Ellipsometry Characterization Research Articles

Spectroscopic ellipsometry characterization of polymer–fullerene blend films

In this work, we have used spectroscopic ellipsometry (SE) and atomic force microscopy (AFM) to characterize the properties of blend films commonly used in organic solar cells, namely poly[3-hexylthiophene-2,5-diyl] (P3HT): [6,6]-phenyl C61 butyric acid methyl ester (PCBM) blends. The blend films were prepared using different solvents, and for different ratios of P3HT:PCBM in order to change the surface roughness and phase separation in the blends. The obtained SE results were analyzed with and without the surface roughness correction to examine how the morphology affects the optical properties.

Comparative investigation of the Si/SiO2 interface layer containing SiC crystallites using spectroscopic ellipsometry, ion beam analysis and XPS

AbstractIt is known from earlier publications that SiC crystallites grow at the interface of a Si/SiO2 system during heat treatment in CO containing ambient. First 100 nm thick SiO2 layers were thermally grown on <100> Si substrates. The Si/SiO2 structures were heat treated in CO containing atmosphere for 20 and 102 hours at 1190 oC for investigation. Spectroellipsometry was applied to study the microstructure of the heat‐treated samples. We assumed a layer at the Si/SiO2 interface that contains crystalline Si and crystalline SiC. After 20 and 102 hour annealing the layer thickness extracted from evaluation of ellipsometric data was 15 nm and 25 nm, the volume fraction of SiC was 38% and 89%, respectively. To confirm the results of the ellipsometry characterization we applied ion beam analysis and X‐ray photoelectron spectroscopy. For determination of the carbon content a 4He+ ion beam of 3.5 MeV was selected to take advantage of the scattering cross section of carbon at 165o detection angle is about six times larger than the Rutherford type one. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ellipsometry characterization of bulk acoustic wave filters

AbstractA complete bulk acoustic wave (BAW) technology was developed to meet the needs of modern wireless communication equipment. Wide spectral range spectroscopic ellipsometry was used to characterize both the thin piezoelectric aluminum nitride film and the acoustic reflector within the tight specifications required by electrical functionality. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Spectroscopic ellipsometry characterization of the optical properties and thermal stability of ZrO2 films made by ion-beam assisted deposition

The optical properties, interface structure, and thermal stability of the ZrO2 films grown on Si(100) were investigated in detail. A 2nm thick interfacial layer (IL) is formed at the ZrO2–Si interface for the as-grown ZrO2. The optical constants of ZrO2 films and IL correspond to amorphous-ZrO2 and amorphous-SiO2, respectively. The oxidation and IL growth at 900°C, as a function of annealing time, exhibit a two-step behavior with a slow and a fast growth-rate zones. The transition from a zone of slow to fast rate is attributed to structurally modified ZrO2 facilitating the faster oxygen transport to the ZrO2∕Si interface.

Spectroscopic ellipsometry characterization of TiO 2 thin films prepared by the sol–gel method

TiO 2 thin films were prepared on SiO 2/Si(100) substrates by the sol–gel process. XRD results indicate that the major phase of TiO 2 thin films is anatase. The surface morphology and cross-section are observed by FE-SEM. The surface of thin films is dense, free of cracks and flat. The average grain size is about 60–100 nm in diameter. The thickness of single layer TiO 2 thin films is about 60 nm, which increases with the concentration of solution. Ellipsometric angles ψ, Δ are investigated by spectroscopic ellipsometry. The optical constant and the thickness of TiO 2 thin films are fitted according to Cauchy dispersion model. The results reveal that the refractive index and the extinction coefficient of TiO 2 thin films in wavelength above 800 nm are about 2.09–2.20 and 0.026, respectively. The influences of processing conditions on the optical constants and thicknesses of TiO 2 thin films are also discussed.

The influence of annealing (900◦C) of ultra-thin PECVD silicon oxynitride layers

This work reports on changes in the properties of ultra-thin PECVD silicon oxynitride layers after high- temperature treatment. Possible changes in the structure, composition and electrophysical properties were investigated by means of spectroscopic ellipsometry, XPS, SIMS and electrical characterization methods (C-V, I-V and charge- pumping). The XPS measurements show that SiOxNy is the dominant phase in the ultra-thin layer and high-temperature annealing results in further increase of the oxynitride phase up to 70% of the whole layer. Despite comparable thickness, SIMS measurement indicates a densification of the annealed layer, because sputtering time is increased. It suggests complex changes of physical and chemical properties of the investigated layers taking place during high-temperature annealing. The C-V curves of annealed layers exhibit less frequency dispersion, their leakage and charge-pumping currents are lower when compared to those of as-deposited layers, proving improvement in the gate structure trapping properties due to the annealing process.

Applying shallow nitrogen implantation from rf plasma for dual gate oxide technology

The goal of this work was to study nitrogen implantation from plasma with the aim of applying it in dual gate oxide technology and to examine the influence of the rf power of plasma and that of oxidation type. The obtained structures were examined by means of ellipsometry, SIMS and electrical characterization methods.

Effect of oxygen partial pressure on the structural and optical properties of ZnO film deposited by reactive sputtering

Effects of variation of the oxygen partial pressure on the structural and optical properties of zinc oxide (ZnO) thin films prepared by reactive radio-frequency sputtering were investigated. Measurements by X-ray diffraction (XRD) and atomic force microscopy (AFM) indicated that the crystallinity and the surface morphology were sensitive to the oxygen partial pressure. The interfacial and optical properties of the targeted films were investigated by spectroscopic ellipsometry (SE) characterization. Based on Tauc-Lorentz (TL) model, the optical constants of ZnO films were tentatively extracted in the photon energy ranging from 1.5 to 6.0 eV. Analyses by XRD and SE revealed that the oxygen partial pressure had effect on the orientation of the ZnO films, the surface morphology, the packing density, and the interfacial layers. And the relationship between crystallinity and interfacial layer, as well as the relationship between surface roughness and packing density was discussed. All these had a significant impact on the optical properties illustrated by SE analysis.

Spectroscopic ellipsometry characterization of ZrO 2 thin films by nitrogen-assisted reactive magnetron sputtering

Spectroscopic ellipsometry (SE) with photon energy 0.75–6.5 eV at room temperature has been used to derive the optical properties of high- k ZrO 2 thin films on Si(1 0 0) substrates prepared by nitrogen-assisted, direct current reactive magnetron sputtering. The Tauc–Lorentz dispersion method was adopted to model the optical dispersion functions of the thin films as a function of annealing temperature. Excellent agreement has been found between the SE fitting results and X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR) results, indicating that our model adequately described the measured SE data. Optical band gaps ( E g) were also obtained based on the extracted absorption edge. Our results suggest that nitrogen-assisted process can effectively limit the interfacial layer growth in high- k oxides.

Spectroscopic ellipsometry characterization of ultrathin silicon-on-insulator films

Spectroscopic ellipsometry is used to characterize the optical response of a series of ultrathin silicon-on-insulator (SOI) films with thickness ranging from 50to2nm. Due to the potential barrier formed by the buried oxide layer and the interface with air, the electrons in the top silicon layer of the thinner samples experience dimensional confinement effects. Transition energies were extracted for the E1 and E2 critical points using reciprocal space analysis. This method offers improved accuracy over conventional regression-based techniques, such as line shape fitting, by eliminating error due to correlation among multiple fit parameters. It is shown that dimensional confinement increases the E1 transition energy of ∼3.375eV for bulk silicon to 3.38, 3.393, 3.42, and 3.45eV for the ∼10, ∼7, ∼4, and ∼2nm SOI films, respectively. This trend resembles the 1∕L2 law predicted by quantum mechanical considerations for a confined particle. The dependence of these critical point transitions is investigated as a function of film thickness L. Additionally, the E2 critical point transition energy is found to be much less affected by quantum confinement, contrary with theoretical predictions.

FTIR and ellipsometry characterization of ultra-thin ALD TaN films

In this paper, Fourier-transform infrared (FTIR) spectroscopy and ellipsometric spectroscopy were used to characterize the optical properties of atomic layer-deposited (ALD) ultra-thin TaN films on a Si(1 0 0) single crystal. The analysis of FTIR spectra indicates that the incorporated impurities are in the form of radicals of NH x , CH x and OH x . SiH x is also detected due to interfacial reactions between NH x and the Si substrate native oxide. These H-containing radicals can be removed by post-annealing the samples. The vibration of Ta–N bonding is at the wavenumber of 1190 cm −1, which is independent of the film thickness and post-annealing temperature. The results of ellipsometric spectra show that the band gaps are 3.28 eV, 2.65 eV and 2.50 eV as the films thicknesses are 1 nm, 5 nm and 10 nm, respectively. A slight red-shift of the band gap takes place after annealing the ultra-thin films. The mechanisms of the film optical properties were analyzed in the paper.

Spectroscopic ellipsometry characterization of nitrogen-incorporated HfO2 gate dielectrics grown by radio-frequency reactive sputtering

Spectroscopic ellipsometry with photon energy 0.75–6.5 eV at room temperature has been used to derive the optical properties of nitrogen-incorporated HfO2 films on Si(100) substrates grown by radio-frequency reactive sputtering using different N2∕(N2+O2+Ar) gas ratios from 20% to 50%. Excellent agreement has been found between the experimental and the simulated spectra, in which an empirical dielectric dispersion relation based on Tauc-Lorentz model has been successfully adopted. Increases in the refractive index n and the extinction coefficient. k, with increases in nitrogen-incorporation content are observed due to the nitrogen-incorporation-induced higher packing density. The change of the complex dielectric functions and reduction in the optical band gap with an increase in nitrogen concentration resulting from the effect of the nitrogen-incorporation on the structure are discussed in detail.

Thermosensitive poly(allylamine)-g-poly(N-isopropylacrylamide): synthesis, phase separation and particle formation

Grafting of poly(N-isopropylacrylamide) (PNIPAAm) having carboxylic groups at one end onto poly(allylamine) (PAH) in the presence of water soluble carbodiimide has yielded PAH-g-PNIPAAm copolymers with grafting ratios of 50, 29 and 18, respectively. These thermosensitive copolymers exhibit a lower critical solution temperature (LCST) at 34°C at a temperature increase cycle regardless of their grafting ratios, a temperature identical to that of PNIPAAm-COOH oligomers. Temperature cycling reveals completely reversible polymer aggregation and dissolution above and below the LCST, respectively. Much smaller particle sizes are observed by scanning force microscopy and transmission electron microscopy compared to dynamic light scattering. A porous sphere model is suggested to depict the structure of the particles formed above the LCST, by which the dependence of the particle sizes on their grafting ratios is interpreted taking into account the surface tension and the spatial aggregation distance. Finally, to demonstrate the capability of the copolymers being used as thermosensitive polyelectrolytes, assembly onto multilayers is conducted and the increase of layer thickness is confirmed by small angle X-ray scattering and ellipsometry characterizations.

Spectroscopic ellipsometry characterization of ZrO2 films on Si(100) deposited by high-vacuum-metalorganic chemical vapor deposition

The integration of high-k dielectric materials into semiconductor devices requires nondestructive, fast, and accurate characterization methods. Spectroscopic ellipsometry (SE) is an outstanding candidate for this purpose. A multisample variable-angle SE method was used to characterize ZrO2 samples deposited on Si(100) by high-vacuum chemical vapor deposition. Proper modeling of the optical properties of the interfacial layer is found to be the key to accurate characterization of ZrO2 films. Based on a stacking model consisting of an effective medium approximation surface-roughness layer, a Tauc–Lorentz (TL) layer to represent the ZrO2 layer, and a second TL layer to represent the interfacial layer, we accurately extract both thickness and optical constants of each layer. The extracted surface-roughness and thickness values were confirmed by atomic force microscopy and transmission electron microscopy results. The optical constants of the interfacial layer suggest that the interfacial layer is composed of nonstoichiometric zirconium silicate.

Infrared ellipsometry characterization of conducting thin organic films

Infrared spectroscopic ellipsometry for wave numbers from 333 to 4000 cm −1 is demonstrated as a useful technique for characterization of structural, vibrational, and free-charge-carrier properties of conducting organic thin layers deposited on electrically conducting as well as on isolating substrates. Pentacene and poly(3,4-ethylenedioxy thiophene)/poly(styrenesulfonate) (PEDOT:PSS) are studied exemplarily. For both materials, the infrared dielectric functions are reported, which can serve as fingerprints for multiple-layer structures analysis. PEDOT:PSS layers deposited onto n-type and p-type silicon substrates reveal different conductivity response, whereas the IRSE data show that the pentacene layers on glass are rendered highly resistive.

Spectroscopic ellipsometry characterization of ZnO–In 2O 3 systems

The pseudobinary oxides of zinc-indium-oxide systems (ZnO–In 2O 3) with high conductivity and transparency were the subject of this work. The films were prepared on heated glass substrates by spray pyrolytic decomposition of zinc chloride with indium chloride in distilled water. The spectroscopic ellipsometry and atomic force microscopy (AFM) were used to analyze the optical properties and the surface structures of ZnO–In 2O 3 films deposited. The ellipsometric parameters tan ψ and cosΔ were measured using a rotating polarizer spectroscopic ellipsometer in the wavelength range (0.4–1.5 μm) at two incident angles of 65 and 70°. The layer roughness was modeled as an effective mixture of 50% ZnO–In 2O 3 and 50% voids in good agreement with the direct AFM measurement. The complex refractive index and electrical resistivity for several [Zn]/ [Zn+In] ratios (at.%) were determined and analyzed.

Ellipsometry characterization of oxidized copper layers for chemical mechanical polishing process

Oxidized copper layers prepared in hydrogen peroxide for chemical mechanical polishing (CMP) have been characterized using spectroscopic ellipsometry. In the spectral analysis of the oxidized copper layers, Lorentz oscillator model is used. Lorentz model was assumed a graded layer based on glow discharge spectroscopy analysis, the precise optical constants and thickness of oxidized copper layers was determined. Its optical constants and FT-IR analysis indicate that the oxidized copper layers consist of CuO and voids. The proportion of void was increases with growth of the oxidized layers. These analyses are useful to investigate an advanced CMP process using organic acid.

Heavy-ion ERDA and spectroscopic ellipsometry characterization of a SiOC:H layered structure as functional coating on polymeric lenses

In order to improve the optical and mechanical performance of plastic ophthalmic lenses the use of surface coatings is necessary. However, the application of such coatings can be limited by bad adhesion to the substrate. One way to overcome this drawback is the use of a layered structure consisting of an adherent layer, an abrasion resistant hard layer and an antireflective (AR) multilayer (ML) stack. In this work we study the preparation of SiO x C y :H layered coatings to increase the mechanical durability of polymeric substrates and to accommodate gradually an external dielectric SiO 2/TiO 2 AR-ML. The coatings were grown by plasma assisted chemical vapor deposition (PACVD) using a mixture of hexamethyldisiloxane (HMDSO) and O 2. The possibility of producing the whole layered stack by adjusting the HMDSO:O 2 ratio was demonstrated. The composition and elemental profiles of the different layers were measured by ERDA using 35 MeV Cl-ions. A polymeric-like gradient layer could be formed followed by a buffer layer Si 28O 47C 15H 10 with a nearly constant composition. The variation of the elemental composition does not affect significantly the optical properties, which are close to that of SiO 2.

Gate oxide metrology and silicon piezooptics

We describe the use of spectroscopic ellipsometry and other characterization techniques for gate oxide process metrology in manufacturing of CMOS transistors for the 130 nm node and beyond. Specifically, we describe the difficulties associated with the introduction of silicon-on-insulator (SOI) substrates, alternative gate dielectrics (silicon oxynitride or metal oxides), and strained Si channels. We predict that spectroscopic ellipsometry by itself will no longer be sufficient for gate oxide metrology, which will make the CMOS gate stack process much more difficult to control.

FTIR phase-modulated ellipsometry characterization of hydrogenated amorphous silicon nitride thin films with embedded nanoparticles

FTIR phase-modulated ellipsometry was used to characterize the time evolution of the optical properties of hydrogenated amorphous silicon nitride thin films with embedded nanoparticles (ns-SiN x :H). Films were produced by PECVD at room temperature using both continuous wave and square wave r.f. power modulation from gas mixtures of SiH 4, NH 3 and Ar. The flow ratio R=[NH 3]/[SiH 4] was varied from 1 to 6. When ns-SiN x :H thin films are exposed to the open air they undergo a spontaneous oxidation process. Dense films deposited at low flow ratios and continuous wave r.f. power are partially oxidized by O, as is denoted by the appearance of the SiO stretching band at 1070 cm −1. Porous films deposited with square wave modulated r.f. power and with continuous wave r.f. power at high flow ratios are fully oxidized by moisture; the IR absorption bands related to N decrease and the IR absorption bands corresponding to H 2O appear. TEM and HR-TEM characterization revealed that films deposited with continuous wave r.f. power present a columnar structure, while films deposited with square wave modulated r.f. power consist of a disordered arrangement of nanoparticles. SAED was used to probe the crystallinity of the nanoparticles.