Thin Film Growth
BaF2 optical coating deposited by sputtering and thermal evaporation
M.Alvisi, A.Rizzo, A.Tagliente and S.Scaglione°
Enea CR Brindisi SS Appia Km 712 Brindisi Italy
°Enea CR Casaccia via Anguillarese Roma, Italy
Fluoride coatings (CaF2, LaF2, BaF2) have a wide range of optical applications, from UV to far infrared. In particular BaF2 have a transparency region from UV to infrared, and it is used as low refractive index material for laser coating optics. With respect to the others fluorides, BaF2 has a poor hygroscopy and a good adhesion, even if the mechanical stability (intrinsic stress) depends on the deposition technique.
BaF2 thin films were deposited by RF magnetron sputtering and thermal evaporation and, in order to obtain film with high mechanical stability and low optical absorption, the deposition parameters were optimized. Different reactive gases (freon, oxygen, air) were used in the deposition process and the optical and microstructural properties were measured. The influence of the momentum transferred to the growing film from the energetic particles on the coating optical features, the microstructural texture and the residual stress was pointed out in the sputtered films. All set of samples has been characterized by means of x-ray diffraction, scanning electron microscopy and spectrophotometry.
Dr. Marco Alvisi
UTS Materiali - Sez. Tecnologie e processi di trattamento e rivestimento dei materiali
Sede di Brindisi
SS. 7, Appia, km 7+300 per Mesagne
Tel.: ++39 0831 507405
Fax: ++39 0831 507656
Co-depositing Sn controls the growth of Al films as surfactant
P. B. Barna1, A. Kovács1, F. Misják1 , C. Eisenmenger-Sittner2, H. Bangert2, C. Tomastik3
1 Research Institute for Technical Physics and Material Science, H-1121 Budapest
2 Institute of Solid State Physics, E-138, University of Technology Vienna
3 Institute of General Physics, E-134, University of Technology Vienna
Earlier experiments of the authors indicated that co-deposited Sn promotes the grain growth of Al films and decreases the effect of environmental oxygen on the structure evolution. The present study investigates the influence of co-deposited Sn on the atomic processes involved in the structure evolution of vapour-deposited Al films.
The films were prepared in HV by thermal evaporation from W sources at 1600C substrate temperature either on Si wafers covered by a thermally grown oxide or on air cleaved mica. By applying the half-shadow technique, pure and Sn-doped Al films could be deposited simultaneously. The samples were investigated by AFM, scanning AES, X-TEM as well as by X-ray diffraction methods.
The grain growth of Al is promoted by Sn in all stages of the film formation. Scanning AES measurements prove the existence of a wetting Sn layer both on the surface of Al islands and on the surface of the continuos Al layer. Excess Sn forms islands on the growth surface. The surface of pure Al layers exhibits grain boundary grooves and bunches of growth steps around terraces, while that of the Sn doped layers is more rounded. The substrate-film interface was covered by a thin Sn layer. AES measurements also prove the presence of Sn on the growth surface of Al films even after termination of Sn addition.
Results of these experiments indicate that during co-deposition of Al and Sn the impinging Al atoms penetrate the wetting layer and are incorporated into the already existing Al crystals. A model has been developed for describing the growth of Al crystals in the presence Sn.
The work was supported by the Austrian-Hungarian Intergovernmental Program TeT under contract no.A-16/99, by the Hungarian Science Foundation OTKA under contract no.T033075 and by the EU under contract no. ICAI-CT-2000-70029.
Epitaxial growth of Cu and Au crystallites on H-terminated monocrystalline silicon and their use as seed layers
N. Benouattas 1,* and A. Bouabellou 2
1 Surface and interface laboratory, Physical department, Sciences faculty, Ferhat Abbas
University, 19000 - Setif, Algeria
2 Interfaces and thin films laboratory, Mentouri University, Constantine - 25000, Algeria.
Copper and gold thin films are deposited by thermal evaporation, at low deposition rate, on both (100) and (111) unetched and etched silicon substrates. The structure of samples are studied by X-ray diffraction with -2 mode whereas the purity and the thickness of the deposited layers are determined by Rutherford backscattering technique. Epitaxial growth of copper on (100)Si and (111)Si, and gold on (111)Si are obtained at room temperature, when the silicon substrate is etched with hydrofluoric acid. Whereas, the copper crystallites grow preferentially along the (111) face on both (111)Si and (100)Si when these substrates are surmounted by a native thin layer of silicon oxide (SiOx). On other hand, the epitaxied copper and gold layers are used as seed layers and lead to the epitaxial relationships (111)Cu//(111)Au//(111)Si and (111)Au//(111)Cu//(111)Si.
Keywords: Gold, copper, silicon, epitaxy, seed layers, X-ray diffraction, backscattering spectrometry.
*Corresponding author: N. BENOUATTAS
Present adress: Physic Department, Sciences Faculty,
Ferhat-Abbas University, Setif - 19000, Algeria.
Fax.: (213) 36 91 28 59
E-mail : email@example.com
Study of the Optical and Structural Properties of GaN Films Grown on Si Substrates with a SiC Layer
M. Cervantes-Contrerasa,b,*, M. López-Lópezb, M. Meléndez-Lirab, and M. Tamurab
a Unidad Profesional Interdisciplinaria de Biotecnología-IPN, Ticomán 07340 D.F. Mexico
b Centro de Investigación y de Estudios Avanzados del IPN, 07000 D.F. Mexico
The molecular beam epitaxial (MBE) growth of GaN directly on Si substrates frequently results in films with a mixture of the stable hexagonal phase (-GaN) and the metastable cubic phase (-GaN). In particular, single crystal -GaN layers with high quality are difficult to grow on Si substrates due to the large lattice mismatch (17%), and the strong interaction of N with Si. In this work, in order to obtain high quality -GaN layers, the substrates were coated with a thin SiC layer to reduce the reaction of N with Si. The SiC layer was formed on Si(100) by annealing the substrates at 900 ºC for 2 min in the MBE preparation chamber under a C2H2 partial pressure of 5x10-6 Torr. Transmission electron microscopy confirmed the formation of a ~2.5 nm-thick SiC epitaxial layer.1 GaN layers were grown by MBE using an RF activated N-plasma source operated at 400 W with a nitrogen gas flow rate of 2 sccm. The substrate temperature was set at 750 ºC, and the flux of Ga atoms was varied by changing the Ga-Knudsen cell temperature (TGa) from 950 to 1100 ºC. From x-ray diffraction (XRD) θ-2 θ scans we found that the sample grown with TGa=950 ºC presented a very poor crystal quality with a mixture of andGaN phases. By increasing TGa the crystal quality increased and the intensity of XRD peaks associated to -GaN decreased. However, when TGa was increased from 950 to 1100 ºC, the rms surface roughness increased from 10 to 37 nm, as measured by atomic force microscopy. High resolution XRD revealed that the increase in surface roughness is related to an increase in domain size from 4.7 to 5.4 nm. 12K-photoluminescence spectra (PL) showed an intense emission at ~3.1 eV associated to a near band-gap transition in GaN. An additional emission at ~2.4 eV was also observed which could be associated to crystal defects. The intensity of this PL peak decreased when increasing TGa. An analysis of 300K-photoreflectance spectra (PR) was carried out using the third-derivative function theory.2 We obtained PR transition energy values of ~3.2 and ~3.4 eV, associated to the band-gap of regions with and-GaN phase, respectively. We found that PR is a very powerful technique to detect even small inclusions of the -GaN phase in the films. The PR intensity of the 3.4 eV transition decreased by increasing TGa. From the above results we conclude that growth emplying Ga-rich conditions leads to a better quality GaN films on SiC coated Si(100) substrates. For comparison purposes Si(111) substrates were also employed, but the growth on SiC-coated Si(111) resulted in predominantly -GaN. This shows the importance of the bonding configuration to obtain single crystalline GaN.
1 Y. Hiroyama and M. Tamura: Jpn. J. Appl. Phys. 37 (1998) L630.
2 D. E. Aspnes and A. Studna: Phys. Rev. B 43 (1991) 9569.
THIN RuO2 CONDUCTING FILMS GROWN BY MOCVD FOR MICROELECTRONIC APPLICATIONS
K. Fröhlich, *1 V. Cambel, 1 D. Machajdík, 1 S. Pignard 2, P.K. Baumann, 3 J. Lindner, 3 M. Schumacher, 3
1Institute of Electrical Engineering, SAS, Dúbravská cesta 9, 84239 Bratislava, Slovakia
2 Laboratoire des Matériaux et du Génie Physique, (UMR 5628 CNRS), ENSPG, BP 46, 38 402 Saint-Martin d'Hères Cedex, France.
3 Aixtron AG, Kackertstr. 15-17, D-52072 Aachen, Germany
Rapid scaling down dimensions of complementary metal oxide semiconductor (CMOS) and random access memory (RAM) based devices demands replacement of SiO2 insulating layer by dielectrics with high permittivity – high- dielectrics. Nearly all of the potential high- dielectrics require metal electrode instead of polysilicon. Recently, RuO2 thin films were evaluated as suitable material for the CMOS and RAM technology. Promising method for growth of conducting oxide films is metal-organic chemical vapour deposition, MOCVD. The MOCVD technique has proven to be quite successful in providing uniform coverage over complicated device topology.
We have prepared thin RuO2 films by MOCVD using thermal evaporation of Ru (thd)2(cod) solid precursor. The films were prepared at deposition temperatures between 250 and 500 °C on silicon and sapphire substrates. Different structure was observed for the RuO2 films on these substrates; the films on Si substrate were polycrystalline, while X-ray diffraction analysis revealed epitaxial growth of RuO2 on sapphire substrates.
Polycrystalline RuO2 films prepared at temperatures below 300 °C on Si substrate exhibit smooth surface and excellent step coverage. Highly conformal growth of the RuO2 films at low temperature and low pressure results in nearly 100% step coverage for sub-m features with 1:1 aspect ratio. Resistivity of the polycrystalline RuO2 at room temperature ranged between 100 and 200 cm. These films are suitable for CMOS and RAM applications.
Epitaxial RuO2 films grown low temperatures on the sapphire substrate exhibited lower room temperature resistivity than the films prepared on silicon. They are promising for future microelectronic applications, since the use of whole epitaxial stack of insulating/conducting films is expected to improve performance of CMOS and RAM devices.
NUMERICAL STUDY OF OXIDE THIN FILMS GROWTH BY USING IR LASER BEAM
J.L. Jiménez Pérez1, P.H. Sakanaka2, M.A. Alagatti3, A. Cruz-Orea4, J.G. Mendoza Alvarez4, N. Muños Aguirre4
CICATA-IPN, Legaria 694, Col. Irrigación, 11500 México D.F.
Departamento de Física Quântica Instituto de Física “Gleb Wataghin” Universidade Estadual de Campinas, 13083-970 Campinas, S.P. Brazil
Departamento de Física e Química, Universidade Estadual Paulista “Julio de Mesquita Filho”, Campus de Guaratíngueta 12500-000 Guaratinguetá, S.P. Brazil
Dpto. de Física, CINVESTAV-IPN, A.P. 14-740, 07300 México D.F., México.
From a previous developed and published model, we study the tridimensional growth rates of oxide on Ti thin films. The thermo-oxidation process of Ti films, deposited over glass substrate, is due to the surface heating while it moves at constant speed in the presence of a intense IR-infrared beam of a pulsed Nd:YAG laser at open air. The computational algorithm used for the calculations in this model takes into account adequate autoconsistent concepts like retroalimentation on the initial values of the heating parameters. This retroalimentation process leads to formation of Ti oxide traces. The theoretical estimation of film thickness and the growth ration show excellent concordance with respect to the measured experimental values.
Hot wall epitaxy grown 1,4-dihydroxy-9,10-anthraquinone films
Aman Mahajan, R. K. Bedi* and Taminder Singh1
Material Science Laboratory, Department of Physics,
Guru Nanak Dev University, Amritsar-143 005, India.
1Department of Physics, Khalsa College, Amritsar-143 005, India.
1,4-Dihydroxy-9,10-anthraquinone films have been prepared by hot wall epitaxy (HWE) technique onto cleaned glass substrates kept at different temperatures in vacuum of the order of 10-5 Torr. HWE technique allows the film deposition very near to thermodynamical equilibrium at high vapour pressure with minimum loss of source material. The films so obtained are systematically studied for nuclear magnetic resonance (NMR), optical absorption (IR, visible, near-UV), X-ray diffraction, and scanning electron microscopy. Besides these, the electrical properties of the films are also determined in the temperature range 290-370 K. The IR and NMR studies confirm the formation of 1,4-dihydroxy-9,10-anthraquinone deposits on the glass substrates. The X-ray diffraction patterns delineate polycrystalline behaviour of films, having prominent crystallographic orientation along (200) plane. The films deposited at elevated temperature show comparatively higher degree of crystallinity. Crystallites as large as 6 µm are observed in the case of films deposited at 348K. Observations reveal that the current-voltage characteristics of films show ohmic behaviour of conduction within the investigated field and temperature range. The conduction appears to take place by thermally activated hopping mechanism. The substrate temperature (Ts) appears to influence the properties of the films. Above Ts = 352 K, the films peels off. The electrical conductivity, carrier concentration and mobility of the films increase with the increase in substrate temperature, whereas the activation energy decreases. Analysis of optical absorption measurements on the films indicate that the interband transition energies lie in the range 1.60-2.20 eV.
* Corresponding author: Prof. R. K. Bedi,
Material Science Laboratory, Department of Physics,
Guru Nanak Dev University, Amritsar - 143 005, India.
Tel: 91-183-258802 (Ext. 3344) (Off.), 91-183-257620(Resi.)
Fax: 91-183-258820 email : firstname.lastname@example.org
TEM INVESTIGATION of DC sputtered CARBON-NITRIDE-Nickel thin films
G. Sáfrán, O. Geszti, G. Radnóczi
Research Institute for Technical Physics and Material Sciences, P.O. Box 49, H-1525 Budapest, Hungary
Deposition of carbon nitride (C-N) and carbon-nitride-nickel (C-N-Ni) films onto glass, NaCl and Si(001) substrates was carried out in a dc magnetron sputtering system. Carbon was deposited from high-purity (99.99%) pyrolytic graphite target, 50 mm in diameter, positioned at 10 cm from a resistance-heated substrate holder. C-N-Ni films were grown by a small Ni plate mounted on the graphite target. The base pressure of the deposition chamber was ~7x10-7 Torr. Films were grown at a substrate temperature of 20-700 oC, in pure N2 at partial pressures of 1.9 -2.2 mTorr and the substrates were held at ground potential. The typical film thickness of 15-30 nm was deposited on all the substrates at a magnetron current of 0.2 and 0.3 A, which resulted in a deposition rate of 1.5-2 nm/s.
Structural characterizations were performed by high-resolution transmission electron microscopy (HRTEM) using a JEOL 3010 operated at 300 kV and a 200 kV Philips CM 20 electron microscope equipped with a Ge detector Noran EDS system. The N content of the C-N samples prepared at room temperature was 22-24% by EDS measurement and showed a decrease to 6-7% at elevated temperatures up to 700 C. The N concentration in the C-N-Ni films was higher: ~38% at RT and ~9% at 700 C. The Ni concentration of C-N-Ni samples was 5-6% and 0.3-0.4% in samples deposited at RT and 700 C respectively. The low Ni content in the latter is attributed to a decrease of the sticking coefficient of the carbon co-deposited Ni at elevated temperatures.
All the samples were found amorphous, or amorphous-like by the selected area electron diffraction (SAED) patterns, however, according to HRTEM, the structures differed from each other:
-homogeneous amorphous structures, showing patterns on a size scale about 1 nm. This is characteristic to low temperature deposited C-N and C-N-Ni films.
-amorphous matrix with bent or curly fringe patterns arranged in more or less separated areas of 10-15 nm typical size. This was found in high temperature C-N films.
-fullerene-like structures, such as tortuous bundles of fringes arranged in onion or fingerprint-like patterns. This shows up in the C-N-Ni samples deposited at 700 C. This we explain by the effect of the co-deposited metal species, which, can katalyze the growth of arranged carbon and carbon-nitride structures.
TEM investigation of the topotactic reacTion of (001) and (111) Ag films and Te.
G. Sáfrán, O. Geszti, G. Radnóczi
Research Institute for Technical Physics and Materials Science
H-1525 Budapest, P.O. Box 49, Hungary
Due to the specific semiconductor properties, ionic conductivity, and polymorphic phase transition Ag2Te attracted interest in microelectronics and stuctural studies . The formation, structure and morphology of Ag2Te phase developed by the reaction of single crystalline Ag films with subsequently vacuum deposited Te vapour was investigated. Silver films 30-40 nm in thickness were deposited at 85-120C by thermal evaporation in vacuum at a base pressure of 4x10-5 mbar. The NaCl substrates were cleaved and saw-cut in order to achieve (001) and (111) surfaces, respectively. The surfaces were treated with water and chlorine  prior to Ag deposition. This preparation resulted in single crystalline Ag films of (001) and (111) orientation. Tellurium was deposited onto the silver at a rate about 0.1 nm/s at 200C i.e. above the temperature of the polymorphic phase transformation from monoclinic to fcc (Tc=150C). The Ag-Te reaction occurred during the Te deposition. The samples were investigated by TEM and SAED in a 200 kV Philips CM 20 electron microscope equipped with a Ge detector Noran EDS system..
Partly tellurized Ag films were prepared by depositing 1nm Te onto the silver films. The cubic polymorph of the Ag2Te was found, accomodating with (111) and (112) orientation on the (001) and (111) Ag. It is suggested that the telluride starts to form in the cubic (high temperature) phase on the Ag films and the phase and orientation of the thin telluride is preserved also during cooling down to room temperature.
In the fully tellurized layers, however, the monoclinic (low temperature) Ag2Te phase was found. It exhibited large single crystals consisting of strictly oriented mosaic grains of 1-2 m size. Surprisingly, the orientation of the telluride was identical (010) on both the (001) and (111) Ag parent films. It is suggested that the final orientation appears during the polymorphic phase transition while cooling to room temperature, regardless to Ag orientation, due to the lower surface energy of the (010) orientation of monoclinic phase nuclei.
This work was supported by the Hungarian National Science Foundation (OTKA T35270 and T03424).
1.) M. Kobayashi, K. Ishikawa, F. Tachibana, H. Okazaki Phys Rev. B 38 (1988) 3050
2.) G.Sáfrán, O.Geszti, P.B.Barna, J.R.Günter: Thin Solid Films, 229, (1993) 37-43
3.) G.Sáfrán, L.Malicskó, O.Geszti, G.Radnóczi: J.Crystal Growth 205 (1999) 153-162.
Corresponding author : G. Sáfrán, Tel.: 36 1 3922222; Fax: 36 1 2754996; E-mail: email@example.com
Research Institute for Technical Physics and Material Sciences, P.O. Box 49, H-1525 Budapest, Hungary
ATOMIC LAYER EPITAXY OF ZnO THIN FLMS
ON GaN TEMPLATES
K. Saito, K. Nagayama, Y. Hosokai, A. Takiguchi, K. Ishida and K. Takahashi
Department of Media Science, Teikyo University of Science and Technology
Zinc Oxide (ZnO) is a II-VI compound semiconductor with a wide direct bandgap of 3.37 eV at room temperature. The main advantage of ZnO for short wavelength optical devices is the large exciton binding energy of 60 meV. However, ZnO is naturally an n-type semiconductor because of a deviation from stoichiometry due to the presence of intrinsic point defects such as O vacancies (VO) and Zn interstitials (Zni). Recently, there are a few reports on the fabrication of p-type ZnO [1-3], however, those studies showed poor controllability and reproducibility.
The growth technique of atomic layer epitaxy is thought to be effective to realize p-type ZnO, because impurity incorporation can be precisely controlled. We have achieved the atomic layer growth of ZnO thin films on sapphire substrates for substrate temperatures ranging from 206 to 268 ℃ . However, the crystal quality of those films were insufficient for the application to optical devices because of the large lattice mismatch of 18 ％ between ZnO and (0 0 0 1) sapphire substrate. In contrast, GaN is a closely lattice matched material to ZnO with a lattice mismatch of 1.8 ％, which is ten times smaller than that of sapphire. In this work, in order to improve the crystal quality, we tried to grow ZnO thin films on GaN templates by atomic layer epitaxy.
The GaN templates we used were 1.5 μm thick GaN epitaxial films on the low temperature GaN buffer layer of 30 nm which were grown by MOCVD on (0 0 0 1) sapphire substrates. Diethylzinc (DEZ) and H2O reactant gases were alternately fed into the growth chamber with argon as a carrier gas. By reflection high-energy electron diffraction (RHEED) measurements, spotty pattern was observed for the ZnO film grown on sapphire substrate, while streaky pattern was observed for that grown on GaN template even at the low growth temperature of 247 ℃. In addition, full-width at half-maximum (FWHM) value of (0 0 0 2) X-ray diffraction (XRD) curve of ZnO film was greatly reduced from 6 to 0.1 degree by using GaN template. These results indicate that the GaN templates were effective to improve the crystal quality of the ZnO thin films.
 K. Minegishi, Y. Koiwai, Y. Kikuchi, K. Yano, M. Kasuga and A. Shimizu, Jpn. J. Appl. Phys. 36, L1453 (1997)
 M. Joseph, H. Tabata and T. Kawai, Jpn. J. Appl. Phys. 38, L1205 (1999)
 Y. R. Ryu, S. Zhu, D. C. Look, J. M. Wrobel, H. M. Jeong and H. W. White, J. Crystal Growth 216, 330 (2000)
 K. Saito, Y. Yamamoto, A. Matsuda, S. Izumi, T. Uchino, K. Ishida and K. Takahashi, Phys. Stat. Sol. (b) 229, 925 (2002)
MODELLING OF COMPOUND MATERIALS SPUTTERING USING GAS MIXTURES: InP SURFACE ETCHING BY METHANE-HYDROGEN PLASMA
M Yehya (Yahia) and PJ Kelly, Institute of Materials Research, University of Salford, Salford M5 4WT, UK
Reactive sputtering of compound materials can be achieved using proper gas mixtures. However, the preferential sputtering of a certain material might lead to significant changes in surface stoichiometry. This leads in turn to changes in the mechanical, optical and electrical properties of the surface which limits the use of reactive ion etching RIE using gas mixtures. These changes could be controlled by controlling the plasma parameters.
In this work, InP surfaces were processed by RF hydrogen and methane/hydrogen plasmas over a range of pressures and power densities. The higher reactivity of hydrogen with phosphorous results in preferential sputtering and, therefore, depletion of this element from the surface. Whereas the higher reactivity of methane with Indium results in etching the remaining layers of the surface composed of Indium and Indium Oxide.
Changing the plasma parameters leads to changes in sputtering parameters and surface stoichiometry. For both hydrogen and methane/hydrogen mixtures, the plasma-surface interaction could be divided into three distinctive zones: neutral-controlled etching; ion-controlled etching; and a mixed effect zone.
The processed surface was analysed using XPS and AFM, while the plasma parameters were monitored by a range of gauges and electrostatic probes. The aim of this approach is to optimise the use of gas mixtures in processing compound materials and to model the process of InP surface etching by methane/hydrogen plasmas.