TF10:
Thin Films for Electronics and Optics
Oral Presentations
TF10.1.O
HIGH-POWER DEVICES – A NEW CHALLENGE
TO THIN FILMS
Jan Vobecký and Pavel Hazdra
Microelectronics Department
Faculty of Electrical Engineering
Czech Technical University in Prague
Technická 2, CZ-166 27 Praha 6, Czech Republic
Increasing demands on the electrical ratings of high-power devices necessitate introduction of modern technologies originally developed for the VLSI circuits. Regarding the thin films, it is the PtSi layer that can give a better contact resistance and lower barrier height to provide much lower forward voltage drop. At the same time, the PtSi layer can serve as a source of platinum for low temperature diffusion (700oC) into the device volume to control the carrier lifetime. The diffusion can be controlled by proximity gettering of the Pt (using radiation defects created by low-dose helium irradiation) to allow for localized lifetime control. This approach enables one to introduce an ideal deep level of substitutional Pt (in terms of the generation-recombination parameters) with concentration profile shaped by the radiation defect profile.
Application of the PtSi layer, that brings the benefits described above, is demonstrated for the first time on a high-power PiN (2.5kV/100A) diode fabricated from the FZ silicon. The diodes show low forward voltage drop, very low leakage current, and low turn-off time and turn-off losses.
TF10.2.O
STUDY OF COBALT SILICIDE FORMATION IN
Co/Ta-W/Si(100) MULTILAYER SYSTEMS
A.Z. Moshfegh * a), S.J. Hashemifar b) , O. Akhavan a) , P. Sangpour a) and R. Azimirad a)
a)Department of Physics, Sharif University of Technology, Tehran, Iran
b)Department of Physics, Isfahan University of Technology, Isfahan, Iran
In this investigation, we have studied growth of CoSi2 thin films in Co/Ta/Si(100), Co/Ta0.5W0.5/Si(100) and Co/W/Si(100) multilayer systems. The evaporated Co layer, with a thickness of about 30 nm is deposited over the 12 nm intermediate Ta and/or W layer that was sputtered on Si(100) substrate. The multilayer systems were annealed at a temperature range from 400 to 1000 oC in an N2(80%)+H2(20%) environment for 60 minutes. We have utilized X-ray diffraction (XRD), four point probe sheet resistance (RS) measurement and scanning electron microscopy (SEM) to determine phase formation, electrical properties and surface morphology of these systems, respectively. According to our data analysis, it was shown that for the Co/Ta/Si(100) system, a suitable temperature to form a crystalline CoSi2 (200) structure is 900 oC. But, due to its decomposition at higher temperatures, Co2Ta phase reappeared indicating thermal instability of this system. In addition, the Ta atoms reacted with the environment forming non-conducting phases. For the Co/Ta0.5W0.5/Si(100) system, the Ta atoms formed a negligible amount of undesired non-conducting phase even at high temperatures, as compared with the Co/Ta/Si(100) system. Furthermore, the CoSi2 layer was formed at about 1000 oC. The CoSi2 (200) was relatively a dominant peak at this temperature. However, it does not yield a desired CoSi2 single crystal structure. Meanwhile, we have not observed a substantial amount of Co2Si phase in the both Co/Ta/Si(100) and Co/Ta0.5W0.5/Si(100) systems. On the other hand, in the Co/W/Si(100) system, Co2Si phase was seen up to 800 oC. While the single crystal CoSi2 (200) phase was observed substantially in a temperature range from 900 to 1000 oC. Therefore, it seems that for the intermediate layer containing Ta, the formation of the Co2Si phase is suppressed due to crystallization of Co2Ta at low temperature, while the presence of W atoms in the intermediate layer induces the formation of a thermally stable single crystal CoSi2 layer.
* Corresponding author:
P.O. Box 11365-9161, Tehran, Iran
Fax: +98-21-601-2983, Tel: +98-21-600-5410
TF10.3.O
OPTICAL PROPERTIES OF ZrO2 THIN FILMS GROWN IN CHLORIDE-BASED ATOMIC LAYER DEPOSITION PROCESS
A.Kasikova, H.Mändarb, V.Sammelselga, J.Aarika
a Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia
b Institute of Materials Science, University of Tartu, Tähe 4, 51010 Tartu, Estonia
Refractive index and extinction coefficient of ZrO2 thin films grown by atomic layer deposition were studied. The films were deposited on silica substrates at temperatures ranging from 180 to 600oC with ZrCl4 used as the zirconium precursor and H2O or an aqueous solution of H2O2 as the oxygen precursor. Arefractive index measured at the wavelength of 500 nm ranged from 1.9 to 2.4 and depended on the deposition temperature as well as on the film thickness. For the films of 200-250 nm in thickness the lowest refractive index value ( 2.0 ) was obtained at the deposition temperature of 180oC. Thehighest refractive index values exceeding 2.2 were obtained at the deposition temperatures of 300-500oC.
Aconsiderable decrease of refractive index was observed with the increase of film thickness. The refractive index values reaching 2.45 were obtained for 40 nm thick films grown at 300oC. With an increase of film thickness, however, the refractive index decreased and did not exceed 1.9 – 2.0 when the thicknesses reached 300 –350 nm. On asame time, fitting the spectrophotometric data with linear inhomogeneity model did not give a better compatibility with measured data than does amodel with atransition layer. Structure studies performed revealed that the refractive index variations were evidently related to the changes in aphase composition and homogeneity of the films. The lowest refractive index values were obtained for the films that contained an amorphous phase or had the roughest surfaces. In addition, co-existence of cubic and tetragonal or tetragonal and monoclinic phases of ZrO2 in the films could also influence the refractive indices.
TF10.4.O
Structural and Electrical Properties of Al-doped ZnO Thin Films Deposited by Spray Pyrolysis Technique
aB. N. Pawar*, S. R. Jadkar, K. C. Mohite and M. G. Takwale
aBharati Vidyapeeth Deemed University, Y. M. College, Pune 411 038 (India)
School of Energy Studies, University of Pune, Pune 411 007 (India)
Abstract
Non-stiochiometric ZnO thin films, in general, is an n-type material, show a high transmittance in visible spectrum, coupled with low electrical resistivity. Such films have wide range applications in electronic and opto-electronic devices, photothermal and photovoltaic conversion, etc. However, electrical conductivity and environmental stability of ZnO films can be further improved by doping it with suitable impurity ions at cation sites.
In this work we report characterization of highly transparent Al doped ZnO films onto glass substrate using an inexpensive spray pyrolysis technique. The Zn(CH3COO)2, 2H2O and AlCl3, 6H2O are used as source chemicals. To achieve the textured and high conducting ZnO films, Al concentration in the starting solution is varied between 1 at. % to 5 at. % at the step of 1 at. %. The effect of Al concentration on the structural and electrical properties of ZnO thin films is investigated in detail. These films were characterized by Four Probe Method, X-ray diffraction and Hall measurement. Under the optimum deposition conditions the films are highly transparent ( 85%) in the visible region of solar radiation and have low sheet resistance ( 69.4 /). It is also observed that incorporation of Al in ZnO films affects the structural and electronic properties. The X-ray diffraction analysis indicates all films are polycrystalline in nature and clearly shows the appropriate incorporation of Al atoms in the ZnO films. Furthermore, it is observed that with increasing Al concentration the preferred growth changes from (002) to (101) and (110) orientations. The variation of texture coefficients [TC(hkl)] and standard deviation (g) with Al concentration are also discussed. The carrier concentration (n) and mobility () values are estimated by measuring Hall voltage at room temperature and atmospheric pressure. At optimized deposition parameters, Al doped ZnO films having low resistivity ( 4x10-3-cm) with the carrier concentration of 6.92x1019 cm-3 and mobility of 22.4 cm2/Vs are obtained. A strong correlation between the structural and electrical properties is also observed.
The highly transparent and conductive Al doped ZnO thin film make it possible for adequate potential applications like transparent conducting and protective coatings.
*Corresponding author:E-mail:,Tele/Fax:(91) (20) 569 5201
TF10.5.O
Transient charging of copper phthalocyanine: model and experiment
I. Thurzo*, P. Giang, T. U. Kampen, D. R. T. ZahnInstitute of Physics, TU Chemnitz, Germany
Thin films of copper phthalocyanine (CuPc) of 330 nm thickness were deposited on tin oxide (ITO) substrates in ultra-high vacuum. Without breaking the vacuum Ag dots (2.12x10-7 m2) were evaporated through a shadow mask. The present contribution is aimed at comparing experimental and simulated data on feedback-charge capacitance/voltage (C/V) [1] and isothermal charge deep-level transient spectroscopy (Q-DLTS) [2] of Ag/CuPc/ITO devices kept at ambient temperature.
Two types of charge relaxation of different origins in response to a bias step (pulse) U could be resolved: a/ dielectric relaxation due to the transient charging of the space-charge region capacitance through the resistance of the “neutral” bulk of CuPc [3]; b/ emission from traps of charges injected and captured at the traps during the pulse. The dielectric relaxation is characterized by a well-defined time constant D 10-4 s and is observable for both polarities of U. Quite a different behavior is characteristic of the b-type of charge relaxation: its onset bias corresponds roughly to that of the forward current and, moreover, a positive U is to be applied to ITO (hole injector). It is impossible to define a discrete time constant for this trap-limited process involving a quasi continuous distribution of trap states in both energy and capture cross section. The latter finding results from the failure to reach saturation of either the shape or the position of the Q-DLTS signal on the rate window axis when increasing pulse durations up to 0.1 s.
Realizing that the traps are also spatially distributed, the model previously applied to C/V of a-Si:H based devices [4] has been updated to obtain at least a qualitative picture about the spatial distribution of the density of traps Nt(x) in CuPc. Surprisingly, Nt(x) is rising super-linearly when approaching the top Ag/CuPc interface. These states are made
responsible for the formation of the Ag/CuPc Schottky barrier after completing the dielectric relaxation. The simple model of the Schottky barrier did perfectly match the reverse current/voltage characteristics of the devices. The reverse bias corresponds to Ag
being biased positively, implying the presence of acceptor-like states, a situation analogous to that reported by Brütting et al. [5] for poly-(p-phenylene-vinylene).
[1] T. J. Mego, Rev. Sci. Instrum. 57 (1986), 2798
[2] J. W. Farmer, C. D. Lamp, and J. M. Meese, Appl. Phys. Lett. 41 (1982), 1064
[3] A. K. Jonscher, Dielectric Relaxation in Solids, Chelsea Dielectric Press, London 1983
[4] I. Thurzo, S. Teramura, R. Durný, V. Nádaždy, M. Kumeda, and T. Shimizu, J. Appl. Phys. 82 (1997), 4372
[5] W. Brütting, M. Meier, M. Herold, S. Karg, M. Schwoerer, Chem. Phys. 227 (1998),
243
*Corresponding author: Inst. Phys., TU Chemnitz, Reichenhainer Str. 70, D-09107 Chemnitz, Germany, Tel: +49 0371 531 3079, E-mail:
TF10.6.O
EFFECT OF RF HYDROGEN PLASMA ANNEALING ON THE PROPERTIES OF SiO2/Si STRUCTURES: A SPECTROSCOPIC ELLIPSOMETRY STUDY
A. Paneva and A. Szekeres
1Faculty of Physics, Sofia University, 5 Bourchier Blvd., Sofia 1126, Bulgaria
2Institute of Solid State Physics, 72 Tzarigradsko Chaussee Blvd., Sofia 1784, Bulgaria
The significant role of hydrogen in MOS-device technology has often been underlined. In practice, post-oxidation and post-metallization thermal annealing of SiO2/Si structures are performed in hydrogen containing ambient. It is reasonable to suppose that hydrogen would act more effectively if it is introduced in SiO2/Si structure by other means, such as through plasma exposure. Plasma treatments have been proposed for effective annealing of defects in the oxide and at the SiO2/Si interface.
In this work results from a detailed spectroscopic ellipsometric study on the properties of SiO2/Si structures subjected to rf hydrogen plasma annealing are reported. The structures were grown at 850oC by dry oxidation of (111)Si up to ~30 nm thick oxide and were annealed at 300oC in a rf (13.56 MHz) planar reactor. The ellipsometric measurements were carried out in the spectral range 280-430 nm. The width and composition of the SiO2/Si interface were determined applying an ellipsometric approach developed by us. According to this approach, the reflection coefficient is approximated with appropriate degree polynomial of the oxide thickness. To obtain at different oxide thicknesses, the SiO2 layer was chemically thinned. Process-induced stress was examined from the analysis of the pseudodielectric function <> of Si.
The results reveal that 850oC oxidation of (111)Si yields an interfacial region of substoichiometric oxide Si0.6(SiO2)0.4 with a thickness of 1 nm. Annealing of the SiO2/Si structure by hydrogen plasma exposure at 300oC results in thinner interfacial region (0.5 nm) with a composition closer to stoichiometry (Si0.3(SiO2)0.7). Shifts of the characteristic peaks in the <2> spectrum towards lower energies and a peak splitting at E1 = 3.4 eV are observed.
TF10.7.O
detection of intrinsic defects in CdSe/ZnSe quantumdots srtuctures by optical and HRXRD methods
T.G. Kryshtab1, E.F. Venger, N.O. Korsunska, Yu.G. Sadofyev2,
G.N. Semenova, L.V. Borkovska, M.O. Mazin, V.I. Kushnirenko
Institute of Semiconductor Physics NASU, Kyiv, Ukraine
1Instituto Politécnico Nacional, ESFM, Mexico D. F., Mexico
2P.N. Lebedev Physical Institute RAS, Moscow, Russia
The CdSe/ZnSe self-assembled quantum dot (QD) heterostructures have been intensively investigated during last years because of their possible application for short-wavelength optoelectronic devices. However, it is obvious that intensity and stability of the emission of such structures will depend on theirdefect structure.
A set of MBE-grown structures were investigated: (i) the samples with single sheet of Cd-rich islands obtained by deposition of CdSe layer with thickness varied between 3 - 5 monolayers, (ii) the samples with 12 vertically stacked of Cd-rich islands separated by ZnSe spacer layer with thickness about 18 nm and 50 nm. Structures were grown on GaAs (001) substrates with a 200 nm ZnSe buffer layer and covered by a 100 nm ZnSe cap layer.
The HRXRD measurements were carried out using a high-resolution x-ray diffractometer (Philips MRD) with a 4xGe(220) monochromator and a 2x Ge(220) analyzer and Cu anode. Pronounce difference between diffraction profiles from structures with different CdSe thickness and QD organization was observed. The impairment between measurements and simulation wascaused by distortion of coherence of x-rays within the layers due to structural defects within ZnSe layers above Cd rich islands.
The photoluminescence (PL) spectra of investigated samples consisted of two bands: QD emission band at 2.32.65 eV and broad defect-related band (ID) at 1.991.82 eV. An increase of Se flux pressure resulted in the increase of ID band intensity that testified the relation of this emission with vacancies in cationic sublattice. The PL maximum position of ID band shifted to the high-energy region with the increase of QD emission energy and approached to the position of well-known defect band in ZnSe attributed to A-centers (VZn+D). Defect level followed the heavy-hole related level of QD. In samples with multistack of QD the ID band often consisted of two components. Spectral position of ID band maximum depended on the energy of excitation quantum. In the PL excitation spectra of ID band besides the features that corresponded to the light absorption in ZnSe barrier and Zn1-xCdxSe wetting layer the peak caused by light absorption in QD’s was observed.
All obtained results allow to conclude that studied defects are localized in different parts of heterostructure: ZnSe barrier layer, Zn1-xCdxSe wetting layer and at quantum dot heterointerface. Their localization was found to depend on the preparation regimes and parameters of investigated structures and it was confirmed by X-ray measurements.[1]
TF10.8.O
PREPARATION AND PROPERTIES OF MgB2 THIN FILMS AND THIN FILM STRUCTURES FOR CRYOELECTRONIC DEVICES
L.Satrapinsky, Zs.Öszi, A.Plecenik, Š.Beňačka, *P.Kúš, **I.Kostič
Institute of Electrical Engineering, SAS, *FMPI, Comenius University, **Institute of Informatics, SAS
The surface morphology, microstructure and transport properties of as grown and patterned microstrips of MgB2 thin films, prepared by thermal co-deposition of boron and magnesium on different substrates, have been studied. A systematic study of the influence of various annealing parameters shows an optimum temperature of about 600oC in a background of argon atmosphere. The best results received until now on sapphire or silicon substrate buffered by NbN: critical temperature at zero resistance Tc 36 K, critical current density at 4K jc107A/cm2. Different approaches in patterning of the films and superconducting weak links will be reported. Influence of lithographic processes, mainly baking procedures of optical and electron beam resist, the resist development and ion beam etching process on superconducting properties of MgB2 thin films structures, including edge type of superconducting weak links, will be analyzed.
A.Plecenik, Institute of Electrical Engineering, SAS, Dúbravská cesta 9, 84239 Bratislava, Slovakia, Tel.; (+4212)54775820, ext.2240, Fax.; (+4212)54775816, E-mail:
TF10.9.O
DIELECTRIC PROPERTIES OF RF-SPUTTERED SILICON NITRIDE THIN FILMS WITH GOLD ELECTRODES
R.D. Gould and S.A. Awan
Thin Films Laboratory, Electronic Engineering Group, Department of Physics,
School of Chemistry and Physics, Keele University, Keele, Staffs. ST5 5BG, U.K.
Amorphous silicon nitride films are widely used in VLSI fabrication for gate dielectrics, diffusion barriers and in encapsulation processing, due to their high breakdown strength and resistivity. Such films are conventionally prepared using chemical vapour deposition methods, such as plasma-enhanced and low pressure chemical vapour deposition (PECVD and LPCVD). Recent work has established that RF-sputtered films, prepared using nitrogen as the sputtering gas to ensure stoichiometry, have bulk trapping levels of similar concentrations to those prepared by the CVD techniques.
DC electrical measurements have previously shown that the conductivity in samples with aluminium electrodes exhibited space-charge-limited conductivity (SCLC), whereas those having gold electrodes showed Poole-Frenkel field excitation, as is also observed in PECVD films. Furthermore, films having gold electrodes showed evidence of electroforming and negative resistance behaviour on the application of a DC voltage in excess of a few volts. In the present work the DC conduction measurements in gold-silicon nitride-gold structures have been extended to include the AC conductivity and dielectric properties.
The sandwich structure films were sputtered from a silicon nitride target at a power of 100 W. The AC conductivity , was observed to follow an expression = As, where A is a constant, is the angular frequency and s is an index. The values of s were found to lie in the range 0.83 - 1.31, showing a systematic increase with increasing frequency in the range 100 Hz - 20 kHz and a decrease with increasing temperature in the range 173 - 373 K. This type of behaviour was associated with a carrier hopping process, having a value of the density of localised states N ~ 1024 m-3. Carrier activation energies were in the range 0.006 - 0.1 eV and increased with increasing temperature, further indicating the presence of hopping rather than free-band conductivity. The capacitance followed a geometric relationship, with relative permittivity approximately 6.8, and showed a moderate decrease with increasing frequency and an increase with increasing temperature, tending towards a constant value at higher frequencies and lower temperatures. Measurements of loss tangent as functions of frequency and temperature showed evidence of a minimum value, which appeared to shift to higher frequencies with increasing temperature. Such measurements were in accordance with an existing model of dielectric behaviour in sandwich samples.