 225 °C is the transition temperature between AlF3 atomic layer deposition and Al2O3 atomic layer etching. The high sensitivity of in vacuo x-ray photoelectron spectroscopy allowed the investigation of the interface reactions for a single etching pulse as well as the initial etch mechanism. The x-ray photoelectron spectroscopy measurements indicated that the fluorinated layer is not completely removed after each trimethylaluminum exposure. The Al2O3 atomic layer etching process mechanism may also be applicable to etch other materials such as HfO2.

Optimization of optoelectronic performance of ITO/AG/ITO electrodes by using taguchi method and spectroscopic ellipsometry technique

In this study, a sandwich-structured electrode composed of indium tin oxide (ITO)/metal silver layer/ITO was prepared by the radio frequency magnetron sputtering method. We used the Taguchi method and spectroscopic ellipsometry (SE) analysis to optimize the geometrical structures of the electrodes and the sputtering power for the silver layer. While the Taguchi method allows us to rapidly optimize the manufacturing parameters, SE analysis enables us to precisely evaluate the thickness of each layer of the electrodes, so that the whole optimization process is more precise and effective. When the silver layers of different samples are sputtered under the same conditions, the difference in their thickness is often [Formula: see text] nm. Thus, it is difficult to understand the influences of the manufacturing parameters on the optoelectronic performance of the electrodes. Experimental results show that the thickness of the silver layer was the main factor affecting the transmittance and sheet resistance of the electrodes. However, the decisive factors for the Haacke index in the visible light range were the thickness of the bottom ITO film. Nonetheless, the signal-to-noise (S/N) ratios of some factors are quite close. Thus, further analyses are needed to understand this phenomenon. After optimization, the Haacke index is [Formula: see text], which is better than the 19.45 of the best sample, suggesting that this experiment has improved the optoelectronic properties of the electrode.

Elevated temperature spectroscopic ellipsometry analysis of the dielectric function, exciton, band-to-band transition, and high-frequency dielectric constant properties for single-crystal ZnGa2O4

We report the elevated temperature (22 °C ≤ T ≤ 600 °C) dielectric function properties of melt grown single crystal ZnGa2O4 using a spectroscopic ellipsometry approach. A temperature dependent Cauchy dispersion analysis was applied across the transparent spectrum to determine the high-frequency index of refraction yielding a temperature dependent slope of 3.885(2) × 10−5 K−1. A model dielectric function critical point analysis was applied to examine the dielectric function and critical point transitions for each temperature. The lowest energy M0-type critical point associated with the direct bandgap transition in ZnGa2O4 is shown to red-shift linearly as the temperature is increased with a subsequent slope of −0.72(4) meV K−1. Furthermore, increasing the temperature results in a reduction of the excitonic amplitude and increase in the exciton broadening akin to exciton evaporation and lifetime shortening. This matches current theoretical understanding of excitonic behavior and critically provides justification for an anharmonic broadened Lorentz oscillator to be applied for model analysis of excitonic contributions.