ICMCTF2000 Session CP: C Poster

Zinc oxide (ZnO) thin films were prepared on a borosilicate glass substrate by a steered and shielded reactive vacuum arc deposition method. The cathode spot was driven on the 64-mm diameter cathode surface by weak and strong permanent magnets, placed behind the cathode. The strengths of radial magnetic flux at the cathode edge were 1.0 mT and 5.5 mT, respectively. The macrodroplet shield plate was placed at 100 mm from the cathode and the substrate was placed at 100 mm from the shield plate. The arc was operated at DC 30 A and the process pressure was varied from 0.1 to 5.0 Pa. No bias was applied to the substrate. The substrate temperature was below 60° C. The crystalline state, transmittance, deposition rate, and resistance of the film were analyzed.

From the X-ray diffraction analysis, all film were found to have ZnO (200) peak, indicating c-axis orientation. Well-crystallized films were obtained at 0.1 Pa and 5.0 Pa for weak magnet, although at 0.5 to 3.0 Pa for strong magnet. A clear relation existed between the crystallinity and the transparency. Namely, highly transparent, more than 90% at visual region, films were obtained at the same conditions. The electrical resistance, which were coarsely measured based on ohmic law, were 10^-4 to 10^-5 Ωcm order. Moreover, the erosion rate of the cathode was almost constant against the pressure for weak magnet, although the erosion rate was decreased against the pressure for strong magnet. Differently from this tendency, the deposition rate for weak magnet increased with the pressure. For strong magnet, the maximum deposition rate, 35 nm/min, was obtained at 1 Pa.

Infrared ellipsometry has emerged in the past few years as a powerful, sensitive and non-intrusive optical technique for the characterization of surfaces, interfaces and thin films. This technique is used in order to obtain information about an optical system that modifies the state of polarization. First applications, using grating or prism spectrometers, were limited in performance. Also the lack of good light sources and efficient polarizers contributed to this limited performance. The recent improvements of Fourier transform techniques and of polarizers, such as tandem wire grid polarizers formerly developed in our group, helped to overcome such problems.

Among the different techniques in use in ellipsometry we opted for a rotating compensator ellipsometer. This technique offers several advantages compared to others ellipsometry methods; like the non-ambiguous determination of the phase shift coefficient, the insensivity to source, and detector polarization and the ability to measure the properties of metals. However, one principal fact prevented a widespread application of rotating compensator ellipsometry for spectroscopic purposes. This fact was the absence of a good spectroscopic retarder. Our group is currently developing a compensator that will allow measurements in a spectral range of 2.5 to 10 microns.

Improvement in measurement speed has also been studied. An accurate synchronization between the different rotating elements of the ellipsometer and the spectrometer has been achieved. The recent performances obtained allow us to ponder the development of in-situ applications in the near future.

The recent discovery of visible light emission from Si nanostructures such as porous Si, Si ultrafine particles and Si doped SiO₂ glass thin films has attracted wide attention because of their potential application to Si light emitting devices. From the practical viewpoint, the Si nanostructures have a serious drawback on the visible light luminescence that the emission spectra are extremely broad and less controllable. It is the purpose of the present report to show a novel technique for obtaining monochromatic light with a desired wavelength from the broad emission spectrum of the Si doped SiO₂ glass using a conventional method, Fabry-Perot cavity composed of twin reflectors.

In the present study, we fabricated a new optical resonator consisted of a light emitting active layer based on the Si doped SiO₂ glass sandwiched by a base multilayered reflector and a top metal one.

The optical resonator as well as the active layer was fabricated by the ion beam sputter-deposition (IBSD) technique. A dual target was introduced: one is a Si/SiO₂ composite target for Si doped SiO₂ glass film deposition and the other is CeO₂. The dielectric multilayered reflector was alternately sputter-deposited using the above two targets. The refractive indices of the Si doped SiO₂ and CeO₂ films fabricated by the present method were 1.5 and 2.4, respectively. Using these values, a multilayered reflector for a desired wavelength was designed along the established design rule. The maximum reflectivity of a multilayered reflector composed of 10pairs of Si doped SiO₂ and CeO₂ films was about 93 % at 580nm.

Since the Si doped SiO₂ glass film as an active layer showed no photoluminescence (PL), the samples were heat-treated in nitrogen gas: PL intensity increased with increasing annealing temperature up to about 900 °C. The luminescent Si doped SiO₂ glass showed extremely broad PL spectra, typically, the full width of half maximum (FWHM) being about 1 eV. When the active layer was placed in a cavity composed of the above-mentioned multilayered and metal reflectors, the FWHM decreased down to 0.3 eV. Significant improvement is expected to be attained by increasing pair number of the multilayered reflector.

Anti-reflectant films or solar cells on polymer films, namely, flexible optical devices are recently attracted attentions. Thus, the demands to deposit oxide optical films such as TiO₂ and SiO₂ at low substrate temperature are emphasized. In this study, we have developed oxygen radical beam assisted evaporation to deposit oxide films by irradiation of oxygen radical (atomic oxygen) beam. The oxygen radicals are very active with the potential energy. Therefore the oxygen radical beam irradiation during the deposition is able to enhance oxidation reaction on the substrate at low temperature. The aim of this study was to deposit high quality optical films on the substrate at room temperature by the oxygen radical beam assisted evaporation.

The oxygen radical beam was irradiated to oxidize the metal films which are simultaneously evaporated from electron beam source. A flux of the oxygen radical beam supplied from an oxygen plasma source was of the order of 10¹⁵ radicals/cm²-s with slight ions. Titanium and silicon were used as the evaporated materials.

The stoichiometric TiO₂ and SiO₂ films with amorphous structure were deposited at room temperature. The optical properties of these films showed that absorption decreased and refractive index did not change, as compared with the films irradiated only neutral oxygen gas. The increase of the ratio of the flux of irradiated oxygen radical beam to one of evaporated titanium and silicon brought about marked decrease of absorption in TiO₂ and SiO₂ films. These results indicated that the oxygen radical beam irradiation was effective in deposition of high quality optical films at low temperature. Moreover multi-coating anti-reflectant films have studied as an application for the flexible optical devices.

A long-standing interest in small metal clusters embedded in dielectric materials has been recently rejuvenated due to their potential for future optical and photonics devices utilizing third-order optical nonlinearity. The peculiar optical response of these materials is known to originate from the surface plasmon resonance in metal particles and the resultant enhancement of local electric field. Accordingly, the volume fraction and the microstructure of incorporated metal clusters, together with the dielectric constant of a dielectric matrix, are key factors that control the optical properties of these materials.

In this work, we used sputtering to fabricate composite films of a metal (Au or Sn) and a dielectric (SiO₂ and/or TiO₂), and post-deposition annealing to modify the microstructure of embedded metal clusters. Note that metal-dielectric composite films in mostly existing studies consist of a high melting-temperature metals such as Au, Cu or Ag and a low refractive index dielectrics such as SiO₂, Al₂O₃, or MgO. In the case of TiO₂-based composite film, a large third-order optical nonlinearity was reported to benefit from a high refractive index of TiO₂. It should be pointed out, however, that crystallization of TiO₂ during post-deposition annealing could render the subsequent analysis unnecessarily complicated. For this reason, we studied composite films of a metal and a mixed-dielectric matrix of TiO₂ stabilized with SiO₂.

In this study, all indium tin oxide(ITO) films were grown by ion beam assisted deposition (IBAD) technique on glass and organic substrates without substrate heating and the effects of oxygen gas flow rate to the ion source chamber on the properties of room temperature deposited ITO films were investigated. Plasma characteristics in the ion source chamber such as oxygen ions and atomic oxygen radicals as a function of oxygen flow rates were observed using optical emission spectroscopy(OES). In addition, oxygen ion density was measured by a Faraday cup.

The increase of oxygen flow rates at a fixed rf power and a fixed ITO evaporation rate decreased oxygen ion density in the plasma and ion beam flux to the substrate, however, it increased the atomic oxygen radical density. Despite the decrease of oxygen ion beam flux to the substrate, the optical transparency of the deposited ITO films was increased. It appears to be from reactive atomic oxygen radical(O^{*! !}) which increases the reaction between the evaporated ITO and oxygen. In the IBAD technique, not only the oxygen ions bombarding to the substrate but also reactive oxygen radicals play an important role, therefore, a clear understanding on the role of reactive atomic oxygen and relationship between the amounts of oxygen radicals and the properties of deposited ITO thin films is required to obtain highly transparent and conductive ITO deposited at room temperature. In this study, the relative effects of oxygen ion beam and the reactive atomic oxygen on the electrical and optical properties of deposited ITO were investigated in details.

Recent development trends for transparent conductive oxide(TCO) thin films can be summarized into high conductivity, transmmision, and chemical stability as well as lower deposition temperature. From a view point of these requirements, fluorine-doped tin oxide(FTO) thin film fabricated by ozone assisted-metal organic chemical vapor deposition(MOCVD) has many possibilities. By introducing oxygen containing about 5mol% ozone, the substrate temperature could be reduced significantly at the same growth rate of the tin oxide grown using pure oxygen because ozone decomposes into reactive oxygen(O^*) and oxygen molecule above 200°C, and the decomposed reactive oxygen atom reacts with TMT(tetramethyltin). FTO has a high conductivity by two defects, that is, intrinsic defect and dopant. An oxygen vacancy in the film creates a donor level in the energy bandgap. Doped fluorine contributes to the increase of free electron concentration. In spite of considerable amount of experimental results on FTO films, there is a lack of knowledge concerning the relation of two defects. In this study, the effects of the two defects varied by deposition conditions on the properties of the films will be discussed.

The chemical composition of the films was analyzed by X-ray photoelectron spectroscopy(XPS). The crystallinity and other structural properties were measured by X-ray diffractometry(XRD). The electrical properties such as resistivity, carrier concentration, and mobility were analyzed using Hall measurement. An UV-spectrophotometer was used to measure the optical transmittance of the films.

The use of oxygen containing ozone instead of pure oxygen reduced substrate temperature by 100~150°C while maintaining the same growth rate. The fluorine doped tin oxide thin films prepared using ozone and HF as a dopant showed the resistivity in the range from 10^-3 Ωcm to 10^-4 Ω cm depending on the relative amount of oxygen vacancy and doped fluorine, optical transmittance higher than 80% at the thickness with less than 4000Å, and the mobility from 10 to 20cm²/Vs.

Tin doped indium oxide (ITO), as an electrode material for flat panel display (FPD) devices such as LCDs, FEDs, VFDs, ELDs requiring high image quality and fast switching speeds, has the lowest electrical resistivity(~10^-4ohm-cm) and the highest optical transparency(above 85% atλ=550nm). Recently, there has been a growing interest in applying organic substrates such as polymers instead of widely used glass substrates. Organic substrate may offer several advantages for lighter, thinner, and flexible devices. Deposition on the polymer substrates, however, requires room-temperature or near-room temperature growth techniques due to their thermal instability at elevated temperatures. For the successful room temperature growth, the use of reactive oxygen ion beams during the film growth is very promising because the energetic bombardment of energetic ion beams significantly enhances the electrical and optical properties of films by improving film quality as well as compensating oxygen deficiency in the evaporated ITO flux. Recently, the bombardment of growing film surfaces by Ar⁺ ion beam only in the oxygen atmosphere resulted in the significant decrease of film resitivities.¹

In this study, ITO films were deposited on glass at room temperature using e-beam evaporated ITO flux and assisted O₂/inert gas mixture ion beam with various flux and energy to improve the conductivity and transparency of the deposited ITO and to elucidate the correlation between ion beam parameters and film properties. The relative intensity of doubly charged oxygen ion (O₂⁺) and the singly charged argon and krypton ion (Ar⁺ and Kr⁺) in the ion source were analyzed by optical emission spectroscopy (OES) to investigate the effects of Ar and Kr addition to the relative intensity of O₂⁺ species in the ion source. The chamber pressure during deposition was maintained at 6x10^-5 ~ 5x10^-4 Torr by fixing the oxygen flow to the ion source at 6 sccm and by adding Ar or Kr flow rate from 0 to 4 sccm respectively. The energy of O₂/inert gas mixture ion beams was varied by increasing the grid acceleration voltage, V_ac, from 0.4 to 2 kV. Various structural, electrical, and optical properties of the grown films were measured with XRD, AFM, four-point probe, α-step, Hall measurement, XPS, and UV-spectrometer. As-deposited films with the film thickness of 1200 Å have the electrical resistivity of as low as ~10^-4 ohm-cm and the visible transmittance of as high as ~ 85%.} ^{1 1} S. Laux, N. Kaiser, and A. Zoller, Thin Solid Films 335, 1 (1998).}

There have been extensive research activities on Cu interconnect technology utilizing low dielectric constant (low-k) interlayer dielectric materials and Cu to replace the conventional Al metallization scheme. One of the candidates for low-k dielectrics is the organic thin films prepared by various methods. Recently, polymer-like thin films deposited by plasma-enhanced chemical vapor deposition (PECVD) using the para-xylene precursor were shown to have the dielectric constant as low as 2.70 and thermal stability up to 450°C ¹. Particularly, these polymer-like thin films have the advantage of not containing fluorine (F) which causes various corrosion problems in interconnect. However, it does not offer good interfacial adhesion to metals due to the absence of bonding state between metals and polymer-like thin films. It has been known that the film surfaces of organic materials treated by O₂ plasma show improved interfacial properties by creating additional functional groups.

In this study, we investigated the interface formation between Cu and low-k polymer-like organic films as a function of plasma-treatment conditions using X-ray photoelectron spectroscopy (XPS). Low-k polymer-like thin films were prepared on silicon substrates by PECVD using the para-xylene precursor at the substrate temperature of 45°C. Plasma-treatments were performed by a magnetically enhanced inductively coupled plasma (MEICP) as a function of inductive power (400 ~ 800W) by keeping the O₂ flow at 10 sccm. Cu was deposited on plasma-treated low-k polymer-like thin films using an electron-beam evaporation at room temperature. Base pressure was 4x10^-5 Torr and deposition rate was kept constant at 0.5Å/sec. Cu film thicknesses were ~70Å. We found that the Cu-O bonding states due to newly created carbonyl group, determined by XPS, were formed at the interface between Cu layer and plasma-treated polymer-like thin films. Details of spectra will be discussed.

¹1. Y.C.Quan, J.R.Joo, and D.G. Jung, Jpn, J. Appl. Phys. 38, 1356 (1999)

Electrochromic materials show optical activity associated to the positive ion injection and extraction in their crystalline lattice. Lithium ions were inserted into WO₃ thin films during the deposition process from a gas phase. We observed a clear relation between the amount of lithium ions inserted and the variation of the optical properties, being the highest variation the obtained for lithium to tungsten atomic ratios near 0.4. In order to calculate how much of this lithium can be extracted of the layer, and thus how much of this lithium is "optically active", cyclic voltammetry and chronoamperometry measurements were performed. From the study of the inserted amount of lithium and the electrically extracted one, the efficiency of the doping process was established.

A series of WO₃ samples varying the lithium to tungsten atomic ratio from 0.3 to 0.5 were deposited onto ITO coated glass. The optical properties were simultaneously recorded with the electrical ones during the lithium extraction process. The results showed a slight reduction of the doping efficiency as the doping ratio was increased.

We compared the coloration efficiency and the speed of the coloration change related to the lithium ions extraction, obtained by this gas phase doping method, with those obtained from liquid insertion of lithium ions from a LiClO₄ based electrolyte.

These results are helpful in the understanding the role played by the lithium ions in the coloration process and in some problems related to the doping process, such as a suitable doping level, diffusion processes of the lithium ions in the bulk of the WO₃ layer and to the surface.