ICMCTF1998 Session CP: C - Poster

Tuesday, April 28, 1998 5:00 PM in Room Atlas Foyer
Tuesday Posters

Time Period TuP Sessions | Topic C Sessions | Time Periods | Topics | ICMCTF1998 Schedule

CP-1 Highly Transparency Nano-Crystalline Diamond Thin Films via Substrate Pretreatment and Methane Fraction Optimization
K.H. Chen, D.M. Bhusari, L.Y. Chen (Institute of Atomic & Molecular Sciences, Taiwan); J.R. Yang, T.Y. Wang, S.T. Lin (National Taiwan Institute of Technology, Taiwan)
Optical Transmittance of nano-crystalline diamond films has been studied as a function of grain size of the diamond powder used for substrate pretrement and methane fraction in the source gas. It has been observed that for CH4 fractions below 13%, the films grown on substrates pretreated with finer diamond powder are more transparent, while this trend reverses for CH4 fraction above 13%. These variations in the transparency of the films correlate very well with their corresponding surface roughness. Nano-crystalline/amorphous diamond films with transmittance of greater than 80% beyond one micron thick and with average surface roughness as low as 61 Å have been obtained for CH4 fraction as high as 42% in the source gas. Interestingly, these films do not show obvious presence of any graphitic carbon, and the structural ordering of the amorphous sp3-bonded phase also seems to be insensitive to the CH4 content of the source gas.
CP-2 SiCN: a New Blue-Light Emitting Material
L.C. Chen (National Taiwan University); D.M. Bhusari (Academia Sinica, Taiwan); K.H. Chen (Institute of Atomic & Molecular Sciences, Taiwan); S.L. Wei (Fu Jen University, Taiwan); J.J. Wu, R.L. Liu (Academia Sinica, Taiwan); T.C. Chang, G.D. Gilliland, M.C. Lin (Emory University)

Despite the tremendous progress of GaN based binary and ternary III-V nitrides for applications in LEDs, challenges remain for applications in laser diodes and high power electronic devices. Therefore, it is of current interest to explore opportunities in other new wide band gap materials. We report here the growth of a novel IV-V nitride (specifically, SiCN compound) as a new addition to the family of wide bandgap nitride semiconductors.

Crystalline thin films of SiCN have been successfully grown by microwave plasma-enhanced chemical vapor deposition using H2, CH4, N2 and SiH4 gases. The new crystalline ternary compound (C; Si)xNy exhibits hexagonal structure and consists of a network wherein the Si and C are substitutional elements. Optical properties of the SiCN compound have been studied by photoluminescence (PL). It is found that the low-lying band gap energies of the SiCN compound is in excess of 3.1 eV. Further, a strong subband-gap emission around 2.8 eV is observed at room temperature.

CP-3 FTIR Based Process Control Concepts for Industrial Scale CVD Reactors
V. Hopfe, B. Schultrich (Fraunhofer Institute - IWS, Germany); H. Mosebach (Kayser-Threde GmbH, Germany); M. Meyer (Daimler - Benz AG, Germany); W. Graehlert, O. Throl (Fraunhofer Institute - IWS, Germany)

Chemical vapour deposition (CVD) as well as infiltration (CVI) processes are key technologies in many industrial sectors, as for manufacturing fibre reinforced ceramic composite materials. Although the techniques are used on a technological scale, the underlying chemistry is not completely understood which seriously retards process control as well as reactor scale-up and optimisation.

Different process control concepts are discussed which are based on a multipurpose, knowledge based feedback system for monitoring the CVD/CVI process with FTIR spectroscopic data as input information. Two commonly used industrial scale CVD/CVI processes are taken as test cases: (i) a thermal high capacity CVI batch process for manufacturing carbon fibre reinforced SiC composites for high temperature applications, and (ii) a laser stimulated CVD process for continuously coating bundles of thin ceramic fibres.

(i) The process operates in a industrial scale CVI reactor near 1000oC, in the low pressure region and with CH3SiCl3 as a precursor for infiltrating SiC into a fibre preform. Based on FTIR emission spectroscopy, an experimental set-up has been established for in-situ monitoring the chemical composition of the gaseous atmosphere near the preform to be infiltrated. Several gaseous species have been detected among them highly reactive intermediates which are the key species of the precipitation process. Data treatment procedures have been developed for on-line monitoring the concentration of different species.

(ii) Based on an industrial 6 kW cw-CO2- laser, a laser driven process currently runs in a prototype coater. Layers of graphitizised pyrolytic carbon and several ceramic materials (SiC, TiCxNy, TiB2, BN, etc.) have been deposited on carbon fibres and on SiC fibres. The process control concept includes FTIR measurements which are carried out by rapid extraction of the gaseous reaction products.

CP-4 Thick SiOxNy and SiO2 Films Obtained by PECVD Technique at Low Temperatures
M.I. Alayo, M.N.P. Carreño, I. Pereyra (Laboratório de Microeletrônica, Brazil)

The fabrication of thick SiOxNy and SiO2 films is nowadays of great interest for many applications as coating layer, isolating substrate and optical devices1,2. Also, being silicon compounds, they permit the integration of optical and microelectronics devices, making optoelectronic structures more plausible. On the other hand the fabrication of these materials through the conventional high temperature thermal oxidation of silicon is not reliable due to the very long times and high thermal stress that the materials have to withstand during device fabrication. In this way the deposition of good quality SiOxNy and SiO2 films utilizing the Plasma Enhanced Chemical Vapor Deposition (PECVD) at low temperatures and at high deposition rates is a very promising alternative.

In previous works we have demonstrated that it is possible to produce high quality PECVD SiO2 at temperatures as low as 320 °C and with thickness less than 1 μmm. We also showed that in this type of material is possible to control efficiently the refractive index varying the SiH4 and N2O concentrations in the gaseous mixture3, which is a fundamental requirement for waveguides fabrication, for example1.

In this work we show that by the appropriate control of the gas mixture composition it is possible to obtain very thick SiO2 and SiOxNy films at high deposition rates (~10 μmm), preserving the properties of the high quality thin films. The samples were characterized by Profile Measurements, Fourier Transform Infra Red Spectroscopy (FTIR) and by Scanning Electron Microscopy (SEM). The results show that the films present a structure and an etching rate very close to thermally grown SiO2, and a well controlled refractive index when varying the composition from stoichiometric SiO2 to SiOxNy.1

1 E. S. Bulat, M. Tabasky, B. Tweed, C. Herrick, S. Hankin, N. J. Lewis, D. Oblas, and T. Fitzgerald, J. Vac. Sci. Technol. A 11(4), 1268 (1993).

2 M. S. Haque, H. A. Naseem, and W. D. Brown, J. Electrochem. Soc., 142 (11), 3864 (1995).

3 I. Pereyra and M. I. Alayo, J. Non-Cryst. Solids. 212 (2-3), 225 (1997).}

CP-5 Ellipsometry, Langmuir Probe, Optical Emission Spectroscopy and Laser Light Scattering Applied to the Characterization of Particle-Containing Depositing Plasmas.
N.C. Cruz, E.C. Rangel, M.A.B. Moraes (State University of Campinas, Brazil)
In recent years the growth process and the behavior of particle clouds formed in processing plasmas have been intensively investigated. These particles can be a serious source of contamination, for example in the manufacture of microelectronic devices. From another point of view, the plasma synthesis of nanosized particles is very interesting for material applications because their properties are significantly different from those of bulk material. Although there are many theoretical studies, there is often a lack of experimental results, particularly in the case of titanium-containing plasmas, where as long as we know there is no published work. In this work, particle-containing plasmas of titanium tetraisopropoxide mixed with argon, helium and oxygen is investigated. The plasmas were generated by the application of radiofrequency (rf) power (13.56 MHz, 100 W) to two parallel plate electrodes fitted into a stainless steel vacuum chamber. Laser light scattering (LLS) was employed to study the behavior of the onset of particle formation and to evaluate the spatial profile of particle distribution. LLS combined with actinometric optical emission spectroscopy, and a Langmuir probe were used to investigate the influence of the particle formation on the plasma electron energy distribution function. Langmuir probe was also employed to obtain information about the ratio of positive to negative ion masses. In situ photometric ellipsometry provided information about the refractive index and size of the particles. The morphology and composition of particles collected onto GaAs substrates were studied respectively by scanning electron microscopy and electron microprobe analysis. The dependence of the onset of formation, spatial profile, particle average size and concentration of each element found in the particles as a function of the applied rf power and the partial pressures of the gases of the mixture is discussed. Comparisons between techniques are made.
CP-6 Optical Effects of Metallic Mirrors Surface Modification
L.V. Poperenko (Kyiv Taras Shevchenko University, Ukraine); V.S. Voitsenya (Kharkov Institute of Physics and Technology, Ukraine); M.V. Vinnichenko (Kyiv Taras Shevchenko University, Ukraine); V.G. Konovalov (Kharkov Institute of Physics and Technology, Ukraine); A. Sagara, K. Sato, K. Tsuzuki (National Institute for Fusion Studies, Japan)
It is urgent to develop the technique for manufacturing of fusion plasma viewing mirrors those optical properties are rather immutable under the action of energetic ion irradiation and contamination by boron sputtered from the protective coatings on the surfaces close to the hot plasma confinement volume. Therefore the optical effects of radiation damage to metal mirrors have been examined using Al-ion beam incident on aluminum mirror with further long-term sputtering of the whole mirror by D+ ions of keV energy range as well as Cr-ion beam incident on the stainless steel (sls) mirrors. Incident metal-ion energies of 1 MeV and 3 MeV respectively were used and irradiation dose levels were examined up to 11 dpa. The modifications of two sls mirrors' optical properties induced by the deposition of the various thickness B layers have also been studied. The boronization was performed by Surface Modification Teststand at vacuum condition of ~10-7 Pa using glow discharge in mixture of 10% B2H6 and 90% He. Ex situ ellipsometric data for multiple angles of probing light incidence (λ=632.8 nm) were recorded both before ion irradiation and boronization and after the treatment. The effective values of the mirrors' refraction n, absorption k indices and the reflection coefficient (RC) were determined. It was shown that such treatment of Al mirrors drastically changed those RC at given wavelength (the decrease of ~25%) in contrary to the bombarded sls mirror (~7%). The boronization was resulted in the noticeable changes of effective values of n, k with slight RC alterations. The boron layer's optical properties on sls substrate (n=2.53, k close to zero) and thickness (7.3 and 16.6 nm) were calculated using thin film on substarte model. The values of thickness are in good agreement with those estimated from the given rates of deposition (10 and 20 nm). The normal angle of incidence reflectometry was also applied to investigate the mirrors overcoated by B in the spectral range 200-800 nm. Noticeable changes of reflection were observed only in the UV. The ellipsometric changes have been attributed to modification of the metallic mirrors' surface microrelief.
CP-7 Optical Properties of RF Sputtered Strontium Substituted Barium Titanate Thin Films
B. Panda, A. Dhar, G.D. Nigam, D. Bhattacharya, S.K. Roy (Indian Institute of Technology, India)
Optically active strontium substituted barium titanate (BST) thin films have been prepared on p-silicon and glass (corning 7059) substrates by rf magnetron sputtering at 400-600°C in a flowing Ar/O2 atmosphere. X-ray diffraction, atomic force microscopy (AFM), and Rutherford back scuttering (RBS) analysis have shown that the growth, orientation, surface morphology and the composition of BST films are highly influenced by the process parameters. From ellipsometry study of the films on silicon it has been inferred that, the refractive index is a linear function of the strontium concentration in the films. In the UV-visible transmission spectra the band edge absorption of the BST films shifts to the lower energies when the material is in the crystalline state rather than the amorphous state. The shift may be due to a stress-induce distortion of the band by the lattice film interaction. The films grown at higher substrate temperature show higher transmittance with higher interference oscillations, which may be due to the grain growth and resultant surface roughness of the films. The optical band gap calculated from UV-visible transmission spectra increases with increasing strontium concentration. It varies between 3.25 eV and 3.41 eV. Extinction coefficient of the films in the visible region is in the order of 10-3. Chemical bonding informations have been explored from the absorption valleys of the infrared transmission spectra.
CP-8 Structural and Optical Modification in Oxide Thin Films Related to the Momentum Parameter Transferred by the Assistance Ion Beam
M. Alvisi (INFM - University of Lecce, Italy); A. Rizzo (Pastis-CNRSM, Italy); F. Sarto, S. Scaglione (ENEA, CRE-Casaccia, Italy); L. Vasanelli (INFM-University of Leece, Italy)
The ion assistance during the deposition process is widely considered a useful method to obtain dense film. In some cases, the knowledge of the physical processes in involved in the growth, helps to specify the key parameters which control the film properties. The ionmomentum transfer per arrival atom can be considered the key parameter for afnia (HfO2) films produced by ion assisted e-beam evaporation. In this work is demonstrated that using proper values of mementum transfer, the orientation of the cyrstal plane can be changed to minimize the residual stress of the films. As far as the densification process is concerned, the difference between the refractive indexes of the film and the bulk material (packing density) can be regarded as indicative of the presence of the microvoids in the film. The relationship between the momentum transfer values and the refractive index (packing density) along with the absorption coefficient (stoichiometry) was worked out. X-ray measurements and spectrophotometric analysis were carried out to asses the structural and optical modifications.
CP-9 Noise Reducing Thin Film Edge Filter For Focal Plane Array Detectore in 7.5 - 10.5 μm Region
A. Ghosh, P. Chandra, P.K. Bandyopadhyay, P. Kant, O.P. Nijhawan (Instruments Research & Development Establishment, India)

Thermal sighting systems often emply focal plane array detectors to sense radiation in 7.5 - 10.5 μm wavelength range. These detectors possess some sensitivity in lower region also which contributes as noise in the image. To ovbiate this an edge filter with a pass band in 7.5-10.5 μm wavelength region and low transmission below 7 μm has been designed following thin film multi-layer gradual evolution synthesis approach. This has shaped into a ten layer, non-quarter, alternate films of ThF4 and Ge which has subsequently been implemented on one side of a 10 mm thick germanium substrate using electron beam gun evaporation technique. The rear side of the substrate has been provided a broad band anti-reflection coating for 7.5-10.5 μm spectral region using five layer non-quarter wave stack of the same material combination. Practically achieved transmission in the pass band is about 90% with cutoff at 6.5 um.

Basing our design ideas on gradual evolution technique we have been able to restrict the number of layers to only ten, all being very thin. This has resulted in excellent environmental stability features due to low stresses in the stack.

CP-10 Extremely Fast Ellipsometry Solutions Using Cascaded Artificial Neural Networks Alone
F.K. Urban, III, D. Barton, N. Boudani (Florida International University)
In ellipsometry, the thickness and optical properties of thin films may be determined by light reflection, both in situ and ex situ. However, these useful film parameters are not measured directly but must be computed from the measured parameters (angles psi and delta) using an appropriate system of equations derived from reflecting surface morphology. The most popular solving method, variably damped least squares (VDLS), is slow and troubled by local minima in the solution surface. Artificial Neural Networks (ANN) avoid these problems but have not been trained to be better than about 5% accurate. The work presented here demonstrates a cascade of three ANN levels exhibiting a typical overall accuracy better than 0.4% with speed orders of magnitude faster than that of VDLS methods. This ANN cascade for a material system contains 1,800 3-layer perceptrons with 10 hidden neurons, each requiring 70 weights plus 20 range variables and other statistics which comes to 16.2 Mbyte for 100 wavelengths. Assuming the ranges of film material optical properties can be fitted into 30 such “subranges” yields 486 Mbytes uncompressed. This data which can easily fit onto a CD-ROM in the form of a semantic database which can efficiently store and selectively retrieve the required data at runtime.
Time Period TuP Sessions | Topic C Sessions | Time Periods | Topics | ICMCTF1998 Schedule