TF3:

Diagnostics, Structure - Properties Relationship

Oral Presentations

TF3.1.O

Using Elastic Peak Electron Spectroscopy for Enhanced Depth Resolution in Sputter Profiling

S. Hofmann1 and V. Kesler2

1) Max-Plank-Institute for Metals Research, Stuttgart, Germany

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2)Institute of Semiconductor Physics SB AS Russia, Novosibirsk, Russia

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Elastic peak electron spectroscopy (EPES) is an alternative to AES in sputter depth profiling of thin film structures [1]. In case of a purely binary system, the dependence of the elastic backscattering yield on the atomic number is sufficient for a characterization of the elemental depth profile. In contrast to AES, EPES depth profiling is not influenced by chemical effects. The high count rate ensures a good signal to noise ratio, that is lower measurement times and/or higher precision. In addition, because of the elastically scattered electrons travel twice through the sample, the effective escape depth is reduced, an important factor for the depth resolution function. Thus, the depth resolution is increased. EPES depth profiling was successfully applied to a Ge/Si multilayer structure. The results were quantitatively evaluated using the mixing-roughness-information depth (MRI)–model [2,3]. For an elastic peak energy of 1.0 keV the information depth is considerably lower (0.8 nm) as compared to the Ge(LMM,1147 eV) peak (1.6 nm) used in AES depth profiling, resulting in a respectively improved depth resolution for EPES profiling under otherwise similar profiling conditions. EPES depth profiling is successfully applied to measure small diffusion lengths at Ge/Si interfaces of the order of 1 nm. A related technique is reflection electron energy loss spectroscopy (REELS), where the plasmon peak is used for depth profiling [4].

[1] Gergely G. Surf. Interface Anal. 1981; 3: 201

[2] Hofmann S. Surf. Interface Anal. 2000; 30: 228

[3] Kesler V, Hofmann S. Surf. Interface Anal., in press

[4] Sanz JM, Hofmann S. Thin Solid Films 1984; 120: 185.

Corresponding Author:

Prof. Dr. Siegfried Hofmann, Max-Planck-Institute for Metals Research, Heisenbergstrasse 3,

70569 Stuttgart, Germany

Tel: + 49 711 689 3357 e-mail:

TF3.2.O

Quantification of Sputtering Induced Surface Roughness in AES Depth Profiling of Polycrystalline Ni/Cr Multilayers

J.Y. Wang(1), S. Hofmann(1), A. Zalar(2)*,and E.J. Mittemeijer(1)

(1) Max-Planck Institute for Metals Research, Heisenbergstrasse 3, D-70569 Stuttgart,

Germany

(2) Institute of Surface Engineering and Optoelectronics, Teslova 30, 1000 Ljubljana,

Slovenia

Ion bombardment induced surface roughening takes place during AES sputter depth profiling of polycrystalline thin metal films, caused by different sputtering yields of the differently oriented grains with lattices in channelling or nonchannelling directions [1]. This effect is the main source of the degradation of depth resolution upon sputtering. In order to remedy this effect and to improve the depth resolution, sample rotation is often applied during depth profiling. In this study, the depth resolution of AES depth profiles obtained from stationary and rotating specimens are compared on the basis of the so-called mixing-roughness-information depth (MRI)-model [2]. The system chosen is a well-studied Ni/Cr multilayer composed of 16 alternating Ni and Cr layers with a single layer thickness of 30 nm. AES depth profiles obtained from both stationary and rotating specimens are fitted by the MRI model by varying three physically well-defined parameters: atomic mixing length w, roughness  and information depth . The depth profile recorded from stationary specimen is fitted by assuming, additionally, that the ion sputtering induced roughness  increases with an exponent of less than 1/2 of the sputtered depth, leaving the other two parameters (as depth independent) equal to those determined from the rotating specimen. The results are discussed, also with reference to data obtained by application of earlier, more simple models to describe the depth resolution.

Key words: AES depth profiling, channelling effect, surface roughness, Ni/Cr multilayer, MRI model.

[1] W. Hösler and W. Pamler, Surf. Interface Anal. 20, 609 (1993)

[2] S. Hofmann, Thin Solid Films, 398-399, 336 (2001)

*Corresponding author:

A. Zalar,

Tel: +386-1-4264592, Fax: +386-1-4264593, email:

Institute of Surface Engineering and Optoelectronics, Teslova 30, 1000 Ljubljana, Slovenia

TF3.3.O

Determination of Interdiffusion Coefficient in Si/Al Thin Films by AES Sputter Depth Profiling

J.Y. Wang(1)*, A. Zalar(2), Y.H. Zhao(1), and E.J. Mittemeijer(1)

(1) Max-Planck Institute for Metals Research, Heisenbergstrasse 3, D-70569 Stuttgart,

Germany

(2) Institute of Surface Engineering and Optoelectronics, Teslova 30, 1000 Ljubljana,

Slovenia

Early-stage interdiffusion processes in Si/Al bilayers and multilayers were studied quantitatively by means of Auger electron spectroscopy (AES) depth profiling. The amorphous Si layers and the crystalline Al layers were sputter deposited onto smooth single crystal silicon substrates under different sputtering conditions. The individual layer thicknesses were determined by cross-sectional transmission electron microscopy (TEM) and focused ion beam (FIB) techniques. The initial stage of interdiffusion at the Si/Al interfaces was induced by short time (20 minutes) isothermal annealing of the samples in an argon atmosphere at temperatures between 1000C and 3000C. A new, direct procedure was developed to determine the interdiffusion coefficients from the AES concentration-depth profiles. Firstly, the concentration depth profile of the annealed sample is calculated from the original layer structure by adopting a suitable diffusion model. Then, this concentration profile is convoluted with the resolution function applying the mixing-roughness-information depth (MRI)-model and as a result a calculated AES depth profile is obtained. Finally, the interdiffusion coefficient is determined by fitting the calculated AES depth profile to the measured one. In this way, the interdiffusion coefficient parameters, the pre-exponential factor and the activation energy of Si/Al thin films, were obtained. The results obtained indicate that the interdiffusion strongly depends on the microstructure of the thin films prepared, and strongly differs from interdiffusion in bulk materials.

Key words: AES depth profiling, Si/Al bilayer and multilayer, interdiffusion, MRI model.

*Corresponding author:

JY Wang,

Tel: +49-711-6893479, Fax: +49-711-6893312, email:

Max Planck Institute for Metals Research, Heisenbergstrasse 3, D-70569 Stuttgart, Germany

TF3.4.O

MODELING THE DIFFRACTION PROFILES OF CVD-GROWN PEROVSKITE OXIDE multilayers

E. Dooryhée(1), M. Nemoz (1), J.A. Rodriguez (1), J.L. Hodeau (1), C.Dubourdieu (2), R.Pantou (2), M.Rosina (2), F.Weiss (2), J.P.Sénateur (2), H.Roussel (2), J. Lindner (3)

(1) CNRS, Laboratoire de Cristallographie, BP166X, 38042 Grenoble, France

(2) Laboratoire des Matériaux et du Génie Physique, INPG/CNRS, ENSPG BP46, 38402 St Martin d’Hères, France

(3) Aixtron AG, Kackerstr. 15-17, D-52072 Aachen, Germany

A major issue is the integration of electrical/magnetic functions into thin oxide layers and multilayers. Such functional systems can be synthesized by the chemical vapor deposition of the organo-metallic precursors (MOCVD). One case of study is the (BaTiO3/SrTiO3)n epitaxial multilayer which exhibits a high dielectric constant and low dielectric losses, important in microelectronics and communications (DRAM memories, delay lines, condensators…).

We have examined by laboratory and synchrotron X-ray techniques (reflectivity and high angle diffraction) both Ba/SrTiO3 single layers and BaTiO3/SrTiO3 multilayers deposited on c-oriented LaAl2O3 and SrTiO3 substrates. The thickness of the single layers is varied between 25 and 200Å. The periodicity of the multilayers ranges from 70 to 200Å, with different Sr/Ba ratios. X-ray diffraction in the /2 symmetric reflection geometry was carried out at the European Synchrotron Radiation Facility at BM2, taking advantage of the high resolution and flux.

A key issue in the structural characterization of such systems is the description of the lattice deviations and defects. We have extended a diffraction model(1), previously applied on metallic multilayers, to the more complex case of perovskite structures. The entire diffraction profiles of the (BaTiO3/SrTiO3)n superlattices are fitted over 8 orders of diffraction. By the means of a computed refinement procedure, we evaluate the presence and the magnitude of the coherence length, the interface roughness, the discrete thickness fluctuations, and the intra-layer gradients of strain and atomic diffusion. We show that the diffraction profiles are highly sensitive to the interface state, in particular the macro-strain profile (lattice parameter gradient) as well as the atomic composition profile.

1 Fullerton et al. Phys. Rev. B45 (1992) 9292.

 Corresponding author *: E. Dooryhée, CNRS Laboratoire de Cristallographie, 25 av. des Martyrs, BP166X, 38042 Grenoble, France. . Tél. 33 4 76 88 11 42. Fax. 33 4 76 88 10 38.

TF3.5.O

Structure of DC sputtered amorphous C-Si-N thin films

G. Radnóczi1, G. Sáfrán1, Zs. Czigány1, T. Berlind2, L. Hultman2

1Research Institute for Technical Physics and Material Sciences, P.O. Box 49, H-1525 Budapest, Hungary

2Thin Film Physics Division, Department of Physics, Linköping University, SE-581 83 Linköping, Sweden

Deposition of carbon nitride films on Si(001) substrates was carried out in a dual dc magnetron sputtering system. High-purity (99.99%) pyrolytic graphite and Si targets of 7.5 cm diameter were sputtered in 1.8-3 mTorr N2. The targets were positioned 10 cm from a resistively-heated substrate holder.The base pressure of the deposition chamber was ~5x10-7 Torr. Films were grown at a substrate temperature of 20-700 oC at floating potential. A series of films with thickness ~1 m were grown on all the substrates at a constant magnetron current of 0.2 A, which resulted in a deposition rate of 0.1-0.3 nm/s.

Structural characterisations were performed by high-resolution transmission electron microscopy (HRTEM) using a Philips CM 20 electron microscope operated at 200 kV (resolution ~2.8 Å) equipped with a Ge detector Noran EDS system. Plan-view and cross-sectional HRTEM samples were obtained by low angle (4) Ar+ ion-beam milling at 10 keV energy, which was decreased to 3 kV in the end of the procedure.

Based on the composition the samples are grouped in one third of the compositional triangle, close to the carbon corner. The maximum Si concentration was 60 at%, while the maximum N concentration was 40 at%, as measured by EDS, confirming the compositions designed in the deposition procedure relatively well.

All the samples were amorphous, no crystalline phase was detected in any of them. The amorphous structures, however, differed quite a lot from each other. Three types of structures could be classified:

-homogeneous amorphous structures, showing no or little density fluctuations on a scale above 10 nm.

- columnar amorphous structures, characteristic for evaporated or sputtered films of amorphous Si and Ge, displaying a column diameter of 10-40 nm

-turbostratic structures, showing stronger or weaker anisotropy in the intensity distribution of the selected area electron diffraction pattern, proving an atomic scale anisotropy, parallel and perpendicular to the surface normal of the films.

The appearance of the above structures depended on film composition. The turbostratic structures are characteristic for large C and N concentrations, near to the C corner of the compositional triangle. Columnar structures appear as a consequence of the increasing Si content. In the middle of the triangle the structures are rather homogeneous.

Apparently, the substrate temperature does not make a strong influence on the above described structures, as long as it does not rise above 700oC.

TF3.6.O

LOW-ENERGY PARTICLE TREATMENT OF GaAs SURFACE

E. Pinčíka,, M. Jergelb,1, C. Falconyb, L. Ortegac, J. Ivančoa, R. Brunnera, M. Kučerad

a Institute of Physics, Slovak Academy of Sciences, Dúbravská cesta 9, 84228Bratislava, Slovakia

b Departmento de Física, CINVESTAV-IPN, Apdo. Postal14-740, 07300México D.F., México

c Laboratoire de Cristallographie du CNRS, BP166, 38042Grenoble Cedex09, France

d Institute of Electrical Engineering, Slovak Academy of Sciences, Dúbravská cesta 9, 84239Bratislava, Slovakia

The paper presents results of a complex study of surface properties of high-doped (2·1018cm-3) and semiinsulating GaAs after an interaction with the particles coming from low-energy ion sources such as rf plasma and ion beams. The virgin samples were mechano-chemically polished liquid-encapsulated Czochralski-grown GaAs (100) oriented wafers. The crystals were mounted on the grounded electrode (holder). The mixture Ar+H2 as well as O2 and CF4 were used as working gases: In addition, a combination of two different in-situ exposures was applied, such as e.g. hydrogen and oxygen.

Structural, electrical and optical properties of the exposed surfaces were investigated using X-ray diffraction at grazing incidence, quasi-static and high-frequency C-V curve measurements, deep-level transient spectroscopy, photoreflectance, and photoluminescence. Plasma and ion beam exposures were performed in a commercial rf capacitively coupled plasma equipment SECON XPL200P and a commercial LPAI device, respectively. The evolution of surface properties as a function of the pressure of working gas and the duration of exposure was observed. The results can be summarized as follows :

i) It has been confirmed, in accordance with our previous experiments, that an angular region around the 311 GaAs diffraction was suitable to detect the formation and size of preferentially oriented domains resulting from the interactions with the particles. The most distinct effect was observed in the case of CF4 plasma.

ii) Low-energy ion beam exposures in Ar+H2 mixture induce the formation of two distinct surface regions – (a) a very thin upper oxide layer formed after the exposure of particle-damaged surface to neutral oxygen or air and (b) a hydrogen passivated layer of ~100nm thickness.

iii) C-V and DLTS measurements confirmed the formation of both continuous interface states and deep levels at the interface between the passivated layer and the GaAs crystal.

TF3.7.O

OPTICAL GAP IN CARBON NITRIDE FILMS

S. E. Rodil, S. Muhl, A. C. Ferrari*

Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Circuito exterior s/n, CU 04510 México D. F. (México).

* Engineering Department, University of Cambridge, Trumpington Street CB2 1PZ Cambridge (UK).

The optical gap in published work on carbon nitride films ranges between 0 and 3 eV and there is no clear reason on what this is dependant. In carbon films, for example, the gap is controlled by the  electron delocalization, not only in ordered rings, but in the whole sp2 phase. It is possible to have films with the same sp3 fraction and different optical properties, depending on the ordering of the remaining sp2 phase that can be monitored by Raman spectroscopy, nevertheless any increase in the sp2 fraction leads to a decrease in the optical gap. However, for nitrogen incorporated into ta-C films, we have found that the optical gap initially decreases as the N content and the sp2 fraction rises, but above a certain N content there is a level-off of the optical gap which then remains constant despite further increases in the fraction and clustering of the sp2 phase. Similarly, we found that paracyanogen-like films deposited by sputtering methods have an optical gap which increases with the nitrogen content. Paracyanogen-like films with a 1:1 stoichiometry are mainly made of sp2 carbons in a disordered structure incorporating nitrogen. In many papers, this gap increment has been interpreted in terms of the hypothetical C3N4 crystalline material, which is expected to have a band-gap of around 6eV. However, the explanation has little foundation in that the samples are amorphous and there was no evidence of extensive tetrahedral CN bonding. Here we discuss the conditions that lead to high optical gap carbon nitride samples, which are clearly not associated to the presence of any crystalline super-hard phase. We also reported other specific properties presented by the paracyanogen-like films such as an increasing deposition rate as the N2 partial pressure increases, an infrared spectra dominated by OH bonds and a strong photoluminescence background in Raman spectroscopy.

Corresponding Autor: Dr. Sandra Rodil

Tel: (52)56224734 Fax: (52)56161251

Email:

TF3.8.O

OPTICAL CONSTANT AND ASSOCIATED FUNCTIOS OF CdGa2Se4 THIN FILMS

1st.M. Salem

National Research Center

Physics Division

Electron Microscopy & Thin Film Lab.

Dokki-Cairo-Egypt

Abstract:

Polycrystalline sample of stoichiometeric ternary compound CdGa2Se4 has been prepared and characterized by X-ray diffraction analysis. Lattice parameters have been determined and compared with literature data. CdGa2Se4 thin films were prepared by thermal evaporation under vacuum (10-3 Pa). X-ray diffraction analysis revealed that, the as-deposited films were amorphous in nature and an amorphous-to-crystalline phase transition with a preferential texture along (112) could be obtained by thermal annealing of the as-deposited films at 425 K for ½ h.

The optical constants of the deposited films were determined in the spectral range 400-2500 nm. Graphical representation of Log () versus Log (1) shows two distinct, linear parts confirm the existence of both direct and indirect optical transitions and the corresponding band gaps values were determined. The refractive index dispersion in the transmission and low absorption region is adequately described by single oscillator model, whereby the values of the oscillator strength, So, oscillator position, o, dispersion parameter Eo/So and the high frequency dielectric constant,  were calculated. The effective number of valence electron, neff per atom, and the static dielectric constant, o,eff are deduced via the use of sum rules and are used to interpret the obtained optical data.

E-mail:

Fax:: + 202 3370931

TF3.9.O

ON INTERACTION OF LOW-ENERGY PARTICLES

WITH a-Si:H AND a-SiGe:H THIN FILMS

E. Pinčíka,, H. Gleskováb, M. Záhoranc, K. Gmucováa, M. Jergeld,1, C. Falconyd,

L. Ortegae, R.Brunnera, T. Holoubekc, R. Juránic

a Institute of Physics, Slovak Academy of Sciences, Dúbravská cesta 9, 84228Bratislava, Slovakia

b Department of Electrical Engineering, Princeton University, Princeton, N.J.08544, USA

c Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia

d Departmento de Física, CINVESTAV-IPN, Apdo. Postal14-740, 07300México D.F., México

e Laboratoire de Cristallographie du CNRS, BP166, 38042Grenoble Cedex09, France

The paper deals with structural and electrical properties of virgin, ion beam and plasma exposed a-Si:H and a-SiGe:H surfaces. a-Si:H and a-SiGe:H semiconductors form intrinsic layers in amorphous silicon solar cells whose performance depends on the defect distribution, particularly on the density of dangling bonds.

Device-quality intrinsic a-Si:H and aSiGe:H layers of 1μm thickness were deposited on n-type Si (100) oriented crystals in 13,56MHz rf excited parallel plate plasma enhanced chemical vapor deposition system. The discharge was ignited in SiH4. The layers were exposed to i) rf plasmas (Ar, O2, H2), ii) Ar and O plasma immersion ion implantation iii) low-energy Ar ion beam. The particle-damaged surfaces were covered by an oxide layer prepared by in-situ exposure to oxygen plasma or neutral oxygen. In all cases, an uppermost very thin oxide overlayer of 5–10nm thickness was formed, thicker than the native oxide after PECVD of an amorphous layer.

Structural properties of virgin and damaged surfaces were investigated by X-ray diffraction at grazing incidence (XRDGI). An important transformation of structural properties of aSi:H (aSiGe:H) on Si(100) was investigated via the evolution of diffraction pattern around 2Θ=28.5° indicating the existence of Si80H20 multiatomic complexes. Electrical properties were determined by capacitance-voltage measurements (C-V) and charge version of deep level transient spectroscopy (QDLTS), a large part of the analyses being devoted to the structures on which the bias annealing procedures were performed.

It can concluded that the decrease of the hydrogen content in the amorphous layer (due to the particle impacts) leads to the disappearance of two basic groups of defects (Dh and Dz) in the QDLTS spectra.