Variable Angle Spectroscopic Ellipsometry Research Articles

Combining spectroscopic techniques to determine the optical constants of powdered lactose.

A method for deriving the optical constants (n/k) of organic powdered materials using pressed pellets in the mid-infrared spectral range is introduced that combines variable angle spectroscopic ellipsometry and transmission spectroscopy. The approach is applied to anhydrous lactose, in which three different forms of pellets were pressed and measured: a pure lactose pellet and a mixed lactose/potassium bromide (KBr) pellet with a large analyte percentage were used for ellipsometric measurements, and a KBr transmission pellet with only a small analyte percentage was used for transmission measurements. The transmittance data provide an initial set of oscillators and improve the spectral fitting of weak absorption features (k<0.01). Ellipsometric data for the pure and mixed pellets are then fit simultaneously to derive the final n/k values for lactose from 6000-400cm-1. An alternative method just using the ellipsometric data from the mixed pellet and the transmittance data is also presented and shows good agreement with the multi-sample analysis, providing a simpler method for powders that do not press easily into pure pellets. Finally, the derived optical constants were used to model the reflectance data, demonstrating a good match with the measured reflectance spectra if non-idealities are included.

In‐Plane and Out‐of‐Plane Optical Properties of Monolayer, Few‐Layer, and Thin‐Film MoS2 from 190 to 1700 nm and Their Application in Photonic Device Design

Monolayer, few‐layer, and thin‐film MoS2 is synthesized using chemical vapor deposition (CVD) and thermal vapor sulfurization (TVS) methods. The complex refractive index of these samples is assessed using variable angle spectroscopic ellipsometry (VASE) measurements over a broad spectral range between 190 and 1700 nm. The ellipsometry data are sensitive to birefringence effects in the thickest thin‐film sample. These birefringence effects are investigated, and an analysis method is developed to extract the in‐plane and out‐of‐plane optical properties. The complex refractive index is then used to calculate reflectance, transmittance, and absorption of the MoS2 films using the transfer‐matrix method (TMM) and is matched with experimentally measured transmittance of the same samples. The modeled results show that the monolayer, few‐layer, and thin‐film MoS2 absorbs 7.4%, 12.6%, and 32.4% of the incident light, respectively, between 300 and 700 nm. When normalized to per unit‐thickness absorption, they absorb 12.1%, 5.9%, and 1.1% nm−1, respectively, clearly showing superior light–matter interaction in the monolayer and few‐layer films. These new complex refractive index data are further used to design optical coatings for these films to either confine absorption in a narrow bandwidth for photodetector applications or enhance broadband absorption for photovoltaic applications.

Synthesis of end group-functionalized PGMA-peptide brush platforms for specific cell attachment by interface-mediated dissociative electron transfer reversible addition-fragmentation chain transfer radical (DET-RAFT) polymerization

Polymer brush synthesis is a powerful approach to fabricate functional bio-interfaces. To enhance the control over brush synthesis and end groups, we have synthesized poly(glycidyl methacrylate) PGMA brushes with carboxylic acid end functional groups by interface-mediated dissociative electron transfer reversible addition-fragmentation chain transfer radical (DET-RAFT) polymerization on titanium surfaces. This method does not require the use of metals and occurs under mild conditions. The brushes obtained were analyzed comprehensively in order to understand how to control cell attachment behavior. The PGMA brushes synthesized by DET-RAFT polymerization were characterized by X-ray photoelectron spectroscopy (XPS), grazing angle Fourier transform infrared (GA-FTIR) spectroscopy, water contact angle measurements and variable angle spectroscopic ellipsometry. The terminal carboxylic acid functional groups were covalently conjugated with arginine-glycine-aspartic acid (RGD) and arginine-alanine-aspartic acid (RAD, negative control) peptides in one step. RGD selective attachment of NIH 3T3 fibroblasts was observed exclusively on PGMA-RGD brushes. Thus, a new versatile strategy has been validated to obtain functional biointerfaces for selective cell attachment in the absence of any metallic catalyst.

Ellipsometric study of the optical properties of TlInSeS layered crystal

TlInSeS optical properties at photon energy ranges from 0.96 to 5.06 eV have been determined by means of variable-angle spectroscopic ellipsometry (VASE). This energy range contains the fundamental band gap. The measured pseudo-dielectric ε(E) spectrum depicts different peaks. The spectrum is analyzed with reference of two inter-band transitions models that postulated for crystal semiconductors, explicitly, critical point parabolic band (CPPB) and standard critical-point (SCP) models. It is noted that both dielectric function models illustrates the plausible agreement with the experiment ε(E) spectra. The optical properties of the present sample as extension coefficient refractive index absorption coefficient and the normal-reflectance, are investigated. The elemental composition of TlInSeS system has been confirmed by means of Energy Dispersive X-ray fluorescence spectrometer (EDXRF).

Low-Temperature and Low-Pressure Silicon Nitride Deposition by ECR-PECVD for Optical Waveguides

We report on low-temperature and low-pressure deposition conditions of 140 °C and 1.5 mTorr, respectively, to achieve high-optical quality silicon nitride thin films. We deposit the silicon nitride films using an electron cyclotron resonance plasma-enhanced chemical vapour deposition (ECR-PECVD) chamber with Ar-diluted SiH4, and N2 gas. Variable-angle spectroscopic ellipsometry was used to determine the thickness and refractive index of the silicon nitride films, which ranged from 300 to 650 nm and 1.8 to 2.1 at 638 nm, respectively. We used Rutherford backscattering spectrometry to determine the chemical composition of the films, including oxygen contamination, and elastic recoil detection to characterize the removal of hydrogen after annealing. The as-deposited films are found to have variable relative silicon and nitrogen compositions with significant oxygen content and hydrogen incorporation of 10–20 and 17–21%, respectively. Atomic force microscopy measurements show a decrease in root mean square roughness after annealing for a variety of films. Prism coupling measurements show losses as low as 1.3, 0.3 and 1.5 ± 0.1 dB/cm at 638, 980 and 1550 nm, respectively, without the need for post-process annealing. Based on this study, we find that the as-deposited ECR-PECVD SiOxNy:Hz films have a suitable thickness, refractive index and optical loss for their use in visible and near-infrared integrated photonic devices.

Spin-speed independent thickness and molecular adsorption behaviour of polyelectrolyte multilayers

The science behind the build-up mechanism of polyelectrolyte multilayers is important for developing devices for various engineering applications. Here we, study the dependency of thickness of polyelectrolyte multilayer films, fabricated using spin-assisted layer-by-layer self-assembly of polyelectrolytes technique, with respect to varying spin-speed while keeping all other parameters of the fabrication process-window constant. The thickness measurements were performed using variable angle spectroscopic ellipsometry and atomic force microscopy. The experimentally observed results were validated mathematically using a Flory type theory. In addition, the bio-molecular adsorption studies on these polyelectrolyte multilayer films fabricated at various spin-speeds, were also quantitatively analyzed using fluorescence microscopy studies. It was seen that the effect of spin-speed on the thickness of polyelectrolyte multilayers was negligible. In addition, it was also observed that the bio-molecular adsorption modalities onto these substrates were also independent of the spin-speed. This finding prompts to develop low-cost alternative technologies for various biomedical engineering applications, like functionalized substrates for centrifugal assay for fluorescence-based cell adhesion, wherein stability of films against strong mechanical forces generated during spinning can play an important role.

Passivation mechanism of the high-performance titanium oxide carrier-selective contacts on crystalline silicon studied by spectroscopic ellipsometry

Variable-angle spectroscopic ellipsometry analysis is performed to study the impact of post-deposition annealing on the passivation performance of the heterocontacts consisting of titanium oxide and silicon oxide on crystalline silicon (c-Si) prepared by atomic layer deposition (ALD) for the development of high-performance ALD-TiO x /SiO y /c-Si heterocontacts. The highest lifetime of 1.8 ms is obtained for the TiO x /SiO y /c-Si heterocontacts grown at 175 °C after annealing at 275 °C for 3 min. With increasing annealing temperature, the TiO x layers of the TiO x /SiO y /c-Si heterocontacts become dominant. Furthermore, the amplitude of dielectric functions of the ALD-TiO x layer decreases as annealing temperature increases, which suggests that enhanced diffusion of Ti into SiO y interlayers at higher annealing temperature. The sufficient diffusion of Ti atoms into SiO y interlayers is caused by annealing at 275 °C for 3 min, yielding high-quality interface passivation.

Nanoscale TiO2 and Ta2O5 as efficient antireflection coatings on commercial monocrystalline silicon solar cell

In this paper, we report the enhancement of photon to electron conversion efficiency of commercial monocrystalline silicon solar cells after deposition of nanoscale TiO2 and Ta2O5 as an antireflection coating. The nanoscale TiO2 and Ta2O5 ARC’s remarkably enhanced PEC efficiency of m-Si solar cells from 17.18% to 17.87% and 18.8% respectably. The enhancement in PEC efficiency is predominantly attributed to the increase in fill factor from 36.8% to 36.9% and 37.2% after deposition of nanoscale TiO2 and Ta2O5 as ARCs respectively. The reflectance of nanoscale TiO2 ARCs increased from 27% to 43% within the wavelength range from to 530 nm and decreases to 34% with increasing wavelength. However, for Ta2O5 the reflectance was 11% at 370 nm and increased up to 29% in the studied wavelength range. The reduced magnitude of reflectance for Ta2O5 throughout the studied wavelength resulted in notable improvement of PEC efficiency compared to TiO2. The phase formation of nanoscale TiO2 characterized by x-ray diffraction reviles the presence of both anatase and rutile phase TiO2 whereas Ta2O5 displays amorphous nature. The oxidation state of titanium (Ti) and tantalum (Ta) was evaluated from x-ray photon emission spectroscopy and observed to be in the form of Ti4+ and Ta5+ chemical state. The nanoscale thickness of both TiO2 and Ta2O5 ARCs was acquired by variable angle spectroscopic ellipsometry and found to be 55.2 nm and 70.8 nm respectively, and the same was confirmed by measuring cross-section thickness of ARCs using a scanning electron microscope.

Functional characterization of nano-porous silicate-polymer composite for bovine serum albumin immobilization

The paper dwells upon the elaboration of a simple and energy-efficient approach for the “bottom-up” fabrication of porous polymeric film, which possesses unique surface, structural and bulk properties, followed by its comprehensive study through various characterization techniques. The fabricated film is multi-layered methyl silsesquioxane and suitably modified with the help of several treatments making the film compatible for biosensing applications. Film characterization reports the self- organized topography of the film deposited over the substrate and confirms the successful bonding between the polymers. The influence of the concentration of polypropylene glycol, which itself acts as thermally labile dendrimer, is studied by observing its bond formation ensuring polymer mixing by using FTIR. Energy dispersive x-ray analysis has been performed for the confirmation of elements. In addition to this, the nanoporous film is also studied with the help of variable angle spectroscopic ellipsometry for the determination of film porosity and refractive index. In this analysis, Cauchy model and graded-index model were chosen for data analysis and the Bruggeman effective medium approximation method was used for evaluating the optical constant. The surface of the porous film has been treated with different silane surfaces, characterized with the help of FTIR, UV-VIS, and AFM and envisioned for protein immobilization.

Optics of Inhomogeneous Thin Films with Defects: Application to Optical Characterization

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.

On the Influence of Hydrocarbon Precursors and Elemental Composition on the Dielectric Properties and Conduction Mechanism of Hydrogenated Silicon Carbonitride Thin Films

Ternary compound thin films have drawn interest since intermediate forms can be developed for materials with tunable properties. Among them, thin films of silicon carbonitride (SiCN) are widely used for protective hard coatings due to their superior mechanical and chemical properties such as high wear resistance, chemical and thermal stability at high temperatures, and hardness. Another area of application of SiCN thin films is as low dielectric constant materials, which are desired for replacing silicon oxide (SiO2) or silicon nitride (Si3N4) in integrated circuits (IC) and charge trapping capacitors. In general, SiCN is an intermediate compound between Si3N4 which is a highly transparent, wide band gap (5 eV) dielectric, and silicon carbide (SiC) with high mechanical durability [1].One of the most common techniques for the fabrication of SiCN thin films is plasma enhanced chemical vapour deposition (PECVD) with alkylsilazane precursors for high composition control [2]. Recently, we reported the compositional and mechanical properties of SiCN:H thin films, which were deposited using electron cyclotron resonance (ECR) PECVD with two different hydrocarbon precursors, acetylene (C2H2) and methane (CH4) [3, 4]. In the present work, we explore how film composition affects the electrical behaviour of the thin films. More specifically, we investigate the dielectric properties of SiCN:H thin films and the charge transportation and trapping mechanisms for different stoichiometries and film densities, as a function of the hydrocarbon precursor.Metal-insulator-semiconductor (MIS) capacitor type structures were formed on p-type (100) silicon substrates. Following the deposition, aluminum (Al) gate electrodes were sputtered for current-voltage (I-V) and capacitance-voltage (C-V) measurements operated at 1 MHz. The results were correlated with composition and density of SiCN:H thin films obtained from Rutherford backscattering spectrometry (RBS), elastic recoil detection (ERD), and variable angle spectroscopic ellipsometry (VASE) measurements. Finally, finite element modeling was performed by COMSOL to compare the capacitance characteristics in MIS structures of the thin films.[1] L.C Chen, C.K. Chen, S.L Wei, D.M Bhusari, K.H. Chen, Y.F. Chen, Y.C. Jong and Y.S. Huang. Crystalline silicon carbon nitride: A wide band gap semiconductor. Applied Physics Letters, 72(19), pp.2463-2465 (1998).[2] S. Bulou, L. Le Brizoual, P. Miska, L. de Poucques, R. Hugon, M. Belmahi, J. Bougdira. The influence of CH4 addition on composition, structure and optical characteristics of SiCN thin films deposited in a CH4/N2/Ar/hexamethyldisilazane microwave plasma. Thin Solid Films, 520(1), 245-250 (2011).[3] A. Abdelal, Z. Khatami and P. Mascher. Influence of Different Carbon Precursors on Optical and Electrical Properties of Silicon Carbonitride Thin Films. ECS Transactions, 97(2), 59 (2020).[4] Z. Khatami, G. B. F. Bosco, J. Wojcik, T. R. Tessler, P. Mascher. Influence of Deposition Conditions on the Characteristics of Luminescent Silicon Carbonitride Thin Films. ECS Journal of Solid-State Science and Technology, 7(2), N7 (2018).

Ellipsometric characterization of inhomogeneous thin films with complicated thickness non-uniformity: application to inhomogeneous polymer-like 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 SiOxCyHz 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.

Facile fabrication and optical characterization of nanoflake aluminum oxide film with high broadband and omnidirectional transmittance enhancement

Abstract In this study, the non-lithography fabrication of nanoflake aluminum oxide (Al2O3) film with omnidirectional broadband antireflection properties was demonstrated. The nanoflake Al2O3 films on glass slide and silicon wafer substrates were sequentially prepared by reactive magnetron sputtering and surface modification with alkali-treatment and hot water treatment processes. The morphologies, chemical compositions and optical properties of the prepared samples were characterized by field-emission scanning electron microscope (FE-SEM), photoelectron spectroscopy (PES), variable angle spectroscopic ellipsometry (VASE) and UV-VIS spectrophotometry with angle-dependent transmittance measurements, respectively. The results indicated that the thickness of the sputtered Al2O3 film was a crucial parameter for the growth of nanoflake for the nanostructure formed by alkali treatment with 0.1 M of potassium hydroxide (KOH) at room temperature and hot water treatment in deionized (DI) water at 80 °C for 3 min. The best optical performance was achieved with the single nanoflake film layer, resulting in enhanced optical transmittance exceeding 90% over the broad range of visible region at wide incident angle. This facile fabrication process of the nanoflake layer was offering the potential benefits for inexpensive omnidirectional anti-reflection (AR) coating in large area.

Comprehensive analysis of the composition determination in epitaxial AlxGa1-xAs films: A multitechnique approach

We present the determination of aluminum concentration x in epitaxial films of AlxGa1-xAs grown by Molecular Beam Epitaxy (MBE) on GaAs (100) substrates. A large variety of techniques such as quantification of atomic fluxes during MBE growth, high resolution X-ray diffraction (HRXRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), variable angle spectroscopic ellipsometry (VASE), photoluminescence (PL) and Raman spectroscopy (RS) have been used. Our Raman spectroscopy measurements show inconsistencies when analyzed with previously reported models. We also found variability within the same sample indicating that it is strongly influenced by other parameters like strain. We conclude that Raman spectroscopy can not be used as a reliable characterization technique without taking these effects into consideration. The combined analysis of all the other techniques allows us to reduce the uncertainty for the concentration value of each sample and correlate device specific quantities with the growth control parameters.

Determination of the refractive index of BaY2F8:Er3+ (0.5 mol% to 30 mol%) in the 300 nm to 1800 nm range by ellipsometry; a record-breaking upconversion material

This work reports the ellipsometric study of trivalent erbium (Er3+) doped monocrystalline barium yttrium fluoride (BaY2F8), which has recently been shown to be one of the best photon upconversion (UC) materials available. This spans the BaY2F8 applications in a large range of wavelengths, from ultraviolet (UV) to near-infrared (NIR). We detail the optical properties of BaY2F8: Er3+ (0.5 mol%, 10 mol%, and 30 mol%), measured via variable angle spectroscopic ellipsometry over a spectral range from 300 nm to 1800 nm, reporting for the first time the indices of refraction for BaY2F8:Er3+. The upconversion external photoluminescence quantum yield (ePLQY) of the BaY2F8:Er3+ samples have also been studied by exciting at λ=1493 nm. The highest ePLQY of BaY2F8 was found for the largest dopant concentration 30 mol% Er3+ reaching the value of 3.62% ± 0.01%, at an irradiance of (6.23 ± 0.45) ×10−2 W/cm2. The refractive index (λ= 589.3 nm) was determined to be 1.4808 ± 0.014 for 0.5 mol%, 1.4980 ± 0.003 for 10 mol%, and 1.5022 ± 0.006 for 30 mol%. Increasing Er3+ doping concentration increased the refractive index. All samples decreased monotonically with increasing wavelength. The Brewster angle of BaY2F8:Er3+ is observed to be ≈56∘, whilst the Abbe number of the samples was found to be as high as 124.62. These findings provide valuable insight into the optical properties of BaY2F8:Er3+ in the wide range of frequencies that is has proven useful.

On the origin of spectrally selective high solar absorptance of TiB2-based tandem absorber with double layer antireflection coatings

Despite significant efforts in developing tandem ceramic coatings for photo-thermal conversion applications, the underlying physics behind spectrally selective high absorptance and thermal stability of the ceramic absorbers remains to be addressed. In this perspective, TiB2/Ti(B,N)/SiON/SiO2 and Ti/TiB2/Ti(B,N)/SiON/SiO2 films were developed on stainless steel substrates (SS 304) using pulsed direct current and radio frequency magnetron sputtering. The addition of double layer antireflection coating not only increases the solar absorptance, but also the thermal stability of the tandem absorber. The amorphous coatings exhibit a high solar absorptance of 0.981 at room temperature and an acceptable thermal emissivity of 0.15 at 82 °C. Variable angle spectroscopic ellipsometry analysis reveals a gradient in the refractive indices of the individual layers from the substrate to the top surface. The coatings with and without titanium interlayer were found to be stable for 2 h in air up to 450 °C and 400 °C, respectively. Under vacuum, the coatings exhibited good thermal stability up to 250 h at 500 °C. We make an attempt to explain the high absorptance of the tandem absorber in terms of the composition and gradient in refractive indices across the stack.

Determining the refractive index and the dielectric constant of PPDT2FBT thin film using spectroscopic ellipsometry

Despite the recent increase in PPDT2FBT polymer thin film applications for optoelectronic devices, a comprehensive study of this material's optical dispersion properties is unavailable. The optical properties of the PPDT2FBT thin film is investigated using variable-angle spectroscopic ellipsometry (VASE) at ambient conditions. Knowledge of optical dispersion properties is essential for designing and fabricating optoelectronic devices such as solar cells, photodetectors, and photodiodes. In this research, we determined the dielectric function of PPDT2FBT thin film using the B-spline model and then reproduced the dielectric function using Psemi-Tri oscillators. We estimated the refractive index (n) of the thin film to be between 2.00 and 2.15 and the extinction coefficient (k) to be in the range of 1.14–1.39 at a wavelength of 632.8 nm. We further verified the estimated optical properties from the model using directly measured quantities such as transmission and absorption data obtained using the ultraviolet–visible (UV–Vis) spectrometer and thicknesses obtained using a surface profilometer. In addition, we determined the optical band gap of PPDT2FBT using the absorption coefficient. • The optical properties such as n, k of the PPDT2FBT polymer thin film are determined. • It was determined in a nondestructive way using variable-angle spectroscopic ellipsometry at ambient conditions. • We applied analytical methods to verify the determined optical properties.

Adhesive Wafer Bonding Using Ultra-Thin Spray-Coated BCB Layers

Adhesive wafer bonding based on BCB bonding layers is already a proven industrial technology. Besides its material properties (optical, mechanical) interesting for various applications the use of BCB for wafer bonding is bringing significant benefits such as good adhesion (high bond strength), low thermal budget, high tolerance to substrate surface quality (microroughness, scratches, small size particles, topography) and the ability to join practically any types of materials [1].Typically the BCB bonding layers are deposited on the surface of one or both substrates using spin-coating method for a final layer thickness ranging typically between 0.5 – 1 µm and up to 50 µm [2].During the bonding process the BCB material is softening and becomes viscous: this behavior can be both useful and not useful for applications.The softening of the BCB layer during bonding allows for compensation of surface defects (surface scratches), incorporation of small particles in the layer or even embedding of significant topography in the bonding layer (electrical interconnects, patterns) [3].The main negative effect of BCB softening is revealed when the two wafers have to be precisely aligned: the compression of the soft bonding layers introduces also a shift of the two wafers, resulting in a significant misalignment budget.One way of overcoming this issue is the partial crosslinking of the BCB material prior bonding [4]: in this approach the BCB is baked additionally or UV flood exposed after the post-coating soft bake. The bond quality is similar (voids, bond strength) to the standard process but with the major benefit of totally preventing the viscous flow during bonding.In this work we report the fabrication of ultrathin BCB bonding layers ranging from 25 µm to 125 µm by spray-coating deposition. Our study is addressing some important technical and economical items related to adhesive wafer bonding using BCB layers: Technical: the use of a thin BCB layer just with soft baking will still allow for extremely low compression of the layer but with no major misalignment budget development. This way it can be used simply as a low temperature bonding layer with the advantage of maintaining the alignment accuracy.Economical: thinner layers will obviously reduce the amount of precursor material used for coating, while the use of spray coating instead of spin coating will further reduce the amount. In spray coating the layer uniformity is not reached by spin-drying (when also a loss of material occurs) but by the spray coating itself. A proprietary spray coating technology developed in house was used to deposit BCB layers on Si test wafers. This technique facilitates the precise droplet size control and therefore allows for obtaining optimized and homogenous ultra-thin layers.For BCB layers quality assessment we used Variable Angle Spectroscopic Ellipsometry (VASE) – for layer thickness and surface microroughness, Atomic Force Microscopy (AFM) – surface microroughness, layer thickness (by scratch in the layer) and Scanning Electron Microscopy (SEM) – precise layer thickness. The redundant use of the three methods is important for results confirmation as they are using significantly different dimensions range for the sampling: SEM is using nanometer range, AFM in micrometer range while VASE is working in millimeter range.In order to successfully adopt the Omnispray® technology in industrial processes the process reproducibility is a key factor. In order to study this aspect, the wafer-to-wafer as well as lot-to-lot variations were qualified in this work.Bonding quality was assessed using Scanning Acoustic Microscopy (SAM) for voids inspection. References F. Niklaus, G. Stemme, J.-Q. Lu , and R. J. Gutmann, „Adhesive wafer bonding“, J. Appl. Phys., 99, 031101 (2006)V. Dragoi, T. Glinsner, G. Mittendorfer, B. Wieder, and P. Lindner, „Adhesive wafer bonding for MEMS applications“, SPIE Proc. Vol. 5116, 160 (2003).V. Dragoi, M. Alexe, M. Hamacher, and H. Heidrich, “Microring resonators fabrication by BCB adhesive wafer bonding”, ECS Trans., 16(8), 105 (2008).F. Niklaus, R.J. Kumar, J.J. McMahon, J. Yu, T. Matthias, M. Wimplinger, P. Lindner, J.-Q. Lu, T.S. Cale, and R.J. Gutmann, “Effects of bonding process parameters on wafer-to-wafer alignment accuracy in benzocyclobutene (BCB) dielectric wafer bonding”, MRS Proc. Vol. 863, B10.8.1 (2005).

Determining shape of thickness non-uniformity using variable-angle spectroscopic ellipsometry

The effects of thickness non-uniformity on measured optical quantities must be often considered in the optical characterization. The effects of thickness non-uniformity can be taken into account by averaging the Mueller matrices over the distribution of local thicknesses within the measured area. The distribution of local thicknesses can be assumed in a certain form (e.g. the uniform distribution), or it can be derived on the basis of a model assuming a certain shape of thickness non-uniformity. The latter approach is especially useful for the variable-angle spectroscopic ellipsometry since it can take into account dependence on the incidence angle due to the changes in the size of the light spot. This paper presents results of the optical characterization of three polymer-like thin films highly non-uniform in thickness using variable-angle spectroscopic ellipsometry. The shapes of the thickness non-uniform films are determined on the basis of a model assuming local thicknesses given by quadratic polynomials in coordinates along the surfaces of the films. The studied areas on the films were also measured by the imaging spectroscopic reflectometry, which provides a more direct method to determine local thicknesses. The results achieved using the imaging spectroscopic reflectometry and variable-angle spectroscopic ellipsometry were then compared.

Thin SiNC/SiOC Coatings with a Gradient of Refractive Index Deposited from Organosilicon Precursor

In this work, optical coatings with a gradient of the refractive index are described. Its aim was to deposit, using the RF PECVD method, films of variable composition (ranging from silicon carbon-oxide to silicon carbon-nitride) for a smooth change of their optical properties enabling a production of the filter with a refractive index gradient. For that purpose, two organosilicon compounds, namely tetramethyldisilazane and hexamethyldisilazane, were selected as precursor compounds. The results reveal better optical properties of the materials obtained from the latter source. Depending on whether deposited in pure oxygen atmosphere or under conditions of pure nitrogen, the refractive index of the coatings amounted to 1.65 and to 2.22, respectively. By using a variable composition N2/O2 gas mixture, coatings of intermediate magnitudes of “n” were acquired. The optical properties were investigated using both UV-Vis absorption spectroscopy and variable angle spectroscopic ellipsometry. The chemical structure of the coatings was studied with the help of Fourier transform infrared and X-ray photoelectron spectroscopies. Finally, atomic force microscopy was applied to examine their surface topography. As the last step, a “cold mirror” type interference filter with a gradient of refractive index was designed and manufactured.